SENSOR ARRAY SYSTEM AND METHOD FOR DETECTING MULTIPLE ANALYTES - Patent application

Abstract

To advantageously analyze multiple analytes together using analyte sensors capable of detecting multiple analytes, because multiple analytes may be dysregulated alone or concurrently in certain physiological conditions.SOLUTION: Analyte sensors capable of detecting multiple analytes may include first and second working electrodes, analyte-responsive active areas disposed on each of the working electrodes, and a reference electrode and a counter electrode. Analyte sensors that include multiple working electrodes but no reference and counter electrodes can also be used in conjunction with another sensor that includes reference and counter electrodes so that these electrodes are shared.SELECTED DRAWING: Figure 5D

Description

[Background technology]

[0001] Detection of various analytes in an individual can sometimes be important for monitoring their health and well-being. Deviations from normal analyte levels can often indicate an underlying physiological condition, such as a metabolic condition or disease, or exposure to a particular environmental condition. While a single analyte may be dysregulated alone for a given physiological condition, sometimes multiple analytes may be dysregulated simultaneously by the same physiological condition or due to coexisting (related) physiological conditions. When multiple analytes are dysregulated simultaneously, the degree of dysregulation may vary from analyte to analyte. For these reasons, monitoring each analyte may be necessary to obtain a thorough assessment of an individual's health.

[0002] Periodic ex vivo analyte monitoring using sampled bodily fluids may be sufficient for many individuals to monitor a given physiological condition. However, ex vivo analyte monitoring may be inconvenient or painful for some individuals, especially if fluid sampling or collection is required quite frequently (e.g., several times per day). Continuous analyte monitoring using implantable in vivo analyte sensors may be a more desirable approach for individuals with severe analyte dysregulation and / or individuals with rapidly fluctuating analyte levels, but other individuals may benefit from the convenience offered. Continuous analyte monitoring may allow individuals or physicians to proactively address abnormal analyte levels before they lead to more serious health consequences, such as organ damage or failure. Subcutaneous, interstitial, or dermal analyte sensors can often provide sufficient measurement accuracy for this purpose while minimizing user discomfort.

[0003] Many analytes are interesting targets for physiological analysis once the appropriate detection chemistry is identified. To this end, amperometric sensors configured to analyze glucose in vivo have been developed and improved in recent years to aid in health monitoring in diabetic individuals. Other analytes that are commonly co-regulated with glucose in diabetic individuals include, for example, lactate, oxygen, pH, A1c, ketones, etc. Sensors configured to detect analytes that are commonly co-regulated with glucose are known but are not currently sufficiently improved.

[0004] In vivo analyte sensors are typically configured to analyze a single analyte to provide a specific analysis, often employing enzymes to provide high specificity for a given analyte. Due to this analyte specificity, current in vivo analyte sensors configured to analyze glucose are generally ineffective for analyzing other analytes that frequently dysregulate in combination with glucose or that result in dysregulated glucose levels. Ideally, current analyte monitoring techniques require diabetic individuals to wear two different in vivo analyte sensors, one configured to analyze glucose and the other configured to analyze another analyte of interest. Analyte monitoring techniques employing multiple in vivo analyte sensors can be very inconvenient for users. Furthermore, when multiple in vivo analyte sensors are used for analyte monitoring, there is an additional equipment cost burden and an increased statistical likelihood that at least one of an individual's in vivo analyte sensors will fail.

[0005] Individuals with diabetes are often particularly susceptible to comorbid conditions, either due to improper management of insulin levels or as a result of having even well-controlled diabetes for a long period of time. For example, diabetic neuropathy can lead to eventual renal failure due to high blood glucose levels. Diabetic neuropathy is the leading cause of renal failure in the United States, affecting a significant number of individuals with diabetes within the first 10 to 20 years of the disease. Diagnostic tests to assess renal function currently rely on measuring elevated creatinine levels in blood and / or urine samples. While it is desirable to detect potential renal failure as early as possible, current diagnostic testing methods are typically performed over long periods (months to years) to ensure that creatinine levels are persistently elevated or trend upward over time. The current infrequent creatinine monitoring can increase the risk of renal failure if abnormal renal function is not detected early enough.

[0006] Ethanol may also play an important role in diabetes management. As used herein, the term "ethanol" refers to the compound CHO and is a component in alcoholic beverages. The terms "alcohol" and "ethanol" are used interchangeably herein unless otherwise specified. Glucose homeostasis, which maintains blood glucose through a balance between insulin and glucagon, is important for the function of the central nervous system and various cellular systems that depend on such homeostasis for proper metabolism. Perturbations in glucose homeostasis (i.e., hyperglycemia, an excess of blood glucose, and hypoglycemia, a deficiency of blood glucose) can disrupt organ and cellular function, particularly by interfering with the production, regulation, and function of insulin and glucose. For example, alcohol can disrupt the production and therefore release of glucose in the liver, increasing the risk of moderate or severe hypoglycemia. Alcohol can also reduce the effectiveness of insulin, thereby increasing the risk of moderate or severe hyperglycemia. Thus, the relationship between alcohol and glucose may not be directly correlated with each other and is individual in many respects (e.g., genetic predisposition), and depends at least on exposure duration and concentration. Furthermore, alcohol can impair an individual's ability to recognize or understand symptoms associated with hyperglycemia and hypoglycemia, thus posing a serious health risk to the individual. Knowledge of alcohol-induced changes in glycemic control can be highly beneficial in individuals with diabetes, whose glucose levels are naturally dysregulated or lack homeostasis without intervention.

[0007] Ketones are another class of analytes commonly dysregulated in individuals with diabetes. Because glucose and ketone concentrations may not directly correlate with each other in diabetic individuals who also exhibit ketoacidosis (ketone dysregulation), simultaneous monitoring of both analytes can be advantageous, potentially leading to improved health outcomes. In addition to providing health benefits to individuals with diabetes, analyte sensors can be beneficial for other individuals who wish to monitor ketone levels, such as those practicing a ketogenic diet. A ketogenic diet is not only beneficial in promoting weight loss but can also help epilepsy patients manage their condition. Simultaneous glucose monitoring during ketogenic diet monitoring can provide related benefits.

[0008] Lactate is another analyte whose in vivo levels can change in response to numerous environmental or physiological factors, including, for example, diet, stress, exercise, sepsis or septic shock, infection, hypoxia, the presence of cancerous tissue, etc. In cases of chronic lactate disorders (e.g., illness), lactate levels can change slowly, making them easily quantifiable using traditional blood sampling and laboratory measurements. Other lactate disorders can be transient in nature, in which case lactate levels can fluctuate very rapidly and erratically. Traditional laboratory measurements can be inadequate for determining lactate levels in such cases because lactate levels can change multiple times between successive measurements, potentially missing some abnormal lactate levels entirely and potentially leading to an inaccurate diagnosis. In cases where lactate levels fluctuate rapidly, it is desirable to continuously measure an individual's lactate levels, for example, using an implantable in vivo lactate sensor. Continuous lactate monitoring can also be beneficial in individuals with chronically slowly changing lactate levels. For example, continuous lactate monitoring can avoid the pain and expense associated with taking multiple blood samples to analyze lactate levels. [Brief explanation of the drawings]

[0009] The following drawings are included to illustrate certain aspects of the present disclosure and should not be viewed as the only embodiments. The disclosed subject matter is susceptible to numerous modifications, substitutions, combinations, and equivalents in form and function without departing from the scope of the present disclosure. [Figure 1] 1 shows a diagram of an exemplary detection system that may include an analyte sensor of the present disclosure. [Figure 2A] 1 shows a cross-sectional view of an exemplary two-electrode analyte sensor configuration having a single working electrode. [Figure 2B] 1 shows a cross-sectional view of an exemplary two-electrode analyte sensor configuration having a single working electrode. [Figure 3A] 1A-1C show plan views of both sides of an exemplary analyte sensor having a single working electrode. [Figure 3B] 1 illustrates a perspective view of an exemplary connector. [Figure 3C] FIG. 1 shows a cross-sectional view of an exemplary three-electrode analyte sensor configuration with a single working electrode. [Figure 4A] 1A-1C show plan views of both sides of an exemplary analyte sensor configuration having two working electrodes. [Figure 4B] 1 illustrates a perspective view of an exemplary connector. [Figure 5A] 1 shows an exploded view of an exemplary analyte sensor configuration having two working electrodes, a counter electrode, and a reference electrode. [Figure 5B] 1 shows a cross-sectional view of an exemplary analyte sensor configuration having two working electrodes, a counter electrode, and a reference electrode. [Figure 5C] 1 shows a cross-sectional view of an exemplary analyte sensor configuration having two working electrodes, a counter electrode, and a reference electrode. [Figure 5D] 1 shows a cross-sectional view of an exemplary analyte sensor configuration having two working electrodes, a counter electrode, and a reference electrode. [Figure 5E] Photographs of the electrode before and after application of the two films are shown. [Figure 5F] Photographs of the electrode before and after application of the two films are shown. [Figure 5G]FIG. 1 shows a top view of an analyte sensor having first and second working electrodes disposed on and in contact with the same surface of a substrate. [Figure 5H] FIG. 1 shows a top view of an analyte sensor having first and second working electrodes, a counter electrode, and a reference electrode disposed on and in contact with the same surface of a substrate. [Figure 6A] FIG. 1 shows a cross-sectional view of an analyte sensor having a sensitive active area located on a separate working electrode. [Figure 6B] 1 shows a cross-sectional view of an analyte sensor having different sensitive active areas and membranes disposed on separate working electrodes. [Figure 6C] 1 shows a cross-sectional view of an analyte sensor having different sensitive active areas and membranes disposed on separate working electrodes on the same side of a substrate. [Figure 7A] Photographs of electrodes coated with different films are shown. [Figure 7B] Photographs of electrodes coated with different films are shown. [Figure 7C] Photographs of electrodes coated with different films are shown. [Figure 7D] FIG. 1 shows exemplary plots of the current response of eight analyte sensors, each containing a glucose-sensitive active area and a ketone-sensitive active area located on a separate working electrode, after exposure to 30 mM glucose and 10 mM ketone at 37° C. for two weeks. [Figure 8A] 1 shows the response of an electrode containing glucose-sensitive and ketone-sensitive regions when exposed to varying glucose and ketone concentrations. [Figure 8B] 7A and 7B upon exposure to 30 mM glucose and 10 mM ketone at 37° C. for two weeks. [Figure 8C] 1 shows an exemplary plot of average current responses to multiple glucose concentrations. [Figure 8D] 1 shows an exemplary plot of average current response to multiple ketone concentrations. [Figure 9A]1 shows the response of an electrode containing glucose-sensitive and lactate-sensitive regions when exposed to varying glucose and lactate concentrations. [Figure 9B] 1 shows the response of an electrode containing glucose-sensitive and lactate-sensitive regions when exposed to 30 mM glucose and 5 mM lactate concentrations at 37° C. for 2 weeks. [Figure 9C] 1 shows an exemplary plot of average current responses to multiple glucose concentrations. [Figure 9D] 1 shows an exemplary plot of average current response to multiple lactate concentrations. [Figure 10A] FIG. 1 is a block diagram illustrating an exemplary embodiment of a sensor control device. [Figure 10B] FIG. 1 is a block diagram illustrating an exemplary embodiment of a sensor control device. [Figure 10C] FIG. 1 is a block diagram illustrating an exemplary embodiment of a sensor control device. [Figure 10D] FIG. 1 is a block diagram illustrating an exemplary embodiment of a sensor control device. [Figure 11] 1 shows an exploded view of a sensor housing containing two sensors. [Figure 12] 1 shows a cross-sectional view of an exemplary analyte sensor configuration having four working electrodes. [Figure 13A] FIG. 1 shows an exploded view of an on-body unit having two sensor housings connected by a printed circuit wire. [Figure 13B] FIG. 1 shows an exploded view of an on-body unit having two sensor housings connected by a flex circuit connection. [Figure 13C] FIG. 1 shows a perspective view of an on-body unit with three connected sensor housings. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present disclosure generally describes analyte sensors employing multiple enzymes to detect multiple analytes, and more specifically, analyte sensors employing multiple working electrodes to detect multiple analytes, such as glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. Multiple sensors may also be employed to analyze multiple analytes. In one embodiment, the sensor includes at least two working electrodes and a counter / reference electrode. In another embodiment, an analyte detection system may include multiple sensors. The system may include a primary sensor having at least one, and optionally at least two, working, counter, and reference electrodes. The system may also include a sub-sensor that includes at least one, and optionally at least two, optionally at least three, and optionally at least four working electrodes, but does not include a counter or reference electrode. The sub-sensor may be implanted and attached near the primary sensor within the user, allowing the sub-sensor to share the counter and reference electrodes in the primary sensor. The sub-sensor may be housed in the same housing as the primary sensor. Optionally, the subsensor may be mounted in a separate sensor housing adjacent to the sensor housing of the primary sensor, so that the primary sensor and the subsensor share the same counter and reference electrodes. In an alternative embodiment, multiple subsensors may share the counter and reference electrodes of the primary sensor.

[0011] As noted above, enzyme-based analyte sensors are typically used to monitor a single analyte, such as glucose, due to their inherent specificity for a particular substrate or class of substrates. Once a suitable sensor format and detection chemistry are identified, other analytes may similarly be monitored. Monitoring multiple analytes is challenging due to the need to employ a corresponding number of analyte sensors, each detecting each analyte independently. Particularly when monitoring with multiple in vivo analyte sensors, this approach can be problematic or undesirable due to the expense of multiple in vivo analyte sensors, the discomfort experienced by users when wearing multiple analyte sensors, and the increased statistical likelihood that at least one of a patient's in vivo analyte sensors will fail.

[0012] Glucose-sensitive analyte sensors are a well-studied and still-developing field for better managing and supporting the health of individuals with diabetes. Despite the prevalence of complications in diabetic individuals, sensor chemistries suitable for in vivo monitoring of other analytes that commonly dysregulate in combination with glucose have lagged significantly behind more developed glucose-sensing chemistries. For example, in addition to glucose, creatinine, lactate, ketones, and ethanol may all be of particular interest for monitoring in individuals with diabetes.

[0013] The present disclosure provides analyte sensors and sensor systems responsive to at least two analytes. Specifically, the present disclosure provides an analyte sensor that can be worn on-body for continuous or near-continuous in vivo monitoring of at least two analyte levels. Analysis of at least two analyte levels with the analyte sensors disclosed herein can provide an individual or medical professional with a more accurate description of various conditions over time than is possible with periodic ex vivo laboratory measurements. For example, analyzing creatinine levels in accordance with the present disclosure may enable earlier medical intervention, limiting potential kidney damage and improving an individual's overall health outcomes.

[0014] The present disclosure provides for monitoring at least two analytes, such as both glucose and another analyte, using one or more in vivo analyte sensors responsive to each analyte, and in particularly advantageous forms, a single analyte sensor responsive to both analytes in vivo may be used. Advantageously and surprisingly, analyte sensors having sensing capabilities for both glucose and another on a single sensor tail can be fabricated by employing the disclosure herein.

[0015] Before describing the analyte sensors of the present disclosure in more detail, embodiments of the present disclosure may be better understood by first providing a brief overview of suitable in vivo analyte sensor configurations and sensor systems employing such analyte sensors. FIG. 1 illustrates a schematic of an exemplary sensing system that may include the analyte sensors of the present disclosure, particularly analyte sensors capable of monitoring multiple analytes. As shown, sensing system 100 includes a sensor controller 102 and a reader 120 configured to communicate with each other via a local communication path or link, which may be wired or wireless, unidirectional or bidirectional, and encrypted or unencrypted. The reader 120, according to some embodiments, may provide an output medium for viewing analyte concentrations determined by the sensor 104 or its associated processor, as well as for viewing alerts or notifications, as well as for enabling one or more user inputs. The reader 120 may be a general-purpose smartphone or a dedicated electronic reader. While only one reader 120 is shown, multiple readers 120 may be present in some cases. The reader 120 may also communicate with a remote terminal 170 and / or a trusted computer system 180 via communication paths / links 141 and / or 142, respectively, which may be wired or wireless, unidirectional or bidirectional, and encrypted or unencrypted. The reader 120 may also, or instead, communicate with a network 150 (e.g., a cellular network, the Internet, or a cloud server) through communication path / link 151. The network 150 may further be communicatively coupled with the remote terminal 170 via communication path / link 152 and / or with the trusted computer system 180 via communication path / link 153. Alternatively, the sensor 104 may communicate directly with the remote terminal 170 and / or the trusted computer system 180 without the presence of the intervening reader terminal 120.According to some embodiments, such as those described by U.S. Patent Application Publication No. 2011 / 0213225, incorporated by reference in its entirety, the sensor 104 may communicate with the remote terminal 170 and / or the trusted computer system 180 via a direct communication link to the network 150. Any suitable electronic communication protocol may be used for each communication path or link, such as near field communication (NFC), radio frequency identification (RFID), BLUETOOTH® or BLUETOOTH® Low Energy protocol, Wi-Fi®, etc. According to some embodiments, the remote terminal 170 and / or the trusted computer system 180 may be accessible by individuals other than the primary user who are interested in the user's analyte levels. The reader 120 may include a display 122 and, optionally, an input component 121. The display 122 may include a touchscreen interface, according to some embodiments.

[0016] The sensor control device 102 includes a sensor housing 103 that houses circuitry and a power source for operating the sensor 104. Optionally, the power source and / or active circuitry may be omitted. A processor (not shown) may be communicatively coupled to the sensor 104, with the processor physically located within the sensor housing 103 or the reading device 120. According to some embodiments, the sensor 104 protrudes from a bottom surface of the sensor housing 103 and extends through an adhesive layer 105 adapted to adhere the sensor housing 103 to a tissue surface, such as skin.

