Wearable device for measuring an ion concentration level of a user

Abstract

Aspects of the present disclosure provide techniques for measuring an ion concentration level of a user of a wearable device. An example method performed by the wearable device includes applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) of a transcutaneous ion sensor of the wearable device, measuring a current associated with the ISE of the transcutaneous ion sensor, adjusting the bias voltage based on the measured current associated with the ISE until the measured current is within a threshold range, determining, based at least in part on the measured current, the ion concentration level of the user, and transmitting an indication of the ion concentration level of the user to a display device for display to the user.

Description

Dexcom Ref. No.: 0946-PCT01WEARABLE DEVICE FOR MEASURING AN ION CONCENTRATION LEVEL OF A USERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 686,662, filed August 23, 2024, which is assigned to the assignee of the present application and is hereby expressly incorporated by reference in its entirety for all applicable purposes, as if fully set forth herein.BACKGROUND

[0002] The present application relates generally to medical devices such as analyte sensors, and more particularly to systems, devices, and methods for measuring an ion concentration level of a user of a wearable device.

[0003] In vivo analyte sensors can typically be configured to analyze a single analyte using an enzyme to provide specificity for the single analyte. Determining concentrations of multiple analytes of physiological relevance can be desirable in certain medical instances. For example, the concentration of an ion, such as sodium, potassium, magnesium, calcium, or ammonium, in a host’s biological fluid can provide important information about that host’s health status. Illustratively, the potassium ion (K+) is a biomarker of cardiovascular disease. In another example, the potassium ion (K+) is a biomarker of kidney disease. Indeed, in the US, about 14.8M individuals with diabetes are diagnosed with kidney disease, for example, impaired renal function; these patients may benefit from frequent measurement of blood potassium to assess kidney function and guide therapies, which may include oral medications, at one end of the spectrum, to dialysis on the other. In yet another example, the potassium ion (K+) is a biomarker of both cardiovascular disease and kidney disease.

[0004] This background is provided to introduce a brief context for the summary and detailed description that follow. This background is not intended to be an aid in determining the scope of the claimed subject matter nor be viewed as limiting the claimed subject matter to implementations that solve any or all of the disadvantages or problems presented above.SUMMARY

[0005] Certain embodiments of the present disclosure provide a wearable device forP+S Ref. No.: DEXC / 0946PC 1Dexcom Ref. No.: 0946-PCT01 measuring an ion concentration level of a user. The wearable device includes transcutaneous ion sensor comprising an ion selective electrode (ISE) and a reference electrode, a potentiostat configured to apply a bias voltage to the ISE of the transcutaneous ion sensor, and one or more processors configured to measure a current associated with the ISE of the transcutaneous ion sensor, adjust the bias voltage based on the measured current associated with the ISE until the measured current is within a threshold range, determine the ion concentration level of the user based at least in part on the adjusted bias voltage, and transmit an indication of the ion concentration level of the user to a display device for display to the user.

[0006] Certain embodiments of the present disclosure provide a method for measuring an ion concentration level of a user performed by a wearable device. The method includes applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) of a transcutaneous ion sensor of the wearable device, measuring a current associated with the ISE of the transcutaneous ion sensor, adjusting the bias voltage based on the measured current associated with the ISE until the measured current is within a threshold range, determining, based at least in part on the measured current, the ion concentration level of the user, and transmitting an indication of the ion concentration level of the user to a display device for display to the user.

[0007] Certain embodiments of the present disclosure provide a wearable device for measuring an ion concentration level of a user. The wearable device includes transcutaneous ion sensor comprising an ion selective electrode (ISE) and a reference electrode, a potentiostat configured to apply a bias voltage to the ISE of the transcutaneous ion sensor, and one or more processors configured measure a current associated with the ISE of the transcutaneous ion sensor, determine, when the measured current is within a threshold range, the ion concentration level of the user based at least in part on the bias voltage, and transmit an indication of the ion concentration level of the user to a display device for display to the user.

[0008] Certain embodiments of the present disclosure provide a method for measuring an ion concentration level of a user performed by a wearable device. The method includes applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) of a transcutaneous ion sensor of the wearable device, after applying the bias voltage to the ISE, measuring a current associated with the ISE of the transcutaneous ion sensor, determining, when the measured current is within aP+S Ref. No.: DEXC / 0946PC 2Dexcom Ref. No.: 0946-PCT01 threshold range, the ion concentration level of the user based at least in part on the bias voltage, and transmitting an indication of the ion concentration level of the user to a display device for display to the user.

[0009] Other aspects provide: an apparatus operable, configured, or otherwise adapted to perform the aforementioned methods as well as those described elsewhere herein; a non-transitory, computer-readable media comprising instructions that, when executed by one or more processors of an apparatus, cause the apparatus to perform the aforementioned methods as well as those described elsewhere herein; a computer program product embodied on a computer-readable storage medium comprising code for performing the aforementioned methods as well as those described elsewhere herein; and an apparatus comprising means for performing the aforementioned methods as well as those described elsewhere herein. By way of example, an apparatus may comprise a processing system, a device with a processing system, or processing systems cooperating over one or more networks.

[0010] The following description and the appended figures set forth certain features for purposes of illustration.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1A illustrates an example diabetes management system, according to some embodiments disclosed herein.

[0012] FIG. 2 illustrates a more detailed view of a health management system including a display device that is communicatively coupled to an analyte sensor system, according to some embodiments disclosed herein.

[0013] FIG. 3A is an example analyte sensor system, in accordance with some embodiments.

[0014] FIG. 3B is an example analyte sensor system, in accordance with some embodiments.

[0015] FIG. 3C illustrates aspects of an example analyte sensor system, in accordance with some embodiments.

[0016] FIGS. 4, 5, and 6 illustrates various simplified block diagrams of a wearable device for measuring an ion concentration level of a user, in accordance with some embodiments.P+S Ref. No.: DEXC / 0946PC 3Dexcom Ref. No.: 0946-PCT01

[0017] FIG. 7 depicts a method for measuring an ion concentration level of a user of a wearable device, according to some embodiments disclosed herein.

[0018] FIG. 8 depicts a method for measuring an ion concentration level of a user of a wearable device, according to some embodiments disclosed herein.

[0019] FIG. 9 depicts aspects of an example communications device, according to some embodiments disclosed herein.DETAILED DESCRIPTION

[0020] Aspects of the present disclosure provide techniques, including apparatuses, methods, processing systems, and computer-readable mediums, for measuring an ion concentration level of a user of a wearable device.Introduction to Health Management Systems

[0021] FIG. 1 depicts a health management system 100 including an example continuous analyte sensor system (SS) 8 having continuous analyte sensor(s) and sensor electronics, in accordance with certain aspects of the present disclosure. For example, SS 8 may be configured to continuously monitor one or more analytes of a user 50, in accordance with certain aspects of the present disclosure.

[0022] As shown, SS 8 includes sensor electronics module 12 and one or more analyte sensor(s) 10 (individually referred to herein as analyte sensor 10 and collectively referred to herein as analyte sensors 10) associated with sensor electronics module 12. In some embodiments, the one or more analyte sensor(s) 10 may comprise one or more continuous analyte sensors configured to provide continuous analyte concentration level measurements. Sensor electronics module 12 may be in wireless communication (e.g., directly or indirectly) with one or more of display devices 110, 120, 130, and 140, and / or server system 134.

[0023] In certain embodiments, the analyte sensor(s) 10 may comprise one or more sensors for detecting and / or measuring analyte(s). The analyte sensor(s) 10 may be a multi-analyte sensor configured to continuously measure two or more analytes or a single analyte sensor configured to continuously measure a single analyte as a non-invasive device, a subcutaneous device, a transcutaneous device, a transdermal device, and / or an intravascular device. In certain embodiments, the analyte sensor(s) 10 may be configured to continuously measure analyte concentration levels of the user 50 using one or moreP+S Ref. No.: DEXC / 0946PC 4Dexcom Ref. No.: 0946-PCT01 techniques, such as enzymatic techniques, chemical techniques, physical techniques, electrochemical techniques, potentiostatic techniques, potentiometric techniques, impedimetric techniques, coulometric techniques, spectrophotometric techniques, polarimetric techniques, calorimetric techniques, iontophoretic techniques, radiometric techniques, immunochemical techniques, and the like. The term “continuous,” as used herein, can mean fully continuous, semi-continuous, periodic, etc. In certain aspects, the analyte sensor(s) 10 provides a data stream indicative of the concentration of one or more analytes of the user 50. The data stream may include raw data signals, which are then converted into a calibrated and / or filtered data stream used to provide estimated analyte value(s) to the user 50.

[0024] In certain embodiments, the analyte sensor(s) 10 may be a multi-analyte sensor, configured to continuously measure one or more analytes in a body of the user 50. In some embodiments, the one or more analytes may include at least one of sodium ions, potassium ions, hydrogen ions, lithium ions, magnesium ions, calcium ions, chloride ions, sulfite ions, sulfate ions, phosphate ions, ammonium ions, uric acid, urea, ketones, and / or glucose.

[0025] In certain embodiments, the analyte sensor(s) 10 may comprise a percutaneous wire that has a proximal portion coupled to the sensor electronics module 12 and a distal portion with several electrodes, such as a measurement electrode and a reference electrode. The measurement (or working) electrode may be coated, covered, treated, embedded, etc., with one or more chemical molecules that react with a particular analyte, and the reference electrode may provide a reference electrical voltage. The measurement electrode may generate the analog electrical signal, which is conveyed along a conductor that extends from the measurement electrode to the proximal portion of the percutaneous wire that is coupled to the sensor electronics module 12. After the SS 8 has been applied to epidermis of the user 50, analyte sensor(s) 10 penetrates the epidermis, and the distal portion extends into the dermis and / or subcutaneous tissue under epidermis. Other configurations of analyte sensor(s) 10 may also be used, such as a multianalyte sensor that includes multiple measurement electrodes, each generating an analog electrical signal that represents the concentration levels of a particular analyte.

[0026] Generally, a single-analyte sensor generates an analog electrical signal that is proportional to the concentration level of a particular analyte. Similarly, each multianalyte sensor generates multiple analog electrical signals, and each analog electricalP+S Ref. No.: DEXC / 0946PC 5Dexcom Ref. No.: 0946-PCT01 signal is proportional to the concentration level of a particular analyte. As an illustrative example, analyte sensor(s) 10 may include a single- analyte sensor configured to measure glucose concentration levels, and another single-analyte sensor configured to measure concentration levels of another analyte of the user 50, such as at least one of a sodium ion concentration level, a potassium ion concentration level, a hydrogen ion concentration level, a lithium ion concentration level, a magnesium ion concentration level, a calcium ion concentration level, a chloride ion concentration level, a sulfite ion concentration level, a sulfate ion concentration level, a phosphate ion concentration level, an ammonium ion concentration level, a uric acid concentration level, a urea concentration level, and / or a ketone concentration level. As another illustrative example, analyte sensor(s) 10 may include a single-analyte sensor configured to measure glucose concentration levels, and one or more multi-analyte sensors configured to measure a sodium ion concentration level, a potassium ion concentration level, a hydrogen ion concentration level, a lithium ion concentration level, a magnesium ion concentration level, a calcium ion concentration level, a chloride ion concentration level, a sulfite ion concentration level, a sulfate ion concentration level, a phosphate ion concentration level, an ammonium ion concentration level, a uric acid concentration level, a urea concentration level, a ketone concentration level, a concentration of lactate, a concentration level of creatinine, etc. As yet another illustrative example, analyte sensor(s) 10 may include a multi-analyte sensor configured to measure glucose concentration levels, a sodium ion concentration level, a potassium ion concentration level, a hydrogen ion concentration level, a lithium ion concentration level, a magnesium ion concentration level, a calcium ion concentration level, a chloride ion concentration level, a sulfite ion concentration level, a sulfate ion concentration level, a phosphate ion concentration level, an ammonium ion concentration level, a uric acid concentration level, a urea concentration level, a ketone concentration level, a concentration of lactate, a concentration level of creatinine, etc.

[0027] Accordingly, analyte sensor(s) 10 is configured to generate at least one analog electrical signal that is proportional to the concentration level of a particular analyte, and sensor electronics module 12 is configured to convert the analog electrical signal into an analyte sensor count values, calibrate the analyte sensor count values based on the sensitivity profile of the analyte sensor(s) 10 to generate measured analyte concentration levels, and transmit the measured analyte concentration level data, including the measured analyte concentration levels, to a display device, such as displayP+S Ref. No.: DEXC / 0946PC 6Dexcom Ref. No.: 0946-PCT01 devices 210, 220, 230, and / or 240, via a wireless connection. For example, sensor electronics module 12 may be configured to sample the analog electrical signal at a particular sampling period (or rate), such as every 1 second (1 Hz), 5 seconds, 10 seconds, 30 seconds, 1 minute, 3 minutes, 5 minutes, etc., and to transmit the measured analyte concentration data to the display device at a particular transmission period (or rate), which may be the same as (or longer than) the sampling period, such as every 1 minute (0.016 Hz), 5 minutes, 10 minutes, 30 minutes, at the conclusion of the wear period, etc. Depending on the sampling and transmission periods, the measured analyte concentration data transmitted to the display device include at least one measured analyte concentration level having an associated time tag, sequence number, etc. Additional details regarding analyte concentration level measurement and the configuration of the analyte sensor(s) 10 and sensor electronics module 12 may be found in U.S. patent application Ser. No. 18 / 241,658 filed on September 1, 2023 and entitled, “DEVICES AND METHODS FOR MEASURING A CONCENTRATION OF A TARGET ANALYTE IN A BIOLOGICAL FLUID IN VIVO,” which is incorporated herein by reference in its entirety.

[0028] In certain embodiments, analyte sensor(s) 10 may incorporate a thermocouple within, or alongside, the percutaneous wire or a temperature sensor to provide an analog temperature signal to the sensor electronics module 12, which may be used to correct the analog electrical signal or the measured analyte data for temperature. In other embodiments, the thermocouple may be incorporated into the sensor electronics module 12 above the adhesive pad, or, alternatively, the thermocouple may contact the epidermis of the patient through openings in the adhesive pad. In some embodiments, the analyte sensor(s) 10 may incorporate a percutaneous flexible planar substrate including a plurality of electrodes, such as 2 electrodes, 3 electrodes, 4 electrodes, 5 electrodes, 6 electrodes, 7 electrodes, or 8 electrodes.

[0029] In certain embodiments, sensor electronics module 12 includes electronic circuitry associated with measuring and processing the continuous analyte sensor data, including prospective algorithms associated with processing and calibration of the sensor data. Sensor electronics module 12 can be physically coupled to analyte sensor(s) 10 and can be integral with (non-releasably attached to) or releasably attachable to analyte sensor(s) 10. Sensor electronics module 12 may include hardware, firmware, and / or software that enable measurement of levels of analyte(s) via analyte sensor(s) 10. For example, sensor electronics module 12 can include an electrochemical analog front endP+S Ref. No.: DEXC / 0946PC 7Dexcom Ref. No.: 0946-PCT01(e.g., a potentiostat, galvanostat, coulostat, etc.), a power source for providing power to the sensor (including power switches and controlling logic), other components useful for signal processing and data storage, and a telemetry module for transmitting data from the sensor electronics module to, e.g., one or more display devices. Electronics can be affixed to a printed circuit board (PCB), or the like, and can take a variety of forms. For example, the electronics can take the form of an integrated circuit (IC), such as an Application- Specific Integrated Circuit (ASIC), an electrochemical analog front end (AFE), a microcontroller, and / or a processor.

[0030] Display devices 110, 120, 130, and / or 140 are configured for displaying displayable sensor data, including analyte data, which may be transmitted by sensor electronics module 12. Each of display devices 110, 120, 130, and / or 140 may include a display such as a touchscreen display 112, 122, 132, and / or 142 for displaying sensor data to a patient and / or for receiving inputs from the patient. For example, a graphical user interface (GUI) may be presented to the patient for such purposes. In certain embodiments, the display devices may include other types of user interfaces such as a voice user interface instead of, or in addition to, a touchscreen display for communicating sensor data to the patient of the display device and / or for receiving patient inputs. In certain embodiments, one, some, or all of display devices 110, 120, 130, 140 may be configured to display or otherwise communicate the sensor information as it is communicated from sensor electronics module 12 (e.g., in a data package that is transmitted to respective display devices), without any additional prospective processing required for calibration and / or real-time display of the sensor data.

[0031] The plurality of display devices 110, 120, 130, 140 depicted in FIG. 1 may include a custom or proprietary display device, for example, display device 110, especially designed for displaying certain types of displayable sensor information associated with analyte data received from sensor electronics module 12 (e.g., a numerical value and / or an arrow, in certain embodiments). In certain embodiments, one of the plurality of display devices 110, 120, 130, 140 includes a smartphone, such as a mobile phone, based on an Android, iOS, or another operating system configured to display a graphical representation of the continuous sensor data (e.g., including current and / or historic data). In some embodiments, one of the plurality of display devices 110, 120, 130, 140 may include a home automation system display or speakers. In certain embodiments, health management system 100 further includes a medical delivery deviceP+S Ref. No.: DEXC / 0946PC 8Dexcom Ref. No.: 0946-PCT01(e.g., an insulin pump or pen). Sensor electronics module 12 may be configured to transmit sensor information and / or analyte data to medical delivery device. The medical delivery device (not shown) may be configured to administer a certain dosage of insulin or another medicament to the user based on the sensor information and / or analyte data (e.g., which may include a recommended insulin dosage) received from the sensor electronics module 12.

[0032] Server system 134 may be used to directly or indirectly collect analyte data from SS 8 and / or the plurality of display devices, for example, to perform analytics thereon, generate universal or individualized models for analyte concentration levels and profiles, provide services or feedback, including from individuals or systems remotely monitoring the analyte data, perform or assist SS 8 and the plurality of display devices with identification, authentication, etc., according to the embodiments described herein, so on. Note that, in certain embodiments, server system 134 may be representative of multiple systems or computing devices that perform the functions of server system 134 (e.g., in a distributed manner).

[0033] The term “analyte” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to a substance or chemical constituent in a biological fluid (e.g., blood, interstitial fluid, cerebral spinal fluid, lymph fluid, urine, sweat, saliva, etc.) that can be analyzed. Analytes can include naturally occurring substances, artificial substances, metabolites, electrolytes, ions, gasses, hormones, proteins, enzymes, neurotransmitters, infectious agents, and / or reaction products. In some examples, the analyte measured by the sensing regions, devices, and methods is glucose. However, other analytes are contemplated as well, including but not limited to acarboxyprothrombin; acylcamitine; adenine phosphoribosyl transferase; adenosine deaminase; albumin; alpha-fetoprotein; amino acid profiles (arginine (Krebs cycle), histidine / urocanic acid, homocysteine, phenylalanine / tyrosine, tryptophan); andrenostenedione; antipyrine; arabinitol enantiomers; arginase; benzoylecgonine (cocaine); bilirubin, biotinidase; biopterin; c-reactive protein; carnitine; camosinase; CD4; ceruloplasmin; chenodeoxycholic acid; chloroquine; cholesterol; cholinesterase; conjugated 1-P hydroxy-cholic acid; cortisol; creatine; creatine kinase; creatine kinase MM isoenzyme; creatinine; cyclosporin A; d-penicillamine; de- ethylchloroquine; dehydroepiandrosterone sulfate; DNA (acetylator polymorphism,P+S Ref. No.: DEXC / 0946PC 9Dexcom Ref. No.: 0946-PCT01 alcohol dehydrogenase, alpha 1 -antitrypsin, cystic fibrosis, Duchenne / Becker muscular dystrophy, glucose-6-phosphate dehydrogenase, hemoglobin A, hemoglobin S, hemoglobin C, hemoglobin D, hemoglobin E, hemoglobin F, D-Punjab, beta-thalassemia, hepatitis B virus, HCMV, HIV-1, HTLV-1, Leber hereditary optic neuropathy, MCAD, RNA, PKU, Plasmodium vivax, 21 -deoxycortisol); desbutylhalofantrine; dihydropteridine reductase; diptheria / tetanus antitoxin; erythrocyte arginase; erythrocyte protoporphyrin; esterase D; fatty acids / acylglycines; free P-human chorionic gonadotropin; free erythrocyte porphyrin; free thyroxine (FT4); free tri-iodothyronine (FT3); fumarylacetoacetase; galactose / gal-1 -phosphate; galactose- 1 -phosphate uridyltransferase; gentamicin; glucose-6-phosphate dehydrogenase; glutathione; glutathione perioxidase; glycerol; glycocholic acid; glycosylated hemoglobin; halofantrine; hemoglobin variants; hexosaminidase A; human erythrocyte carbonic anhydrase I; 17-alpha-hydroxyprogesterone; hypoxanthine phosphoribosyl transferase; immunoreactive trypsin; beta-hydroxybutyrate; ketones; lactate; lead; lipoproteins ((a), B / A-l, P); lysozyme; mefloquine; netilmicin; oxygen; phenobarbitone; phenytoin; phytanic / pristanic acid; potassium, sodium, and / or other blood electrolytes; progesterone; prolactin; prolidase; purine nucleoside phosphorylase; quinine; reverse tri-iodothyronine (rT3); selenium; serum pancreatic lipase; sissomicin; somatomedin C; specific antibodies (adenovirus, anti-nuclear antibody, anti-zeta antibody, arbovirus, Aujeszky's disease virus, dengue virus, Dracunculus medinensis, Echinococcus granulosus, Entamoeba histolytica, enterovirus, Giardia duodenalisa, Helicobacter pylori, hepatitis B virus, herpes virus, HIV-1, IgE (atopic disease), influenza virus, Leishmania donovani, leptospira, measles / mumps / rubella, Mycobacterium leprae, Mycoplasma pneumoniae, Myoglobin, Onchocerca volvulus, parainfluenza virus, Plasmodium falciparum, poliovirus, Pseudomonas aeruginosa, respiratory syncytial virus, rickettsia (scrub typhus), Schistosoma mansoni, Toxoplasma gondii, Trepenoma pallidium, Trypanosoma cruzi / rangeli, vesicular stomatis virus, Wuchereria bancrofti, yellow fever virus); specific antigens (hepatitis B virus, HIV-1); succinylacetone; sulfadoxine; theophylline; thyrotropin (TSH); thyroxine (T4); thyroxine-binding globulin; trace elements; transferrin; UDP-galactose-4-epimerase; urea; uric acid; uroporphyrinogen I synthase; vitamin A; white blood cells; and zinc protoporphyrin. Salts, sugar, protein, fat, vitamins, and hormones naturally occurring in blood or interstitial fluids can also constitute analytes in certain examples. The analyte can be naturally present in the biological fluid, or endogenous, for example, a metabolic product, a hormone, an antigen, an antibody, andP+S Ref. No.: DEXC / 0946PC 10Dexcom Ref. No.: 0946-PCT01 the like. Alternately, the analyte can be introduced into the body, or exogenous, for example, a contrast agent for imaging, a radioisotope, a chemical agent, a fluorocarbon- based synthetic blood, or a drug or pharmaceutical composition, including but not limited to insulin; ethanol; cannabis (marijuana, tetrahydrocannabinol, hashish); inhalants (nitrous oxide, amyl nitrite, butyl nitrite, chlorohydrocarbons, hydrocarbons); cocaine (crack cocaine); stimulants (amphetamines, methamphetamines, Ritalin, Cylert, Preludin, Didrex, PreState, Voranil, Sandrex, Plegine); depressants (barbiturates, methaqualone, tranquilizers such as Valium, Librium, Miltown, Serax, Equanil, Tranxene); hallucinogens (phencyclidine, lysergic acid, mescaline, peyote, psilocybin); narcotics (heroin, codeine, morphine, opium, meperidine, Percocet, Percodan, Tussionex, Fentanyl, Darvon, Talwin, Lomotil); designer drugs (analogs of fentanyl, meperidine, amphetamines, methamphetamines, and phencyclidine, for example, Ecstasy); anabolic steroids; and nicotine. The metabolic products of drugs and pharmaceutical compositions are also contemplated analytes. Analytes such as neurochemicals and other chemicals generated within the body can also be analyzed, such as, for example, ascorbic acid, uric acid, dopamine, noradrenaline, 3-methoxytyramine (3MT), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5 -hydroxy tryptamine (5HT), 5- hydroxyindoleacetic acid (FHIAA), and histamine.

[0034] The term “ion” as used herein is a broad term, and is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and is not to be limited to a special or customized meaning), and refers without limitation to an atom or molecule with a net electric charge due to the loss or gain of one or more electrons. Ions in a biological fluid is referred to as “electrolytes.” Non-limiting examples of ions in biological fluids include sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+), hydrogen (H+), lithium (Li+), chloride (Cl-), sulfide (S2‘), sulfite (SO32’), sulfate (SO42’), phosphate (PO43'),and ammonium (NFLA). An ion is an example of an analyte.

[0035] FIG. 2 illustrates a more detailed view of health management system 100 including a display device 150 that is communicatively coupled to SS 8. In certain embodiments, display device 150 may be any one of display devices 110, 120, 130, and 140 of FIG. 1. In some embodiments, the display device 150 includes smartphone, such as a mobile phone, based on an Android, iOS, or another operating system configured to display a graphical representation of the continuous sensor data (e.g., including current and / or historic data). In some embodiments, the display device 150 may be a smartwatchP+S Ref. No.: DEXC / 0946PC 11Dexcom Ref. No.: 0946-PCT01 or another type of device, such as an insulin pump or other type of pump.

[0036] The communication path between SS 8 and display device 150 is shown as wireless communication path 180. In certain embodiments, SS 8 and display device 150 are configured to wirelessly communicate over wireless communication path 180 using low range and / or distance wireless communication protocols. Examples of low range and / or distance wireless communication protocols include Bluetooth and Bluetooth Low Energy (BLE) protocols. In certain embodiments, other short range wireless communications may include Near Field Communications (NFC), radio frequency identification (RFID) communications, IR (infra-red) communications, optical communications. In certain embodiments, wireless communication protocols other than low range and / or distance wireless communication protocols may be used for wireless communication path 180, such as WiFi Direct. Display device 150 is also configured to connect to network 190 (e.g., local area network (LAN), wide area network (WAN), the Internet, etc.). For example, display device 150 may connect to network 190 via a wired (e.g., Ethernet) or wireless (e.g., WLAN, wireless WAN, cellular, Mesh network, personal area network (PAN) etc.) interface. Display device 150 is able to communicate with server system 134 through network 190. The communication path between display device 150 and server system 134 is shown as communication path 181 via network 190.

[0037] Note that, in certain embodiments, SS 8 may be able to independently (e.g., wirelessly) communicate with server system 134 through network 190. An independent communication path between SS 8 and server system 134 is shown as communication path 182. However, in certain other embodiments, SS 8 may not be configured with the necessary hardware / software to establish, for example, an independent wireless communication path with server system 134 through network 190. In such embodiments, SS 8 may communicate with server system 134 through display device 150. An indirect or pass-through communication path between SS 8 and server system 134 is shown as communication path 183.

[0038] In embodiments where display device 150 is a proprietary display device, such as display device 110 designed specifically for the communication of analyte data, display device 150 may not be configured with the necessary hardware / software for independently connecting to network 190. Instead, in certain such embodiments, display device 150 is configured to establish a wired or wireless communication path 184 (e.g., through a Universal System Bus (USB) connection) with computer device 103, which isP+S Ref. No.: DEXC / 0946PC 12Dexcom Ref. No.: 0946-PCT01 configured to communicate with server system 134 through network 190. For example, computer device 103 may connect to network 190 via a wired (e.g., Ethernet) or wireless (e.g., WLAN, wireless WAN, cellular, etc.) interface. In some embodiments, the display device 150 may be capable of independently communicating with server system 134 through network 190, independent of computer device 103.

[0039] Health management system 100 additionally includes server system 134, which in turn includes server 135 that is coupled to storage 136 (e.g., one or more computer storage systems, cloud-based storage systems and / or services, etc.). In certain embodiments, server system 134 may be located or execute in a public or private cloud. In certain embodiments, server system 134 is located or executes on-premises (“on- prem”). As discussed, server system 134 is configured to receive, collect, and / or monitor information, including analyte data and related information, as well as encryption / authentication information from SS 8 and / or display device 150. Such information may include input responsive to the analyte data or input (e.g., the user’s analyte concentration measurements and other physiological / behavioral information) received in connection with an analyte monitoring or sensor application running on SS 8 or display device 150. This information may be stored in storage 136 and may be processed, such as by an analytics engine capable of performing analytics on the information. An example of an analyte sensor application that may be executable on display device 150 is analyte sensor application 121, as further described below.

[0040] In certain embodiments, server system 134 at least partially directs communications between SS 8 and display device 150, for example, for facilitating authentication therebetween. Such communications include messaging (e.g., advertisement, command, or other messaging), message delivery, and analyte data. For example, in certain embodiments, server system 134 may process and exchange messages between SS 8 and display device 150 related to frequency bands, timing of transmissions, security, alarms, and so on. In certain embodiments, server system 134 may also update information stored on SS 8 and / or display device 150. In certain embodiments, server system 134 may send / receive information to / from SS 8 and or display device 150 in realtime or sporadically. Further, in certain embodiments, server system 134 may implement cloud computing capabilities for SS 8 and / or display device 150.

[0041] FIG. 2 also illustrates the components of SS 8 in further detail. As shown, in certain embodiments, SS 8 includes analyte sensor 10 coupled to sensor electronicsP+S Ref. No.: DEXC / 0946PC 13Dexcom Ref. No.: 0946-PCT01 module 12. As shown, the sensor electronics module 12 includes one or more hardware components, such one or more processors 11, sensor measurement circuitry 13, memory 14, connectivity interface 15, and real time clock (RTC) 17. In some embodiments, the one or more hardware components of the sensor electronics module 12 may be implemented as ASIC on a printed circuit board (PCB).

[0042] As shown, sensor electronics module 12 includes the sensor measurement circuitry 13 that is coupled to analyte sensor 10 (such as a potentiostat) for processing and managing sensor data. Sensor measurement circuitry 13 may also be coupled to the one or more processors 11 of the sensor electronics module 12. In some embodiments, the one or more processors 11 may be a general-purpose or application-specific microprocessor, an ASIC, a field programmable gate array (FPGA), etc., that executes instructions to perform control, computation, input / output, etc. functions for the sensor electronics module 12. The one or more processors 11 may include a single integrated circuit, such as a micro processing device, or multiple integrated circuit devices and / or circuit boards working in cooperation to accomplish the appropriate functionality.

[0043] In some embodiments, the one or more processors 11 may be configured to sample an analog electrical signal received from the analyte sensor(s) 10 using the analog- to-digital (A / D) signal processing circuitry, such as the sensor measurement circuitry 13, at regular intervals (such as the sampling period) to generate analyte sensor count values based on the analog electrical signals received from the analyte sensor(s) 10, calibrate the analyte sensor count values based on the sensitivity profile of the analyte sensor(s) 10 to generate measured analyte concentration levels, and generate measured analyte data from the measured analyte concentration levels, generate sensor data packages that include, inter alia, the measured analyte concentration level data. The one or more processors 11 may store the measured analyte concentration level data in memory 14, and generate the sensor data packages at regular intervals (such as the transmission period) for transmission to the display device 150. The one or more processors 11 may also add additional data to the sensor data packages, such as supplemental sensor information that includes a sensor identifier, a sensor status, temperatures that correspond to the measured analyte data, etc. The sensor data packages are then wirelessly transmitted over a wireless connection to the display device 150. In certain embodiments, the wireless connection is a Bluetooth or Bluetooth Low Energy (BLE) connection. In such embodiments, the sensor data packages are transmitted in the form of Bluetooth or BLE data packets to theP+S Ref. No.: DEXC / 0946PC 14Dexcom Ref. No.: 0946-PCT01 display device 150.

[0044] In some embodiments, the one or more processors 11 may perform part or all of the functions of the sensor measurement circuitry 13 for obtaining and processing sensor measurement values from analyte sensor 10. The one or more processors 11 may also be coupled to the memory 14 and the RTC 17 for storing and tracking sensor data. In addition, the one or more processors 11 may be further coupled to the connectivity interface 15, which includes a radio unit or transceiver (TRX) 16 for sending sensor data (e.g., measured analyte concentration levels) and receiving requests and commands from an external device, such as display device 150. As used herein, the term transceiver generally refers to a device or a collection of devices that enable SS 8 to (e.g., wirelessly) transmit and receive data. It is contemplated that, in some embodiments, the sensor measurement circuitry 13 may carry out all the functions of the one or more processors 11 or vice versa.

[0045] Transceiver 16 may be configured with the necessary hardware and wireless communications protocols for enabling wireless communications between SS 8 and other devices, such as display device 150 and / or server system 134. For example, as described above, transceiver 16 may be configured with the necessary hardware and communication protocols to establish a Bluetooth or BLE connection with display device 150. As one of ordinary skill in the art appreciates, in such an example, the necessary hardware may include a Bluetooth or BLE security manager and / or other Bluetooth or BLE related hardware / software modules configured for Bluetooth or BLE communications standards. In some embodiments where SS 8 is configured to establish an independent communication path with server system 134, transceiver 16 may be configured with the necessary hardware and communication protocols (e.g., long range wireless cellular communication protocol, such as, GSM, CDMA, LTE, VoLTE, 3G, 4G, 5G communication protocols) for establishing a wireless connection to network 190 to connect with server system 134. As discussed elsewhere, other short range protocols, may also be used for communication between display device 150 and a SS 8 such as NFC, RFID, etc.

[0046] FIG. 2 similarly illustrates the components of display device 150 in further detail. As shown, display device 150 includes connectivity interface 128, one or more processors 126, one or more memories 127, a real time clock (RTC) 163, a display 125 for presenting a graphical user interface (GUI), and a storage 123. Abus (not shown here)P+S Ref. No.: DEXC / 0946PC 15Dexcom Ref. No.: 0946-PCT01 may be used to interconnect the various elements of display device 150 and transfer data between these elements. Connectivity interface 128 includes a transceiver (TRX) 129 used for receiving sensor data (e.g., measured analyte concentration levels) from SS 8 and for sending requests, instructions, and / or data to SS 8 as well as server system 134. Transceiver 129 is coupled to other elements of display device 150 via connectivity interface 128 and / or the bus. Transceiver 129 may include multiple transceiver modules operable on different wireless standards. For example, transceiver 129 may be configured with one or more communication protocols, such as wireless communication protocol(s) for establishing a wireless communication path with network 190 and / or low range wireless communication protocol(s) (e.g., Bluetooth or BLE) for establishing a wireless communication path 180 with SS 8. Additionally, connectivity interface 128 may in some cases include additional components for controlling radio and / or wired connections, such as baseband and / or Ethernet modems, audio / video codecs, and so on.

[0047] In some embodiments, when a standardized communication protocol is used between display device 150 and SS 8, commercially available transceiver circuits may be utilized that incorporate processing circuitry to handle low level data communication functions such as the management of data encoding, transmission frequencies, handshake protocols, security, and the like. In such embodiments, the one or more processors 126 of display device 150 and / or the one or more processors 11 of SS 8 may not need to manage these activities, but instead provide desired data values for transmission, and manage high level functions such as power up or down, set a rate at which messages are transmitted, and the like. Instructions and data values for performing these high level functions can be provided to the transceiver circuits via a data bus and transfer protocol established by the manufacturer of transceivers 129 and 16. However, in embodiments where a standardized communication protocol is not used between transceivers 129 and 16 (e.g., when non- standardized or modified protocols are used), the one or more processors 126 and 11 may be configured to execute instructions associated with proprietary communications protocols (e.g., one or more of the communications protocols described herein) to control and manage their respective transceivers. In addition, when non-standardized or modified protocols are used, customized circuitries may be used to service such protocols.

[0048] The one or more processors 126 may include processor sub-modules, including, by way of example, an applications processor that interfaces with and / orP+S Ref. No.: DEXC / 0946PC 16Dexcom Ref. No.: 0946-PCT01 controls other elements of display device 150 (e.g., connectivity interface 128, analyte sensor application 121 (hereinafter “sensor application 121”), display 125, RTC 163, one or more memories 127, storage 123, etc.). In certain embodiments, the one or more processors 126 is configured to perform functions related to device management, such as, for example, managing lists of available or previously paired devices, information related to network conditions (e.g., link quality and the like), information related to the timing, type, and / or structure of messaging exchanged between SS 8 and display device 150, and so on. The one or more processors 126 may further be configured to receive and process user input, such as, for example, a user's biometric information, such as the user’s finger print (e.g., to authorize the user's access to data or to be used for authorization / encryption of data, including analyte data), as well as analyte data.

[0049] The one or more processors 126 may include and / or be coupled to circuitry such as logic circuits, memory, a battery and power circuitry, and other circuitry drivers for periphery components and audio components. The one or more processors 126 and any sub-processors thereof may include logic circuits for receiving, processing, and / or storing data received and / or input to display device 150, and data to be transmitted or delivered by display device 150. As described above, the one or more processors 126 may be coupled by a bus to display 125, connectivity interface 128, storage 123, etc. Hence, the one or more processors 126 may receive and process electrical signals generated by these respective elements and thus perform various functions. By way of example, the one or more processors 126 may access stored content from storage 123 and one or more memories 127 at the direction of analyte sensor application 121, and process the stored content to be displayed by display 125. Additionally, the one or more processors 126 may process the stored content for transmission via connectivity interface 128 to SS 8 and / or server system 134. Display device 150 may include other peripheral components not shown in detail in FIG. 2.

[0050] In certain embodiments, the one or more memories 127 may include volatile memory, such as random access memory (RAM) for storing data and / or instructions for software programs and applications, such as analyte sensor application 121. Display 125 presents a GUI associated with operating system 162 and / or analyte sensor application 121. In various embodiments, a user may interact with analyte sensor application 121 via a corresponding GUI presented on display 125. By way of example, display 125 may be a touchscreen display that accepts touch input. Analyte sensor application 121 mayP+S Ref. No.: DEXC / 0946PC 17Dexcom Ref. No.: 0946-PCT01 process and / or present analyte -related data received by display device 150 and present such data via display 125. Additionally, analyte sensor application 121 may be used to obtain, access, display, control, and / or interface with analyte data and related messaging and processes associated with SS 8 (e.g., and / or any other medical device (e.g., insulin pump or pen) that are communicatively coupled with display device 150), as is described in further detail herein.