[0017] The sensor 104 is adapted to be at least partially inserted into a tissue of interest, such as the dermis or subcutaneous layer of the skin. The sensor 104 may include a sensor tail of sufficient length to be inserted to a desired depth into a given tissue. The sensor tail may include at least one working electrode and a first analyte-sensitive active region disposed thereon. Optionally, a second analyte-sensitive active region may be disposed on the sensor tail to facilitate detection of the analyte, optionally in combination with the second working electrode. A counter electrode may be present in combination with the at least one working electrode. Specific electrode configurations on the sensor tail are described in more detail below with reference to Figures 2-5 and 11.

[0018] Continuing with reference to FIG. 1 , the sensor 104 may automatically transfer data to the reader 120. For example, analyte concentration data may be automatically and periodically communicated (e.g., every minute, every five minutes, or other predetermined time), such as at a certain frequency as the data is acquired, or after a certain period of time during which the data is stored in memory prior to transmission. In other embodiments, the sensor 104 may communicate with the reader 120 in a non-automatic manner rather than according to a set schedule. For example, data may be communicated from the sensor 104 using RFID technology when the sensor electronics are brought within communication range of the reader 120. The data may remain stored in the memory of the sensor 104 until communicated to the reader 120. Thus, the user does not have to constantly hold the reader 120 nearby, but instead can upload the data at a convenient time. In still other embodiments, a combination of automatic and non-automatic data transfer may be implemented. For example, data transmission may continue automatically until the reader 120 is no longer within communication range of the sensor 104.

[0019] The introducer may be temporarily present to facilitate the introduction of the sensor 104 into the tissue. In an exemplary embodiment, the introducer may comprise a needle or similar sharp object. It should be understood that other types of introducers, such as a sheath or blade, may be present in alternative embodiments. More specifically, the needle or other introducer may be temporarily present near the sensor 104 prior to tissue insertion and then withdrawn. While present, the needle or other introducer may facilitate the insertion of the sensor 104 into the tissue by opening an access path for the sensor 104 to follow. For example, according to one or more embodiments, the needle may facilitate penetration of the epidermis as an access path to the dermis, allowing implantation of the sensor 104 to occur. After opening the access path, the needle or other introducer is withdrawn and therefore does not present a sharps hazard. In an exemplary embodiment, a suitable needle may be solid or hollow, beveled or non-beveled, and / or circular or non-circular in cross section. In more specific embodiments, suitable needles may have a cross-sectional diameter and / or tip design similar to an acupuncture needle having a cross-sectional diameter of about 250 microns (μm). However, suitable needles may have larger or smaller cross-sectional diameters as required for a particular application.

[0020] In some embodiments, the tip of the needle (while present) may be angled over the end of the sensor 104 so that the needle penetrates the tissue first to open an access passage for the sensor 104. In other exemplary embodiments, the sensor 104 may reside in a lumen or needle groove, with the needle similarly opening an access passage for the sensor 104. In either case, the needle is withdrawn after facilitating sensor insertion.

[0021] The analyte sensors disclosed herein may feature different types of active regions (e.g., a glucose active region and a ketone, lactate, creatinine, or ethanol active region) on a single working electrode or on two or more separate working electrodes. According to various embodiments of the present disclosure, as further described herein, single working electrode sensor configurations may employ two-electrode or three-electrode detection motifs. Figures 2A-2B show cross-sectional views of an exemplary two-electrode analyte sensor configuration with a single working electrode compatible for use in some embodiments disclosed herein. As shown, the analyte sensor 200 includes a substrate 212 disposed between a working electrode 214 and a counter / reference electrode 216. Alternatively, the working electrode 214 and the counter / reference electrode 216 may be located on the same side of the substrate 212 with a dielectric material between them (configuration not shown). Figure 2A shows a single active region 218. Multiple active areas 218a and 218b (i.e., glucose-sensitive active areas and ketone-sensitive active areas) are laterally spaced from one another on the surface of working electrode 214. In various sensor configurations illustrated herein, active areas 218a and 218b may comprise multiple spots or a single spot configured to detect each analyte. Analyte sensor 200 may be operable to analyze glucose and ketones by any of the following electrochemical detection techniques: coulometry, amperometry, voltammetry, or potentiometry.

[0022] When a single working electrode is present in the analyte sensor, a three-electrode sensor configuration may include a working electrode, a counter electrode, and a reference electrode (see FIGS. 2A and 2B). A related two-electrode sensor configuration may include a working electrode and a second electrode, and the second electrode may function as both the counter electrode and the reference electrode (i.e., the counter / reference electrode). In both two-electrode and three-electrode sensor configurations, both the first and second analyte-sensitive active regions may be disposed on the single working electrode. In some embodiments, the various electrodes may be at least partially stacked (layered) on top of each other and / or laterally spaced apart from each other on the sensor tail. Suitable sensor configurations may be substantially planar or substantially cylindrical in shape, with the first and second analyte-sensitive active regions laterally spaced apart on the working electrode. In all of the sensor configurations disclosed herein, the various electrodes may be electrically insulated from each other by a dielectric material or similar insulator.

[0023] Analyte sensors featuring multiple working electrodes may also include at least one additional electrode. If one additional electrode is present, the one additional electrode may function as a counter / reference electrode for each of the multiple working electrodes. If two additional electrodes are present, one of the additional electrodes may function as a counter electrode for each of the multiple working electrodes, and the other additional electrode may function as a reference electrode for each of the multiple working electrodes.

[0024] Analyte sensor configurations having a single working electrode will now be described in more detail. FIG. 2A is a cross-sectional view of an exemplary two-electrode analyte sensor configuration having a single working electrode, which is compatible for use in several embodiments disclosed herein. As shown, analyte sensor 200 includes a substrate 212 disposed between a working electrode 214 and a counter / reference electrode 216. Alternatively, working electrode 214 and counter / reference electrode 216 may be located on the same side of substrate 212 with a dielectric material between them (configuration not shown). Active area 218 is disposed on working electrode 214. As seen in FIG. 2B, when multiple active areas are present on a single working electrode 214, active areas 218a and 218b (e.g., a glucose-sensitive active area and a ketone-sensitive active area) are laterally spaced from each other on the surface of working electrode 214. In the various sensor configurations shown herein, active area 218a and active area 218b may comprise multiple spots or a single spot configured to detect each analyte. Analyte sensor 200 may be operable to analyze glucose and ketones by any of the following electrochemical detection techniques: coulometric, amperometric, voltammetric, or potentiometric.

[0025] A sensor having a single working electrode and monitoring a single analyte is shown in FIG. 3A. Three electrodes are screen-printed on both sides of a substrate (e.g., a PET substrate) with an insulating layer between them. As seen in FIG. 3C, the analyte sensor 201 includes a substrate 212 disposed between a working electrode 214 and a counter electrode 217. Alternatively, the working electrode 214 may be located on the same side of the substrate 212 as the counter electrode 217, with a dielectric material between them (configuration not shown). The reference electrode 216 is electrically insulated from the working electrode 214 by a dielectric layer 219b. Outer dielectric layers 219a and 219c are disposed on the reference electrode 216 and the counter electrode 217. An analyte-specific sensitive active region 218 (e.g., a glucose-sensitive active region, a creatinine-sensitive active region, or a lactate-sensitive active region) may be disposed as at least one layer on at least a portion of the working electrode 214. As described further herein, the analyte-sensitive active area may comprise multiple spots / areas or a single spot / area configured to detect the analyte. A layer of reference material 230 (e.g., Ag / AgCl) may be present on the reference electrode 216, and the location of the layer of reference material 230 is not limited to the location shown in Figure 3C. As seen in Figure 3B, the connector 250 includes three openings 252 to provide connection between the working, counter, and reference electrodes via a printed circuit board (not shown).

[0026] A sensor having two working electrodes and monitoring two analytes is shown in FIG. 4A. In this embodiment, four electrodes are screen-printed on both sides of a substrate (e.g., a PET substrate) with an insulating layer to electrically isolate the electrodes. As seen in FIG. 4A, working electrode 214a and reference electrode 216 are printed on one side, and working electrode 214b and counter electrode 217 are printed on the other side. As seen in FIG. 4B, connector 250 includes four openings 252 to provide connection between the two working electrodes and the counter and reference electrodes via a printed circuit board (not shown).

[0027] 5A and 5B show diagrams of an exemplary four-electrode analyte sensor configuration compatible with use in the disclosures herein. As shown, analyte sensor 201 includes a substrate 212 disposed between working electrodes 214a and 214b. Alternatively, working electrodes 214a and 214b may be located on the same side of substrate 212 with a dielectric material between them (configuration not shown). Analyte-specific sensitive active areas 218a and / or 218b (e.g., glucose-sensitive, creatinine-sensitive, or lactate-sensitive active areas) may be disposed as at least one layer on at least a portion of working electrodes 214a and / or 214b. As described further herein, the analyte-sensitive active areas may include multiple spots / areas or a single spot / area configured to detect the analyte. A reference electrode may be disposed on either working electrode 214a or 214b with a separating layer of dielectric material therebetween. The counter electrode may be disposed on the other of the working electrodes 214a or 214b with a separating layer of dielectric material therebetween. For example, as shown in Figure 5B, dielectric layers 219b and 219c separate electrodes 214a, 214b, 216, and 217 from one another and provide electrical insulation. Outer dielectric layers 219a and 219d are disposed on the reference electrode 216 and counter electrode 217.

[0028] Alternatively, at least one of electrodes 214a, 214b, 216, and 217 may be disposed on the opposite side of substrate 212. Thus, in some embodiments, electrode 214a (working electrode) and electrode 216 (counter electrode) may be disposed on the opposite side of substrate 212 from electrode 217 (reference electrode), and working electrode 214b may be disposed on the opposite side of the substrate. A layer of reference material 230 (e.g., Ag / AgCl) may be present on reference electrode 216, and the location of reference material layer 230 is not limited to the location shown in FIG. 5A . As in sensor 202 shown in FIG. 5B , analyte-sensitive active area 218 in analyte sensor 202 may comprise multiple spots or a single spot. Additionally, analyte sensor 202 may be operable to analyze the analyte by any of the following electrochemical detection techniques: coulometry, amperometry, voltammetry, or potentiometry. While Figure 5B shows electrodes 214a, 214b, 216, and 217 as all being covered by membrane 220, it should be understood that in some embodiments, only working electrodes 214a and 214b may be covered. Furthermore, the thickness of membrane 220 on each of electrodes 214a, 214b, 216, and 217 may be the same or different. As in two-electrode analyte sensor configurations (e.g., Figures 2A and 2B), one or both sides of analyte sensor 202 may be covered by membrane 220 in the sensor configuration of Figure 5A, or the entire analyte sensor 202 may be covered. Therefore, it should be understood that the multi-electrode sensor configurations shown in Figures 5A and 5B are not limited to the embodiments disclosed herein, and alternative electrode and / or layer configurations are within the scope of the present disclosure.

[0029] 5B , membrane 220 optionally covers at least analyte-sensitive active areas 218a and 218b, and some or all of working electrode 214a and / or working electrode 214b and / or reference electrode 216 and / or counter electrode 217, or the entire analyte sensor 202 according to some embodiments. One or both sides of analyte sensor 202 may be covered by membrane 220. Membrane 220 may include one or more polymeric membrane materials that function to limit the flux of analyte to active areas 218 (i.e., membrane 220 is a mass transport limiting membrane that has some permeability to the analyte being measured). The composition and thickness of membrane 220 may be modified to promote the desired flux of analyte to analyte-sensitive active areas 218a, 218b, thereby providing the desired signal strength and stability. Analyte sensor 200 may be operable to analyze the analyte by any of the following electrochemical detection techniques: coulometric, amperometric, voltammetric, or potentiometric.

[0030] FIG. 5C shows a diagram of an exemplary four-electrode analyte sensor configuration compatible for use in the disclosures herein. As shown, the analyte sensor 232 comprises a substrate 212 disposed between a working electrode 214a and a counter electrode 216. The working electrodes 214a and 214b are disposed on the same side of the substrate 212 with a dielectric material 219b between them. The counter electrode 216 and the reference electrode 217 are disposed on opposite sides of the substrate 212 with a dielectric material 219c between them. An analyte-specific sensitive active region 218a (e.g., a ketone-sensitive active region) may be disposed as at least one layer on at least a portion of the working electrode 214a. An analyte-specific sensitive active region 218b (e.g., glucose-sensitive) may be disposed as at least one layer on at least a portion of the working electrode 214b. Active region 218a (e.g., ketone-sensitive active region) may be positioned closer to end A than analyte-specific sensitive active region 218b (e.g., glucose-sensitive). As described further herein, the analyte-sensitive active region may comprise multiple spots / regions or a single spot / region configured to detect the analyte. As shown in FIG. 5C, dielectric layers 219b and 219c separate electrodes 214a, 214b, 216, and 217 from one another and provide electrical insulation. Outer insulating layers 219a and 219d are disposed on working electrode 214b and counter electrode 217. A layer 230 of reference material (e.g., Ag / AgCl) (not shown) may be present on reference electrode 216 or another suitable location on the sensor. 5B and 5C, the analyte-sensitive active area 218 in the analyte sensor 202, 232 may comprise multiple spots or a single spot. Additionally, the analyte sensor 202, 232 may be operable to analyze the analyte by any of the following electrochemical detection techniques: coulometry, amperometry, voltammetry, or potentiometry.

[0031] 5D shows a diagram of an exemplary four-electrode analyte sensor configuration compatible for use in the disclosures herein. As shown, the analyte sensor 242 comprises a substrate 212 disposed between a working electrode 214a and a counter electrode 216. The working electrodes 214a and 214b are disposed on the same side of the substrate 212 with a dielectric material 219b between them. The counter electrode 216 and the reference electrode 217 are disposed on opposite sides of the substrate 212 with a dielectric material 219c between them. An analyte-specific sensitive active region 218a (e.g., a ketone-sensitive active region) may be disposed as at least one layer on at least a portion of the working electrode 214a. An analyte-specific sensitive active region 218b (e.g., glucose-sensitive) may be disposed as at least one layer on at least a portion of the working electrode 214b. Active region 218a (e.g., ketone-sensitive active region) may be positioned closer to end A than analyte-specific sensitive active region 218b (e.g., glucose-sensitive). As described further herein, the analyte-sensitive active region may comprise multiple spots / regions or a single spot / region configured to detect the analyte. As shown in FIG. 5C, dielectric layers 219b and 219c separate electrodes 214a, 214b, 216, and 217 from one another and provide electrical insulation. Outer dielectric layers 219a and 219d are disposed on working electrode 214b and counter electrode 217. A layer 230 of reference material (e.g., Ag / AgCl) may be present on reference electrode 216 or another suitable location on the sensor. 5B-5D, the analyte-sensitive active region 218a, 218b in the analyte sensor 202, 232, 242 may comprise multiple spots or a single spot. Additionally, the analyte sensor 202, 232, 242 may be operable to analyze the analyte by any of the following electrochemical detection techniques: coulometry, amperometry, voltammetry, or potentiometry.

[0032] Active area 218a may be closer to end A (the distal end of the sensor inserted into the subject) than active area 218b. Active area 218a may have a length between about 0.7 mm and about 1.3 mm, alternatively between about 0.8 mm and about 1.2 mm, alternatively between about 0.9 mm and about 1.1 mm, alternatively about 0.8 mm, alternatively about 0.9 mm, alternatively about 1.0 mm, alternatively about 1.1 mm, alternatively about 1.2 mm. Active area 218b may have a length longer than active area 218a. Active area 218b may have a length between about 0.7 mm and about 1.5 mm, alternatively between about 0.8 mm and about 1.4 mm, alternatively between about 0.9 mm and about 1.3 mm, alternatively about 0.8 mm, alternatively about 0.9 mm, alternatively about 1.0 mm, alternatively about 1.1 mm, alternatively about 1.2 mm, alternatively about 1.3 mm, alternatively about 1.4 mm. Active area 218a and active area 218b are separated by a distance x, which may be between about 0.4 mm and about 1.1 mm, alternatively between about 0.5 mm and about 1.0 mm, alternatively between about 0.6 mm and about 0.9 mm, alternatively between about 0.7 mm and about 0.9 mm, alternatively about 0.4 mm, alternatively about 0.5 mm, alternatively about 0.6 mm, alternatively about 0.7 mm, alternatively about 0.8 mm, alternatively about 0.9 mm, alternatively about 1.0 mm, alternatively at least about 0.2 mm, alternatively at least about 0.4 mm, alternatively at least about 0.6 mm, alternatively at least about 0.8 mm (e.g., the proximal end of active area 218a may be separated from the distal end of active area 218b).

[0033] Sensors 232, 242 may include two membranes 220, 222. As seen in Figures 5C and 5D, membrane 222 may cover only a portion of working electrode 214a, including active area 218a (e.g., the ketone-sensitive active area). Membrane 220 may cover both active area 218a (e.g., the ketone-sensitive active area) and active area 218b (e.g., the glucose-sensitive active area). Membrane 220 may also cover counter electrode 216 and reference electrode 217 on the opposite side of substrate 212. Thus, active area 218a (e.g., the ketone-sensitive active area) may have a bilayer membrane including membranes 222 and 220, while active area 218b may have only a single layer of membrane 220. While Figures 5C and 5D show electrodes 214a, 214b, 216, and 217 as all being covered by membrane 220, it should be understood that in some embodiments, only working electrodes 214a and 214b may be covered. Furthermore, the thicknesses of membranes 220, 222 on each of electrodes 214a, 214b, 216, and 217 may be the same or different from one another. As with two-electrode analyte sensor configurations (e.g., Figures 2A and 2B), one or both sides of analyte sensor 202 may be covered by membrane 220 in the sensor configuration of Figure 5A, or the entire analyte sensor 202 may be covered. Therefore, it should be understood that the multi-electrode sensor configuration shown in Figures 5A and 5B is not limited to the embodiments disclosed herein, and alternative electrode and / or layer configurations are within the scope of the present disclosure.