[0051] Storage 123 may be a non-volatile storage for storing software programs, instructions, data, etc. For example, storage 123 may store analyte sensor application 121 that, when executed using the one or more processors 126, for example, receives input (e.g., by a conventional hard / soft key or a touch screen, voice detection, or other input mechanism), and allows a user to interact with the analyte data and related content via display 125. In various embodiments, storage 123 may also store user input data and / or other data collected by display device 150 (e.g., input from other users gathered via analyte sensor application 121). Storage 123 may further be used to store volumes of analyte data received from SS 8 (or any other medical data received from other medical devices (e.g., insulin pump, pen, etc.) for later retrieval and use, e.g., for determining trends and triggering alerts.

[0052] As described above, SS 8, in certain embodiments, gathers analyte data (e.g., measured analyte concentration levels) from analyte sensor 10 and transmits the same or a modified version of the collected data to display device 150. Data points regarding analyte values may be gathered and transmitted over the life of analyte sensor 10 (e.g., in the range of 1 to 30 days or more). New measurements may be transmitted often enough to adequately monitor analyte concentration levels. In certain embodiments, rather than having the transmission and receiving circuitry of each of SS 8 and display device 150 continuously communicate, SS 8 and display device 150 may regularly and / or periodically establish a communication channel among each other. Thus, in such embodiments, SS 8 may, for example, communicate with display device 150 at predetermined time intervals. The duration of the predetermined time interval can be selected to be long enough so that SS 8 does not consume too much power by transmitting data more frequently than needed, yet frequent enough to provide substantially real-time sensor information (e.g., measured glucose values or analyte data) to display device 150 for output (e.g., via display 125) to the user. While the predetermined time interval is every five minutes in some embodiments, it is appreciated that this time interval can beP+S Ref. No.: DEXC / 0946PC 18Dexcom Ref. No.: 0946-PCT01 varied to be any desired length of time. In other embodiments, transceivers 129 and 16 may be continuously communicating. For example, in certain embodiments, transceivers 129 and 16 may establish a session or connection there between and continue to communicate together until the connection is lost.

[0053] Analyte sensor application 121 may be downloaded, installed, and initially configured / setup on display device 150. For example, display device 150 may obtain analyte sensor application 121 from server system 134, or from another source, such as an application store or the like, via a network, e.g., network 190. Following installation and setup, analyte sensor application 121 may be configured to access, process, and / or interface with analyte data (e.g., whether stored on server system 134, locally from storage 123, from SS 8, or any other medical device). By way of example, analyte sensor application 121 may present a menu that includes various controls or commands that may be executed in connection with the operation of SS 8, display device 150, one or more other display devices (e.g., display device 110, 130, 140, etc.), and / or one or more other partner devices, such as an insulin pump. For example, analyte sensor application 121 may be used to interface with or control other display and / or partner devices, for example, to deliver or make available thereto analyte data, including for example by receiving / sending analyte data directly to the other display and / or partner device and / or by sending an instruction for SS 8 and the other display and / or partner device to be connected.

[0054] In certain embodiments, after downloading analyte sensor application 121, as one of the initial steps, the user may be directed by analyte sensor application 121 to establish a secure wireless connection between the display device 150 to the SS 8 of the user, which the user may have already placed on their body. A wireless communication path 180 between display device 150 and SS 8 allows SS 8 to transmit analyte measurements to display device 150 and for the two devices to engage in any of the other interactions described above.

[0055] FIG. 3A illustrates a perspective view of the SS 8 described with respect to FIGS. 1 and 2. As shown, the sensor electronics module 12 of the SS 8 may include an outer housing with a first, top portion 392 and a second, bottom portion 394. In embodiments, the outer housing may include a clamshell design.

[0056] As shown in FIG. 3A, the outer housing may feature a generally oblongP+S Ref. No.: DEXC / 0946PC 19Dexcom Ref. No.: 0946-PCT01 shape. The outer housing may further include aperture 396 disposed substantially through a center portion of outer housing and adapted for analyte sensor(s) 10 and needle insertion through a bottom of SS 8. In embodiments, aperture 396 may be a channel or elongated slot. SS 8 may further include an adhesive patch 326 configured to secure SS 8 to epidermis of a user (e.g., user 50 described with respect to FIG. 1). In embodiments, adhesive patch 326 may include an adhesive suitable for skin adhesion, for example a pressure sensitive adhesive (e.g., acrylic, rubber-based, or other suitable type) bonded to a carrier substrate (e.g., spun lace polyester, polyurethane film, or other suitable type) for skin attachment, though any suitable type of adhesive is also contemplated. As shown, adhesive patch 326 may feature an aperture 398 aligned with aperture 396 such that analyte sensor(s) 10 may pass through a bottom of SS 8 and through adhesive patch 326.

[0057] FIG. 3B illustrates a bottom perspective view of SS 8 of FIG. 3A. FIG. 3B further illustrates aperture 396 disposed substantially in a center portion of a bottom of SS 8, and aperture 398, both adapted for analyte sensor(s) 10 and needle insertion.

[0058] FIG. 3C illustrates a cross-sectional view of SS 8 of FIGs. 3A and 3B. FIG. 3C illustrates the first, top portion 392 and the second, bottom portion 394 of the outer housing, adhesive patch 326, aperture 396 in the center portion of SS 8, aperture 398 in the center portion of adhesive patch 326, and analyte sensor(s) 10 passing through aperture 396. As sensor electronics module 12, previously described in connection with FIGS. 1 and 2, may further include a PCB 304 for communicatively coupling one or more hardware components of the sensor electronics module 12 of the SS 8, such as the analyte sensor(s) 10, the one or more processors 11, the sensor measurement circuitry 13, the memory 14, the connectivity interface 15, and the RTC 17. Additionally, as shown, the sensor electronics module 12 may include a battery 302, which may be electrically coupled to the PCB 304 and configured to provide power to the one or more hardware components of the SS.

[0059] Further, as shown, the analyte sensor(s) 10 includes one or more electrodes configured for sensing or measuring analyte concentration levels of a user (e.g., user 50). For example, as shown, the analyte sensor(s) 10 includes an ion selective electrode (ISE) 337 (e.g., a working electrode (WE)) and a reference electrode (RE) 339. In some embodiments, while not shown in FIG. 3C, the ISE 337 and RE 339 may be electrically coupled to one or more other hardware components of the sensor electronics module 12 (e.g., the one or more processors 11 and / or the sensor measurement circuitry 13) viaP+S Ref. No.: DEXC / 0946PC 20Dexcom Ref. No.: 0946-PCT01 respective input pins on the PCB 304.

[0060] In some embodiments, the ISE 337 may be coated, covered, treated, embedded, etc., with one or more chemical molecules that react with a particular analyte of a user and produce a measurable electrical analog signal proportional to a concentration of that particular analyte. The RE 339 may be used to provide a stable, known potential or voltage, against which a potential of the ISE 337 may be measured, ensuring precise control and accurate measurement of the concentration level of the analyte within the user. Additional details regarding working electrodes and reference electrodes may be found in U.S. patent application Ser. No. 18 / 241,658 filed on September 1, 2023 and entitled, “DEVICES AND METHODS FOR MEASURING A CONCENTRATION OF A TARGET ANALYTE IN A BIOLOGICAL FLUID IN VIVO,” which, as noted above, is incorporated herein by reference in its entirety.Wearable Device for Measuring an Ion Concentration Level of a User

[0061] The continuous measurement of circulating electrically charged ions or analytes (e.g., sodium ions, potassium ions, chloride ions, magnesium ions, etc.) within individuals has remained a major challenge in medicine. The ability to measure electrolyte analytes, in real time, would facilitate improved outcomes for those individuals with acute and chronic disease in disparate fields such as nephrology, hepatology, and cardiology. As an example, dialysis prolongs millions of lives for those with end-stage renal disease but results in substantial healthcare burden due to the need for frequent blood sampling to assess electrolyte balance or level(s). Indeed, bedside and point-of-care instrumentation for the assessment of electrolytes in whole blood samples have been commercially available for the past five decades. However, this point-of-care instrumentation only provides a single snapshot-in-time measurement, which has limited clinical utility.

[0062] Accordingly, there is a need to provide instrumentation that is capable of more frequent (e.g., periodic) or continuous ion concentration level (e.g., analyte concentration level) measurements. Such instrumentation may include, for example, a wearable device that is configured for continuous or periodic ion sensing. In some cases, this continuous ion sensing may be enabled through the use of a potentiometric ion sensor configured to perform potentiometric-based ion measurements.

[0063] In some cases, to ensure accuracy of the potentiometric-based ionP+S Ref. No.: DEXC / 0946PC 21Dexcom Ref. No.: 0946-PCT01 measurements, the potentiometric -based ion measurements may be performed using a transcutaneous ion sensor based on an open circuit potential (OCP) in which the ion sensor has very low input current (e.g., ideally zero or substantially close to zero) and a very high input impedance. To perform the measurements, the wearable device receives or accesses a first signal on an ion selective electrode (ISE) or working electrode (WE) of the ion sensor and a second signal on a reference electrode (RE) of the ion sensor. Both signals may be input into a differential amplifier of a galvanostat (e.g., controlling or fixing the current and measuring the resulting potential or voltage) of the wearable device configured to output an output signal having an output voltage representing a differential between the first signal from the ISE and the second signal from the RE. The output signal, which may represent or be associated with an ion concentration level of a user of the wearable device, may then be filtered by a low pass filter (LPF) to remove any high frequency noises before being input into an analog-to-digital converter (ADC) of the wearable device configured to convert the output signal to a digital signal. The digital signal may then be processed by one or more processors of the wearable device, which may be configured to convert the digital signal into an estimated ion value (e.g., potassium ion concentration, for example, 4.25 mEq / L (milliequivalents per liter) (4.25 mmol / L)), representing the ion concentration level of the user. An indication of the estimated ion value may then be transmitted by the wearable device to a display device for display to the user.

[0064] As discussed above, an ion concentration level in interstitial fluid of a user of the wearable device may be measured using a potentiometric system by measuring the OCP between the ISE and the RE of the ion sensor of the wearable device. These measurements may be performed using a differential amplifier of a galvanostat, which uses a very high input impedance to precisely control or minimize current flow from the ISE and RE, ensuring accurate measurements and reducing interference. However, in addition to being costly to implement, such high input impedance may be susceptible to environmental noise, which may induce leakage currents and negatively affect measurement of the OCP and corresponding ion concentration level. In some cases, shielding or guard rings disposed around the ISE may be used to create a Faraday cagelike effect to help reduce leakage currents.

[0065] Another method of measuring an ion concentration level may be to use amperometric sensing. Unlike potentiometric sensing, which relies on high inputP+S Ref. No.: DEXC / 0946PC 22Dexcom Ref. No.: 0946-PCT01 impedance to minimize current flow and ensure accurate OCP measurements, amperometric sensing involves using a potentiostat to apply a constant bias voltage to the ISE and measuring the resulting current, which correlates with the ion concentration level being measured. Since amperometric sensing does not rely on high input impedance to perform the ion concentration level measurements, amperometric sensing is less susceptible to leakage currents and environmental noise compared to potentiometric sensing. However, a significant challenge with amperometric sensing is that the initial OCP (or voltage associated with the ion concentration) can drift or change over time, complicating the ability to maintain a consistent bias voltage throughout the operating life of the wearable device. Consequently, due to the drift in the OCP, determining and adjusting the appropriate bias potential becomes increasingly difficult, which may affect the overall accuracy and reliability of the measurements.

[0066] Accordingly, aspects of the present disclosure provide techniques for improving the accuracy of ion concentration measurements by a wearable device. For example, to reduce the negative effect of changing / drifting OCP (which be caused by one or more factors including temperature, environmental noise, ion concentration, sensor membrane chemistry degradation, etc.) associated with amperometric-based sensing while also reducing the negative effects of environmental noise and leakage currents (and cost) associated with potentiometric -based sensing, the techniques presented herein may involve using amperometric -based sensing to indirectly measure or determine the OCP of the ion sensor, which may then be used to determine an ion concentration level of a user.

[0067] For example, in some embodiments, indirectly measuring or determining the OCP of the ion sensor may involve using a potentiostat to iteratively adjust (e.g., increase or decrease by a particular amount) a bias voltage applied to the ISE of the ion sensor until the bias voltage is equal to the OCP of the ion sensor. For example, when the bias voltage applied by the potentiostat is greater than or less than the OCP associated with the ISE, the potentiostat will measure a current either flowing into or out of the ISE. However, when the bias voltage is equal to the OCP of the ion sensor, the current measured by the potentiostat will reach a minimum value (e.g., a null current or substantially zero current). Accordingly, when the current measured by the potentiostat reaches a minimum value or null current, the corresponding bias voltage may be indicative of the OCP of the ion sensor and the ion concentration level of the user of theP+S Ref. No.: DEXC / 0946PC 23Dexcom Ref. No.: 0946-PCT01 wearable device. For example, the bias voltage resulting in the null current may change in accordance with a Nemst relation (e.g., Nemst equation), allowing for the ion concentration level to be extracted or determined from the bias voltage / OCP. Further, as the ion concentration level changes, the bias voltage resulting in the null current will also change, signifying the change in the ion concentration level. Accordingly, the bias voltage may be updated, iteratively, on a fixed time interval, or dynamically depending upon the rate of change of the null current or magnitude of the current measured.

[0068] In some embodiments, because the OCP of the ion sensor is initially unknown, the wearable device may be configured to select a random bias voltage or a pre-defined bias voltage (e.g., one stored in memory of the wearable device, for instance, stored prior to an analyte sensor session, during manufacturing, etc.) as a starting point for the incremental adjustment described above. For example, after selecting the random or pre-defined bias voltage, the potentiostat of the wearable device may then apply the randomly selected or pre-defined bias voltage to the ISE of the ion sensor. Thereafter, the bias voltage may be iteratively adjusted until the measured current associated with the ISE reaches the minimum value (e.g., the null current). As noted above, the bias voltage resulting in the null current or substantially zero current may be indicative of the OCP of the ion sensor and may be used to extract or determine the ion concentration level of the user of the wearable device based on the Nemst relation.

[0069] In some cases, the random bias voltage and / or pre-defined bias voltage may be significantly different from the OCP of the ion sensor. As such, selecting the random bias voltage or the pre-defined bias voltage as the starting point may lead to an increase in time in determining the OCP of the ion sensor since the bias voltage may need to be iteratively adjusted more (e.g., increasing or decreasing voltage), leading to increased wait times for the user to obtain their estimated ion concentration level and poor user experience. Additionally, in some cases, applying a random bias voltage or a pre-defined bias voltage that is significantly different from the OCP of the ion sensor may increase an amount of time for the ion sensor to recover from a disturbance caused by the significantly different random bias voltage or pre-defined bias voltage, again leading to increased wait times for the user to obtain their estimated ion concentration level and poor user experience.

[0070] Accordingly, to reduce the time it takes to determine the OCP of the ion sensor through incremental adjustment of the bias voltage applied by the potentiostat, theP+S Ref. No.: DEXC / 0946PC 24Dexcom Ref. No.: 0946-PCT01 techniques presented herein may involve equipping the wearable device with potentiometric-based circuitry, such as a galvanostat, and using the galvanostat to directly measure the OCP of the ion sensor. In some embodiments, because the potentiometricbased circuitry is inherently susceptible to environmental noises that can affect accuracy of OCP measurements, the OCP measured by the galvanostat may represent a rough estimate of the OCP of the ion sensor.

[0071] Accordingly, the measured OCP may be used as the starting point for the incremental adjustment described above. For example, after directly measuring the OCP of the ion sensor using the galvanostat, the measured OCP may then be applied to the ISE of the ion sensor as the bias voltage by the potentiostat and used in indirectly determining or measuring the “true” or substantially accurate OCP of the ion sensor (e.g., with substantially no noise from the environment, leakage currents, etc.). For example, after applying the measured OCP to the ISE of the ion sensor as the bias voltage, the bias voltage may be iteratively adjusted by the potentiostat until the measured current associated with the ISE reaches the minimum value (e.g., the null current or substantially zero current). As noted above, the bias voltage resulting in the null current (e.g., due to the incremental adjustment) may be indicative of the “true” or accurate OCP of the ion sensor. Accordingly, the indirectly determined / measured OCP may then be used to extract or determine the ion concentration level of the user of the wearable device based on the Nemst relation. In some cases, by using the potentiometrically measured OCP as the starting point for the incremental adjustment of the bias voltage, the bias voltage may not have to be iteratively adjusted as much in order to reach the true OCP of the ion sensor (e.g., as compared to using the randomly selected bias voltage or pre-defined bias voltage), resulting in shorter wait times for the user to obtain their estimated ion concentration level and improved user experience.Example Circuitry for Measuring an Ion Concentration Level

[0072] FIG. 4 illustrates a simplified block diagram of an application specific integrated circuit (ASIC) of a wearable device 400 configured to measure an ion concentration of a user of the wearable device 400 using amperometric-based circuitry. In some embodiments, the wearable device 400 may be an example of the SS 8 illustrated and described with respect to FIGS. 1, 2, 3A, 3B, and 3C.

[0073] For example, as illustrated, the wearable device 400 includes aP+S Ref. No.: DEXC / 0946PC 25Dexcom Ref. No.: 0946-PCT01 transcutaneous ion sensor 402 comprising an ion selective electrode (ISE) or working electrode (WE) and a reference electrode (RE) for measuring the ion concentration of the user. In some embodiments, the ion sensor 402 may be an example of the analyte sensor 10 depicted and described with respect to FIGS. 1, 2, 3A, 3B, and 3C. Similarly, the ISE and RE of the ion sensor 402 may be examples of the ISE 337 and the RE 339, respectively, described with respect to FIG. 3C.

[0074] Additionally, as shown, the wearable device 400 includes an analog front end (AFE) 404. In some embodiments, the AFE 404 may be an example of the sensor measurement circuitry 13 illustrated and described with respect to FIG. 2. As shown, the AFE 404 includes amperometric -based circuity, such as the potentiostat 406, configured to output a bias voltage to the ion sensor 402 and measure a current associated with the ISE or WE of the ion sensor 402, as described in greater detail below. In some aspects, potentiostat 406 maintains the bias voltage substantially fixed while the current associated with the ISE is measured.

[0075] Additionally, as shown, the wearable device 400 includes a microcontroller unit (MCU) 408. The MCU 408 includes one or more processors 410, one or more memories 412, and a transceiver 414. In some embodiments, the one or more processors 410 may be configured to control the potentiostat 406 when measuring an ion concentration level. In some embodiments, the one or more processors 410 may be further configured to generate an estimated ion concentration level of the user based on measurements from the AFE 404. In some embodiments, the estimated ion concentration level may be stored in the one or more memories 412. In some embodiments, the one or more processors 410 may be configured to transmit the estimated ion concentration level using the transceiver 414 to a display device (e.g., display device 150) for display to the user.

[0076] In some embodiments, the one or more processors 410 of the MCU 408 may be configured to generate the estimated ion concentration level of the user based on an OCP between the ISE and the RE of the ion sensor 402. In some embodiments, as discussed above, the OCP of the ion sensor 402 may be indirectly measured or determined based on a bias voltage applied by the potentiostat 406 to the ion sensor 402.

[0077] For example, in some embodiments, the one or more processors 410 of the MCU 408 may be configured to determine a bias voltage to be applied to the ISE of ionP+S Ref. No.: DEXC / 0946PC 26Dexcom Ref. No.: 0946-PCT01 sensor 402 of the wearable device 400. In some embodiments, to determine the bias voltage, the one or more processors 410 may select a random bias voltage (e.g., within a particular voltage range) or a pre-defined bias voltage stored in the one or more memories 412 (e.g., prior to an analyte sensor session, during manufacture, for instance, at a factory, etc.). The one or more processors 410 may then configure the potentiostat 406 with the determined bias voltage, as shown at 416.

[0078] Thereafter, when the ion concentration level of the user is to be measured or determined, the potentiostat 406 may apply (e.g., output) a first bias voltage (configured by the MCU 408 using bias voltage module 416) to the ISE of the ion sensor 402. For example, as shown, the potentiostat 406 may include one or more amplifiers and one or more transistors that may be used to apply the bias voltage to the ISE of the ion sensor 402. Bias voltage module 416 may include circuitry for configuring a bias voltage or supplying or coupling (e.g., via one or more wires or traces) a bias voltage or signal from the MCU 408. In some embodiments, potentiostat 406 includes operational amplifiers 430 and 432, and a transistor 440 (e.g., a MOSFET) which enables potentiostat 406 to fix or hold voltage constant or substantially constant while measuring a current of the ISE. In some embodiments, bias voltage module 416 may be coupled to the non-inverting inputs of operational amplifiers 430 and 432 which allows bias voltage module 416 to apply a bias voltage to operational amplifiers 430 and 432 and thereby the ISE or WE and RE. The output of operational amplifier 430 may be coupled to the gate of transistor 440. The inverting input of operational amplifier 430 may be coupled to the source of transistor 440 and the ISE of the ion sensor 402 (and optionally LC elements 420). The inverting input of operational amplifier 432 may be coupled to the output of operational amplifier 432 and the RE of the ion sensor 402. In some embodiments, the operational amplifiers 430 and 432 have a gain of one or a unity gain and may function as buffer of the bias voltage. Potentiostat 406 may further include analog-to -digital converter (ADC) 418 which converts a current received via transistor 440 to a digital signal, which may be provided to the MCU 408. The drain of transistor 440 may be coupled to the ADC 418. In some embodiments, the first bias voltage may be applied as a constant or a complex waveform of changing / s witching potentials. In such cases, an amplitude of the waveforms may be defined by the OCP of the ion sensor 402 and received by the MCU 408 (via the ADC 418).

[0079] In some embodiments, the first bias voltage applied to the ISE of the ionP+S Ref. No.: DEXC / 0946PC 27Dexcom Ref. No.: 0946-PCT01 sensor 402 may cause a first current to flow (e.g., when the bias voltage is not equal to the OCP of the ion sensor 402) into or out of the ISE of the ion sensor 402. Accordingly, when the first bias voltage is applied to the ISE of the ion sensor 402, the first bias voltage may cause the first current associated with the ISE of the ion sensor 402 to be received by the ADC 418. The ADC 418 may then convert the first current associated with the ISE to a first digital signal, which may be provided to the MCU 408.

[0080] The MCU 408 may then measure the first current associated with the ISE of the ion sensor 402 based on the first digital signal received from the ADC 418. In some embodiments, when the first current associated with the ISE does not have a particular value (e.g., close to zero current, an approximately or substantially zero current, a minimal current, etc.) or amperage or is not within a threshold range (e.g., plus or minus one or more picoamps, for example, a range between negative 5 picoamps (pA) and positive 5 pA, a range of negative or positive three pA to 100 pA, between negative 50 pA and positive 200 pA, etc.), the one or more processors 410 may be configured to iteratively adjust the bias voltage until the current associated with the ISE of the ion sensor 402 attains the particular value and / or is within the threshold range.

[0081] For example, in some embodiments, the one or more processors 410 of the MCU 408 may be configured to adjust the bias voltage and configure the potentiostat 406 with the adjusted bias voltage. Thereafter, the potentiostat 406 may apply a second bias voltage (e.g., the adjusted bias voltage) to the ISE of the ion sensor 402. The second bias voltage may cause a second current to be received by the ADC 418. The second current may be converted to a digital signal by the ADC 418 before being provided to the MCU 408. The MCU 408 may again measure the second current associated with the ISE and determine whether the second current associated with the ISE has attained that particular value or is within the threshold range.

[0082] As noted above, the one or more processors 410 may be configured to iteratively adjust the bias voltage and configure the potentiostat 406 to output the adjusted bias voltage until the current associated with the ISE of the ion sensor 402 has attained the particular value or is within the threshold range. In some embodiments, when the current associated with the ISE is above the particular value and / or the threshold range, the one or more processors 410 may be configured to iteratively decrease the bias voltage by a first threshold amount until the current associated with the ISE is within the threshold range and / or is determined to have reached the particular value. In some embodiments,P+S Ref. No.: DEXC / 0946PC 28Dexcom Ref. No.: 0946-PCT01 when the current associated with the ISE is below the threshold range and / or particular value, the one or more processors 410 may be configured to iteratively increase the bias voltage by a second threshold amount until the current associated with the ISE is within the threshold range and / or is determined to have reached the particular value. In some embodiments, the first threshold amount and the second threshold amount may be the same or different.

[0083] In some embodiments, the one or more processors 410 may be configured to adjust the bias voltage based on a comparison between measurements of the current associated with the ISE. For example, as noted above, the one or more processors 410 of the MCU 408 may measure a first current associated with a first bias voltage and a second current associated with a second bias voltage. In some embodiments, the second bias voltage may be greater than the first bias voltage. The one or more processors 410 may then be configured to determine if the measured second current is greater than the measured first current. Assuming that the measured first current is positive, if the measured second current is greater than the measured first current, the one or more processors 410 may instruct the potentiostat 406 to revert back to the first bias voltage or may configure the potentiostat 406 with an adjusted third bias voltage that is lower than the first bias voltage. In some embodiments, if the measured second current is less than the measured first current, the one or more processors 410 may increase the bias voltage and configure the potentiostat 406 to apply a third bias voltage that is higher than the second bias voltage.

[0084] In some embodiments, the one or more processors 410 may be configured to iteratively adjust the bias voltage (and configure the potentiostat 406 with the adjusted bias voltage) according to a fixed periodicity (e.g., every second, 5 seconds, 10 seconds, one or more minutes, etc.). In some aspects, the periodicity may be associated with a physiological relevant time period related to an ion being measured (e.g., a time associated with an average amount of time it takes for potassium ion concentration to change in the human body that is relevant to health of the human.) In some embodiments, the one or more processors 410 may be configured to iteratively adjust the bias voltage (and configure the potentiostat 406 with the adjusted bias voltage) according to a dynamic periodicity. In some embodiments, the dynamic periodicity may be based on at least one of a magnitude of the current associated with the ISE or a rate of change of the current associated with the ISE. In some embodiments, the dynamic periodicity may further beP+S Ref. No.: DEXC / 0946PC 29Dexcom Ref. No.: 0946-PCT01 based on a rate of change of the ion being measured (e.g., the faster the increase or decrease of the ion concentration the more frequent the measurements). In some embodiments, the one or more processors 410 may be configured to determine the magnitude of the current associated with the ISE and / or rate of change of the current associated with the ISE based on the one or more digital signal(s) received from the ADC 418 corresponding to the current associated with the ISE.

[0085] As noted above, the one or more processors 410 may be configured to continue iteratively adjusting the bias voltage and configuring the potentiostat 406 to apply the adjusted bias voltage until the current associated with ISE of the ion sensor 402 is within the threshold range or attains the particular value. In some embodiments, the threshold range may be pre-defined or predetermined (e.g., in a factory, prior to a sensor session, etc.). In some embodiments, the threshold range may be defined relative to the particular value. The particular value may be zero amps, approximately zero amps, close to zero amps, or substantially zero amps. In some embodiments, the particular value may be a lowest or minimum amperage among all the current measurements performed by the one or more processors 410 of the MCU 408 (e.g., during a particular time period). In some embodiments, the threshold range may negative five pA to positive five pA. In some embodiments, threshold range may be a range of negative or positive three pA to 100 pA.

[0086] In some embodiments, the adjusted bias voltage that results in or causes the current associated with ISE of the ion sensor 402 to be within the threshold range and / or to attain the particular value may correspond to the true or noise-free or substantially noise free OCP of the ion sensor 402. In some embodiments, the one or more processors 410 may record the adjusted bias voltage that results in or causes the current associated with the ISE to be within the threshold range and / or to attain the particular value (e.g., the noise-free, substantially noise free, or true OCP). The one or more processors 410 of the MCU 408 may then be configured to determine an estimated ion concentration level corresponding to the recorded bias voltage (e.g., based on a Nernst relation, Goldman- Hodgkin-Katz (GHK) voltage equation, Donnan Equilibrium, etc.). The one or more processors 410 of the MCU 408 may compute or output an estimated ion concentration level of a user using a relation or equation that relates estimated ion concentration level of a user to the OCP voltage of the sensor for a particular bias voltage. The inputs may include one or more constants, the OCP voltage (or bias voltage associated with the particular current (e.g., substantially zero current) measured by the potentiostat or aP+S Ref. No.: DEXC / 0946PC 30Dexcom Ref. No.: 0946-PCT01 current below or equal to a threshold), and one or more environmental factors (e.g., temperature). The one or more processors of the MCU 408 may access one or more of the inputs from one or more memories 412, from a component or portion of the analyte sensor 10 (e.g., a temperature sensor, a potentiostat, a galvanostatic, etc.), use the inputs to calculate an estimate ion concentration level and store the estimated ion concentration level of the user in the one or more memories 412. The one or more inputs may include constants stored in one or more memories 412 (e.g., constants mentioned below). Based on the inputs and values accessed from memories 412, MCU 408 may determine an ion concentration level that correlates to the OCP voltage (e.g., of the ion sensor 402). The determined ion concentration level may be an estimate ion concentration level of the user. The one or more processors 410 of the MCU may then transmit an indication of the ion concentration level of the user to a display device for display to the user.

[0087] In some embodiments, the bias voltage initially applied to the ISE of the ion sensor 402 may correspond to a first estimate of the ion concentration level of the user. As the one or more processors 410 of the MCU 408 iteratively adjust the bias voltage to attain the particular current value (e.g., substantially zero current or until the measured current is within a threshold range), the adjusted bias voltage may correspond to a second estimate of the ion concentration level of the user. The second estimate of the ion concentration level may more closely reflect the actual ion concentration level of the user relative to the first estimate of the ion concentration level.

[0088] Further, in some embodiments, the bias voltage initially applied to the ISE of the ion sensor 402 may be associated with a first accuracy level of the ion concentration level of the user, while the adjusted bias voltage may be associated with a second accuracy level of the ion concentration level of the user. In some embodiments, the second accuracy level may be higher than the first accuracy level. For example, if the initially applied bias voltage deviates from the true OCP, the resulting current associated with the ISE or working electrode may include background current components that do not reflect the ion concentration of interest. This background current may arise due to an incorrect bias voltage being applied, causing prolonged current flow before reaching a null or zerocurrent state (e.g., substantially zero or until the current is within a threshold range). Such current flow may introduce measurement artifacts that may not be conventional noise but are instead systematic deviations tied to incorrect biasing (e.g., not associated with a bias that is substantially similar to the true OCP or the OCP of the sensor).P+S Ref. No.: DEXC / 0946PC 31Dexcom Ref. No.: 0946-PCT01

[0089] By iteratively adjusting the bias voltage to approach the true OCP (e.g., where the current associated with the ISE is minimized or substantially zero or until the current is within a threshold range) the influence of background current may be reduced. This reduction in background current may lead to improved accuracy in the estimated ion concentration level of the user. For example, if an initial a bias voltage is applied that results in a current of 500 picoamps, and through iterative adjustment of the bias voltage reduces the current to 50 picoamps, the latter condition may be more representative of the true electrochemical equilibrium. The ion concentration level calculated or estimated under the adjusted bias voltage may thus be considered more accurate due to the reduced interference from background current.

[0090] In some embodiments, the one or more processors 410 may be configured to determine the estimated ion concentration level by inverting the Nernst relation using the recorded bias voltage and a known offset potential. The Nernst equation is used in chemistry to determine how the voltage (or electrical potential) of a system, like a battery or cell, relates to the activity of ions (which is associated with ion concentration level) in that system. The Nernst equation indicates how the voltage of a system changes based on the balance of ions inside and outside a cell or solution. Using the voltage, the Nernst equation can be used to calculate the concentration of a specific ion, e.g., sodium or potassium in solution using the voltage generated by a chemical reaction. The Nernst equation relates the cell potential E of an electrochemical cell to its standard potential E°, temperature T, the number of electrons transferred n, and the reaction quotient Q. An example of the Nernst relation is shown in Equation 1, below.E„U = Ec'tll- ( ) In g) (1)

[0091] In Equations 1 and 2, Eceu is the cell potential at the temperature (T) of interest, Eceu is the standard cell potential, R is the universal gas constant (e.g., 8.314 J / (mol-K)) (stored in the one or more memories 412), T is the operating temperature in kelvins from a temperature sensor (e.g., of analyte system 8), n is the valency or stoichiometric number of electrons partaking in the reaction for each target ion (e.g., 1 for K+, 1 for Na+, 1 for H+, 1 for Li+, 1 for NH4+, 2 for Mg+2, 2 for Ca+2, etc.), F is Faraday’s constant (e.g., approximately 96,485 coulombs per mole (C / mol)), lois theP+S Ref. No.: DEXC / 0946PC 32Dexcom Ref. No.: 0946-PCT01 concentration of the ion outside the ion selective membrane (ISM), and h is the concentration of the ion within the ISM. In some embodiments, Eceu in Equation 1 may be equal to the determined OCP (e.g., the recorded bias voltage that results in or causes the current associated with the ISE to be within the threshold range and / or to attain theI particular value), - may be equal to the ion concentration level of interest, and isthe Nernst relation discussed above. Accordingly, in some embodiments, to determine the ion concentration level, the one or more processors 410 of the MCU 408 may be configured, as shown in Equation 2, to invert the Nernst relation (e.g., resulting inand use the determined OCP (e.g., Eceu) to solve for the ion concentration level (e.g., — ).

[0092] In some embodiments, the change in ion concentration level may be computed by taking into account the charge accumulated on the ISE over time (t). For example, the following equation may be used:

[0093] In Equations 3 and 4, t is the time in seconds since the start of the analyte or ion concentration monitoring started, for example, the current time in seconds of an ion sensor session, for which ion concentration change is being measured, Qtis the charge accumulated on the ISE over time t, R is the universal gas constant (e.g., 8.314 J / (mol-K)), T is the operating temperature in kelvins from a temperature sensor (e.g., of analyte system 8), zi is the is the valency or stoichiometric number of electrons partaking in the reaction for each target ion (e.g., 1 for K+, 1 for Na+, 1 for H+, 1 for Li+, 1 for NH4+, 2 for Mg+2, 2 for Ca+2, etc.), F is Faraday’s constant (e.g., approximately 96,485 coulombs per mole (C / mol)), a11is the initial ion activity level at time t=0, a^inis the ainifinal ion activity at time t (e.g., during the sensor session measurement), —777 is the change aj in ion concentration over the time t, Cpoiis the capacitance of the conducting polymer (CP) layer (e.g., in the range of 1 microFarad - 1 miliFarad), and Rmem is the membrane resistance (e.g., in the range of lOOkOhm-lOOMOhm). It is appreciated that the initial ion activity level and final ion activity level may be associated or correlate with respectiveP+S Ref. No.: DEXC / 0946PC 33Dexcom Ref. No.: 0946-PCT01 the ion concentration levels. The values of Cpoiand Rmem may be determined (and stored in the one or more memories 412) prior to the start of the ion concentration monitoring or sensor session (e.g., during manufacture, calibration, etc.). The values of t, R, F, T (received from a temperature sensor), Cpoi, Rmem, and zi can be stored in memory (e.g., i i one or more memories 412) and used as inputs by MCU 408 to calculate the change aj in ion concentration of interest (e.g., using equation 4, which is associated with the change in ion concentration level of interest over time t). The change in ion concentration over time t may then be added to a prior determined ion concentration (e.g., an initial ion concentration, for instance by a potentiometric OCP measurement or calibration value, or a previously determined ion concentration level, for instance, determined based on a bias voltage associated with a particular current or within a threshold as described herein) to determine an ion concentration level at time t which may then be output. The one or more processors 410 of the MCU may then transmit an indication of the ion concentration level of the user to a display device for display to the user.

[0094] Thereafter, the estimated ion concentration level may be transmitted by the wearable device 400 to a display device (e.g., display device 150) for display to the user of the wearable device 400. In some embodiments, the estimated ion concentration may be stored in the one or more memories 412 of the wearable device 400. In some embodiments, the estimated ion concentration may be transmitted to a Cloud-based data repository for storage, review, and sharing.

[0095] In some embodiments, the estimated ion concentration level determined by the one or more processors 410 of the MCU 408 may comprise an initial estimated ion concentration level. In some embodiments, one or more processors 410 may be configured to determine changes in the estimated ion concentration level by continuing to measure the current associated with the ISE of the ion sensor 402. For example, once the adjusted bias voltage (e.g., the true, noise-free, or substantially noise free OCP) that results in or causes the current associated with the ISE to be within the threshold range and / or to attain the particular value (e.g., a substantially null or zero current), the adjusted bias voltage may be applied by the potentiostat 406 for a fixed period of time. Thereafter, the one or more processors 410 may then periodically perform subsequent measurements of the current associated with the ISE based on digital signals received from the ADC 418 to determine whether there has been any change in the current associated with the ISE ofP+S Ref. No.: DEXC / 0946PC 34Dexcom Ref. No.: 0946-PCT01 the ion sensor 402 and thereby a change of the ion concentration of the user.

[0096] For example, any change in the current associated with the ISE of the ion sensor (e.g., relative to the null current or current with the particular value) may correspond to a change in the ion concentration level of the user. Accordingly, when the one or more processors 410 measure a change in the current associated with the ISE, the one or more processors 410 may then use the measured change in the current to determine a change in the ion concentration level of the user from the initial ion concentration level of the user. In other words, the one or more processors 410 may be configured to determine an updated ion concentration level (e.g., relative to the initial or previous ion concentration level) based on the measured change in the current associated with the ISE of the ion sensor 402.