[0034] 5C and 5D, membrane 222 optionally covers only active area 218a (e.g., ketone-sensitive active area) and not active area 218b (e.g., glucose-sensitive). Membrane 220 optionally covers at least analyte-sensitive active areas 218a and 218b, and some or all of working electrode 214a and / or working electrode 214b and / or reference electrode 216 and / or counter electrode 217, or, according to some embodiments, the entire analyte sensor 202. Membrane 220 may include one or more polymeric membrane materials that function to limit the flux of analyte to active area 218 (i.e., membrane 220 is a mass transport-limiting membrane that has some permeability to the analyte being measured). The composition and thickness of membrane 220 may be modified to promote the desired flux of analyte to analyte-sensitive active areas 218a, 218b, thereby providing the desired signal strength and stability. As seen in FIG. 5D, the distal portion 221 of the sensor 242 may be thicker (thickness w compared to w') or spherical in shape compared to the proximal portion of the sensor tail. The thickness of the distal portion 221 of the sensor 242 may be between about 0.203 mm (0.008") and about 0.356 mm (0.014"), alternatively between about 0.229 mm (0.009") and about 0.33 mm (0.013"), alternatively between about 0.254 mm (0.010") and about 0.33 mm (0.013"), alternatively between about 0.254 mm (0.010") and about 0.305 mm (0.012"), alternatively between about 0.15 mm and about 0.4 mm, alternatively between about 0.2 mm and about 0.4 mm, alternatively between about 0.2 mm and about 0.4 mm, alternatively between about 0.25 mm and about 0.4 mm, alternatively between about 0.25 mm and about 0.35 mm. The analyte sensor may be operable to analyze the analyte by any of the following electrochemical detection techniques: coulometry, amperometry, voltammetry, or potentiometry.

[0035] The membrane 222 may be dip-coated onto the active region 218a (e.g., the ketone-sensitive active region). For example, the sensor 232 may be partially immersed in the membrane solution, so that only the end near end A, including active region 218a but not active region 218b, is immersed in the membrane solution. Application of the membrane 222 may be accomplished in a single immersion procedure or may require multiple immersions in the membrane solution to achieve a dense membrane. A larger portion of the sensor 232, 242, including both active regions 218a and 218b, may then be immersed in a different membrane solution. Thus, the active region 218a located closer to distal end A will have a bilayer membrane, while the active region 218b, which is more proximal than active region 218a, will have a single layer membrane. Dip-coating in this manner has a number of advantages. First, applying both sensing layers on one side of the substrate 212 without the need to flip the substrate 212 simplifies and improves the manufacturing process. Second, this dipping method allows the use of the same membrane dipping equipment used for both membrane 222 and membrane 220 by simply changing the membrane solution and adjusting the dipping depth.

[0036] FIG. 5E shows a sensor with ketone active site 218a (with two spots) on the front side, closer to distal end A of the sensor, and glucose active site 218b (with two spots) on the back side of the sensor, located further from distal end A than ketone active site 218a. The sensor in FIG. 5E is not yet covered by a membrane. As seen in FIG. 5F (see dotted line), in the first immersion, the sensor is immersed to a position between ketone active site 218a and glucose active site 218b, so that ketone active site 218a is immersed in the membrane solution, but glucose active site 218b is not. After any multiple immersions and curing in the first membrane solution, the sensor is immersed in a second solution such that the sensor is immersed to a position proximal to or above glucose active site 218b, so that both ketone active site 218a and glucose active site 218b are immersed. As seen in the side view of FIG. 5F, the distal portion 221 having the double-layered membrane has a spherical shape, or a flared tip, with a thickness w, which is larger than the proximal portion of the sensor tail, with a thickness w′, where only a single layer of membrane covers the sensor. The thickness w may be between about 0.203 mm (0.008") and about 0.356 mm (0.014"), alternatively between about 0.229 mm (0.009") and about 0.33 mm (0.013"), alternatively between about 0.254 mm (0.010") and about 0.33 mm (0.013"), alternatively between about 0.254 mm (0.010") and about 0.305 mm (0.012"), alternatively between about 0.15 mm and about 0.4 mm, alternatively between about 0.2 mm and about 0.4 mm, alternatively between about 0.3 mm and about 0.4 mm, alternatively between about 0.25 mm and about 0.35 mm.Conversely, the thickness w' may be between about 0.127 mm (0.005") and about 0.254 mm (0.01"), alternatively between about 0.127 mm (0.005") and about 0.229 mm (0.009"), alternatively between about 0.152 mm (0.006") and about 0.229 mm (0.009"), alternatively between about 0.152 mm (0.006") and about 0.203 mm (0.008"), alternatively between about 0.178 mm (0.007") and about 0.203 mm (0.008"), alternatively between about 0.1 mm and about 0.3 mm, alternatively between about 0.1 mm and about 0.25 mm, alternatively between about 0.15 mm and about 0.25 mm. The difference between w and w' may be between about 0.003" and about 0.005", alternatively between about 0.003" and about 0.004", alternatively between about 0.05 and about 0.15 mm, alternatively between about 0.07 and about 0.1 mm, alternatively between about 0.07 and about 0.1 mm, alternatively between about 0.075 and about 0.125 mm.

[0037] In another embodiment, as shown in Figures 5G and 5H, the first working electrode 214a and the second working electrode 214b may be located on the same side of the substrate 212 or directly on the surface of the substrate 212, so that a dielectric or insulating layer does not separate the first working electrode 214a and the second working electrode 214b from the same substrate surface. Furthermore, the first working electrode 214a and the second working electrode 214b are not stacked on top of each other and are not separated by a dielectric layer. Instead, the first working electrode 214a and the second working electrode 214b are spatially separated on the same surface of the substrate. This arrangement may simplify manufacturing because the first working electrode 214a and the second working electrode 214b can be printed in the same layer on the substrate 212. As can be seen in FIG. 5H, the counter electrode 216 and working electrode 217 may also be spatially separated and printed directly on the same side of the substrate (i.e., not stacked), in which case no dielectric layer separates the counter electrode 216 and reference electrode 217 from the surface of the substrate 212 or from each other.

[0038] The analyte sensors disclosed herein may include multiple active areas either on the same working electrode or on different working electrodes. The analyte sensors disclosed herein may feature the same type of active area (e.g., two glucose active areas) on a single working electrode or on two or more separate working electrodes. The analyte sensors disclosed herein may feature different types of active areas (e.g., a glucose active area and a ketone active area, or a lactate active area) on a single working electrode or on two or more separate working electrodes. As described further herein in accordance with various embodiments of the present disclosure, single working electrode sensor configurations may employ two-electrode or three-electrode detection motifs. According to various embodiments of the present disclosure, sensor configurations may suitably incorporate a first analyte-sensitive active area (e.g., for monitoring glucose) and a second analyte-sensitive active area (e.g., for monitoring ketones). Sensor configurations featuring multiple working electrodes are described hereinafter with reference to the figures.

[0039] In an alternative embodiment, both working electrode 214a and working electrode 214b may have the same analyte, such as a glucose-sensitive active area. When multiple working electrodes 214a and 214b are present, as seen in Figure 6A, a sensitive active area for a particular single analyte may be disposed on both working electrode 214a and working electrode 214b. A membrane 220 may then be dip-coated onto the sensitive active area 218.

[0040] In an alternative embodiment, different analytes are analyzed at different working electrodes. As described further herein, and not immediately apparent from FIGS. 5 and 6, the composition of membrane 220 may be varied between active regions 218a and 218b to individually control the flux of analyte at each location. For example, membrane 220 may be sprayed and / or printed onto active regions 218a and 218b, such that the composition of membrane 220 varies at each location. Alternatively, if multiple analytes are being analyzed and multiple working electrodes 214a and 214b are present, sensitive active region 218a specific to a first analyte, such as a ketone, may be located on the first working electrode, and sensitive active region 218b specific to a second analyte, such as glucose, may be located on the second working electrode.

[0041] Sensor configurations employing multiple working electrodes may be highly advantageous for incorporating multiple different sensitive active regions, according to the disclosures herein, because mass transport limiting membranes with different compositions and / or different permeability values ​​may be deposited more quickly during fabrication when the active regions are separated and / or spaced apart by this method. Suitable techniques for depositing the mass transport limiting membranes disclosed herein include, for example, spray coating, painting, striping, inkjet printing, stenciling, roller coating, slot dye coating, dip coating, etc., and combinations thereof. For example, referring to FIG. 6B , membrane 222 may be deposited by stripe coating, or membrane 220 may be deposited by dip coating starting from end A of analyte sensor 200. In particular, membrane 222 may be striped over active region 218a using a first coating formulation. Alternatively, membrane 222 may be coated over working electrode 214a, for example, by spray coating or painting. The sensor may then be laser cut to dip in second membrane 220, which covers the entire tip of the sensor. After partially curing the first coating formulation on active region 218a to form film 222, end A of analyte sensor 200 may be dipped into a second coating formulation to cover both active region 218a and active region 218b with the second coating formulation, forming film 220. In this manner, film 220 may be continuous and feature two layers in 218a and homogeneous in active region 218b. For example, with reference to FIG. 6C , when active region 218a and active region 218b are disposed on the same side of substrate 212 and are separated by distance x, film 220 and film 222 may be deposited by dip coating starting from end A of analyte sensor 200. In particular, end A of analyte sensor 200 may be dipped (one or more times) into the first coating formulation to cover only active region 218a, but not active region 218b.After partially curing the first coating formulation on active region 218a to form film 222, end A of analyte sensor 200 may be dipped into a second coating formulation to cover both active region 218a and active region 218b with the second coating formulation, forming film 220. Thus, film 220 may be continuous and feature a bilayer in 218a and homogeneous in active region 218b. If film 222 is denser than film 200, film 222 will primarily define the diffusion characteristics around sensitive active region 218a. While active region 218a and active region 218b are shown on the same side of the substrate in FIGS. 5D and 6C, active region 218a and active region 218b may also be on opposite sides of substrate 212, separated by a distance x, e.g., measured along an axis parallel to substrate 212.

[0042] Film 222 may include polyvinylpyridine and a cross-linker such as a polyethylene glycol diglycidyl ether (PEGDGE), for example, PEGDGE 400. Film 220 may include polyvinylpyridine-co-styrene and a cross-linker such as a polyethylene glycol diglycidyl ether (PEGDGE), for example, PEGDGE 400.

[0043] Sensor configurations employing multiple working electrodes may be highly advantageous for incorporating any of multiple different sensitive active regions in accordance with the present disclosure, since mass transport limiting membranes having different compositions and / or different permeability values ​​may be deposited more rapidly during fabrication when the active regions are separated and / or spaced apart by this method. Suitable techniques for depositing the mass transport limiting membranes disclosed herein include, for example, spray coating, painting, inkjet printing, stenciling, roller coating, dip coating, etc., and any combination thereof.

[0044] Figures 7A-7C are photographs of various electrodes coated with different membranes. Figures 7A-7C contain ketone- and glucose-specific sensitive active regions. Figure 7A shows an electrode with a ketone-sensitive active region coated first with a PVP membrane and then with a polyvinylpyrrolidone-co-styrene membrane. Figure 7B shows an electrode with a glucose-sensitive active region coated only with a polyvinylpyrrolidone-co-styrene membrane. The electrodes shown in Figures 7A and 7B are opposite sides of the same sensor tail. Figure 7C shows an electrode with a ketone-sensitive active region stripe-coated with a PVP membrane. Figure 7C is an example of what the electrode in Figure 7A looks like after being coated with PVP but before being coated with 10Q5. Typical membrane compositions for these electrodes can be found in U.S. Application No. 16 / 774,835 (U.S. Publication No. 2020 / 0237275; Serial No. 13548USO1), which is incorporated herein by reference in its entirety for all purposes. Figure 7D is a graph of the current response of eight analyte sensors, each containing a glucose-sensitive active area and a ketone-sensitive active area located on separate working electrodes on opposite sides of the sensor tail, after two weeks of exposure to 30 mM glucose and 10 mM ketone, demonstrating the different membrane requirements for glucose and ketone sensors achieved by the dual membrane described above. Similarly, typical membrane compositions for lactate sensors can be found in U.S. Application No. 16 / 259,157 (U.S. Publication No. 2019 / 0320947; Serial No. 13335USO1), which is incorporated herein by reference in its entirety for all purposes. Exemplary membrane compositions for ethanol sensors are found in U.S. Application No. 16 / 774,909 (U.S. Publication No. 2020 / 0237277; Attorney Docket No. 13622USO1), which is incorporated herein by reference in its entirety for all purposes. Exemplary membrane compositions for creatinine sensors are found in U.S. Application No. 16 / 582,583 (U.S. Publication No. 2020 / 0241015; Attorney Docket No. 13547USO1), which is incorporated herein by reference in its entirety for all purposes.Further exemplary membrane compositions can be found in U.S. Application No. 16 / 774,841 (U.S. Publication No. 2020 / 0237276; Attorney Docket No. 13210USO1), which is incorporated by reference in its entirety for all purposes.

[0045] 8A-8D and 9A-9D (see further description in the Examples) are calibration graphs for the glucose / ketone and glucose / lactate dual sensors, respectively. The calibration graphs demonstrate that these dual sensors, which include multiple working electrodes with glucose-sensitive and ketone-sensitive / lactate-sensitive regions, function as expected.

[0046] Exemplary Embodiments of On-Body Devices An in-vivo monitoring system may include a sensor that contacts a user's bodily fluid while positioned in vivo and senses the analyte level therein. The sensor may be part of an on-body device ("OBD") that resides on the user's body and includes electronics and a power source that enable and control analyte sensing. On-body devices and the like may be referred to as "sensor devices," "on-body electronics devices," "sensor control devices," or "sensor communication devices," to name a few. As used herein, these terms are not limited to devices with in-vivo analyte sensors but also include devices with other types of ex-vivo sensors, whether biometric (e.g., photonic analyte sensors, heart rate sensors, temperature sensors, etc.) or non-biometric. The term "on-body" encompasses devices that reside directly on the body (e.g., attached to the skin), entirely within the body (e.g., fully implanted devices), or near the body, such as wearable devices (e.g., eyeglasses, watches, wristbands or bracelets, collars or necklaces, etc.) or devices in a pocket.

[0047] The in-vivo monitoring system may also include one or more reading devices that read information regarding the sensed levels from the on-body devices. These reading devices may process and / or display the sensed analyte information to the user in any format. These devices and the like may be referred to as "handheld reading devices," "readers," "handheld electronics (or handheld terminals)," "portable data processing" devices or units, "information receivers," "receiver" devices or units (or simply receivers), "relay" devices or units, to name a few.

[0048] In vivo analyte monitoring systems can be distinguished from "in vitro" systems, which contact a biological sample outside the body, and "ex vivo" systems, which obtain information about the body or a substance within the body but remain entirely outside the body without extracting a biological sample from inside the body. In vitro systems may include a measurement device having a port for receiving an analyte test strip carrying a user's bodily fluid, the analyte test strip being analyzed to determine the user's analyte level. As noted above, the embodiments described herein may be used with in vivo systems, ex vivo systems, in vitro systems, and combinations thereof.

[0049] 10A-D are block schematic diagrams illustrating an exemplary embodiment of a sensor controller or OBD 102 having an analyte sensor 104 and sensor electronics 310 (including analyte monitoring circuitry), which may contain most of the processing functionality to make final result data suitable for display to a user. In FIG. 10A, a single semiconductor chip 301 is shown, which may be a custom application-specific integrated circuit (ASIC). Certain high-level functional units are shown within ASIC 301, including an analog front-end (AFE) 302, power management (or control) circuitry 304, a processor 306, and communication circuitry 308 (which may be implemented as a transmitter, receiver, transceiver, passive circuitry, or other circuitry according to a communication protocol). In this embodiment, both AFE 302 and processor 306 are used as analyte monitoring circuitry, although in other embodiments, either circuitry may perform the analyte monitoring function. The processor 306 may include one or more processors, microprocessors, controllers, and / or microcontrollers, each of which may be a separate chip or may be distributed among (and portions of) multiple different chips.

[0050] The memory 303 may also be included in the ASIC 301, shared by the various functional units present in the ASIC 301, or distributed among two or more of them. The memory 303 may be a separate chip. The memory 303 may be volatile and / or non-volatile memory. In this embodiment, the ASIC 301 is coupled to a power source 310, which may be a coin cell battery or the like. The AFE 302 interfaces with the in-vivo analyte sensor 104, receives measurement data therefrom, and outputs the data in digital form to a processor 306, which in turn processes the data to arrive at individual glucose final results and trend values, etc. The data may be provided to the communications circuitry 208 for transmission via antenna 311 to a reader 120 (not shown), where minimal further processing by a resident software application is required to display the data.

[0051] FIG. 10B is a block diagram illustrating an alternative exemplary embodiment of a sensor control device or on-body device (“OBD”) 102 having an analyte sensor 104 and sensor electronics 310 (including analyte monitoring circuitry). The sensor electronics may be implemented in one or more semiconductor chips. In the embodiment of FIG. 10B, the sensor electronics 310 resides in a single semiconductor chip 301, which may be a custom application-specific integrated circuit (ASIC). Certain high-level functional units are shown within the ASIC 301, including an analog front-end (AFE) 302, a power management (or control) circuit 304, a processor or processing circuit 306, a memory 303, a timing circuit 312, a first communication circuit 302, and a second communication circuit 314. In this embodiment, both the AFE 302 and the processor 306 are used as analyte monitoring circuitry, although in other embodiments, either circuit (or others) may perform the analyte monitoring function.

[0052] OBD 102 may be implemented in a highly interconnected manner, where power source 312 is coupled to each of the components shown in FIG. 10B, and these components that communicate or receive data or information or commands (e.g., AFE 302, power management circuit 304, processor 306, memory 303, timing circuit 312, first communication circuit 308, and second communication circuit 314) may be communicatively coupled to any other such components, for example, via one or more communication connections or bus 320. FIG. 10B is a simplified representation of typical hardware and functionality present in a dedicated reader, and those skilled in the art will readily appreciate that other hardware and functionality (e.g., codecs, drivers, glue logic) may also be included.

[0053] 10C is a block diagram illustrating an alternative exemplary embodiment of an OBD 102 having an analyte sensor 104 and sensor electronics (including analyte monitoring circuitry). The sensor electronics may be implemented in one or more semiconductor chips, such as application-specific integrated circuits (ASICs), off-the-shelf (OTS) chips, programmable devices (e.g., PGAs or FPGAs), etc. The OBD 102 includes certain high-level functional units, including an analog front-end (AFE) 302, a power management (or control) circuit 304, a processor or processing circuit 306, memory 303, a first communication circuit 308, and a second communication circuit 314. In this embodiment, both the AFE 302 and the processor 306 are used as analyte monitoring circuitry, although in other embodiments, either circuit (or others) may perform the analyte monitoring function.

[0054] OBD 102 may be implemented in a highly interconnected manner, where power supply 310 is coupled to each of the components shown in FIG. 10C , and these components that communicate or receive data or information or commands (e.g., AFE 302, power management circuit 304, processor 306, memory 303, first communication circuit 308, and second communication circuit 314) may be communicatively coupled to any other such component, for example, via one or more communication connections or buses 320. FIG. 10C simply illustrates typical hardware and functionality present in OBD 102, and those skilled in the art will readily appreciate that other hardware and functionality (e.g., codecs, drivers, glue logic, crystal oscillators, phase-locked loops (PLLs)) may also be included.

[0055] 10D is a block diagram illustrating another exemplary embodiment of the OBD 102. Here, the OBD 102 includes two semiconductor chips 301 and 361. Chip 301 is an ASIC that includes an AEF 302 and communication circuitry 308 for an NFC link. Chip 361 is a chip that includes a processor 306, memory 303, communication circuitry 314 for a BT link, and power management circuitry 304. The communication interface may be configured in any desired manner. In one embodiment, chip 361 is a Bluetooth® or BLE radio chip, and the communication interface is a serial interface, such as a serial peripheral interface (SPI).

[0056] Communications received by OBD 102 over the NFC link may include commands for OBD 102 to take some action, such as connecting power to the internal circuitry of one or both of chips 301 and 316, activating sensor 104, reading data stored in memory 303 (e.g., measured analyte data, data identifying OBD 102 (e.g., software version, serial number, etc.)), performing diagnostics, establishing Bluetooth® pairing, etc. The commands may be specified in the applicable NFC standard or may be custom commands requiring a custom response. Received communications often require transmission of a response back to reader 120.

[0057] 10D embodiment, some NFC communications received by communications circuitry 308 may be processed and responded to directly by ASIC 301 without intervention from chip 361. However, some commands may require a response generated by a more robust entity, such as processor 306. In these instances, ASIC 301 may forward the relevant portion of the received communication to chip 361 for generating the response. Chip 361 may then generate the response and, once the response is obtained, output the response back to ASIC 301 for transmission from OBD 102 over the NFC link.

[0058] Communications sent over an NFC link may have certain timing constraints. To comply with the ISO 15693 standard, most NFC commands, including, for example, read multiple block commands, read single block commands, custom commands, and proprietary commands, must be responded to within a set time limit. In one embodiment, ISO 15693 specifies that a command be responded to by the tag within 232 microseconds (μs) from the time the tag receives the command. Situations may exist in which the chip 361 takes longer than the set time limit to generate a response. This processing delay may result in a violation of the set time limit and non-compliance with the NFC standard. This may be a particular problem when the reader 120 is a commercial smartphone, as the smartphone will treat this violation as an error or malfunction and prevent the communication from completing.

[0059] The example embodiments disclosed herein can compensate for this processing delay and maintain compatibility by transmitting one or more responses that include a predefined payload, referred to herein as dummy data. The reader 120 may be programmed or configured to recognize responses whose payloads include byte values ​​that match the predefined payloads as dummy data (e.g., ABCD, FFFF), and may continue to monitor the NFC link 141 for response transmissions that include payload data other than dummy data.

[0060] For all of the above embodiments, the communication circuitry 308 and the communication circuitry 314 may be coupled to the antenna 311 and the antenna 316, respectively, which may be on-chip or off-chip. The first communication circuitry 308 and the antenna 311 are configured to communicate (transmit and / or receive) over a communication link, and the second communication circuitry 314 and the antenna 316 are configured to communicate over different communication links. In some embodiments, the antenna 311 and the antenna 316 may be a single shared antenna (e.g., capable of transmitting and receiving over NFC and UHF frequencies). The communication circuits 308 and 314 may be implemented as one or more components (e.g., transmitters, receivers, transceivers, passive circuits, encoders, decoders, and / or other communication circuitry) that perform functions for communicating over their respective communication links. The communication circuits 308 and 314 may receive timing information from the timing circuitry 312. The timing circuitry 312 may include a crystal oscillator, a phase-locked loop (PLL), and / or other circuitry that generates stable frequencies for timing purposes.

[0061] Without being limited thereto, in some embodiments, the communications circuitry 308 is passive and uses only power harvested from a transmission received from a second device (e.g., reader 120) to generate and propagate a response transmission back to the second device (e.g., when the communications link is an NFC link). In these and other embodiments, the communications circuitry 314 may be active and may use power from the OBD power supply 312 to generate and propagate a transmission to the second device. The active communications circuitry 314 allows the OBD 102 to generate a transmission spontaneously and upon prompting from another device (e.g., without first receiving a request, polling signal, timing signal, etc. from the second device).

[0062] Processor 306 may include one or more processors, microprocessors, controllers, and / or microcontrollers, each of which may be a separate chip or distributed among (and portions of) many different chips. Processor 306, in conjunction with communications circuitry 308 and communications circuitry 314, may perform analog-to-digital conversion, encoding and decoding, digital signal processing, and other functions to facilitate conversion of data signals into a format (e.g., in-phase and quadrature) suitable for supply to communications circuitry 308 and communications circuitry 314, which may then transmit the signals wirelessly. Processor 306, in conjunction with communications circuitry 308 and 314, may perform the reverse functions necessary to receive wireless transmissions and convert them into digital data or information.

[0063] Processor 306 may execute software instructions stored in memory 308. These instructions may cause processor 306 to cause communications circuitry 308 and communications circuitry 314 to transmit communications generated by processor 306, read and act on received transmissions, adjust the timing of timing circuitry 312, collect temperature information from a temperature sensor, record and / or process measurements from analyte sensor 314, monitor collected analyte data for actual or potential alarm conditions, generate and transmit alarm indications using communications circuitry 314, process data and information received from other devices (e.g., reader 120), perform tasks and maintain synchronization with reader 120, etc.

[0064] Memory 308 may also be included within ASIC 301, shared by various components present within ASIC 301, or distributed among two or more of them. Memory 308 may be a separate chip. Memory 308 may be persistent, and may be volatile and / or non-volatile memory. ASIC 301 may be coupled to an optional temperature (or other environmental factor) sensor 321 and a power source 310, which may be a coin cell battery or the like. AFE 302 interfaces with in-vivo analyte sensor 104, receives measurement data therefrom, converts it to digital form, and outputs it to digital processor 306, which in some embodiments processes it in any manner described elsewhere herein. Data may be provided to communication circuitry 308 and communication circuitry 314 for transmission via antenna 311 and antenna 316 to reader 120 (not shown), where minimal further processing by a resident software application is required, for example to display the data. Antenna 311 and antenna 316 may be configured according to the needs of the application and communication protocol. Antenna 311 and antenna 316 may have the same or different configurations, such as a printed circuit board (PCD) wire antenna, a ceramic antenna, or a separate metal antenna. Antennas 311 and 316 may be configured as monopole antennas, dipole antennas, F-type antennas, loop antennas, etc.

[0065] Multiple sensors in a single housing In alternative embodiments, additional analytes can be monitored by adding a second sensor or subsensor that includes one or more working electrodes but does not include a reference or counter electrode. As shown in FIG. 11, placing a subsensor 203 near a primary sensor 202 that includes a reference and counter electrode, as shown in FIGS. 3-5, allows the subsensor 203 to share the counter and reference electrodes in the primary sensor. As shown in FIG. 12, the subsensor 203 includes four working electrodes 214a, 214b, 214c, and 214d, two on each side of the substrate 212. The working electrodes on the same side of the substrate 212 are separated by dielectric material 219b and 219c sandwiched between them. Outer dielectric layers 219a and 219d are disposed over the working electrodes 214a and 214d. The analyte-specific sensitive active regions 218a-218d (e.g., glucose-sensitive active regions, creatinine-sensitive active regions, or lactate-sensitive active regions) may be disposed as at least one layer on at least a portion of the working electrodes 214a-214d. As described further herein, the analyte-sensitive active regions may comprise multiple spots / regions or a single spot / region configured to detect the analyte. Both the primary sensor 202 and the sub-sensor 203 are contained within the same sensor housing 103 and attached to the patient's skin by an adhesive layer 104. For example, two, three, four, or more additional sub-sensors may be added within the same sensor housing unit to increase the number of analytes being monitored.

[0066] Referring to the multiple-sensor embodiment described for a single housing, as shown in Figure 11, OBD 102 may include any of the sensor electronics described in Figures 10A-10D. Housing 103 includes AFE 302, which receives analyte data from the working electrodes in the primary sensor and the subsensor. The AFE outputs one or more signals related to the analyte level detected by each of the working electrodes in the primary sensor and the subsensor using shared counter and reference electrodes in the primary sensor.

[0067] Multiple sensors in multiple housings In an alternative embodiment, additional analytes can be monitored by adding subsensors installed in additional sensor housings connected or coupled to the sensor housing housing containing the primary sensor. Similar to the embodiment described above with reference to FIG. 11, as seen in FIGS. 13A-13B, subsensor 203 can be positioned near primary sensor 202, which includes a reference electrode and a counter electrode, as shown in FIGS. 3-5, allowing subsensor 203 to share the counter and reference electrodes in the primary sensor. As seen in FIG. 12, subsensor 203 includes four working electrodes 214a, 214b, 214c, and 214d, two on each side of substrate 212. Working electrodes on the same side of substrate 212 are separated by dielectric material 219b and 219c sandwiched between them. Outer dielectric layers 219a and 219d are disposed on working electrodes 214a and 214d. Analyte-specific sensitive active regions 218a-218d (e.g., glucose-sensitive, creatinine-sensitive, or lactate-sensitive active regions) may be disposed as at least one layer on at least a portion of the working electrodes 214a-214d. As described further herein, the analyte-sensitive active regions may comprise multiple spots / regions or a single spot / region configured to detect the analyte. In an alternative embodiment shown in FIG. 13A, the primary sensor 202 is housed in a primary sensor housing 103a, and the subsensor 203 is housed in a different sensor housing 103b, both of which are attached to the patient's skin by an adhesive layer 104. Similar to FIG. 11, the sensor housing 103b is located near the primary sensor housing 103a, allowing the subsensor 203 to connect to the AFE 302 located in the primary sensor housing 103a, thereby enabling the subsensor 203 to share the counter and reference electrodes in the primary sensor. Therefore, the sub-sensor housing 103b may not contain any electronics. Alternatively, the AFE 302 may be located within the sub-sensor housing 103b.As shown in FIG. 13A , conductive lines 303 may be printed on the back of the adhesive layer 104 to connect the sub-sensors 203 to the AFE 302 installed in the primary sensor housing 103a. Both sensor housings 103a and 103b may have connector pins (not shown) on the bottom of the housing that press onto the printed conductive line terminal pads 303 when the sensor housings are laminated to the back of the skin adhesive patch 104. The printed conductive lines 303 may be flexible to accommodate skin movement. The connection (conductive lines) 303 between the primary sensor housing 103a and the sub-sensor housing 103b, including the contacts, may also be sufficiently isolated and sealed from any moisture to avoid any moisture leakage that may interfere with the sensor signal. For example, two, three, four, or more additional sub-sensors may be added in additional individual sensor housing units located near the primary sensor housing 103a to increase the number of analytes being monitored.

[0068] 13B, the sub-sensor 203 may be coupled to the AFE 302 in the primary sensor housing 103a via a flex circuit connection 305. The connection (conductive wire) 303 between the primary sensor housing 103a and the sub-sensor housing 103b, including the contacts, may be sufficiently isolated and sealed from any moisture to avoid any moisture leakage that may interfere with the sensor signal. Additional sub-sensors, for example, two, three, four, or more, may be added in additional separate sensor housing units, and the additional sub-sensors may be coupled to the AFE 302 installed in the primary sensor housing 103a to increase the number of analytes being monitored.

[0069] As shown in FIG. 13C , additional sub-sensor housings 103b and 103c each contain a sub-sensor coupled to AFE 302 in primary sensor housing 103a. The sub-sensors and AFEs located in primary sensor housing 103a may be coupled or connected by printed circuit wires, small flex circuits, or another system known in the art. If the primary sensor includes two working electrodes, such as sensor 202, and the sub-sensors housed in 103b and 103c each include a sensor with four working electrodes, 10 analytes may be monitored. Similarly, if there is only one such connected primary sensor housing connected to a single such sub-sensor housing, six analytes may be monitored.

[0070] In an alternative embodiment, the AFE 302 is located within the sub-sensor housings 103b, 103c. In this alternative embodiment, the electrodes (working, counter, reference) in the primary sensor 202 may be connected or coupled to the AFE 302 as described above for the sub-sensors (e.g., via printed circuit lines, a small flex circuit, or another system known in the art), so that the AFE 302 outputs one or more signals related to the analyte levels detected by each of the working electrodes in the primary sensor and the sub-sensor using the shared counter and reference electrodes in the primary sensor.

[0071] Sensitive active region Different detection chemistries must be immobilized on different sensitive active areas specific for various analytes. The enzymes involved in the detection of the analytes may be covalently attached to a polymer in or near the sensitive area. Suitable polymers include, but are not limited to, polyvinylpyridine. The covalently attached polymer may help to immobilize the enzyme in a desired location relative to the sensitive active area.

[0072] In any of the exemplary sensor configurations disclosed herein, each analyte-sensitive active region includes an electron transfer agent. When both the first analyte-sensitive active region and the second analyte-sensitive active region are present on the same sensor and / or the same working electrode, the electron transfer agents may be the same or different depending on the particular sensor configuration employed. A suitable electron transfer agent can facilitate the transport of electrons to the working electrode after an enzymatic oxidation or reduction reaction occurs, thereby generating a current indicative of the presence of a particular analyte and proportional to the amount of analyte present. For example, when the first analyte-sensitive active region and the second analyte-sensitive active region are disposed on the same working electrode, the electron transfer agents in each active region may be different from each other (e.g., chemically distinct so that the electron transfer agents exhibit different redox potentials). When multiple working electrodes are present, the electron transfer agents in each active region may be the same or different from each other, since each working electrode may be independently interrogated when a signal is acquired. The electron transfer agent may be covalently attached to a polymer in any of the active regions disclosed herein.

[0073] According to various embodiments of the present disclosure, suitable electron transfer agents may include electroreducible and electrooxidizable ions, complexes or molecules (e.g., quinones) with redox potentials several hundred millivolts above or below the redox potential of a standard calomel electrode (SCE). According to some embodiments, suitable electron transfer agents may include low-potential osmium complexes, such as those described in U.S. Pat. Nos. 6,134,461 and 6,605,200, the disclosures of which are incorporated herein by reference in their entireties. Further examples of suitable electron transfer agents include those described in U.S. Pat. Nos. 6,736,957, 7,501,053, and 7,754,093, the disclosures of each of which are incorporated herein by reference in their entireties. Other suitable electron transfer agents include metal compounds or complexes of, for example, ruthenium, osmium, iron (e.g., polyvinylferrocene or ferricyanide), or cobalt, including, for example, metallocene compounds thereof. Suitable ligands for metal complexes may also include bidentate or higher dentate ligands such as, for example, bipyridine, biimidazole, phenanthroline, or pyridyl (imidazole). Other suitable bidentate ligands may include, for example, amino acids, oxalic acid, acetylacetone, diaminoalkanes, or o-diaminoarenes. Any combination of monodentate, bidentate, tridentate, tetradentate, or higher dentate ligands may be present in the metal complex to achieve the maximum coordination sphere.

[0074] Active regions suitable for detecting multiple analytes may also include polymers to which electron transfer agents are covalently attached. Any of the electron transfer agents disclosed herein may include suitable functional groups to facilitate covalent attachment to the polymer within the active region. Suitable examples of polymer-bound electron transfer agents may include those described in U.S. Pat. Nos. 8,444,834, 8,268,143, and 6,605,201, the disclosures of which are incorporated herein by reference in their entireties. Polymers suitable for inclusion within the active region may include, but are not limited to, polyvinylpyridine (e.g., poly(4-vinylpyridine)), polyvinylimidazole (e.g., poly(1-vinylimidazole)), or any copolymers thereof. Exemplary copolymers that may be suitable for inclusion within the active region include those containing monomer units such as styrene, acrylamide, methacrylamide, or acrylonitrile. The polymers within each active region may be the same or different from one another.