[0097] As noted, the bias voltage that results in or causes the current associated with the ISE to be within the threshold range and / or to attain the particular value (e.g., the null current) may be equal to the true or noise-free OCP between the ISE and the RE of the ion sensor 402. By indirectly determining the OCP in this manner (e.g., by iteratively adjusting the bias voltage until the null current is determined), the wearable device 400 may be able to avoid or reduce the environmental noise / interference associated with a direct measurement of the OCP using potentiometric-based circuitry, resulting in a more accurate initial ion concentration level measurement. Additionally, since the amperometric-based circuitry (e.g., the potentiostat 406) is less susceptible to environmental noises relative to potentiometric-based circuity, determining the updated ion concentration levels based on the measured change in the current associated with the ISE may be more accurate.

[0098] As noted above, in some embodiments, the one or more processors 410 of the MCU 408 may be configured to select a random bias voltage or a pre-defined bias voltage (e.g., one stored in memory of the wearable device) as a starting point for the incremental adjustment described above. However, because the random / pre-defined bias voltage may be significantly different from the OCP of the ion sensor, selecting the random bias voltage or the pre-defined bias voltage as the starting point may lead to an increase in time in determining the OCP of the ion sensor since the bias voltage may need to be iteratively adjusted more, leading to increased wait times for the user to obtain their estimated ion concentration level and poor user experience. More power may also be consumed using a random or predefined OCP relative to using a measured OCP.P+S Ref. No.: DEXC / 0946PC 35Dexcom Ref. No.: 0946-PCT01Accordingly, to help reduce these wait times, the wearable device 400 may be equipped with potentiometric-based circuitry configured to measure directly measure “rough,” “estimated,” or “approximate” OCP of the ion sensor 402, which may then be used as an initial bias voltage for the incremental adjustment. By using the directly measured OCP as the initial bias voltage, the wearable device 400 may not need to increment or decrement the bias voltage as much in order to determine the bias voltage that results in or causes the current associated with the ISE to be within the threshold range and / or to attain the particular value (e.g., null current).

[0099] For example, as shown in FIG. 5, in addition to including the amperometricbased circuitry, such as the potentiostat 406, the AFE 404 of the wearable device 400 may be equipped with potentiometric -based circuity, such as the galvanostat 502. Additionally, as shown, the wearable device 400 may also be equipped with a plurality of switches (e.g., SI, S2, and S3) that may be used by the one or more processors 410 to selectively connect or couple the ISE and the RE of the ion sensor 402 to the galvanostat 502 and the potentiostat 406.

[0100] In some embodiments, the one or more processors 410 of the MCU 408 of the wearable device 400 may be configured to couple the ISE and RE of the ion sensor 402 to the galvanostat 502 of the potentiometric-based circuitry using the switch SI and the switch S2, respectively. Thereafter, the galvanostat 502 may then be used to directly measure the OCP between the ISE and the RE of the ion sensor 402. In some cases, because the potentiometric -based circuitry is susceptible to environmental or other noise, the measured OCP may represent an estimated or rough OCP of the ion sensor 402. In other words, the measured OCP or rough OCP may be associated with a first noise level. However, this rough OCP may be used to indirectly measure or determine the noise-less, substantially noiseless, or true OCP of the ion sensor 402 (e.g., by using the rough OCP as a starting point for the potentiostat 406 to find a particular current or a current is within a threshold range).

[0101] For example, after measuring the OCP of the ion sensor 402, the galvanostat 502 may provide the measured OCP to the one or more processors 410 of the MCU 408. The one or more processors 410 of the MCU 408 may then be configured to use the measured OCP to determine an initial bias voltage for the potentiostat 406 to apply to the ISE of the ion sensor 402. For example, in some embodiments, the initial bias voltage may be set to the measured OCP. The one or more processors 410 may then configure theP+S Ref. No.: DEXC / 0946PC 36Dexcom Ref. No.: 0946-PCT01 potentiostat 406 with the initial bias voltage.

[0102] Thereafter, when a measurement of the ion concentration level is to be performed, the one or more processors 410 may be configured to couple the ISE and RE of the ion sensor 402 to the potentiostat 406 using switch SI and switch S2, respectively (e.g., to ISE and RE ports of the potentiostat 406). The wearable device 400 may then use the techniques related to iteratively adjusting the bias voltage described above with respect to FIG. 4 to determine the bias voltage that results in the current associated with the ISE of the ion sensor 402 (e.g., the true, noise-free, or substantially noise free OCP of the ion sensor 402).

[0103] For example, the potentiostat 406 may first apply the initial bias voltage (e.g., determined based on the measured OCP of the ion sensor 402 by the galvanostat 502 associated with the first noise level) to the ISE of the ion sensor 402. A current associated with the ISE of the ion sensor 402 may then be provided by the potentiostat 406 to the one or more processors 410 of the MCU 408. Assuming that the current associated with the ISE of the ion sensor has not attained the particular value and / or is not within the threshold range described above, the one or more processors 410 may then adjust the bias voltage and configure the potentiostat 406 with a second bias voltage. The potentiostat 406 may then apply the second bias voltage to the ISE of the ion sensor 402. The second bias voltage may result in a second current associated with the ISE of the ion sensor 402, which may be provided by the potentiostat 406 to the one or more processors 410 and used to adjust the bias voltage again. As described above with respect to FIG. 4, this process of iteratively adjusting the bias voltage may continue until the current associated with the ISE of the ion sensor 402 is within the threshold range and / or attains the particular value (e.g., the null current or approximately zero).

[0104] As noted above, the adjusted bias voltage that results in or causes the current associated with the ISE of the ion sensor 402 to be within the threshold range and / or to attain the particular value (e.g., ideally zero or substantially zero or a current that is within a threshold range) may correspond to the true, noise-free, or substantially noise-free OCP of the ion sensor 402. In other words, the OCP associated with the adjusted bias voltage may be associated with a second noise level, which may be less than the first noise level. Accordingly, by iteratively adjusting the bias voltage, the wearable device 400 is able to indirectly measure the OCP of the ion sensor without the negative effects associated with environmental or other noise. The one or more processors 410 may then be used to convertP+S Ref. No.: DEXC / 0946PC 37Dexcom Ref. No.: 0946-PCT01 the bias voltage that resulted in or caused the current associated with the ISE to be within the threshold range and / or to attain the particular value (e.g., the true OCP of the ion sensor 402) into an initial estimated ion concentration level of the user of the wearable device 400 based on the Nernst relation, as described above. The estimated ion concentration level may be stored in the one or more memories 412 of the MCU 408 and transmitted, by the transceiver 414, to a display device for display to the user.

[0105] Additionally, as described above with respect to FIG. 4, changes in the ion concentration level may be determined based on changes in the current associated with the ISE of the ion sensor 402. For example, once the bias voltage (e.g., the true, noise- free, or substantially noise OCP) that results in or causes the current associated with the ISE to be within the threshold range and / or to attain the particular value (e.g., the null current) is determined, this bias voltage may be applied by the potentiostat 406 for a fixed period of time. The one or more processors 410 may then be configured to determine how the current associated with the ISE of the ion sensor 402 changes over the fixed period of time. For example, as the current associated with the ISE of the ion sensor 402 changes over the fixed period of time, the one or more processors 410 may be configured to determine a change in the estimated ion concentration level based on the change in the current associated with the ISE of the ion sensor. In some cases, the wearable device 400 may then be configured to transmit, via the transceiver 414, any changes in the ion concentration level to the display device periodically.

[0106] In some embodiments, the OCP of the ion sensor 402 may change over time (e.g., due to drift, environmental noise, for instance, temperature and / or pressure, change of one or more membrane properties, etc.), which may affect the accuracy of the estimated ion concentration level determined by the wearable device 400. Accordingly, in some embodiments, the wearable device 400 may be configured to periodically re-perform the techniques described above for iteratively adjusting the bias voltage to indirectly measure the OCP of the ion sensor 402. For example, in some embodiments, after determining a first bias voltage that results in or causes the current associated with the ISE of the ion sensor 402 to be within the threshold range and / or to attain the particular value (e.g., a first OCP), the potentiostat 406 of the wearable device 400 may be configured to apply this bias voltage to the ion sensor 402 for a first fixed period of time.

[0107] After the first fixed period of time, the wearable device 400 may then be configured to re-perform the incremental adjustment of the bias voltage to determine aP+S Ref. No.: DEXC / 0946PC 38Dexcom Ref. No.: 0946-PCT01 second bias voltage that results in or causes the current associated with the ISE of the ion sensor 402 to be within the threshold range and / or to attain the particular value (e.g., a second OCP). The potentiostat 406 may then be configured to apply the second bias voltage to the ion sensor 402 for a second fixed period of time following the first fixed period of time. In some embodiments, the first bias voltage may be used as a starting point for iteratively adjusting the bias voltage to determine the second bias voltage (e.g., the second OCP). In some embodiments, the galvanostat 502 may be configured to perform another “rough” measurement of the OCP of the ion sensor 402, which may then be used as a starting point for iteratively adjusting the bias voltage to determine the second bias voltage (e.g., the second OCP).

[0108] In some embodiments, a change in the OCP of the ion sensor 402 over time may be associated with a change in the health of the ion sensor 402 (e.g., a sensitivity of the ion sensor 402 may be degrading, damage to a membrane of the ion sensor 402, etc.). Accordingly, in some embodiments, if the wearable device 400 detects a difference between the first bias voltage (e.g., first OCP) and the second bias voltage (e.g., second OCP), the wearable device 400 may be configured to send a notification to a display device indicating a change in the health of the ion sensor 402. For example, in some embodiments, the notification may notify a user of the display device that a sensitivity of the ion sensor 402 is degrading and to replace the wearable device 400.

[0109] In some embodiments, rather than iteratively adjusting the bias voltage using the techniques described above, the wearable device 400 may be configured to measure the “rough” OCP of the ion sensor 402 using the galvanostat 502, configure the potentiostat 406 with a bias voltage corresponding to the measured OCP, and apply this bias voltage to the ISE of the ion sensor 402. The bias voltage applied by the potentiostat 406 may result in or cause a current associated with the ISE of the ion sensor 402 to be received and measured by the one or more processors 410 of the MCU 408. Thereafter, the one or more processors 410 may be configured to determine an initial estimated ion concentration level based on the measured OCP (e.g., using techniques described above relating to inverting the Nemst relation and solving for the ion concentration level). The one or more processors 410 may then be configured to use the measured current to determine a change in the initial estimated ion concentration level of the user of the wearable device 400. In some embodiments, because the amperometric-based circuitry (e.g., the potentiostat 406) is less susceptible to environmental noises while also having aP+S Ref. No.: DEXC / 0946PC 39Dexcom Ref. No.: 0946-PCT01 higher sensitivity (e.g., relative to the potentiometric-based circuitry, including the galvanostat 502), using the measured current to determine changes in the initial estimated ion concentration level based on the current received and measured one or more processors 410 may be more accurate (e.g., as compared to determining the changes in the estimated ion concentration level based on the “rough” OCP measured by the galvanostat 502).

[0110] In certain scenarios, when the wearable device 400 is in an idle mode and not performing measurements of an ion concentration level, charge may accumulate on the ISE or working electrode and reference electrode of the analyte sensor, causing the OCP of the ion sensor 402 to rise and reducing the accuracy of the OCP measurement performed by the galvanostat 502. In some embodiments, to avoid scenarios in which accumulated charge on the working electrode and / or reference electrode of the ion sensor 402 negatively affects an accuracy of OCP performed by the galvanostat 502, the one or more processors 410 of the wearable device 400 may be configured to use switch S3 of the plurality of switches to selectively short the ISE and the RE of the ion sensor 402, to remove any accumulated charge (e.g., while switches SI and S2 are open). Thereafter, the ISE and the RE of the ion sensor 402 may then be un-shorted or un-coupled (e.g., via switch S3), allowing the ion sensor 402 to reach a new equilibrium more quickly and allow the galvanostat 502 to more accurately measure the OCP. In some embodiments, the ISE and the RE of the ion sensor 402 may be briefly connected to ground to bleed off any accumulated charge. In some embodiments, to ensure accuracy, the wearable device 400 may be configured to selectively short the ISE and the RE of the ion sensor 402 using switch S3 before each ion concentration measurement.

[0111] As discussed above, the bias voltage applied by the potentiostat 406 may be iteratively adjusted until the current associated with the ISE of the ion sensor 402 is within the threshold range and / or attains the particular value (e.g., the null current). In some embodiments, the bias voltage may be iteratively adjusted in different manners. For example, in some embodiments, the bias voltage may be iteratively adjusted using digital means at the MCU 408, such as by executing a min- search algorithm in firmware of the MCU 408 to identify the null current or current having the particular value.

[0112] In some embodiments, the bias voltage may be iteratively adjusted based on analog feedback (e.g., a current feedback amplifier) to set the bias voltage until the current associated with the ISE is within the threshold range and / or attains the particular value,P+S Ref. No.: DEXC / 0946PC 40Dexcom Ref. No.: 0946-PCT01 null current, or substantially null current. FIG. 6 illustrates an example of using analog feedback to iteratively adjust the bias voltage. For example, as shown, FIG. 6 again includes the wearable device 400 (e.g., in an analog configuration). In FIG. 6, the one or more processors 410 of the MCU 408 may be configured to select an initial bias voltage that estimates the OCP of the ion sensor 402 (e.g., selecting a random bias voltage or a pre-defined bias voltage). The one or more processors 410 may then configure the potentiostat 406 with the initial bias voltage at 416.

[0113] Thereafter, the potentiostat 406 may apply the configured initial bias voltage to the ISE of the ion sensor 402. Based on the initial bias voltage applied to the ISE of the ion sensor 402, an analog signal representing the current associated with the ISE may then be received at a feedback and signal conditioning (FSC) module 602. The FSC module 602 may be configured to filter the analog signal representing the current associated with the ISE to remove any undesired noise, convert the filtered analog signal representing the current associated with the ISE to a voltage signal, and offset or scale the voltage signal with adjustable gains. Thereafter, based on the received analog signal representing the current associated with the ISE, the FSC module 602 may output the voltage signal to a feedback amplifier 604. As shown, the feedback amplifier 604 may be configured to receive, as input, the initial bias voltage configured by the one or more processors 410 of the MCU and the voltage signal from the FSC module 602. The feedback amplifier 604 may then output a signal representing an adjusted bias voltage, which may be used to configure the potentiostat 406 at bias voltage module 416.

[0114] The potentiostat 406 may then apply the adjusted bias voltage to the ISE of the ion sensor 402, which may result in another analog signal representing a new current associated with the ISE of the ion sensor 402 being received at the FSC module 602. The FSC module 602 may then output another voltage signal based on the new current associated with the ISE of the ion sensor 402, causing the bias voltage to again be adjusted by the feedback amplifier 604. This process may be repeated until the current associated with the ISE of the ion sensor 402 is within the threshold range and / or attains the particular value (e.g., the null current).

[0115] In some embodiments, for each subsequent bias voltage adjustment, the feedback amplifier 604 may be configured to receive, as input, the initial bias voltage set by the MCU 408 (e.g., the random / pre-defined bias voltage or the bias voltage set based on the measured OCP) or the bias voltage from a previous adjustment step. After eachP+S Ref. No.: DEXC / 0946PC 41Dexcom Ref. No.: 0946-PCT01 adjustment, when the current associated with the ISE is high, negative feedback causes the feedback amplifier 604 to decrease the bias voltage set at bias voltage module 416 is reduced. This decreased bias voltage may then be used as an input to the feedback amplifier 604 at the next adjustment step. As a result of the decreased bias voltage, the current associated with the ISE may be lowered. As this process continues, the adjust bias voltage set at bias voltage module 416 and applied by the potentiostat 406 will gradually get closer to the OCP of the ion sensor 402 resulting in the current associated with the ISE of the ion sensor 402 being within the threshold range and / or attaining the particular value (e.g., the null current).

[0116] In some embodiments, another method for adjusting the bias voltage to be applied by the potentiostat 406 may be to use a voltammetry sweep at the potentiostat 406. In some embodiments, voltammetry waveforms may be continuously or quasi- continuously recorded to identify the null current or substantially null current. In some cases, square-wave or differential pulse voltammetry or pulsed amperometry may be performed to identify the null current or substantially null current.

[0117] In some embodiments, a dither may be applied to the bias voltage in the vicinity of the OCP to reduce or average out noise while maintaining a measurable, nonzero current. For example, if the ion sensor 402 suffers from sudden signal increases / decreases, in some embodiments, a dither or a certain level of random noise may be introduced into the bias voltage to smooth out these sudden signal increases / decreases .

[0118] In some embodiments, a resonance circuit may be used to dynamically adjust the bias voltage to determine the null current or substantially null current. For example, in some cases, a tuned frequency circuit with a fixed value inductor may be used in conjunction with the ion sensor 402, which functions as a capacitive element in the tuned circuit. For example, as shown in FIG. 4, the wearable device 400 may optionally include one or more inductive and / or capacitive (LC) elements 420. In some embodiments, the one or more LC elements 420 may include a fixed value inductor, which may be coupled in series with the ISE of the ion sensor 402. In such cases, the ion sensor 402, which may be associated with a capacitance value that varies with the ion concentration level, may resonate with the fixed value inductor of the one or more LC elements 420 at a particular frequency. For example, as the ion concentration level varies, so will the capacitance value associated with the ion sensor 402, resulting in a change in the tuned resonanceP+S Ref. No.: DEXC / 0946PC 42Dexcom Ref. No.: 0946-PCT01 frequency.

[0119] Accordingly, the one or more processors 410 of the wearable device 400 may be configured to incrementally adjust (e.g., increase or decrease) the bias voltage until the ion sensor 402 resonates with the fixed value inductor of the one or more LC elements 420 at the tuned resonance frequency. The bias voltage at which the ion sensor 402 resonates with the inductor may then be used by the one or more processors 410 to determine an initial estimated ion concentration level of the user based on the Nernst relation. Thereafter, any changes in the tuned resonance frequency between the ion sensor 402 and the inductor may be used to determine changes in the ion concentration level of the user since the tuned resonance frequency varies in accordance with changes in the ion concentration level.

[0120] In some embodiments, a sensitivity of ion concentration measurements and baseline dispersion reduction of the ion sensor 402 may be improved by applying a nonzero current mode, such as amperometry. For example, in some embodiments, to improve sensitivity when measuring an ion concentration level, the wearable device 400 may first be configured to apply a bias voltage to the ISE of the ion sensor 402. In some embodiments, the bias voltage may be determined using the techniques described above. Thereafter, based on the applied bias voltage, the one or more processors 410 of the wearable device 400 may be configured to receive and measure a current associated with the ISE over a measurement period using the potentiostat 406. In some embodiments, the one or more processors 410 may be configured to use the measured current associated with the ISE of the ion sensor 402 to measure or determine an estimated ion concentration level of the user of the wearable device 400.

[0121] In some embodiments, to improve sensitivity of the ion concentration level measurements, the one or more processors 410 of the wearable device 400 may be configured to integrate the measured current, with respect to time, over the measurement period, resulting in a coulometric profile. An initial ion concentration level may be determined (e.g., using a potentiostat, galvanostat, or a combination thereof as mentioned herein) at the start of the measurement period. During the measurement period, the integrated current may be used to determine a change in the ion concentration level for each measurement interval (e.g., 30 second, one minute, 5 minutes, etc.) within the measurement period. At the end of a first measurement interval at the beginning of the measurement period, the ion concentration level of the user may be determined byP+S Ref. No.: DEXC / 0946PC 43Dexcom Ref. No.: 0946-PCT01 combining or adding the initial ion concentration to the change in ion concentration measured based on the integrated current during the first measurement interval.