[0075] The method of covalent bonding between the electron transfer agent and the polymer within each active region is not considered to be particularly limiting. The covalent bonding of the electron transfer agent to the polymer may be achieved by polymerization of a monomer unit having a covalently bonded electron transfer agent, or the electron transfer agent may react with the polymer independently after the polymer has already been synthesized. According to some embodiments, a bifunctional spacer may covalently bond the electron transfer agent to the polymer within the active region, with a first functional group reacting with the polymer (e.g., a functional group capable of quaternizing a pyridine nitrogen atom or an imidazole nitrogen atom) and a second functional group reacting with the electron transfer agent (e.g., a functional group reactive with a ligand that coordinates a metal ion).

[0076] Similarly, one or more of the enzymes within an active region may be covalently bound to the polymer. When an enzyme system comprising multiple enzymes is present within a given active region, in some embodiments, all of the enzymes may be covalently bound to the polymer, while in other embodiments, only a portion of the enzymes may be covalently bound to the polymer. For example, one or more enzymes comprising the enzyme system may be covalently bound to the polymer, while at least one enzyme may be non-covalently bound to the polymer, such that the non-covalently bound enzyme is physically entrapped within the polymer. According to more specific embodiments, the covalent binding of the enzymes to the polymer within a given active region may be achieved by cross-linking induced by a suitable cross-linking agent. Suitable cross-linking agents for reaction with free amino groups (e.g., free side chain amines of lysine) within the enzyme may include, for example, polyethylene glycol diglycidyl ether (PEGDGE) or other polyepoxides, cyanuric chloride, N-hydroxysuccinimide, imidoesters, epichlorohydrin, or derivatized variants thereof. Suitable cross-linking agents for reaction with free carboxylic acid groups within the enzyme may include, for example, carbodiimides. Cross-linking of the enzyme to the polymer is generally intermolecular, but in some embodiments may be intramolecular. In certain embodiments, all of the enzymes herein may be covalently bound to the polymer.

[0077] The electron transfer agent and / or enzyme may also be bound to the polymer in the active area by means other than covalent bonding. In some embodiments, the electron transfer agent and / or enzyme may be ionically or coordinatively bound to the polymer. For example, a charged polymer may be ionically bound to an oppositely charged electron transfer agent or enzyme. In yet other embodiments, the electron transfer agent and / or enzyme may be physically entrapped within an unbound polymer. The physically entrapped electron transfer agent and / or enzyme may further suitably interact with the fluid to facilitate detection of the analyte without substantially leaching from the active area.

[0078] Creatinine As described below with reference to Figures 2A and 2B of U.S. Application No. 16 / 582,583 (U.S. Publication No. 2020 / 0241015; Attorney Docket No. 13547USO1), previously incorporated by reference in its entirety for all purposes, the creatinine-sensing active region may comprise an enzyme system including multiple enzymes capable of acting in concert to facilitate the detection of creatinine. Creatinine can reversibly react hydrolytically in the presence of creatinine amidohydrolase (CNH) to produce creatine. Creatine can then undergo catalytic hydrolysis in the presence of creatine amidohydrolase (CRH) to produce sarcosine. Sarcosine produced by the hydrolysis of creatine can be oxidized in the presence of the oxidized form of sarcosine oxidase (SOX-ox) to produce glycine and formaldehyde, thereby producing the reduced form of sarcosine oxidase (SOX-red) in this process. Hydrogen peroxide can also be produced in the presence of oxygen. The reduced form of sarcosine oxidase can then undergo reoxidation in the presence of the oxidized form of the electron transfer agent (e.g., Os(III)), thereby generating the corresponding reduced form of the electron transfer agent (e.g., Os(II)) and delivering electron flow to the working electrode.

[0079] ethanol As described below with reference to Figures 5A-5B of U.S. Application Serial No. 16 / 774,909 (Attorney Docket No. 13622USO1), previously incorporated by reference in its entirety for all purposes, an ethanol-sensing active region may comprise an enzyme system including multiple enzymes capable of acting cooperatively to facilitate ethanol detection. For example, a cooperative enzymatic reaction of alcohol oxidase and xanthine oxidase may be used to sense ethanol. Xanthine oxidase may be covalently bound to a polymer within the active region of the analyte sensor, or alcohol oxidase may be non-covalently bound to a polymer within the active region. In addition to xanthine oxidase, an osmium or other transition metal complex capable of exchanging electrons with the enzyme is also covalently bound to the polymer. Ethanol reacts with oxidized (active) alcohol oxidase in the presence of a flavin cofactor (FAD already bound to alcohol oxidase), thereby producing reduced alcohol oxidase, acetaldehyde, and hydrogen peroxide. The reduced alcohol oxidase is reoxidized by molecular oxygen, as shown, returning alcohol oxidase to its catalytically active, oxidized form. The acetaldehyde produced from ethanol by the catalytic reaction then undergoes a secondary reaction with the oxidized form of xanthine oxidase in the presence of a flavin cofactor naturally present with the enzyme. Acetic acid is produced in this process, and xanthine oxidase is converted to its reduced state. The reduced xanthine oxidase may then react with a transition metal electron transfer agent bound to the polymer to transfer electrons to the working electrode, thereby generating a current and regenerating the oxidized form of xanthine oxidase. Hydrogen peroxide can be independently removed from the sensor environment by catalase present in the active region. The amount of acetaldehyde produced by the catalytic reaction is proportional to the amount of ethanol originally present. Thus, the current generated at the working electrode during xanthine oxidase oxidation of acetaldehyde can be proportional to the amount of acetaldehyde, and therefore the amount of ethanol, present. Correlation of working electrode current to ethanol concentration may be performed by referencing a look-up table of currents at known ethanol concentrations or by using a calibration curve.

[0080] Ketones As described below with reference to Figures 2A-2C of U.S. Application No. 16 / 774,835 (U.S. Publication No. 2020 / 0237275; Attorney Docket No. 13548USO1), previously incorporated by reference in its entirety for all purposes, a ketone-sensing active region may comprise an enzyme system including multiple enzymes capable of acting cooperatively to facilitate ketone detection. For example, β-hydroxybutyrate dehydrogenase (HBDH) and diaphorase may be deposited within the ketone-sensing active region on the surface of at least one working electrode, as further described herein. The ketone-sensing active region includes this pair of cooperative enzymes, where β-hydroxybutyrate dehydrogenase can convert β-hydroxybutyrate and oxidized nicotinamide adenine dinucleotide (NAD+) to acetoacetate and reduced nicotinamide adenine dinucleotide (NADH), respectively. The enzyme cofactors NAD+ and NADH help facilitate the cooperative enzymatic reactions described herein. NADH can then undergo diaphorase-mediated reduction, and the electrons transferred during this process provide a basis for ketone detection at the working electrode. Thus, there is a 1:1 molar correspondence between the amount of electrons transferred to the working electrode and the amount of converted β-hydroxybutyrate, thereby providing a basis for ketone detection and quantification based on the measured amount of current at the working electrode. The transfer of electrons resulting from NADH reduction to the working electrode may be achieved through an electron transfer agent, such as an osmium (Os) complex, as described further below. Albumin may be present as a stabilizer along with this pair of cooperating enzymes. According to certain embodiments, β-hydroxybutyrate dehydrogenase and diaphorase may be covalently bound to a polymer within the ketone-sensitive active region of the analyte sensor. While NAD+ may or may not be covalently bound to the polymer, if NAD+ is not covalently bound, NAD+ may be physically retained within the ketone-sensitive active region. The membrane covering the ketone-sensitive active region can serve to retain NAD+ within the ketone-sensitive active region while allowing sufficient inward diffusion of ketones to enable their detection. Suitable membrane polymers for covering the ketone-sensitive active region are further described herein.

[0081] In an alternative system, β-hydroxybutyrate dehydrogenase (HBDH) can convert β-hydroxybutyrate and NAD+ back to acetoacetate and NADH, respectively. Instead of electron transfer to the working electrode being completed by diaphorase and a transition metal electron transfer agent, the reduced form of NADH oxidase (NADHOx(Red)) undergoes a reaction to generate the corresponding oxidized form (NADHOx(Ox)). NADHOx(Red) can then be regenerated by reaction with molecular oxygen to generate superoxide, which undergoes secondary conversion to hydrogen peroxide mediated by superoxide dismutase (SOD). Hydrogen peroxide can then be reduced at the working electrode to provide a signal that can be correlated with the amount of ketone originally present. According to various embodiments, SOD can be covalently attached to a polymer within the ketone-sensitive active region. As in previously described enzyme systems, β-hydroxybutyrate dehydrogenase and NADH oxidase may be covalently bound to a polymer within the ketone-sensing active region, and NAD may or may not be covalently bound to a polymer within the ketone-sensing active region. If NAD+ is not covalently bound, it may be physically retained within the ketone-sensing active region, with the membrane polymer facilitating the retention of NAD+ within the ketone-sensing active region.

[0082] Another enzymatic ketone detection chemistry uses β-hydroxybutyrate dehydrogenase (HBDH) to convert β-hydroxybutyrate and NAD+ to acetoacetate and NADH, respectively. The electron transfer cycle in this case is completed by poly-1,10-phenanthroline-5,6-dione at the working electrode to regenerate NAD. The poly-1,10-phenanthroline-5,6-dione may or may not be covalently bound to a polymer within the ketone-sensitive active region. As in previously described enzyme systems, β-hydroxybutyrate dehydrogenase may or may not be covalently bound to a polymer within the ketone-sensitive active region, and NAD may or may not be covalently bound to a polymer within the ketone-sensitive active region. The inclusion of albumin within the active region can provide a surprising improvement in sensing stability. An appropriate membrane polymer can promote the retention of NAD+ within the ketone-sensitive active region.

[0083] Lactic acid As shown below in U.S. Application No. 16 / 259,157 (U.S. Publication No. 2019 / 0320947; Attorney Docket No. 13335USO1), previously incorporated by reference in its entirety for all purposes, the lactate-sensitive active region may include an enzyme system including multiple enzymes capable of acting in concert to facilitate lactate detection. The lactate-sensitive active region may replace glucose oxidase with lactate oxidase to facilitate lactate detection. Such lactate-sensitive analyte sensors based on modified glucose-sensitive sensor chemistry are described in commonly owned U.S. Patent No. 9,914,952, incorporated herein by reference in its entirety. As described herein, when lactate oxidase is present instead, improved analytical sensitivity and some sensing stability for lactate may be achieved by modifying the glucose-sensitive sensor chemistry to include catalase within the active region. Incorporation of catalase assists to some extent, but does not completely stabilize the long-term sensing of the analyte sensor. In fact, the lactate signal in catalase-containing analyte sensors decreases by up to about 10% over 48 hours of monitoring. Because catalase is known to be sensitive to hydrogen peroxide, the stabilizing effect of catalase in lactate-sensitive analyte sensors is believed to involve scavenging excess hydrogen peroxide that would otherwise affect the activity of lactate oxidase. While catalase improves the performance of lactate-sensitive analyte sensors, further performance enhancements may still be required for such analyte sensors to sense true potential.

[0084] The performance of lactate-sensitive analyte sensors can be improved by using other stabilizers, such as albumin, instead of catalase and by varying the mass transport-limiting membrane deposited over the active area. As described in previously incorporated by reference U.S. Application No. 16 / 259,157 (U.S. Publication No. 2019 / 0320947; Docket No. 13335USO1), several different membrane chemistries or morphologies can promote improved analyte sensor performance for lactate analytes.

[0085] According to the present disclosure, analytes may be monitored in any biological fluid of interest, such as dermal fluid, interstitial fluid, plasma, blood, lymphatic fluid, synovial fluid, cerebrospinal fluid, saliva, bronchoalveolar lavage, amniotic fluid, etc. In certain embodiments, the analyte sensors of the present disclosure may be applied to analyze dermal or interstitial fluid to determine the concentration of the analyte in vivo.

[0086] Different analyte-sensitive active regions may be located on the same or different working electrodes on the same sensor, for example, in some embodiments of the present disclosure, a creatinine-sensitive analyte sensor may further incorporate a glucose-sensitive active region to sense both creatinine and glucose.

[0087] When the first and second analyte-sensitive active regions are disposed on a single working electrode, one of the active regions may be configured to be independently interrogated to facilitate detection of each analyte, as described below. In particular, the first and second analyte-sensitive active regions may contain different electron transfer agents, resulting in one active region independently generating a signal from the other. Either the first or second analyte-sensitive active region may be configured independently to generate a signal from the other active region.

[0088] In embodiments in which the first analyte-sensitive active region and the second analyte-sensitive active region are disposed on a single working electrode, the redox potential associated with the second analyte-sensitive active region may be separated from the redox potential of the first analyte-sensitive active region by at least about 100 mV, or at least about 150 mV, or at least about 200 mV. The upper limit of dissociation between the redox potentials is determined by the in vivo electrochemical window of operation. By having the redox potentials of the two active regions sufficiently separated in magnitude from each other, electrochemical reactions may occur within the two active regions without substantially inducing electrochemical reactions within the other active region. Thus, signals from either the first analyte-sensitive active region or the second analyte-sensitive active region may be independently generated at or above the corresponding redox potential (lower redox potential) but below the redox potential (higher redox potential) of the other sensitive active region. In contrast, electrochemical reactions may occur within both active regions above the redox potential (higher redox potential) of the other, previously uninterrogated, active region. Thus, generating a signal above the redox potential may include signal contributions from both the first and second analyte-sensitive active regions, and the observed signal is a composite signal. The signal contribution from one active region (either the first or second analyte-sensitive active region) above the redox potential may then be determined by subtracting from the composite signal the signal above its corresponding redox potential obtained solely from either the first or second analyte-sensitive active region.

[0089] In more specific embodiments, when the active regions are located on the same working electrode, the first analyte-sensitive active region and the second analyte-sensitive active region may contain different electron transfer agents, resulting in redox potentials that are sufficiently separated in magnitude from each other. More specifically, the first analyte-sensitive active region may contain a first electron transfer agent, and the second analyte-sensitive active region may contain a second electron transfer agent, where the first and second electron transfer agents are different from each other. According to various embodiments of the present disclosure, the metal center and / or ligands present in a given electron transfer agent may be varied to provide sufficient separation of the redox potentials in the two regions.

[0090] Ideally, the first and second analyte-sensitive active regions disposed on a single working electrode may be configured to rapidly reach a steady-state current when the analyte sensor is operated at a given potential. Rapid attainment of a steady-state current may be facilitated by selecting an electron transfer agent for each active region that rapidly changes oxidation state upon exposure to a potential equal to or greater than the redox potential. Rapid attainment of a steady-state current may also be facilitated by making the active regions as thin as possible. For example, a suitable thickness for the sensitive active regions may be from about 0.1 microns (μm) to about 10 microns (μm). In some or other embodiments, rapid attainment of a steady-state current may be facilitated by including a conductive material, such as carbon nanotubes, graphite, or metal nanoparticles, within one or more active regions. A suitable amount of conductive molecule may range from about 0.1% to about 50% by weight, or from about 1% to about 50% by weight, or from about 0.1% to about 10% by weight, or from about 1% to about 10% by weight of the active region. Stabilizers may also be employed to promote sensory stability.

[0091] The sensitivity (output current) of the analyte sensor to each analyte can be altered by varying the coverage (area or size) of the active regions, the area ratio of the active regions to each other, and the identity, thickness, and / or composition of the mass transport limiting membrane covering the active regions. Variations of these parameters can be readily implemented by one of ordinary skill in the art having the benefit of the description herein.

[0092] Other embodiments of the analyte sensors disclosed herein may feature a first analyte-sensitive active region and a second analyte-sensitive active region on the surface of different working electrodes. Such analyte sensors may further include a second working electrode, a second analyte-sensitive active region disposed on the surface of the second working electrode, and a second membrane permeable to the second analyte and covering the second analyte-sensitive active region. The second analyte-sensitive active region may include a second electron transfer agent, a third polymer, and an enzyme covalently bound to the third polymer. When the first analyte-sensitive active region and the second analyte-sensitive active region are disposed on separate working electrodes, the electron transfer agents associated with each active region may be the same or different.

[0093] film Even with controlled and appropriate detection chemistries, incorporating two different types of active regions (either on the same working electrode or on different working electrodes) on a single analyte sensor is not always straightforward. Analyte sensors often employ a membrane covering the active region to function as a mass transport limiting membrane and / or to improve biocompatibility. Restricting the access of the analyte to the active region with a mass transport limiting membrane helps avoid sensor overload (saturation), thereby improving detection performance and accuracy. When analyzing multiple analytes using a single analyte sensor, different analytes across a given mass transport limiting membrane may exhibit different permeability values, potentially resulting in widely differing sensitivities for each analyte. Incorporating different mass transport limiting membranes on each active region can be problematic in some instances. Surprisingly and advantageously, certain analytes, such as glucose and creatinine, can be successfully analyzed using compositionally identical mass transport limiting membranes at each location, thereby simplifying the fabrication of analyte sensors capable of sensing both analytes.

[0094] As described in more detail below, at least one mass transport limiting membrane may cover the first analyte-sensitive active area and, when present, optionally the second analyte-sensitive active area. For example, if present, the glucose-sensitive active area may include a glucose-sensitive enzyme. The mass transport limiting membrane may also cover an oxygen scavenger (e.g., glucose oxidase), which may be sandwiched between separate membrane layers.