[0122] For each subsequent ion concentration determination for each measurement interval, the ion concentration may be determined at the end of the measurement interval by adding the change of the ion concentration based on the integrated current to the ion concentration at the start of the measurement interval (e.g., the ion concentration level determined at the end of the previous measurement interval). For example, the measurement period may be 23 hours, 11 hours, or 5 hours, and the initial ion concentration may be determined (e.g., using a potentiostat, galvanostat, or a combination thereof as mentioned herein) with one or more current or voltage measurements in the one hour, 30 minutes, or 10-minute period before the start of the measurement period. In some embodiments, the coulometric profile may be used to determine the estimated ion concentration level and / or trends in the ion concentration level (e.g., the ion concentration level as risen or dropped by a certain amount). In some embodiments, the one or more processors 410 may be configured to integrate the measured current, with respect to time, over the measurement period in at least one of an analog domain using an integrator circuit of the wearable device or a digital domain using an integral approximation method (e.g. Riemann sum, midpoint Rule, trapezoidal Rule, Simpson's rule, etc.) over the measurement period.

[0123] In some cases, the coulometric profile may allow for adjusting a sensitivity and / or response time associated with the ion sensor 402. For example, in some cases, based on the coulometric profile, the sensitivity may be proportional to the capacitance of a solid contact material (e.g., carbon solid contact layer or conducting polymers) used in fabrication of the ISE of the ion sensor 402. Accordingly, the sensitivity of the ion sensor 402 may be readily tunable (e.g. 10'8-10'5coulombs / decade (C / dec) of ion concentration change) based on capacitance associated with the ISE of the ion sensor 402. Additionally, in some cases, a response time of the ion sensor 402 may also be tuned (e.g. 30 seconds, 1 minute, 5 minutes, 10 minutes, 15 minutes, etc.) by tailoring the surface area and thickness of the solid contact material and an ion selective membrane of the ion sensor 402, respectively.

[0124] As noted above, in some embodiments, as shown in FIG. 4, the wearable device 400 may optionally include the one or more LC elements 420. In some embodiments, for example, the one or more LC elements 420 may include one or moreP+S Ref. No.: DEXC / 0946PC 44Dexcom Ref. No.: 0946-PCT01 capacitors coupled in series with the ISE of the ion sensor 402. The one or more capacitors may be configured to significantly improve amperometric / coulometric measurement response times and drift profiles associated with the ion sensor 402. For example, a total capacitance of the circuit may depend on a reciprocal sum of the one or more capacitors and ion sensor 402. Therefore, coupling the one or more capacitors in series with the ISE of the ion sensor 402 may modulate the total capacitance and, thus, improve the response time associated with the ion sensor 402. However, because the overall sensitivity of the ion sensor 402 is proportional to the capacitance, capacitance values of the one or more capacitors may be selected in a manner that balances the improved response time of the ion sensor 402 with a reduction in the sensitivity of the ion sensor 402 (e.g., captaincies in the range of 1-200 microfarads).

[0125] In some cases, the one or more capacitors may comprise a variable capacitor. In some cases, the one or more processors 410 of the wearable device 400 may be configured to adjust the variable capacitor to adjust at the sensitivity and response time associated with the analyte sensor. For example, in some cases, the one or more processors 410 may detect that at least one of the response time associated with the ion sensor 402 exceeds a particular response time threshold (e.g., it is taking longer than usual to measure the ion concentration level, for instance, determined based on the time to measure the ion concentration level exceeding a threshold which may be determined based on the time for one or more previous ion concentration levels, such as an average, based on a time configured or set prior to an analyte sensor session, based on a time configured at a factory or during manufacture, longer than a measurement interval, for example, greater than 5 minutes, 10 minutes, 15 minutes, etc.) or the sensitivity associated with the ion sensor 402 has fallen below a particular sensitivity threshold (e.g., the ion concentration level measurements are not as granular or accurate, for example, less than 10'8, 10'10, 102C / dec). In such cases, the one or more processors 410 of the wearable device 400 may be configured to adjust a capacitance value of the variable capacitor such that the response time is reduced back to at least the particular response time threshold and sensitivity is increased back to at least the particular sensitivity threshold.Example Operations of a Wearable Device

[0126] FIG. 7 shows an example of a method 700 for measuring an ion concentration level of a user of a wearable device. The method 700 may be performed by the wearable device, such as the SS 8 described with respect to FIGS. 1, 2, 3A, 3B, and 3C and / or theP+S Ref. No.: DEXC / 0946PC 45Dexcom Ref. No.: 0946-PCT01 wearable device 400 described with respect to FIGS. 4, 5, and 6. In some embodiments, method 700 may be performed by one or more processors of the wearable device, such as the one or more processors 11 and / or the one or more processors 410, based on instructions stored in one or more memories. For example, in some embodiments, the wearable device may include one or more memories, such as the one or more memories 14 and / or the one or more memories 412, including instructions that, when executed by the one or more processors, cause the wearable device to perform the method 700.

[0127] As shown, method 700 begins at 702 with the wearable device applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) or working electrode of a transcutaneous ion sensor of the wearable device.

[0128] At 704, the wearable device measures a current associated with the ISE or working electrode of the transcutaneous ion sensor after applying the bias voltage to the ISE or working electrode.

[0129] At 706, the wearable device adjusts the bias voltage based on the measured current associated with the ISE or working electrode until the measured current is within a threshold range.

[0130] At 708, the wearable device determines, based at least in part on the adjusted bias voltage, the ion concentration level of the user.

[0131] At 710, the wearable device transmits an indication of the ion concentration level of the user to a display device for display to the user.

[0132] In some embodiments, the threshold range is negative five to positive five picoamps.

[0133] In some embodiments, the threshold range is three to 100 picoamps.

[0134] In some embodiments, the bias voltage is associated with a first estimate of the ion concentration level and the adjusted bias voltage is associated with a second estimate of the ion concentration level. In some embodiments, the second estimate of the ion concentration level is closer to the ion concentration of the user relative to the first estimate of the ion concentration level.

[0135] In some embodiments, the bias voltage is associated with a first accuracy level of the ion concentration level and the adjusted bias voltage is associated with a second accuracy level of ion concentration level. In some embodiments, the secondP+S Ref. No.: DEXC / 0946PC 46Dexcom Ref. No.: 0946-PCT01 accuracy level is higher than the first accuracy level.

[0136] In some embodiments, adjusting the bias voltage at 708 includes iteratively adjusting the bias voltage. In some embodiments, the method 700 may further include iteratively applying the adjusted bias voltage to the ISE or working electrode. In some embodiments, the method 700 may further include iteratively measuring the current associated with the ISE or working electrode after applying the adjusted bias voltage. In some embodiments, iteratively adjusting the bias voltage, iteratively applying the adjusted bias voltage to the ISE or working electrode, and iteratively measuring the current associated with the ISE or working electrode are performed until the current associated with the ISE or working electrode is within the threshold range.

[0137] In some embodiments, the threshold range is defined relative to a particular value. In some embodiments, the particular value is approximately or substantially zero amps.

[0138] In some embodiments, when the current associated with the ISE or working electrode is above the threshold range, iteratively adjusting the bias voltage comprises iteratively decreasing the bias voltage by a first threshold amount until the current associated with the ISE or working electrode is within the threshold range.

[0139] In some embodiments, when the current associated with the ISE or working electrode is below the threshold range, iteratively adjusting the bias voltage comprises iteratively increasing the bias voltage by a second threshold amount until the current associated with the working electrode is within the threshold range.

[0140] In some embodiments, iteratively adjusting the bias voltage comprises iteratively adjusting the bias voltage according to a fixed periodicity.

[0141] In some embodiments, iteratively adjusting the bias voltage comprises iteratively adjusting the bias voltage according to a dynamic periodicity. In some embodiments, the dynamic periodicity is based on at least one of: a magnitude of the current associated with the ISE, a rate of change of the current associated with the ISE, or a physiological relevant time period related to an ion for which the ion concentration level is being measured.

[0142] In some embodiments, determining the ion concentration level at 710 is further based on the adjusted bias voltage that results in or causes the current associated with the working electrode to be within the threshold range.P+S Ref. No.: DEXC / 0946PC 47Dexcom Ref. No.: 0946-PCT01

[0143] In some embodiments, determining the ion concentration level of the user comprises inverting a Nemst relation based on the applied bias voltage and an offset voltage associated with the transcutaneous ion sensor.

[0144] In some embodiments, determining the bias voltage to be applied to the working electrode at 702 comprises measuring, by a galvanostat of the wearable device, an open circuit potential (OCP) between the working electrode transcutaneous ion sensor and a reference electrode of the transcutaneous ion sensor. In some embodiments determining the bias voltage to be applied to the ISE or working electrode at 702 comprises selecting the OCP as the bias voltage to be applied to the ISE or working electrode.

[0145] In some embodiments, the OCP measured by the galvanostat is associated with a first noise level and an OCP (e.g., measured by the potentiostat) associated with the adjusted bias voltage is associated with a second noise level. In some embodiments, the second noise level is less than the first noise level.

[0146] In some embodiments, the method 700 further includes using a plurality of switches of the wearable device to connect the galvanostat to the ISE or working electrode and the reference electrode when measuring the OCP. In some embodiments, method 700 further includes using the plurality of switches to connect the potentiostat to the ISE or working electrode and the reference electrode when applying the bias voltage and measuring the current associated with the ISE or working electrode.

[0147] In some embodiments, method 700 further includes using the plurality of switches to short the ISE or working electrode and the reference electrode.

[0148] In some embodiments, using the plurality of switches to short the ISE or working electrode and the reference electrode comprises using the plurality of switches to connect the ISE or working electrode and the reference electrode to ground.

[0149] In some embodiments, using the plurality of switches to short the ISE or working electrode and the reference electrode comprises using the plurality of switches to short the ISE or working electrode and the reference electrode prior to measuring the OCP.

[0150] In some embodiments, measuring the current associated with the ISE or working electrode at 706 comprises measuring the current associated with the ISE or working electrode over a measurement period.P+S Ref. No.: DEXC / 0946PC 48Dexcom Ref. No.: 0946-PCT01

[0151] In some embodiments, determining the ion concentration level 710 comprises determining a coulometric profile associated with the ion concentration level by integrating the measured current, with respect to time, over the measurement period. In some embodiments, determining the ion concentration level 710 determining the ion concentration level based on the coulometric profile.

[0152] In some embodiments, integrating the measured current, with respect to time, over the measurement period is performed in at least one of an analog domain using an integrator circuit of the wearable device or a digital domain using a Riemann sum over the measurement period.

[0153] In some embodiments, measuring the current associated with the ISE or working electrode at 706 is based on one or more capacitors connected in series between the potentiostat and the ISE or working electrode.

[0154] In some embodiments, the one or more capacitors comprise at least one variable capacitor.

[0155] In some embodiments, method 700 further includes detecting that at least one of a response time associated with the transcutaneous ion sensor exceeds a particular response time threshold or a sensitivity associated with the transcutaneous ion sensor has fallen below a particular sensitivity threshold. In some embodiments, method 700 further includes adjusting, based on the detection, a capacitance of the variable capacitor such that at least one of the response time associated with the transcutaneous ion sensor is reduced back to at least the particular response time threshold or the sensitivity associated with the transcutaneous ion sensor is increased back to at least the particular sensitivity threshold.

[0156] In some embodiments, the wearable device includes one or more inductors coupled in series with the ISE of the transcutaneous ion sensor. In some embodiments, the one or more inductors comprise one or more fixed value inductors. In some embodiments, the transcutaneous ion sensor is associated with a particular capacitance value (e.g., 1-200 microfarads). In some embodiments, the particular capacitance value varies with the ion concentration level. In some embodiments, adjusting the bias voltage at 708 includes iteratively adjusting the bias voltage until, based on the particular capacitance value associated with the transcutaneous ion sensor, the transcutaneous ion sensor resonates with the one or more inductors at a particular resonance frequency. InP+S Ref. No.: DEXC / 0946PC 49Dexcom Ref. No.: 0946-PCT01 some embodiments, iteratively adjusting the bias voltage may include at least one of iteratively increasing the bias voltage or iteratively decreasing the bias voltage. In some embodiments, determining the ion concentration level of the user may be based on the particular resonance frequency. In some embodiments, method 700 may further include determining a change in the ion concentration level based on a change in the particular resonance frequency at which the transcutaneous ion sensor resonates with the one or more inductors.

[0157] FIG. 8 shows an example of a method 800 for measuring an ion concentration level of a user of a wearable device. The method 800 may be performed by the wearable device, such as the SS 8 described with respect to FIGS. 1, 2, 3A, 3B, and 3C and / or the wearable device 400 described with respect to FIGS. 4, 5, and 6. In some embodiments, method 800 may be performed by one or more processors of the wearable device, such as the one or more processors 11 and / or the one or more processors 410, based on instructions stored in one or more memories. For example, in some embodiments, the wearable device may include one or more memories, such as the one or more memories 14 and / or the one or more memories 412, including instructions that, when executed by the one or more processors, cause the wearable device to perform the method 800.

[0158] As shown, method 800 begins at 802 with the wearable device applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) or working electrode of a transcutaneous ion sensor of the wearable device.

[0159] At 804, the wearable device measures a current associated with the ISE or working electrode of the transcutaneous ion sensor after applying the bias voltage to the ISE or working electrode.

[0160] At 806, the wearable device determines, when the measured current is within a threshold range, the ion concentration level of the user based at least in part on the bias voltage.

[0161] At 810, the wearable device transmits an indication of the ion concentration level of the user to a display device for display to the user.

[0162] In some embodiments, the threshold range is negative five to positive five picoamps.

[0163] In some embodiments, the threshold range is three to 100 picoamps.P+S Ref. No.: DEXC / 0946PC 50Dexcom Ref. No.: 0946-PCT01

[0164] In some embodiments, determining the bias voltage to be applied to the ISE or working electrode comprises measuring, by a galvanostat of the wearable device, an open circuit potential (OCP) between the ISE or working electrode of the transcutaneous ion sensor and a reference electrode of the transcutaneous ion sensor. In some embodiments, determining the bias voltage to be applied to the ISE or working electrode comprises selecting the OCP as the bias voltage to be applied to the ISE or working electrode.

[0165] In some embodiments, method 800 further includes using a plurality of switches of the wearable device to couple the galvanostat to the ISE and the reference electrode when measuring the OCP. In some embodiments, method 800 further includes using the plurality of switches to couple the potentiostat to the ISE and the reference electrode when applying the bias voltage and measuring the current associated with the ISE.

[0166] In some embodiments, method 800 further includes using the plurality of switches to short the ISE and the reference electrode.

[0167] In some embodiments, using the plurality of switches to short the ISE and the reference electrode comprises using the plurality of switches to couple the ISE and the reference electrode to ground.

[0168] In some embodiments, using the plurality of switches to short the ISE and the reference electrode comprises using the plurality of switches to short the ISE and the reference electrode prior to measuring the OCP.

[0169] In some embodiments, measuring the current associated with the ISE comprises measuring the current associated with the ISE over a measurement period.

[0170] In some embodiments, determining the ion concentration level comprises determining a coulometric profile associated with the ion concentration level by integrating the measured current, with respect to time, over the measurement period. In some embodiments, determining the ion concentration level comprises determining the ion concentration level based on the coulometric profile.

[0171] In some embodiments integrating the measured current, with respect to time, over the measurement period is performed in at least one of: an analog domain using an integrator circuit of the wearable device or a digital domain using a Riemann sum over the measurement period.P+S Ref. No.: DEXC / 0946PC 51Dexcom Ref. No.: 0946-PCT01

[0172] In some embodiments, measuring the current associated with the ISE is based on one or more capacitors coupled in series between the potentiostat and the ISE.

[0173] In some embodiments, the one or more capacitors comprise at least one variable capacitor.

[0174] In some embodiments, method 800 further includes detecting that at least one of a response time associated with the transcutaneous ion sensor exceeds a particular response time threshold or a sensitivity associated with the transcutaneous ion sensor has fallen below a particular sensitivity threshold. In some embodiments, method 800 further includes adjusting, based on the detection, a capacitance of the variable capacitor such that at least one of the response time associated with the transcutaneous ion sensor is reduced back to at least the particular response time threshold or the sensitivity associated with the transcutaneous ion sensor is increased back to at least the particular sensitivity threshold.

[0175] In some embodiments, the wearable device includes one or more inductors coupled in series with the ISE of the transcutaneous ion sensor.

[0176] In some embodiments, the one or more inductors comprise one or more fixed value inductors.

[0177] In some embodiments, the transcutaneous ion sensor is associated with a particular capacitance value.

[0178] In some embodiments, the particular capacitance value varies with the ion concentration level.

[0179] In some embodiments, method 800 further includes iteratively adjusting the bias voltage until, based on the particular capacitance value associated with the transcutaneous ion sensor, the transcutaneous ion sensor resonates with the one or more inductors at a particular resonance frequency.

[0180] In some embodiments, determining the ion concentration level of the user is based on the particular resonance frequency.

[0181] In some embodiments, method 800 further includes determining a change in the ion concentration level based on a change in the particular resonance frequency at which the transcutaneous ion sensor resonates with the one or more inductors.Example Communications DeviceP+S Ref. No.: DEXC / 0946PC 52Dexcom Ref. No.: 0946-PCT01

[0182] FIG. 9 depicts aspects of an example communications device 900. In some aspects, communications device 900 is a wearable device, such as the SS 9 described with respect to FIGS. 1, 2, 3A, 3B, and 3C and / or the wearable device described with respect to FIGS. 4, 5, 6, and / or 7.

[0183] The communications device 900 includes a processing system 905 coupled to the transceiver 955 (e.g., a transmitter and / or a receiver). The transceiver 955 is configured to transmit and receive signals for the communications device 900 via the antenna 960, such as the various signals and messages as described herein. The processing system 905 may be configured to perform processing functions for the communications device 900, including processing signals received and / or to be transmitted by the communications device 900.

[0184] The processing system 905 includes one or more processors 910. In various aspects, the one or more processors 910 may be representative of the one or more processors 11, as described with respect to FIG. 2. The one or more processors 910 are coupled to a computer-readable medium / memory 930 via a bus 950. In some aspects, the computer-readable medium / memory 930 may be representative of the one or more memories 14, as described with respect to FIG. 2. In certain aspects, the computer- readable medium / memory 930 is configured to store instructions (e.g., computerexecutable code) that when executed by the one or more processors 910, cause the one or more processors 910 to perform the method 700 described with respect to FIG. 7, or any aspect related to this method. Note that reference to a processor performing a function of communications device 900 may include one or more processors 910 performing that function of communications device 900.