[0095] The in vivo analyte sensor may also include a membrane deposited on at least the implanted portion of the analyte sensor. In one embodiment, the membrane may improve the biocompatibility of the analyte sensor. In another embodiment, the membrane may be permeable or semi-permeable to the analyte of interest and limit the overall analyte flux to the active area of ​​the analyte sensor. That is, the membrane may function as a mass transport limiting membrane. Restricting the access of the analyte to the active area of ​​the sensor with a mass transport limiting membrane can help avoid sensor overload (saturation), thereby improving detection performance and accuracy. Such membranes may be highly specialized to limit the mass transport of a particular analyte, while other substances permeate the membrane at significantly different rates. The different membrane permeabilities of various potential analytes present a significant obstacle to developing analyte sensors configured to analyze multiple analytes. That is, varying membrane permeability values ​​can lead to significantly different sensitivities to multiple analytes, thereby making analysis difficult. Differential sensitivity to multiple analytes can often be partially overcome by using active areas of different sizes (e.g., smaller active areas for analytes with high sensitivity / permeability and larger active areas for analytes with low sensitivity / permeability), but this approach can present significant manufacturing challenges and is not applicable in all cases.

[0096] In certain embodiments of the present disclosure, the mass transport limiting membrane covering the analyte-sensitive active area may comprise at least a crosslinked polyvinylpyridine homopolymer or copolymer, including a polyvinylpyridine-co-styrene polymer. A mass transport limiting membrane of similar composition may also cover an oxygen scavenger, such as glucose oxidase. When a mass transport limiting membrane covers each active area, the compositions of the mass transport limiting membranes may be the same or different. Suitable techniques for depositing the mass transport limiting membrane on the active area may include, for example, spray coating, painting, inkjet printing, stenciling, roller coating, striping, slot dye coating, dip coating, etc., and combinations thereof.

[0097] Thus, an analyte sensor of the present disclosure capable of detecting multiple analytes may include an implantable sensor tail including a first working electrode, a second working electrode, where the first and second working electrodes are separated by a substrate, a reference electrode, a counter electrode, a layer of reference material, a first analyte-sensitive active region disposed on a surface of the first working electrode, and a second analyte-sensitive active region disposed on a surface of the second working electrode.

[0098] A detection method for analyzing multiple analytes includes exposing an analyte sensor to a fluid containing at least a first analyte and a second analyte, the analyte sensor comprising an implantable sensor tail including a first working electrode, a second working electrode, a reference electrode, a counter electrode, a layer of reference material, a first analyte-sensitive active area disposed on a surface of the first working electrode, and a second analyte-sensitive active area disposed on a surface of the second working electrode, the first and second working electrodes being separated by a substrate; The method may include applying a potential (or different potentials) to one working electrode and a second working electrode, obtaining a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid, obtaining a second signal at or above the redox potential of the second analyte-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid, and correlating the first signal to the concentration of the first analyte in the fluid and the second signal to the concentration of the second analyte in the fluid. The signals may be measured simultaneously or at different times.

[0099] In an alternative embodiment, the analyte sensor (or subsensor) comprises a first working electrode, a second working electrode electrically isolated from the first working electrode, a first analyte-sensitive active region disposed on the surface of the first working electrode, and a second analyte-sensitive active region disposed on the surface of the second working electrode. If the sensor tail does not include a counter electrode and / or a reference electrode, the subsensor may share the counter electrode and / or the reference electrode from another sensor. The sensor may further comprise additional (e.g., third and fourth) working electrodes. The third working electrode may further comprise a third analyte-sensitive active region comprising a third electron transfer agent, a third polymer, and an enzyme system including multiple enzymes capable of acting in concert to facilitate detection of the third analyte. The fourth working electrode may further comprise a fourth analyte-sensitive active region comprising a fourth electron transfer agent, a fourth polymer, and an enzyme system including multiple enzymes capable of acting in concert to facilitate detection of the third analyte.

[0100] A detection method for analyzing multiple analytes may include exposing an analyte sensor to a fluid containing at least a first analyte and a second analyte, the analyte sensor comprising an implantable sensor tail including a first working electrode, a second working electrode, a first analyte-sensitive active region disposed on the surface of the first working electrode, and a second analyte-sensitive active region disposed on the surface of the second working electrode, the analyte sensor not including a counter electrode or a reference electrode; applying a potential to the first and second working electrodes; obtaining a first signal equal to or greater than the redox potential of the first analyte-sensitive active region, the first signal proportional to the concentration of the first analyte in the fluid; obtaining a second signal equal to or greater than the redox potential of the second analyte-sensitive active region, the second signal proportional to the concentration of the second analyte in the fluid; and correlating the first signal to the concentration of the first analyte substance in the fluid and the second signal to the concentration of the second analyte in the fluid. If additional working electrodes are present, the method may include applying a potential to the third and fourth working electrodes, obtaining a third signal at or above the redox potential of the third analyte-sensitive active region, the third signal being proportional to the concentration of the third analyte in the fluid, obtaining a fourth signal at or above the redox potential of the fourth analyte-sensitive active region, the fourth signal being proportional to the concentration of the fourth analyte in the fluid, and correlating the third signal to the concentration of the third analyte in the fluid and correlating the fourth signal to the concentration of the fourth analyte in the fluid.

[0101] In another embodiment, an on-body device of the present disclosure may include a housing and first and second sensors disposed within the housing, where the first sensor includes an implantable sensor tail including a first working electrode, a second working electrode, a shared reference electrode, and a shared counter electrode, and the second sensor includes an implantable sensor tail including the first working electrode and the second working electrode, and the second sensor does not include a counter electrode or a reference electrode. In some embodiments, the second sensor may include a third and a fourth working electrode. The third and fourth working electrodes may include a fifth analyte-sensitive active region disposed on a surface of the third working electrode of the second sensor and a sixth analyte-sensitive active region disposed on a surface of the fourth working electrode of the second sensor.

[0102] In another embodiment, an on-body device of the present disclosure may include a first housing, a first sensor disposed within the first housing, the first sensor including an implantable sensor tail including a first working electrode, a second working electrode, a reference electrode, and a counter electrode, a second housing, and a second sensor disposed within the second housing, the second sensor including an implantable sensor tail including the first working electrode and the second working electrode, but without a counter electrode or a reference electrode. In some embodiments, the second sensor may include a third working electrode and a fourth working electrode. The third and fourth working electrodes may include a fifth analyte-sensitive active region disposed on a surface of the third working electrode of the second sensor and a sixth analyte-sensitive active region disposed on a surface of the fourth working electrode of the second sensor.

[0103] A detection method for analyzing multiple analytes includes exposing an analyte sensor system to a fluid containing at least a first analyte, a second analyte, a third analyte, and a fourth analyte, the analyte sensor system comprising a first sensor and a second sensor, the first sensor comprising an implantable sensor tail comprising a first working electrode, a second working electrode, a shared reference electrode, and a shared counter electrode, the second sensor comprising an implantable sensor tail comprising the first working electrode and the second working electrode, the second sensor not comprising a counter electrode or a reference electrode, the first and second working electrodes of the first sensor each comprising a first analyte-sensitive active area and a second analyte-sensitive active area, respectively, and the first and second working electrodes of the second sensor each comprising a third analyte-sensitive active area and a fourth analyte-sensitive active area, respectively; The method may include applying a potential to the first and second working electrodes of the first and second sensors; obtaining a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid; obtaining a second signal at or above the redox potential of the second analyte-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid; obtaining a third signal at or above the redox potential of the third analyte-sensitive active region, the third signal being proportional to the concentration of the third analyte in the fluid; obtaining a fourth signal at or above the redox potential of the third analyte-sensitive active region, the third signal being proportional to the concentration of the fourth analyte in the fluid; and correlating the first, second, third, and fourth signals to the concentrations of the first, second, third, and fourth analytes in the fluid, respectively. With respect to the potentials applied to the first electrode, second electrode, third electrode, and fourth electrode, the same potential may be applied to all electrodes, or different potentials may be applied to different electrodes, or the same potential may be applied to some of the electrodes and different potentials may be applied to other electrodes.

[0104] In some embodiments, the analytes detected include, but are not limited to, glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0105] In some embodiments, the analyte sensor may further comprise a first membrane permeable to a first analyte and covering the first analyte-sensitive active region, and a second membrane permeable to a second analyte and covering the second analyte-sensitive active region. The membranes may have the same composition or different compositions. In a sensor device having multiple sensitive active regions, the sensor may include as many different membranes as there are different sensitive active regions.

[0106] In some embodiments, the layer of reference material in the sensor tail may include Ag and AgCl. The layer of reference material may be disposed on the counter electrode or the reference electrode. In some embodiments, the first and second analyte-sensitive active regions each comprise an electron transfer agent covalently bonded to a polymer in each of the first and second analyte-sensitive active regions, or the first analyte-sensitive active region further comprises a first electron transfer agent, a first polymer, and an enzyme system including multiple enzymes capable of acting in concert to facilitate detection of the first analyte, and the second analyte-sensitive active region further comprises a second electron transfer agent, a second polymer, and an enzyme system including multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0107] In embodiments that do not include counter and reference electrodes on the implantable sensor tail but include a subsensor that shares the counter and reference electrodes of another sensor, the sensor system may include an analog front-end circuit that receives analyte data from all of the subsensor's working electrodes in addition to the working electrodes of the sensor where the counter and reference electrodes are located. For example, if the primary sensor has two working electrodes, a counter electrode, and a reference electrode, and the subsensor has four working electrodes (no counter or reference electrode), the analog front-end circuit may receive data from the first and second working electrodes of the first (primary) sensor and the first, second, third, and fourth working electrodes of the second (subsensor). The analog front-end circuit may be located within the primary sensor housing or within the subsensor housing.

[0108] In some embodiments, the signal can be correlated to the corresponding concentration of the analyte by consulting a look-up table or calibration curve. An analyte look-up table can be added by analyzing multiple samples with known analyte concentrations and recording the sensor response at each concentration. Similarly, an analyte calibration curve can be determined by plotting the analyte sensor response as a function of analyte concentration and determining an appropriate calibration function (e.g., by regression, particularly linear regression) over the calibration range.

[0109] The processor determines which sensor response value in the lookup table is closest to the one measured for the sample with the unknown analyte concentration, and then reports the analyte concentration based thereon. In some embodiments or other embodiments, if the sensor response value for the sample with the unknown analyte concentration is between two values ​​recorded in the lookup table, the processor may interpolate between the two values ​​in the lookup table to estimate the analyte concentration. Interpolation may assume a linear concentration change between the two values ​​recorded in the lookup table. Interpolation may be employed if the sensor response differs significantly, such as by 10% or more, from a given value in the lookup table.

[0110] Similarly, according to some or various other embodiments, the processor may input the sensor response values ​​for samples with unknown analyte concentrations into a corresponding calibration function, and the processor may then report the analyte concentration based thereon.

[0111] The sensor tail may further comprise an additional working electrode having an analyte-sensitive active region disposed thereon, the analyte-sensitive active region including a second electron transfer agent, a third polymer, and an enzyme covalently bound to the third polymer. Thus, the method may further include applying a potential to the additional working electrode, obtaining an additional signal equal to or greater than the redox potential of each analyte-sensitive active region, the additional signal being proportional to the concentration of the analyte in the fluid, and correlating the additional signal to the concentration of the analyte in the fluid.

[0112] In more specific embodiments, the redox potential associated with the first analyte-sensitive active region may be at least about 100 mV, or at least about 150 mV, or at least about 200 mV away from the redox potential of the second analyte-sensitive active region to provide sufficient separation to independently generate a signal from the first active region. The difference in redox potential may be due to the incorporation of different electron transfer agents within the active regions. Similarly, the redox potential associated with each of the third analyte-sensitive active region, the fourth analyte-sensitive active region, the fifth analyte-sensitive active region, the sixth analyte-sensitive active region, the seventh analyte-sensitive active region, the eighth analyte-sensitive active region, the ninth analyte-sensitive active region, or the tenth analyte-sensitive active region may be at least about 100 mV, or at least about 150 mV, or at least about 200 mV away from any of the other redox potentials to provide sufficient separation to independently generate a signal from the first active region.

[0113] The method may further include applying a potential to the first working electrode and applying a potential to the second working electrode; obtaining a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid; obtaining a second signal at or above the redox potential of the glucose-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid; and correlating the first signal to the concentration of the first analyte in the fluid and correlating the second signal to the concentration of the second analyte in the fluid.

[0114] According to more specific embodiments, signals from different working electrodes may be measured at different times. For example, if two working electrodes are present, a potential may be applied to the first and second working electrodes alternately. In other specific embodiments, the first and second signals may be measured simultaneously through the first and second channels, in which case a potential may be applied to both electrodes simultaneously. In other cases, the signals associated with each active region may be correlated to the respective analyte concentrations using a lookup table and calibration function in a manner similar to that described above.

[0115] Figures 8A-D show exemplary plots of analyte sensor response to varying concentrations of glucose and ketones. As shown in Figures 8C and 8D, the analyte sensors exhibited linear response to both analytes across the concentration range tested. As shown in Figure 8A, the sensor response was rapid for both analytes and remained stable at a given analyte concentration. Figures 9A-D show exemplary plots of analyte sensor response to varying concentrations of glucose and lactate. As shown in Figures 9C and 9D, the analyte sensors exhibited linear response to both analytes across the concentration range tested. As shown in Figure 9A, the sensor response was rapid for both analytes and remained stable at a given analyte concentration. Exemplary compositions of glucose, ketone, and lactate active sites and membranes can be found in U.S. Application No. 16 / 774,835 (U.S. Publication No. 2020 / 0237275; Docket No. 13548USO1) and U.S. Application No. 16 / 259,157 (U.S. Publication No. 2019 / 0320947; Docket No. 13335USO1), previously incorporated by reference in their entireties for all purposes.

[0116] The embodiments described herein are restated and expanded in the following paragraphs without explicit reference to the figures. In many embodiments, an analyte sensor is described that includes a first working electrode, a second working electrode, where the first and second working electrodes are separated by a substrate, a reference electrode, a counter electrode, a layer of reference material, a first analyte-sensitive active area disposed on a surface of the first working electrode, and a second analyte-sensitive active area disposed on a surface of the second working electrode.

[0117] In some embodiments, the analyte sensor also includes a first membrane permeable to the first analyte and covering the first analyte-sensitive active area, and a second membrane permeable to the second analyte and covering the second analyte-sensitive active area, hi some embodiments, the first membrane covers the first analyte-sensitive active area and the second analyte-sensitive active area.

[0118] In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region.

[0119] In some embodiments, the first analyte-sensitive active region further comprises a first electron transfer agent, a first polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the first analyte.

[0120] In some embodiments, the second analyte-sensitive active region further comprises a second electron transfer agent, a second polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0121] In some embodiments, the layer of reference material comprises Ag and AgCl. In some embodiments, a layer of reference material is disposed over the counter electrode or the reference electrode.

[0122] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid. In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0123] In some embodiments, the implantable sensor tail is configured to be inserted into tissue. In some embodiments, the first and second films have different compositions.

[0124] In some embodiments, the first and second films have the same composition. In some embodiments, the first working electrode is separated from the counter or reference electrode by a dielectric layer.

[0125] In some embodiments, the second working electrode is separated from the counter or reference electrode by a dielectric layer. In some embodiments, the analyte sensor further includes a first dielectric layer and a second dielectric layer disposed over the reference electrode and the counter electrode.

[0126] In many embodiments, a method is described that includes the steps of exposing an analyte sensor to a fluid containing at least a first analyte and a second analyte, the analyte sensor comprising an implantable sensor tail including a first working electrode, a second working electrode, a reference electrode, a counter electrode, a layer of reference material, a first analyte-sensitive active area disposed on a surface of the first working electrode, and a second analyte-sensitive active area disposed on a surface of the second working electrode, the first and second working electrodes being separated by a substrate; The method includes applying a potential to the first working electrode and the second working electrode, obtaining a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid, obtaining a second signal at or above the redox potential of the second analyte-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid, and correlating the first signal to the concentration of the first analyte in the fluid and the second signal to the concentration of the second analyte in the fluid.

[0127] In some embodiments, the implantable sensor tail further comprises a first membrane permeable to the first analyte and covering the first analyte-sensitive active area, and a second membrane permeable to the second analyte and covering the second analyte-sensitive active area.

[0128] In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region.

[0129] In some embodiments, the first analyte-sensitive active region further comprises a first electron transfer agent, a first polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the first analyte.

[0130] In some embodiments, the second analyte-sensitive active region further comprises a second electron transfer agent, a second polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0131] In some embodiments, the layer of reference material comprises Ag and AgCl. In some embodiments, a layer of reference material is disposed over the counter electrode or the reference electrode.

[0132] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid. In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0133] In some embodiments, the implantable sensor tail is configured to be inserted into tissue. In some embodiments, the first membrane and the second membrane have different compositions from each other. In some embodiments, the first membrane and the second membrane have the same composition as each other.

[0134] In some embodiments, the first working electrode is separated from the counter or reference electrode by a dielectric layer. In some embodiments, the second working electrode is separated from the counter or reference electrode by a dielectric layer.

[0135] In some embodiments, the analyte sensor further includes a first dielectric layer and a second dielectric layer disposed over the reference electrode and the counter electrode. In some embodiments, the fluid is a biological fluid and the analyte sensor is exposed to the biological fluid in vivo.

[0136] In some embodiments, the first signal and the second signal are measured at different times. In some embodiments, the first signal and the second signal are measured simultaneously.

[0137] In some embodiments, the first and second signals are acquired simultaneously through the first and second channels. In many embodiments, an analyte sensor is described that includes an implantable sensor tail that includes a first working electrode, a second working electrode electrically isolated from the first working electrode, a first analyte-sensitive active region disposed on a surface of the first working electrode, and a second analyte-sensitive active region disposed on a surface of the second working electrode.