[0185] In the depicted example, computer-readable medium / memory 930 stores code (e.g., executable instructions), such as code for determining 935, code for applying936, code for measuring 937, code for adjusting 938, code for transmitting 939, code for inverting 940, code for selecting 941, code for using 942, and code for detecting 943. Processing of the code for determining 935, code for applying 936, code for measuring937, code for adjusting 938, code for transmitting 939, code for inverting 940, code for selecting 941, code for using 942, and code for detecting 943 may cause the communications device 900 to perform the method 700 described with respect to FIG. 7, or any aspect related to these methods.P+S Ref. No.: DEXC / 0946PC 53Dexcom Ref. No.: 0946-PCT01

[0186] The one or more processors 910 include circuitry configured to implement (e.g., execute) the code stored in the computer-readable medium / memory 930, including circuitry for determining 915, circuitry for applying 916, circuitry for measuring 917, circuitry for adjusting 918, circuitry for transmitting 919, circuitry for inverting 920, circuitry for selecting 921, circuitry for using 922, and circuitry for detecting 923. Processing with circuitry for determining 915, circuitry for applying 916, circuitry for measuring 917, circuitry for adjusting 918, circuitry for transmitting 919, circuitry for inverting 920, circuitry for selecting 921, circuitry for using 922, and circuitry for detecting 923 may cause the communications device 900 to perform the method 700 described with respect to FIG. 7, or any aspect related to these methods.Example Clauses

[0187] Implementation examples are described in the following numbered clauses:

[0188] Clause 1: A method, by a wearable device, for measuring an ion concentration level of a user of the wearable device, comprising: applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) of a transcutaneous ion sensor of the wearable device; after applying the bias voltage to the ISE, measuring a current associated with the ISE of the transcutaneous ion sensor; adjusting the bias voltage based on the measured current associated with the ISE until the measured current is within a threshold range; determining, based at least in part on the adjusted bias voltage, the ion concentration level of the user; and transmitting an indication of the ion concentration level of the user to a display device for display to the user.

[0189] Clause 2: The method of Clause 1, wherein the threshold range is negative five to positive five picoamps.

[0190] Clause 3: The method of Clause 1, wherein the threshold range is three to 100 picoamps.

[0191] Clause 4: The method of any one of Clauses 1-3, wherein: the bias voltage is associated with a first estimate of the ion concentration level and the adjusted bias voltage is associated with a second estimate of the ion concentration level; and the second estimate of the ion concentration level is closer to the ion concentration of the user relative to the first estimate of the ion concentration level.P+S Ref. No.: DEXC / 0946PC 54Dexcom Ref. No.: 0946-PCT01

[0192] Clause 5: The method of any one of Clauses 1-4, wherein: the bias voltage is associated with a first accuracy level of the ion concentration level and the adjusted bias voltage is associated with a second accuracy level of ion concentration level; and the second accuracy level is higher than the first accuracy level.

[0193] Clause 6: The method of any one of Clauses 1-5, wherein: adjusting the bias voltage comprises iteratively adjusting the bias voltage; and the method further comprises: iteratively applying the adjusted bias voltage to the ISE; and iteratively measuring the current associated with the ISE after applying the adjusted bias voltage; and iteratively adjusting the bias voltage, iteratively applying the adjusted bias voltage to the ISE, and iteratively measuring the current associated with the ISE are performed until the current associated with the ISE is within the threshold range.

[0194] Clause 7: The method of Clause 6, wherein the threshold range is defined relative to a particular value; and the particular value is approximately or substantially zero amps.

[0195] Clause 8: The method of any one of Clauses 6-7, wherein iteratively adjusting the bias voltage comprises: when the current associated with the ISE is above the threshold range, iteratively decreasing the bias voltage by a first threshold amount until the current associated with the ISE is within the threshold range; and when the current associated with the ISE is below the threshold range, iteratively increasing the bias voltage by a second threshold amount until the current associated with the ISE is within the threshold range.

[0196] Clause 9: The method of any one of Clauses 6-8, wherein iteratively adjusting the bias voltage comprises iteratively adjusting the bias voltage according to a fixed periodicity.

[0197] Clause 10: The method of any one of Clauses 6-8, wherein: iteratively adjusting the bias voltage comprises iteratively adjusting the bias voltage according to a dynamic periodicity; and the dynamic periodicity is based on at least one of: a magnitude of the current associated with the ISE; a rate of change of the current associated with the ISE; or a physiological relevant time period related to an ion for which the ion concentration level is being measured.

[0198] Clause 11: The method of any one of Clauses 6-10, wherein determining the ion concentration level is further based on the adjusted bias voltage that results in orP+S Ref. No.: DEXC / 0946PC 55Dexcom Ref. No.: 0946-PCT01 causes the current associated with the ISE to be within the threshold range.

[0199] Clause 12: The method of Clause 11, wherein determining the ion concentration level of the user comprises inverting a Nernst relation based on the applied bias voltage and an offset voltage associated with the transcutaneous ion sensor.

[0200] Clause 13: The method of any one of Clauses 1-12, wherein determining the bias voltage to be applied to the ISE comprises: measuring, by a galvanostat of the wearable device, an open circuit potential (OCP) between the ISE of the transcutaneous ion sensor and a reference electrode of the transcutaneous ion sensor; and selecting the OCP as the bias voltage to be applied to the ISE.

[0201] Clause 14: The method of Clause 13, wherein: the OCP measured by the galvanostat is associated with a first noise level and an OCP associated with the adjusted bias voltage is associated with a second noise level; and the second noise level is less than the first noise level.

[0202] Clause 15: The method of any one of Clauses 13-14, further comprising: using a plurality of switches of the wearable device to couple the galvanostat to the ISE and the reference electrode when measuring the OCP; and using the plurality of switches to couple the potentiostat to the ISE and the reference electrode when applying the bias voltage and measuring the current associated with the ISE.

[0203] Clause 16: The method of Clause 15, further comprising using the plurality of switches to short the ISE and the reference electrode.

[0204] Clause 17: The method of Clause 16, wherein using the plurality of switches to short the ISE and the reference electrode comprises using the plurality of switches to couple the ISE and the reference electrode to ground.

[0205] Clause 18: The method of Clause 15, wherein using the plurality of switches to short the ISE and the reference electrode comprises using the plurality of switches to short the ISE and the reference electrode prior to measuring the OCP.

[0206] Clause 19: The method of any one of Clauses 1-18, wherein measuring the current associated with the ISE comprises measuring the current associated with the ISE over a measurement period.

[0207] Clause 20: The method of Clause 19, wherein determining the ion concentration level comprises: determining a coulometric profile associated with the ionP+S Ref. No.: DEXC / 0946PC 56Dexcom Ref. No.: 0946-PCT01 concentration level by integrating the measured current, with respect to time, over the measurement period; and determining the ion concentration level based on the coulometric profile.

[0208] Clause 21: The method of Clause 20, wherein integrating the measured current, with respect to time, over the measurement period is performed in at least one of: an analog domain using an integrator circuit of the wearable device; or a digital domain using a Riemann sum over the measurement period.

[0209] Clause 22: The method of any one of Clauses 1-21, wherein measuring the current associated with the ISE is based on one or more capacitors coupled in series between the potentiostat and the ISE.

[0210] Clause 23: The method of Clause 22, wherein the one or more capacitors comprise at least one variable capacitor.

[0211] Clause 24: The method of Clause 23, further comprising: detecting that at least one of a response time associated with the transcutaneous ion sensor exceeds a particular response time threshold or a sensitivity associated with the transcutaneous ion sensor has fallen below a particular sensitivity threshold; and adjusting, based on the detection, a capacitance of the variable capacitor such that at least one of the response time associated with the transcutaneous ion sensor is reduced back to at least the particular response time threshold or the sensitivity associated with the transcutaneous ion sensor is increased back to at least the particular sensitivity threshold.

[0212] Clause 25: The method of any one of Clauses 1-24, wherein the wearable device includes one or more inductors coupled in series with the ISE of the transcutaneous ion sensor.

[0213] Clause 26: The method of Clause 25, wherein the one or more inductors comprise one or more fixed value inductors.

[0214] Clause 27: The method of any one of Clauses 25-26, wherein the transcutaneous ion sensor is associated with a particular capacitance value.

[0215] Clause 28: The method of Clause 27, wherein the particular capacitance value varies with the ion concentration level.

[0216] Clause 29: The method of any one of Clauses 27-28, wherein adjusting the bias voltage includes iteratively adjusting the bias voltage until, based on the particularP+S Ref. No.: DEXC / 0946PC 57Dexcom Ref. No.: 0946-PCT01 capacitance value associated with the transcutaneous ion sensor, the transcutaneous ion sensor resonates with the one or more inductors at a particular resonance frequency.

[0217] Clause 30: The method of Clause 29, wherein determining the ion concentration level of the user is based on the particular resonance frequency.

[0218] Clause 31: The method of Clause 30, further comprising determining a change in the ion concentration level based on a change in the particular resonance frequency at which the transcutaneous ion sensor resonates with the one or more inductors.

[0219] Clause 32: A wearable device for measuring an ion concentration level of a user of the wearable device, comprising: a transcutaneous ion sensor comprising an ion selective electrode (ISE) and a reference electrode; a potentiostat configured to apply a bias voltage to the ISE of the transcutaneous ion sensor; and one or more processors configured to: measure a current associated with the ISE of the transcutaneous ion sensor; adjust the bias voltage applied by the potentiostat based on the measured current associated with the ISE until the measured current is within a threshold range; determine the ion concentration level of the user based at least in part on the adjusted bias voltage; and transmit an indication of the ion concentration level of the user to a display device for display to the user.

[0220] Clause 33: The wearable device of Clause 32, wherein the threshold range is negative five to positive five picoamps.

[0221] Clause 34: The wearable device of any one of Clauses 32-33, wherein the threshold range is three to 100 picoamps.

[0222] Clause 35: The wearable device of any one of Clauses 32-34, wherein: the bias voltage is associated with a first estimate of the ion concentration level and the adjusted bias voltage is associated with a second estimate of the ion concentration level; and the second estimate of the ion concentration level is closer to the ion concentration of the user relative to the first estimate of the ion concentration level.

[0223] Clause 36: The wearable device of any one of Clauses 32-35, wherein: the bias voltage is associated with a first accuracy level of the ion concentration level and the adjusted bias voltage is associated with a second accuracy level of ion concentration level; and the second accuracy level is higher than the first accuracy level.P+S Ref. No.: DEXC / 0946PC 58Dexcom Ref. No.: 0946-PCT01

[0224] Clause 37: The wearable device of any one of Clauses 32-36, wherein: in order to adjust the bias voltage, the one or more processors are configured to iteratively adjust the bias voltage; the potentiostat is further configured to iteratively apply the adjusted bias voltage to the ISE; and the one or more processors are further configured to iteratively measure the current associated with the ISE after the potentiostat applies the adjusted bias voltage; the one or more processors are configured to iteratively adjust the bias voltage and iteratively measure the current associated with the ISE until the current associated with the ISE is within the threshold range; and the potentiostat is configured to iteratively apply the adjusted bias voltage to the ISE until the current associated with the ISE is within the threshold range.

[0225] Clause 38: The wearable device of Clause 37, wherein the threshold range is defined relative to a particular value; and the particular value is approximately or substantially zero amps.

[0226] Clause 39: The wearable device of any one of Clauses 37-38, wherein, in order to iteratively adjust the bias voltage, the one or more processors are configured to: when the current associated with the ISE is above the threshold range, iteratively decrease the bias voltage by a first threshold amount until the current associated with the ISE is within the threshold range; and when the current associated with the ISE is below the threshold range, iteratively increase the bias voltage by a second threshold amount until the current associated with the ISE is within the threshold range.

[0227] Clause 40: The wearable device of any one of Clauses 37-39, wherein the one or more processors are configured to iteratively adjust the bias voltage according to a fixed periodicity.

[0228] Clause 41: The wearable device of any one of Clauses 37-39, wherein: the one or more processors are configured to iteratively adjust the bias voltage according to a dynamic periodicity; and the dynamic periodicity is based on at least one of: a magnitude of the current associated with the ISE; a rate of change of the current associated with the ISE; or a physiological relevant time period related to an ion for which the ion concentration level is being measured.

[0229] Clause 42: The wearable device of any one of Clause 37-41, wherein the one or more processors are configured to determine the ion concentration level based further on the adjusted bias voltage that causes the current associated with the ISE to be withinP+S Ref. No.: DEXC / 0946PC 59Dexcom Ref. No.: 0946-PCT01 the threshold range.

[0230] Clause 43: The wearable device of Clause 42, wherein, in order to determine the ion concentration level of the user, the one or more processors are configured to invert a Nernst relation based on the applied bias voltage and an offset voltage associated with the transcutaneous ion sensor.

[0231] Clause 44: The wearable device of any one of Clause 32-43, wherein: the wearable device further comprises a galvanostat configured to measure an open circuit potential (OCP) between the ISE of the transcutaneous ion sensor and the reference electrode of the transcutaneous ion sensor; and in order to determine the bias voltage to be applied to the ISE, the one or more processors are configured to select the OCP as the bias voltage to be applied to the ISE.

[0232] Clause 45: The wearable device of Clause 44, wherein: the OCP measured by the galvanostat is associated with a first noise level and an OCP associated with the adjusted bias voltage is associated with a second noise level; and the second noise level is less than the first noise level.

[0233] Clause 46: The wearable device of any one of Clauses 44-45, wherein: the wearable device further comprises a plurality of switches; and the one or more processors are further configured to: use the plurality of switches to couple the galvanostat to the ISE and the reference electrode to allow the galvanostat to measure the OCP; and use the plurality of switches to couple the potentiostat to the ISE and the reference electrode to allow the potentiostat to apply the bias voltage and measure the current associated with the ISE.

[0234] Clause 47: The wearable device of Clause 46, wherein the one or more processors are further configured to use the plurality of switches to short the ISE and the reference electrode.

[0235] Clause 48: The wearable device of Clause 47, wherein, in order to short the ISE and the reference electrode, the one or more processors are configured to use the plurality of switches to couple the ISE and the reference electrode to ground.

[0236] Clause 49: The wearable device of any one of Clauses 46-48, wherein the one or more processors are configured to use the plurality of switches to short the ISE and the reference electrode prior to the galvanostat measuring the OCP.P+S Ref. No.: DEXC / 0946PC 60Dexcom Ref. No.: 0946-PCT01

[0237] Clause 50: The wearable device of any one of Clauses 32-49, wherein the one or more processors are configured to measure the current associated with the ISE over a measurement period.

[0238] Clause 51: The wearable device of Clause 50, wherein, in order to determine the ion concentration level, the one or more processors are configured to: determine a coulometric profile associated with the ion concentration level; and determine the ion concentration level based on the coulometric profile.

[0239] Clause 52: The wearable device of Clause 51, wherein, in order to determine the coulometric profile associated with the ion concentration level, the one or more processors are configured to integrate the measured current, with respect to time, over the measurement period.

[0240] Clause 53: The wearable device of Clause 52, wherein, the one or more processors are configured to integrate the measured current, with respect to time, over the measurement period is performed in at least one of: an analog domain using an integrator circuit of the wearable device; or a digital domain using a Riemann sum over the measurement period.

[0241] Clause 54: The wearable device of any one of Clauses 32-53, wherein the one or more processors are configured to measure the current associated with the ISE based on one or more capacitors coupled in series between the potentiostat and the ISE.

[0242] Clause 55: The wearable device of Clause 54, wherein the one or more capacitors comprise at least one variable capacitor.

[0243] Clause 56: The wearable device of Clause 55, wherein the one or more processors are further configured to: detect that at least one of a response time associated with the transcutaneous ion sensor exceeds a particular response time threshold or a sensitivity associated with the transcutaneous ion sensor has fallen below a particular sensitivity threshold; and adjust, based on the detection, a capacitance of the variable capacitor such that at least one of the response time associated with the transcutaneous ion sensor is reduced back to at least the particular response time threshold or the sensitivity associated with the transcutaneous ion sensor is increased back to at least the particular sensitivity threshold.

[0244] Clause 57: The wearable device of any one of Clauses 32-56, wherein the wearable device includes one or more inductors coupled in series with the ISE of theP+S Ref. No.: DEXC / 0946PC 61Dexcom Ref. No.: 0946-PCT01 transcutaneous ion sensor.

[0245] Clause 58: The wearable device of Clause 57, wherein the one or more inductors comprise one or more fixed value inductors.

[0246] Clause 59: The wearable device of any one of Clauses 57-58, wherein the transcutaneous ion sensor is associated with a particular capacitance value.

[0247] Clause 60: The wearable device of Clause 59, wherein the particular capacitance value varies with the ion concentration level.

[0248] Clause 61: The wearable device of any one of Clauses 59-60, wherein, in order to adjust the bias voltage, the one or more processors are configured to iteratively adjust the bias voltage until, based on the particular capacitance value associated with the transcutaneous ion sensor, the transcutaneous ion sensor resonates with the one or more inductors at a particular resonance frequency.

[0249] Clause 62: The wearable device of Clause 61, wherein the one or more processors are configured to cause the wearable device to determine the ion concentration level of the user based on the particular resonance frequency.

[0250] Clause 63: The wearable device of Clause 62, wherein the one or more processors are further configured to cause the wearable device to determine a change in the ion concentration level based on a change in the particular resonance frequency at which the transcutaneous ion sensor resonates with the one or more inductors.

[0251] Clause 64: A method, by a wearable device, for measuring an ion concentration level of a user of the wearable device, comprising: applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) of a transcutaneous ion sensor of the wearable device; after applying the bias voltage to the ISE, measuring a current associated with the ISE of the transcutaneous ion sensor; determining, when the measured current is within a threshold range, the ion concentration level of the user based at least in part on the bias voltage; and transmitting an indication of the ion concentration level of the user to a display device for display to the user.

[0252] Clause 65: The method of Clause 64, wherein determining the bias voltage to be applied to the ISE comprises: measuring, by a galvanostat of the wearable device, an open circuit potential (OCP) between the ISE of the transcutaneous ion sensor and a reference electrode of the transcutaneous ion sensor; and selecting the OCP as the biasP+S Ref. No.: DEXC / 0946PC 62Dexcom Ref. No.: 0946-PCT01 voltage to be applied to the ISE.

[0253] Clause 66: The method of Clause 65, further comprising: using a plurality of switches of the wearable device to couple the galvanostat to the ISE and the reference electrode when measuring the OCP; and using the plurality of switches to couple the potentiostat to the ISE and the reference electrode when applying the bias voltage and measuring the current associated with the ISE.

[0254] Clause 67: The method of Clause 66, further comprising using the plurality of switches to short the ISE and the reference electrode.

[0255] Clause 68: The method of Clause 67, wherein using the plurality of switches to short the ISE and the reference electrode comprises using the plurality of switches to couple the ISE and the reference electrode to ground.

[0256] Clause 69: The method of Clause 66, wherein using the plurality of switches to short the ISE and the reference electrode comprises using the plurality of switches to short the ISE and the reference electrode prior to measuring the OCP.

[0257] Clause 70: The method of any one of Clauses 64-69, wherein measuring the current associated with the ISE comprises measuring the current associated with the ISE over a measurement period.

[0258] Clause 71: The method of Clause 70, wherein determining the ion concentration level comprises: determining a coulometric profile associated with the ion concentration level by integrating the measured current, with respect to time, over the measurement period; and determining the ion concentration level based on the coulometric profile.