[0138] In some embodiments, the analyte sensor further includes a first membrane that is permeable to the first analyte and that covers the first analyte-sensitive active area. In some embodiments, the analyte sensor further includes a second membrane that is permeable to a second analyte and that covers the second analyte-sensitive active area.

[0139] In some embodiments, the first working electrode and the second working electrode are separated by a substrate. In some embodiments, the first working electrode and the second working electrode are separated by a dielectric layer.

[0140] In some embodiments, a third working electrode and a third analyte-sensitive active region disposed on a surface of the third working electrode. In some embodiments, the analyte sensor further includes a third working electrode and a third analyte-sensitive active region disposed on the surface of the third working electrode, hi some embodiments, the analyte sensor further includes a fourth working electrode and a fourth analyte-sensitive active region disposed on the surface of the fourth working electrode.

[0141] In some embodiments, each of the first analyte-sensitive active region and the second analyte-sensitive active region comprises an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region, respectively.

[0142] In some embodiments, the analyte sensor further comprises a first analyte-sensitive active region further comprising a first electron transfer agent, a first polymer, and an enzyme system including a plurality of enzymes capable of acting in concert to facilitate detection of the first analyte.

[0143] In some embodiments, the analyte sensor further comprises a second analyte-sensitive active region further comprising a second electron transfer agent, a second polymer, and an enzyme system including multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0144] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid. In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0145] In some embodiments, the implantable sensor tail is configured to be inserted into tissue. In some embodiments, the analyte sensor does not include a counter electrode and a reference electrode.

[0146] In some embodiments, the analyte sensor is configured to electrically couple to an additional analyte sensor that includes a counter electrode and a reference electrode. In many embodiments, a method is described that includes exposing an analyte sensor system to a fluid containing at least a first analyte and a second analyte, the analyte sensor system including a first analyte sensor and a second analyte sensor, the first analyte sensor including an implantable sensor tail including a reference electrode and a counter electrode, the second analyte sensor including an implantable sensor tail including a first working electrode, a second working electrode, a first analyte-sensitive active area disposed on a surface of the first working electrode, and a second analyte-sensitive active area disposed on a surface of the second working electrode, the second analyte sensor including a counter electrode and and a reference electrode; applying an electrical potential to the first analyte sensor and the second analyte sensor; obtaining a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid; obtaining a second signal at or above the redox potential of the second analyte-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid; and correlating the first signal to the concentration of the first analyte in the fluid and the second signal to the concentration of the second analyte in the fluid.

[0147] In some embodiments, the first analyte sensor further includes at least one working electrode and at least one analyte-sensitive region disposed on a surface of the working electrode. In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region.

[0148] In some embodiments, the second analyte sensor further comprises a first analyte-sensitive active region comprising a first electron transfer agent, a first polymer, and an enzyme system including multiple enzymes capable of acting in concert to facilitate detection of the first analyte.

[0149] In some embodiments, the second analyte sensor further comprises a second analyte-sensitive active region comprising a second electron transfer agent, a second polymer, and an enzyme system including multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0150] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid. In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0151] In some embodiments, the implantable sensor tails of the first and second sensors are configured to be inserted into tissue. In some embodiments, the fluid is a biological fluid and the analyte sensor is exposed to the biological fluid in vivo.

[0152] In some embodiments, the first signal and the second signal are measured at different times. In some embodiments, the first signal and the second signal are measured simultaneously.

[0153] In some embodiments, the first and second signals are acquired simultaneously through the first and second channels. In some embodiments, the second analyte sensor further comprises a third working electrode, the third working electrode further comprising a third analyte-sensitive active region comprising a third electron transfer agent, a third polymer, and an enzyme system including a plurality of enzymes capable of acting in concert to facilitate detection of the third analyte. In some embodiments, the second analyte sensor further comprises a fourth working electrode, the fourth working electrode further comprising a fourth analyte-sensitive active region comprising a fourth electron transfer agent, a fourth polymer, and an enzyme system including a plurality of enzymes capable of acting in concert to facilitate detection of the third analyte.

[0154] In some embodiments, the method further includes applying a potential to the third working electrode, the fourth working electrode, and the first sensor; obtaining a third signal at or above the redox potential of the third analyte-sensitive active region, the third signal being proportional to the concentration of the third analyte in the fluid; obtaining a fourth signal at or above the redox potential of the fourth analyte-sensitive active region, the fourth signal being proportional to the concentration of the fourth analyte in the fluid; and correlating the third signal to the concentration of the third analyte in the liquid and correlating the fourth signal to the concentration of the fourth analyte in the liquid.

[0155] In many embodiments, an on-body device for use in an analyte monitoring system is described. The on-body device may include a housing and a first sensor and a second sensor disposed within the housing, where the first sensor includes an implantable sensor tail including a first working electrode, a second working electrode, a shared reference electrode, and a shared counter electrode, and the second sensor includes an implantable sensor tail including the first working electrode and the second working electrode, where the second sensor does not include a counter electrode or a reference electrode.

[0156] In some embodiments, the first sensor further comprises a first analyte-sensitive active region disposed on the surface of the first working electrode of the first sensor and a second analyte-sensitive active region disposed on the surface of the second working electrode of the first sensor. In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each further comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region. In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the first sensor further comprises a first membrane permeable to the first analyte and covering the first analyte-sensitive active area, and a second membrane permeable to the second analyte and covering the second analyte-sensitive active area.

[0157] In some embodiments, the second sensor further comprises a third analyte-sensitive active region disposed on the surface of the first working electrode of the second sensor and a fourth analyte-sensitive active region disposed on the surface of the second working electrode of the second sensor. In some embodiments, the third analyte-sensitive active region and the fourth analyte-sensitive active region each further comprise an electron transfer agent covalently bonded to a polymer in the third analyte-sensitive active region and the fourth analyte-sensitive active region, respectively. In some embodiments, the third analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the fourth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the second sensor further comprises a third membrane permeable to a third analyte and covering the third analyte-sensitive active area, and a fourth membrane permeable to a fourth analyte and covering the fourth analyte-sensitive active area.

[0158] In some embodiments, the implantable sensor tails of the first and second sensors are configured to be inserted into tissue. In some embodiments, the second sensor further comprises a third working electrode and a fourth working electrode. In some embodiments, the second sensor further comprises a fifth analyte-sensitive active region disposed on the surface of the third working electrode of the second sensor and a sixth analyte-sensitive active region disposed on the surface of the fourth working electrode of the second sensor. In some embodiments, the fifth analyte-sensitive active region and the sixth analyte-sensitive active region each further comprise an electron transfer agent covalently bonded to a polymer in the fifth analyte-sensitive active region and the sixth analyte-sensitive active region, respectively. In some embodiments, the fifth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the sixth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0159] In some embodiments, the device further includes an analog front-end circuit disposed within the housing, the analog front-end circuit receiving analyte data from the first and second working electrodes of the first sensor and the first and second working electrodes of the second sensor. In some embodiments, the first and second working electrodes of the second sensor are connected to the analog front-end circuit by circuit lines. In some embodiments, the first and second working electrodes of the second sensor are connected to the analog front-end circuit by flexible circuit connections.

[0160] In some embodiments, the device further includes an analog front-end circuit disposed within the housing, the analog front-end circuit receiving analyte data from the first and second working electrodes of the first sensor and the first, second, third, and fourth working electrodes of the second sensor. In some embodiments, the first, second, third, and fourth working electrodes of the second sensor are connected to the analog front-end circuit by circuit lines. In some embodiments, the first, second, third, and fourth working electrodes of the second sensor are connected to the analog front-end circuit by flexible circuit connections.

[0161] In many embodiments, a method is described that includes the steps of exposing an analyte sensor system to a fluid containing at least a first analyte, a second analyte, a third analyte, and a fourth analyte, the analyte sensor system including a first sensor and a second sensor, the first sensor including an implantable sensor tail including a first working electrode, a second working electrode, a shared reference electrode, and a shared counter electrode, the second sensor including an implantable sensor tail including the first working electrode and the second working electrode, the second sensor not including a counter electrode and a reference electrode, the first and second working electrodes of the first sensor each including a first analyte-sensitive active area and a second analyte-sensitive active area, respectively, and the first and second working electrodes of the second sensor each including a third analyte-sensitive active area and a fourth analyte-sensitive active area, respectively; acquiring a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid; acquiring a second signal at or above the redox potential of the second analyte-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid; acquiring a third signal at or above the redox potential of the third analyte-sensitive active region, the third signal being proportional to the concentration of the third analyte in the fluid; acquiring a fourth signal at or above the redox potential of the third analyte-sensitive active region, the third signal being proportional to the concentration of the fourth analyte in the fluid; and correlating the first, second, third, and fourth signals to the concentrations of the first, second, third, and fourth analytes in the fluid, respectively.

[0162] In some embodiments, the first analyte-sensitive active region, the second analyte-sensitive active region, the third analyte-sensitive active region, and the fourth analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first active region, the second active region, the third active region, and the fourth active region, respectively.

[0163] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid. In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0164] In some embodiments, the third analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the fourth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0165] In some embodiments, the implantable sensor tails of the first and second sensors are configured to be inserted into tissue. In some embodiments, at least a portion of the implantable sensor tail of the first sensor further comprises a first film deposited on the first analyte-sensitive active area and a second film deposited on the second analyte-sensitive active area.

[0166] In some embodiments, at least a portion of the implantable sensor tail of the second sensor further comprises a third film deposited on the third analyte-sensitive active region and a fourth film deposited on the fourth analyte-sensitive active region.

[0167] In some embodiments, the first working electrode of the first sensor is separated from the counter or reference electrode by a dielectric layer. In some embodiments, the second working electrode of the first sensor is separated from the counter or reference electrode by a dielectric layer.

[0168] In some embodiments, the analyte sensor system further includes a first dielectric layer and a second dielectric layer disposed on the reference electrode and the counter electrode. In some embodiments, the fluid is a biological fluid and the analyte sensor is exposed to the biological fluid in vivo.

[0169] In some embodiments, the first signal, the second signal, the third signal, and the fourth signal are measured at different times from one another. In some embodiments, the first signal, the second signal, the third signal, and the fourth signal are measured simultaneously.

[0170] In some embodiments, the first signal, the second signal, the third signal, and the fourth signal are acquired simultaneously through different channels. In some embodiments, the fluid includes a fifth analyte and a sixth analyte, and the implantable sensor tail of the second sensor further comprises a third working electrode and a fourth working electrode, each of the third and fourth working electrodes of the second sensor comprising a fifth analyte-sensitive active area and a sixth analyte-sensitive active area, respectively.

[0171] In some embodiments, the method further includes applying a potential to the third and fourth working electrodes of the second sensor; obtaining a fifth signal equal to or greater than the redox potential of the fifth analyte-sensitive active region, the fifth signal being proportional to the concentration of the fifth analyte in the fluid; obtaining a sixth signal equal to or greater than the redox potential of the sixth analyte-sensitive active region, the sixth signal being proportional to the concentration of the sixth analyte in the fluid; and correlating the fifth and sixth signals to the concentrations of the fifth and sixth analytes in the fluid, respectively.

[0172] In some embodiments, the first sensor and the second sensor are located within the same housing. In some embodiments, the first sensor is disposed in the first housing and the second sensor is disposed in the second housing. In some embodiments, the analyte sensor system further includes an analog front-end circuit disposed in the first housing, the analog front-end circuit receiving analyte data from the first and second working electrodes of the first sensor and the first and second working electrodes of the second sensor.

[0173] In some embodiments, the analyte sensor system further includes an analog front-end circuit disposed in the first housing, the analog front-end circuit receiving analyte data from the first and second working electrodes of the first sensor and the first, second, third, and fourth working electrodes of the second sensor.

[0174] In some embodiments, the analyte sensor system further includes a third sensor, the third sensor comprising an implantable sensor tail including first and second working electrodes, and the third sensor does not include a counter electrode or a reference electrode. In some embodiments, the third sensor is disposed in a third housing. In some embodiments, the fluid includes a seventh analyte and an eighth analyte, and the implantable sensor tail of the third sensor further comprises first and second working electrodes, each of the first and second working electrodes of the third sensor comprising a seventh analyte-sensitive active area and an eighth analyte-sensitive active area, respectively. In some embodiments, the method further includes applying a potential to the first and second working electrodes of the third sensor; obtaining a seventh signal that is equal to or greater than the redox potential of the seventh analyte-sensitive active region and proportional to the concentration of the seventh analyte in the fluid; obtaining an eighth signal that is equal to or greater than the redox potential of the eighth analyte-sensitive active region and proportional to the concentration of the eighth analyte in the fluid; and correlating the seventh and eighth signals to the concentrations of the seventh and eighth analyte in the fluid, respectively.

[0175] In some embodiments, the fluid includes a ninth analyte and a tenth analyte, and the implantable sensor tail of the third sensor further comprises a third working electrode and a fourth working electrode, each of the third working electrode and the fourth working electrode of the third sensor comprising a ninth analyte-sensitive active area and a tenth analyte-sensitive active area, respectively. In some embodiments, the method further comprises applying a potential to the third working electrode and the fourth working electrode of the third sensor, obtaining a ninth signal equal to or greater than the redox potential of the ninth analyte-sensitive active area, the ninth signal being proportional to the concentration of the ninth analyte in the fluid, obtaining a tenth signal equal to or greater than the redox potential of the tenth analyte-sensitive active area, the tenth signal being proportional to the concentration of the eighth analyte in the fluid, and correlating the ninth and tenth signals to the concentrations of the ninth and tenth analytes in the fluid, respectively.

[0176] In some embodiments, an on-body device for use in an analyte monitoring system is described, the device including: a first housing; a first sensor disposed within the first housing, the first sensor including an implantable sensor tail with a first working electrode, a second working electrode, a reference electrode, and a counter electrode; a second housing; and a second sensor disposed within the second housing, the second sensor including an implantable sensor tail with the first working electrode and the second working electrode, but not including a counter electrode or a reference electrode.

[0177] In some embodiments, the device also includes an adhesive layer, with the first housing and the second housing disposed on the adhesive layer. In some embodiments, the first sensor further comprises a first analyte-sensitive active region disposed on the surface of the first working electrode of the first sensor and a second analyte-sensitive active region disposed on the surface of the second working electrode of the first sensor. In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each further comprise an electron transfer agent covalently bonded to a polymer in the first analyte-sensitive active region and the second analyte-sensitive active region, respectively. In some embodiments, the first analyte is selected from the group consisting of glucose, β-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the second analyte is selected from the group consisting of glucose, β-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the second sensor further comprises a third analyte-sensitive active region disposed on the surface of the first working electrode of the second sensor and a fourth analyte-sensitive active region disposed on the surface of the second working electrode of the second sensor. In some embodiments, the third and fourth analyte-sensitive active regions each further comprise an electron transfer agent covalently bonded to a polymer in each of the third and fourth analyte-sensitive active regions. In some embodiments, the third analyte is selected from the group consisting of glucose, β-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid. In some embodiments, the fourth analyte is selected from the group consisting of glucose, β-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid.

[0178] In some embodiments, the implantable sensor tails of the first and second sensors are configured to be inserted into tissue. In some embodiments, the second sensor further comprises a third working electrode and a fourth working electrode. In some embodiments, the second sensor further comprises a fifth analyte-sensitive active region disposed on the surface of the third working electrode of the second sensor and a sixth analyte-sensitive active region disposed on the surface of the fourth working electrode of the second sensor. In some embodiments, the fifth analyte-sensitive active region and the sixth analyte-sensitive active region each further comprise an electron transfer agent covalently bonded to a polymer in the fifth analyte-sensitive active region and the sixth analyte-sensitive active region, respectively. In some embodiments, the fifth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the sixth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0179] In some embodiments, the analyte system further includes an analog front-end circuit disposed in the first housing, the analog front-end circuit receiving analyte data from the first and second working electrodes of the first sensor and the first and second working electrodes of the second sensor. In some embodiments, the first and second working electrodes of the second sensor are connected to the analog front-end circuit by circuit lines. In some embodiments, the first and second working electrodes of the second sensor are connected to the analog front-end circuit by flexible circuit connections.

[0180] In some embodiments, the analyte system further includes an analog front-end circuit disposed within the housing, the analog front-end circuit receiving analyte data from the first and second working electrodes of the first sensor and the first, second, third, and fourth working electrodes of the second sensor. In some embodiments, the first, second, third, and fourth working electrodes of the second sensor are connected to the analog front-end circuit by circuit lines. In some embodiments, the first, second, third, and fourth working electrodes of the second sensor are connected to the analog front-end circuit by flexible circuit connections.

[0181] In some embodiments, the analyte system further includes a third housing disposed on the adhesive layer and a third sensor disposed within the second housing, the third sensor comprising an implantable sensor tail including a first working electrode and a second working electrode, and the third sensor does not include a counter electrode or a reference electrode. In some embodiments, the third sensor further includes a seventh analyte-sensitive active region disposed on the surface of the first working electrode of the third sensor and an eighth analyte-sensitive active region disposed on the surface of the second working electrode of the third sensor. In some embodiments, the seventh analyte-sensitive active region and the eighth analyte-sensitive active region each further comprise an electron transfer agent covalently bonded to a polymer in the seventh analyte-sensitive active region and the eighth analyte-sensitive active region, respectively. In some embodiments, the seventh analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketone, creatinine, ethanol, and lactate. In some embodiments, the eighth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate.

[0182] In some embodiments, the analyte system further includes an analog front-end circuit disposed in the first housing, the analog front-end circuit receiving the analyte data from the first and second working electrodes of the third sensor. In some embodiments, the first and second working electrodes of the third sensor are connected to the analog front-end circuit by circuit lines. In some embodiments, the first and second working electrodes of the third sensor are connected to the analog front-end circuit by flexible circuit connections.

[0183] In some embodiments, the implantable sensor tail of the third sensor further comprises a third working electrode and a fourth working electrode, a ninth analyte-sensitive active region disposed on the surface of the third working electrode of the third sensor, and a tenth analyte-sensitive active region disposed on the surface of the fourth working electrode of the third sensor. In some embodiments, the ninth analyte-sensitive active region and the tenth analyte-sensitive active region each further comprise an electron transfer agent covalently bonded to a polymer in the ninth analyte-sensitive active region and the tenth analyte-sensitive active region, respectively. In some embodiments, the ninth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the tenth analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the analyte system also includes an analog front-end circuit disposed within the first housing, the analog front-end circuit receiving analyte data from the third and fourth working electrodes of the third sensor. In some embodiments, the third and fourth working electrodes of the third sensor are connected to the analog front-end circuit by circuit lines. In some embodiments, the third and fourth working electrodes of the third sensor are connected to the analog front-end circuit by flexible circuit connections.

[0184] In many embodiments, an analyte sensor is described that includes an implantable sensor tail comprising a substrate having a first side and a second side, a first working electrode disposed on the substrate, a second working electrode disposed on the substrate, a first analyte-sensitive active region disposed on a surface of the first working electrode, and a second analyte-sensitive active region disposed on a surface of the second working electrode, the first analyte-sensitive active region being disposed closer to a distal end of the substrate than the second analyte-sensitive active region, and a distance between a proximal end of the first analyte-sensitive active region and a distal end of the second analyte-sensitive active region is at least about 0.2 mm.

[0185] In some embodiments, the first and second working electrodes are separated by an insulating or dielectric layer. In some embodiments, a first working electrode is disposed on a first side of the substrate and a second working electrode is disposed on a second side of the substrate.

[0186] In some embodiments, the first working electrode and the second working electrode are disposed on a first side of the substrate. In some embodiments, the distance between the proximal end of the first analyte-sensitive active region and the distal end of the second analyte-sensitive active region is between about 0.4 and about 1.1 mm.

[0187] In some embodiments, the analyte sensor further includes a first membrane permeable to a first analyte and covering the first analyte-sensitive active area, and a second membrane permeable to a second analyte and covering the first analyte-sensitive active area and the second analyte-sensitive active area. In some embodiments, the first membrane and the second membrane have different compositions. In some embodiments, the first membrane and the second membrane have the same composition.

[0188] In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region.

[0189] In some embodiments, the first analyte-sensitive active region further comprises a first electron transfer agent, a first polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the first analyte.

[0190] In some embodiments, the second analyte-sensitive active region further comprises a second electron transfer agent, a second polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0191] In some embodiments, the analyte sensor further comprises a reference electrode and a counter electrode. In some embodiments, the analyte sensor further comprises a layer of reference material on a surface of the reference electrode. In some embodiments, the reference material comprises Ag and AgCl.

[0192] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid, hi some embodiments, the first analyte is ketones or beta-hydroxybutyrate.

[0193] In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the second analyte is glucose.

[0194] In some embodiments, the implantable sensor tail is configured to be inserted into tissue. In some embodiments, the distal portion of the implantable sensor tail has a maximum thickness of between about 0.25 mm and about 0.4 mm.

[0195] In many embodiments, a method is described that includes exposing an analyte sensor to a fluid containing at least a first analyte and a second analyte, the analyte sensor comprising an implantable sensor tail including a substrate having a first side and a second side, a first working electrode disposed on the first side of the substrate, a second working electrode disposed on the first side of the substrate, a first analyte-sensitive active region disposed on a surface of the first working electrode, and a second analyte-sensitive active region disposed on a surface of the second working electrode, the first analyte-sensitive active region being disposed closer to a distal end of the substrate than the second analyte-sensitive active region, and a proximal end of the first analyte-sensitive active region and a distal end of the second analyte-sensitive active region being disposed closer to a distal end of the substrate than the second analyte-sensitive active region. The method includes exposing an analyte sensor to a fluid having a distance of at least about 0.2 mm between the distal end of the substance-sensitive active region and the first working electrode; applying a potential to the first working electrode and the second working electrode; obtaining a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid; obtaining a second signal at or above the redox potential of the second analyte-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid; and correlating the first signal to the concentration of the first analyte in the fluid and the second signal to the concentration of the second analyte in the fluid.

[0196] In some embodiments, the first working electrode and the second working electrode are separated by an insulating layer. In some embodiments, the implantable sensor tail further comprises a first membrane permeable to the first analyte and covering the first analyte-sensitive active area, and a second membrane permeable to the second analyte and covering the first analyte-sensitive active area and the second analyte-sensitive active area.

[0197] In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region.

[0198] In some embodiments, the first analyte-sensitive active region further comprises a first electron transfer agent, a first polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the first analyte.

[0199] In some embodiments, the second analyte-sensitive active region further comprises a second electron transfer agent, a second polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0200] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactic acid, hi some embodiments, the first analyte is ketones or beta-hydroxybutyrate.

[0201] In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the second analyte is glucose.

[0202] In some embodiments, the first and second films have different compositions. In some embodiments, the first working electrode is separated from the second working electrode by a dielectric layer.

[0203] In some embodiments, the fluid is a biological fluid and the analyte sensor is exposed to the biological fluid in vivo. In some embodiments, the first signal and the second signal are measured at different times.

[0204] In some embodiments, the first signal and the second signal are measured simultaneously. In some embodiments, the first and second signals are acquired simultaneously through the first and second channels.

[0205] In some embodiments, the distal portion of the implantable sensor tail has a maximum thickness of between about 0.25 mm and about 0.4 mm. In many embodiments, an analyte sensor is described that includes an implantable sensor tail that includes a substrate having a first side and a second side, a first working electrode disposed on and in contact with the first side of the substrate, a first analyte-sensitive active region disposed on a surface of the first working electrode, a second working electrode disposed on and in contact with the first side of the substrate, a second analyte-sensitive active region disposed on a surface of the second working electrode, a counter electrode, and a reference electrode, wherein the first analyte-sensitive active region is disposed closer to a distal end of the substrate than the second analyte-sensitive active region.

[0206] In some embodiments, the distance between the proximal end of the first analyte-sensitive active region and the distal end of the second analyte-sensitive active region is between about 0.4 mm and about 1.1 mm. In some embodiments, the first working electrode and the second working electrode are not separated from the first side of the substrate by a dielectric layer.

[0207] In some embodiments, the counter electrode and the reference electrode are disposed on and in contact with a first side of the substrate, hi some embodiments, the counter electrode and the reference electrode are not separated from the first side of the substrate by a dielectric layer.

[0208] In some embodiments, the counter electrode and the reference electrode are located on and in contact with the second side of the substrate. In some embodiments, the analyte sensor further includes a first membrane that is permeable to the first analyte and that covers the first analyte-sensitive active area, and a second membrane that is permeable to the second analyte and that covers the first analyte-sensitive active area and the second analyte-sensitive active area.

[0209] In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region.

[0210] In some embodiments, the first analyte-sensitive active region further comprises a first electron transfer agent, a first polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the first analyte.

[0211] In some embodiments, the second analyte-sensitive active region further comprises a second electron transfer agent, a second polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0212] In some embodiments, the distal portion of the implantable sensor tail has a maximum thickness of between about 0.25 mm and about 0.4 mm. In many embodiments, a method is described that includes exposing an analyte sensor to a fluid containing at least a first analyte and a second analyte, the analyte sensor comprising an implantable sensor tail including a substrate having a first side and a second side, a first working electrode disposed on and in contact with the first side of the substrate, a first analyte-sensitive active region disposed on a surface of the first working electrode, a second working electrode disposed on and in contact with the first side of the substrate, a second analyte-sensitive active region disposed on a surface of the second working electrode, a counter electrode, and a reference electrode, wherein the first analyte-sensitive active region is larger than the second analyte-sensitive active region. the method includes exposing an analyte sensor disposed closer to the distal end of the substrate than the substrate; applying a potential to the first working electrode and the second working electrode; acquiring a first signal at or above the redox potential of the first analyte-sensitive active region, the first signal being proportional to the concentration of the first analyte in the fluid; acquiring a second signal at or above the redox potential of the second analyte-sensitive active region, the second signal being proportional to the concentration of the second analyte in the fluid; and correlating the first signal to the concentration of the first analyte in the fluid and the second signal to the concentration of the second analyte in the fluid.

[0213] In some embodiments, the distance between the proximal end of the first analyte-sensitive active region and the distal end of the second analyte-sensitive active region is between about 0.4 mm and about 1.1 mm. In some embodiments, the first working electrode and the second working electrode are not separated from the first side of the substrate by a dielectric layer.

[0214] In some embodiments, the counter electrode and the reference electrode are disposed on and in contact with a first side of the substrate, hi some embodiments, the counter electrode and the reference electrode are not separated from the first side of the substrate by a dielectric layer.

[0215] In some embodiments, the counter electrode and the reference electrode are located on and in contact with the second side of the substrate. In some embodiments, the analyte system further includes a first membrane that is permeable to the first analyte and covers the first analyte-sensitive active area, and a second membrane that is permeable to the second analyte and covers the first analyte-sensitive active area and the second analyte-sensitive active area.

[0216] In some embodiments, the first analyte-sensitive active region and the second analyte-sensitive active region each comprise an electron transfer agent covalently bonded to a polymer in each of the first analyte-sensitive active region and the second analyte-sensitive active region.

[0217] In some embodiments, the first analyte-sensitive active region further comprises a first electron transfer agent, a first polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the first analyte.

[0218] In some embodiments, the second analyte-sensitive active region further comprises a second electron transfer agent, a second polymer, and an enzyme system comprising multiple enzymes capable of acting in concert to facilitate detection of the second analyte.

[0219] In some embodiments, the fluid is a biological fluid and the analyte sensor is exposed to the biological fluid in vivo. In some embodiments, the first signal and the second signal are measured at different times.

[0220] In some embodiments, the first signal and the second signal are measured simultaneously. In some embodiments, the first and second signals are acquired simultaneously through the first and second channels.

[0221] In some embodiments, the first analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the first analyte is beta-hydroxybutyrate or a ketone. In some embodiments, the second analyte is selected from the group consisting of glucose, beta-hydroxybutyrate, uric acid, ketones, creatinine, ethanol, and lactate. In some embodiments, the second analyte is glucose.

[0222] In some embodiments, the distal portion of the implantable sensor tail has a maximum thickness of between about 0.25 mm and about 0.4 mm. Unless otherwise indicated, all numbers expressing quantities and the like in the specification and the related claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties sought to be obtained by embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding techniques.

[0223] One or more exemplary embodiments incorporating various features are described herein. For clarity, not all features of a physical implementation are described or shown in this application. In developing a physical implementation, including embodiments of the present invention, many implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related constraints, business-related constraints, government-related constraints, and other constraints, which vary by implementation and time. While the developer's efforts may require significant time, such efforts are nevertheless routine for one of ordinary skill in the art having the benefit of this disclosure.

[0224] Although various systems, tools, and methods are described herein using the term "comprising" various components or steps, the systems, tools, and methods may also "consist essentially of" or "consist of" various components and steps.

[0225] As used herein, the phrase "at least one" may be used to refer to any combination of items, with the term "and" or "or" separating any of the items. The phrase "at least one of" modifies the list as a whole rather than each element (i.e., each item) of the list. The phrase "at least one" allows for the inclusion of at least one of any one of the items, and / or at least one of any combination of the items, and / or at least one of each of the items. By way of example, the phrases "at least one of A, B, and C" or "at least one of A, B, or C" each refer to A only, B only, or C only, and / or any combination of A, B, and C, and / or at least one of each of A, B, and C.

[0226] Thus, the disclosed systems, tools, and methods are well adapted to achieve the objects and advantages mentioned, as well as those inherent therein. The specific embodiments disclosed above are illustrative only, as the teachings of the present disclosure may be modified and practiced in different, but equivalent manners, apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design shown herein, other than as described in the following claims. It is therefore evident that the specific exemplary embodiments disclosed above may be altered, combined, or modified, and all such variations are deemed to be within the scope of the present disclosure. The systems, tools, and methods illustratively disclosed herein may suitably be practiced in the absence of elements not specifically disclosed herein and / or any of the optional elements disclosed herein. Although systems, tools, and methods have been described using the terms "comprising," "containing," or "including" various components or steps, the systems, tools, and methods may also "consist essentially of" or "consist of" the various components and steps. All numerical values ​​and ranges disclosed above may be modified by some amount. Whenever a numerical range with a lower and upper limit is disclosed, any encompassed range within any numerical value and range is also specifically disclosed. In particular, any range of values ​​disclosed herein (in the form "from about a to about b," or, equivalently, "from about a to b," or, equivalently, "from about a to b") should be understood to define any numerical value or range encompassed within the broader range of values. Furthermore, terms used in the claims have their plain and ordinary meaning unless clearly and explicitly defined otherwise by the patentee. Furthermore, the indefinite article "a" or "an," as used in the claims, is defined herein to mean one or more of the element with which it is introduced.If there is a discrepancy in the usage of a word or term in this specification and one or more patents or other documents incorporated herein by reference, the consistent definition in this specification should control.

Claims

1. a first working electrode; a second working electrode; a ketone-sensitive active area disposed on a surface of the first working electrode, the ketone-sensitive active area including an enzyme system including at least two enzymes that facilitate detection of nicotinamide adenine dinucleotide (NAD) and a ketone; a glucose-sensitive active area disposed on a surface of the second working electrode, the glucose-sensitive active area including a glucose-sensitive enzyme; a first membrane disposed directly on the ketone-sensitive active area; a second membrane disposed on the first membrane and on the glucose-sensitive active area; 1. An electrochemical analyte sensor for continuous in vivo glucose and ketone detection, comprising: the first and second membranes have different permeability values ​​to separately control the flux of the test substance in the ketone-sensitive active area and the glucose-sensitive active area; the ketone-sensitive active region is located closer to the distal end of the sensor than the glucose-sensitive active region; The sensor, wherein the distance between the ketone-sensitive active area and the glucose-sensitive active area is between 0.4 mm and 1.1 mm.

2. 10. The sensor of claim 1, wherein the ketone-sensitive active region comprises a first polymer and a first electron transfer agent covalently bonded to the first polymer.

3. 10. The sensor of claim 1, wherein the glucose-sensing active region comprises a second polymer and a second electron transfer agent covalently bonded to the second polymer.

4. The sensor of claim 1 , wherein the first film and the second film have different compositions.

5. The sensor of claim 1 , wherein the distal end of the sensor has a maximum thickness of about 0.2 mm to about 0.4 mm.

6. The sensor of claim 1 , wherein the first film comprises polyvinylpyridine.

7. 10. The sensor of claim 1, wherein the second membrane comprises polyvinylpyridine-co-styrene.

8. The sensor of claim 1 , further comprising a substrate, wherein the first working electrode and the second working electrode are disposed on the substrate.

9. 9. The sensor of claim 8, wherein the distance between the ketone-sensitive active area and the glucose-sensitive active area is the distance along the length of the substrate between a proximal end of the ketone-sensitive active area and a distal end of the glucose-sensitive active area.

10. The sensor of claim 2 , wherein one or more of the at least two enzymes is covalently bound to the first polymer.

11. The sensor of claim 2 , wherein each of the at least two enzymes is covalently bound to the first polymer.

12. The sensor of claim 2 , wherein the enzyme system comprises hydroxybutyrate dehydrogenase (HBDH) and diaphorase.

13. 13. The sensor of claim 12, wherein the hydroxybutyrate dehydrogenase and diaphorase are covalently bound to the first polymer.

14. The sensor of claim 1 , wherein the ketone-sensitive active region further comprises albumin.

15. 10. The sensor of claim 1, wherein the first membrane is selectively positioned over the ketone-sensitive active area relative to the glucose-sensitive active area.

16. exposing the analyte sensor of claim 1 to a fluid containing at least glucose and ketones; applying a first potential to the first working electrode and a second potential to the second working electrode; obtaining a first signal at or above the redox potential of the ketone-sensitive active region, the first signal being proportional to a ketone concentration in the fluid; obtaining a second signal at or above the redox potential of the glucose sensitive active region, the second signal being proportional to the glucose concentration in the fluid; correlating the first signal to the ketone concentration in the fluid and correlating the second signal to the glucose concentration in the fluid.

17. 17. The method of claim 16, wherein the first signal and the second signal are measured at different times.

18. The method of claim 16 , wherein the first signal and the second signal are measured simultaneously.

19. 17. The method of claim 16, wherein the fluid is interstitial fluid.

20. Sensor electronics and 16. The sensor of claim 1, wherein the sensor acquires a first signal indicative of a ketone concentration and a second signal indicative of a glucose concentration, and transmits the first signal and the second signal to the sensor electronics; A sensor control device comprising:

21. The sensor control device of claim 20 , wherein the sensor electronics is configured to correlate the first signal to a ketone concentration.

22. 22. The sensor control device of claim 20 or 21, wherein the sensor electronics is configured to correlate the second signal to a glucose concentration.

23. (i) sensor electronics; (ii) a sensor according to any one of claims 1 to 15, which acquires a first signal indicative of a ketone concentration and a second signal indicative of a glucose concentration, and transmits the first signal and the second signal to the sensor electronics; 1. A glucose and ketone sensing system comprising: The glucose and ketone sensing system is configured such that the sensor electronics (a) correlates the first signal acquired by the sensor to a ketone concentration, (b) correlates the second signal acquired by the sensor to a glucose concentration, and (c) transmits the ketone concentration and the glucose concentration to a reader for display.

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