[0259] Clause 72: The method of Clause 71, wherein integrating the measured current, with respect to time, over the measurement period is performed in at least one of: an analog domain using an integrator circuit of the wearable device; or a digital domain using a Riemann sum over the measurement period.

[0260] Clause 73: The method of any one of Clauses 64-72, wherein measuring the current associated with the ISE is based on one or more capacitors coupled in series between the potentiostat and the ISE.

[0261] Clause 74: The method of Clause 73, wherein the one or more capacitors comprise at least one variable capacitor.P+S Ref. No.: DEXC / 0946PC 63Dexcom Ref. No.: 0946-PCT01

[0262] Clause 75: The method of Clause 74, further comprising: detecting that at least one of a response time associated with the transcutaneous ion sensor exceeds a particular response time threshold or a sensitivity associated with the transcutaneous ion sensor has fallen below a particular sensitivity threshold; and adjusting, based on the detection, a capacitance of the variable capacitor such that at least one of the response time associated with the transcutaneous ion sensor is reduced back to at least the particular response time threshold or the sensitivity associated with the transcutaneous ion sensor is increased back to at least the particular sensitivity threshold.

[0263] Clause 76: The method of any one of Clauses 74-75, wherein the wearable device includes one or more inductors coupled in series with the ISE of the transcutaneous ion sensor.

[0264] Clause 77: The method of Clause 76, wherein the one or more inductors comprise one or more fixed value inductors.

[0265] Clause 78: The method of any one of Clauses 76-77, wherein the transcutaneous ion sensor is associated with a particular capacitance value.

[0266] Clause 79: The method of Clause 78, wherein the particular capacitance value varies with the ion concentration level.

[0267] Clause 80: The method of any one of Clauses 78-79, further comprising iteratively adjusting the bias voltage until, based on the particular capacitance value associated with the transcutaneous ion sensor, the transcutaneous ion sensor resonates with the one or more inductors at a particular resonance frequency.

[0268] Clause 81: The method of Clause 80, wherein determining the ion concentration level of the user is based on the particular resonance frequency.

[0269] Clause 82: The method of Clause 81, further comprising determining a change in the ion concentration level based on a change in the particular resonance frequency at which the transcutaneous ion sensor resonates with the one or more inductors.

[0270] Clause 83: A wearable device for measuring an ion concentration level of a user of the wearable device, comprising: a transcutaneous ion sensor comprising an ion selective electrode (ISE) and a reference electrode; a potentiostat configured to apply a bias voltage to the ISE of the transcutaneous ion sensor; and one or more processorsP+S Ref. No.: DEXC / 0946PC 64Dexcom Ref. No.: 0946-PCT01 configured to: measure a current associated with the ISE of the transcutaneous ion sensor; determine, when the measured current is within a threshold range, the ion concentration level of the user based at least in part on the bias voltage; and transmit an indication of the ion concentration level of the user to a display device for display to the user.

[0271] Clause 84: The wearable device of Clause 83, wherein: the wearable device further comprises a galvanostat configured to measure an open circuit potential (OCP) between the ISE of the transcutaneous ion sensor and the reference electrode of the transcutaneous ion sensor; and in order to determine the bias voltage to be applied to the ISE, the one or more processors are configured to select the OCP as the bias voltage to be applied to the ISE.

[0272] Clause 85: The wearable device of Clause 84, wherein: the wearable device further comprises a plurality of switches; and the one or more processors are further configured to: use the plurality of switches to couple the galvanostat to the ISE and the reference electrode to allow the galvanostat to measure the OCP; and use the plurality of switches to couple the potentiostat to the ISE and the reference electrode to allow the potentiostat to apply the bias voltage and measure the current associated with the ISE.

[0273] Clause 86: The wearable device of Clause 85, wherein the one or more processors are further configured to use the plurality of switches to short the ISE and the reference electrode.

[0274] Clause 87: The wearable device of Clause 86, wherein, in order to short the ISE and the reference electrode, the one or more processors are configured to use the plurality of switches to couple the ISE and the reference electrode to ground.

[0275] Clause 88: The wearable device of any one of Clauses 85-87, wherein the one or more processors are configured to use the plurality of switches to short the ISE and the reference electrode prior to the galvanostat measuring the OCP.

[0276] Clause 89: The wearable device of any one of Clauses 83-88, wherein the one or more processors are configured to measure the current associated with the ISE over a measurement period.

[0277] Clause 90: The wearable device of Clause 89, wherein, in order to determine the ion concentration level, the one or more processors are configured to: determine a coulometric profile associated with the ion concentration level; and determine the ion concentration level based on the coulometric profile.P+S Ref. No.: DEXC / 0946PC 65Dexcom Ref. No.: 0946-PCT01

[0278] Clause 91: The wearable device of Clause 90, wherein, in order to determine the coulometric profile associated with the ion concentration level, the one or more processors are configured to integrate the measured current, with respect to time, over the measurement period.

[0279] Clause 92: The wearable device of Clause 91, wherein, the one or more processors are configured to integrate the measured current, with respect to time, over the measurement period is performed in at least one of: an analog domain using an integrator circuit of the wearable device; or a digital domain using a Riemann sum over the measurement period.

[0280] Clause 93: The wearable device of any one of Clauses 83-92, wherein the one or more processors are configured to measure the current associated with the ISE based on one or more capacitors coupled in series between the potentiostat and the ISE.

[0281] Clause 94: The wearable device of Clause 93, wherein the one or more capacitors comprise at least one variable capacitor.

[0282] Clause 95: The wearable device of Clause 94, wherein the one or more processors are further configured to: detect that at least one of a response time associated with the transcutaneous ion sensor exceeds a particular response time threshold or a sensitivity associated with the transcutaneous ion sensor has fallen below a particular sensitivity threshold; and adjust, based on the detection, a capacitance of the variable capacitor such that at least one of the response time associated with the transcutaneous ion sensor is reduced back to at least the particular response time threshold or the sensitivity associated with the transcutaneous ion sensor is increased back to at least the particular sensitivity threshold.

[0283] Clause 96: The wearable device of any one of Clauses 83-95, wherein the wearable device includes one or more inductors coupled in series with the ISE of the transcutaneous ion sensor.

[0284] Clause 97: The wearable device of Clause 96, wherein the one or more inductors comprise one or more fixed value inductors.

[0285] Clause 98: The wearable device of any one of Clauses 96-97, wherein the transcutaneous ion sensor is associated with a particular capacitance value.

[0286] Clause 99: The wearable device of Clause 98, wherein the particularP+S Ref. No.: DEXC / 0946PC 66Dexcom Ref. No.: 0946-PCT01 capacitance value varies with the ion concentration level.

[0287] Clause 100: The wearable device of any one of Clauses 98-99, wherein, in order to adjust the bias voltage, the one or more processors are configured to iteratively adjust the bias voltage until, based on the particular capacitance value associated with the transcutaneous ion sensor, the transcutaneous ion sensor resonates with the one or more inductors at a particular resonance frequency.

[0288] Clause 101: The wearable device of Clause 100, wherein the one or more processors are configured to cause the wearable device to determine the ion concentration level of the user based on the particular resonance frequency.

[0289] Clause 102: The wearable device of Clause 101, wherein the one or more processors are further configured to cause the wearable device to determine a change in the ion concentration level based on a change in the particular resonance frequency at which the transcutaneous ion sensor resonates with the one or more inductors.

[0290] Clause 103: An apparatus, comprising: one or more processors configured to execute instructions stored on one or more memories and to cause the apparatus to perform a method in accordance with any combination of Clauses 1-31 or Clauses 64-82.

[0291] Clause 104: An apparatus, comprising means for performing a method in accordance with any combination of Clauses 1-31 or Clauses 64-82.

[0292] Clause 105: A non-transitory computer-readable medium comprising executable instructions that, when executed by one or more processors of an apparatus, cause the apparatus to perform a method in accordance with any combination of Clauses 1-31 or Clauses 64-82.

[0293] Clause 106: A computer program product embodied on a computer-readable storage medium comprising code for performing a method in accordance with any combination of Clauses 1-31 or Clauses 64-82.Additional Considerations

[0294] In this document, the terms “computer program medium” and “computer usable medium” and “computer readable medium”, as well as variations thereof, are used to generally refer to transitory or non-transitory media. These and other various forms of computer program media or computer usable / readable media may be involved in carrying one or more sequences of one or more instructions to a processing device for execution.P+S Ref. No.: DEXC / 0946PC 67Dexcom Ref. No.: 0946-PCT01Such instructions embodied on the medium, may generally be referred to as “computer program code” or a “computer program product” or “instructions” (which may be grouped in the form of computer programs or other groupings). When executed, such instructions may enable a computing module, such as the SS 8, display device 150, circuitry related thereto, and / or a processor thereof or connected thereto to perform features or functions of the present disclosure as discussed herein (for example, in connection with methods described above and / or in the claims), including for example when the same is / are incorporated into a system, apparatus, device and / or the like.

[0295] Various embodiments have been described with reference to specific example features thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the various embodiments as set forth in the appended claims. The specification and figures are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will be appreciated that, for clarity purposes, the above description has described embodiments with reference to different functional units. However, it will be apparent that any suitable distribution of functionality between different functional units may be used without detracting from the invention. For example, functionality illustrated to be performed by separate computing devices may be performed by the same computing device. Likewise, functionality illustrated to be performed by a single computing device may be distributed amongst several computing devices. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

[0296] Although described above in terms of various example embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead may be applied, alone or in various combinations, to one or more of the other embodiments of the present application, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the present application should not be limited by any of the above-described example embodiments.

[0297] Terms and phrases used in the present application, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed toP+S Ref. No.: DEXC / 0946PC 68Dexcom Ref. No.: 0946-PCT01 limiting. As examples of the foregoing: the term “including” should be read as meaning “including, without limitation” or the like; the term “example” is used to provide illustrative instances of the item in discussion, not an exhaustive or limiting list thereof; the terms “a” or “an” should be read as meaning “at least one,” “one or more” or the like; the term “set” should be read to include one or more objects of the type included in the set; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Similarly, the plural may in some cases be recognized as applicable to the singular and vice versa. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.

[0298] The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. The use of the term “module” does not imply that the components or functionality described or claimed as part of the module are all configured in a common package. Indeed, any or all of the various components of a module, whether control logic, circuitry, or other components, may be combined in a single package or separately maintained and may further be distributed in multiple groupings or packages or across multiple locations.

[0299] Additionally, the various embodiments set forth herein are described in terms of example block diagrams, flow charts, and other illustrations. As will become apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives may be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular architecture or configuration. Moreover, the operations and sub-operations of various methods described herein are not necessarily limited to the order described or shown in the figures, and one of skill in the art will appreciate, upon studying the present disclosure, variations of the order of the operations described herein that are within the spirit and scope of the disclosure.P+S Ref. No.: DEXC / 0946PC 69Dexcom Ref. No.: 0946-PCT01

[0300] It will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by execution of computer program instructions. These computer program instructions may be loaded onto a computer or other programmable data processing apparatus (such as a controller, microcontroller, microprocessor or the like) in a sensor electronics system to produce a machine, such that the instructions which execute on the computer or other programmable data processing apparatus create instructions for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks presented herein.

[0301] It should be appreciated that all methods and processes disclosed herein may be used in any glucose or other analyte monitoring system, continuous or intermittent. It should further be appreciated that the implementation and / or execution of all methods and processes may be performed by any suitable devices or systems, whether local or remote. Further, any combination of devices or systems may be used to implement the present methods and processes.

[0302] In addition, the operations and sub-operations of methods described herein may be carried out or implemented, in some cases, by one or more of the components, elements, devices, modules, circuitry, processors, etc. of systems, apparatuses, devices, environments, and / or computing modules described herein and referenced in various of figures of the present disclosure, as well as one or more sub- components, elements, devices, modules, processors, circuitry, and the like depicted therein and / or described with respect thereto. In such instances, the description of the methods or aspects thereof may refer to a corresponding component, element, etc., but regardless of whether an explicit reference is made, one of skill in the art will recognize upon studying the presentP+S Ref. No.: DEXC / 0946PC 70Dexcom Ref. No.: 0946-PCT01 disclosure when the corresponding component, element, etc. may be used. Further, it will be appreciated that such references do not necessarily limit the described methods to the particular component, element, etc. referred to. Thus, it will be appreciated by one of skill in the art that aspects and features described above in connection with (sub-) components, elements, devices, modules, and circuitry, etc., including variations thereof, may be applied to the various operations described in connection with methods described herein, and vice versa, without departing from the scope of the present disclosure.P+S Ref. No.: DEXC / 0946PC 71

Claims

Dexcom Ref. No.: 0946-PCT01CLAIMS1. A wearable device for measuring an ion concentration level of a user of the wearable device, comprising: a transcutaneous ion sensor comprising an ion selective electrode (ISE) and a reference electrode; a potentiostat configured to apply a bias voltage to the ISE of the transcutaneous ion sensor; and one or more processors configured to: measure a current associated with the ISE of the transcutaneous ion sensor; adjust the bias voltage applied by the potentiostat based on the measured current associated with the ISE until the measured current is within a threshold range; determine the ion concentration level of the user based at least in part on the adjusted bias voltage; and transmit an indication of the ion concentration level of the user to a display device for display to the user.

2. The wearable device of claim 1, wherein: the bias voltage is associated with a first estimate of the ion concentration level and the adjusted bias voltage is associated with a second estimate of the ion concentration level; and the second estimate of the ion concentration level is closer to the ion concentration of the user relative to the first estimate of the ion concentration level.

3. The wearable device of claim 1, wherein: in order to adjust the bias voltage, the one or more processors are configured to iteratively adjust the bias voltage; the potentiostat is further configured to iteratively apply the adjusted bias voltage to the ISE; and the one or more processors are further configured to iteratively measure the current associated with the ISE after the potentiostat applies the adjusted bias voltage;P+S Ref. No.: DEXC / 0946PC 72Dexcom Ref. No.: 0946-PCT01 the one or more processors are configured to iteratively adjust the bias voltage and iteratively measure the current associated with the ISE until the current associated with the ISE is within the threshold range; and the potentiostat is configured to iteratively apply the adjusted bias voltage to the ISE until the current associated with the ISE is within the threshold range.

4. The wearable device of claim 3, wherein, in order to iteratively adjust the bias voltage, the one or more processors are configured to: when the current associated with the ISE is above the threshold range, iteratively decrease the bias voltage by a first threshold amount until the current associated with the ISE is determined to be within the threshold range; and when the current associated with the ISE is below the threshold range, iteratively increase the bias voltage by a second threshold amount until the current associated with the ISE is determined to be within the threshold range.

5. The wearable device of claim 3, wherein: the one or more processors are configured to iteratively adjust the bias voltage according to a dynamic periodicity; and the dynamic periodicity is based on at least one of: a magnitude of the current associated with the ISE; a rate of change of the current associated with the ISE; or a physiological relevant time period related to an ion for which the ion concentration level is being measured.

6. The wearable device of claim 3, wherein: the one or more processors are configured to determine the ion concentration level based further on the adjusted bias voltage that results in the current associated with the ISE being within the threshold range; and in order to determine the ion concentration level of the user, the one or more processors are configured to invert a Nemst relation based on the applied bias voltage and an offset voltage associated with the transcutaneous ion sensor.

7. The wearable device of claim 1, wherein:P+S Ref. No.: DEXC / 0946PC 73Dexcom Ref. No.: 0946-PCT01 the wearable device further comprises a galvanostat configured to measure an open circuit potential (OCP) between the ISE of the transcutaneous ion sensor and the reference electrode of the transcutaneous ion sensor; and in order to determine the bias voltage to be applied to the ISE, the one or more processors are configured to select the OCP as the bias voltage to be applied to the ISE.

8. The wearable device of claim 7, wherein: the wearable device further comprises a plurality of switches; and the one or more processors are further configured to: use the plurality of switches to couple the galvanostat to the ISE and the reference electrode to allow the galvanostat to measure the OCP; and use the plurality of switches to couple the potentiostat to the ISE and the reference electrode to allow the potentiostat to apply the bias voltage and measure the current associated with the ISE.

9. The wearable device of claim 8, wherein the one or more processors are further configured to, prior to measurement of the OCP, use the plurality of switches to short the ISE and the reference electrode and couple the ISE and the reference electrode to ground.

10. The wearable device of claim 1, wherein: the one or more processors are configured to measure the current associated with the ISE over a measurement period; in order to determine the ion concentration level, the one or more processors are configured to: determine a coulometric profile associated with the ion concentration level; and determine the ion concentration level based on the coulometric profile; in order to determine the coulometric profile associated with the ion concentration level, the one or more processors are configured to integrate the measured current, with respect to time, over the measurement period in at least one of: an analog domain using an integrator circuit of the wearable device; or a digital domain using a Riemann sum over the measurement period.P+S Ref. No.: DEXC / 0946PC 74Dexcom Ref. No.: 0946-PCT0111. The wearable device of claim 1, wherein: the one or more processors are configured to measure the current associated with the ISE based on one or more capacitors coupled in series between the potentiostat and the ISE; and the one or more capacitors comprise at least one variable capacitor.

12. The wearable device of claim 11, wherein the one or more processors are further configured to: detect that at least one of a response time associated with the transcutaneous ion sensor exceeds a particular response time threshold or a sensitivity associated with the transcutaneous ion sensor has fallen below a particular sensitivity threshold; and adjust, based on the detection, a capacitance of the variable capacitor such that at least one of the response time associated with the transcutaneous ion sensor is reduced back to at least the particular response time threshold or the sensitivity associated with the transcutaneous ion sensor is increased back to at least the particular sensitivity threshold.

13. The wearable device of claim 1, wherein: the wearable device includes one or more inductors coupled in series with the ISE of the transcutaneous ion sensor; the one or more inductors comprise one or more fixed value inductors; the transcutaneous ion sensor is associated with a particular capacitance value; and the particular capacitance value varies with the ion concentration level.

14. The wearable device of claim 13, wherein: in order to adjust the bias voltage, the one or more processors are configured to iteratively adjust the bias voltage until, based on the particular capacitance value associated with the transcutaneous ion sensor, the transcutaneous ion sensor resonates with the one or more inductors at a particular resonance frequency; the one or more processors are configured to cause the wearable device to determine the ion concentration level of the user based on the particular resonance frequency; andP+S Ref. No.: DEXC / 0946PC 75Dexcom Ref. No.: 0946-PCT01 the one or more processors are further configured to cause the wearable device to determine a change in the ion concentration level based on a change in the particular resonance frequency at which the transcutaneous ion sensor resonates with the one or more inductors.

15. A method, by a wearable device, for measuring an ion concentration level of a user of the wearable device, comprising: applying, using a potentiostat of the wearable device, a bias voltage to an ion selective electrode (ISE) of a transcutaneous ion sensor of the wearable device; after applying the bias voltage to the ISE, measuring a current associated with the ISE of the transcutaneous ion sensor; adjusting the bias voltage based on the measured current associated with the ISE until the measured current is within a threshold range; determining, based at least in part on the adjusted bias voltage, the ion concentration level of the user; and transmitting an indication of the ion concentration level of the user to a display device for display to the user.P+S Ref. No.: DEXC / 0946PC 76

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