SENSORS AND METHODS FOR MEASURING pH

Abstract

To provide sensors and methods for measuring pH.SOLUTION: It can be particularly difficult to measure pH in vivo using current electrochemical sensors because of sensor drift and fouling of a sensor surface. Sensors suitable for measuring pH, particularly in vivo, comprise: a sensor tail comprising a first working electrode, a second working electrode, and at least one other electrode; a first active portion located upon the first working electrode, the first active portion comprising a substance having pH-dependent oxidation-reduction chemistry; and a second active portion located upon the second working electrode, the second active portion comprising a substance having oxidation-reduction chemistry that is substantially invariant with pH. A difference between a first signal from the first active portion and a second signal from the second active portion may be correlated with a pH value of a fluid.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a sensor and method for measuring pH. [Background technology]

[0002] Detecting various analytes in the body can be essential for monitoring health and well-being. Deviations from normal analyte levels are often indicative of underlying physiological conditions, such as metabolic states or disease.

[0003] Monitoring of analytes in the body may occur periodically or continuously over a period of time. Periodic analyte monitoring may be performed by taking samples of bodily fluids, such as blood, at set time intervals and analyzing them ex vivo. Continuous analyte monitoring may be performed using one or more sensors at least partially implanted in tissue within the body, such as through the skin, subcutaneously, or intravenously, such that the analysis is performed inside the body (in vivo). The implanted sensors may collect analyte data at any prescribed rate depending on the individual's particular health needs and / or previously measured analyte levels.

[0004] Periodic in vitro analyte monitoring is sufficient to determine physiological status for many individuals. However, in vitro analyte monitoring can be inconvenient or painful for some individuals. Furthermore, if analyte measurements are not taken in a timely manner, there is no way to recover lost data.

[0005] Continuous analyte monitoring with an implanted sensor is a more desirable approach for individuals with severe analyte dysregulation and / or rapidly fluctuating analyte levels, but may also be beneficial for others. Although continuous analyte monitoring with an implanted sensor is advantageous, there are challenges associated with this type of measurement. Intravenous analyte sensors have the advantage of producing analyte concentrations directly from the blood, but are invasive and may be painful to the individual wearing them, especially over long periods of time. Subcutaneous, interstitial, or dermal analyte sensors are often less painful to the individual wearing them and can produce sufficient measurement accuracy.

[0006] Any analyte may be suitable for in vivo analysis if an appropriate chemical reaction for sensing the analyte can be identified. Indeed, in vivo amperometric sensors configured for analyzing glucose have been developed and improved in recent years. Other analytes subject to physiological dysregulation that may also be desirable to monitor include, but are not limited to, lactate, oxygen, pH, A1e, ketones, drug levels, and the like.

[0007] The pH level in the body usually remains within a significant narrow range for normal biological functions to occur. For example, normal blood pH is about 7.4, and blood pH values ​​below 6.9 or above 7.6 can be life-threatening. Consequences of biological pH dysregulation include, but are not limited to, undesirable conditions such as precipitation in vivo of one or more components in bodily fluids, hypoactivity or hyperactivity of enzymes, changes in biological membrane permeability, and predisposition to certain cancers. Examples of some conditions that may lead to an offset in pH measurements include respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. With regard to acidosis, respiratory acidosis can be caused by chest deformation or injury, chronic lung and airway disease, sedative abuse, or obesity, etc. Metabolic acidosis can be caused by prolonged exercise, oxygen deficiency, certain medications such as salicylates, hypoglycemia, alcohol, stroke, liver failure, some cancers, kidney disease, severe dehydration, and poisoning (e.g., methanol poisoning), etc. With regard to alkalosis, respiratory alkalosis can be caused by oxygen deficiency, fever, lung disease, liver disease, and salicylate poisoning. Metabolic alkalosis is rare but can be caused by severe dehydration, cystic fibrosis, and overuse of alkalotic agents such as antacids.

[0008] In addition to the health effects that can be directly attributed to dysregulated pH values ​​in vivo, the detection of chemical reactions associated with certain analytes can be affected by the local pH environment and / or changes in the local pH environment. Detection of urea, for example, can be based on the change in pH that occurs when biological fluids interact with urease to produce ammonia as a product. Since ammonia changes the local pH environment, the urea concentration can be analyzed by measuring the pH. However, without a way to accurately measure pH, it is difficult to obtain reliable concentration measurements of urea and similar analytes, even when the pH level in vivo does not directly affect the analyte concentration itself.

[0009] Measurement of internal pH levels is traditionally performed by taking fluid samples at set time intervals and analyzing them ex vivo. While this approach is acceptable in some cases, when pH levels change rapidly, it is difficult to measure pH levels fast enough to determine when pH dysregulation has occurred. Furthermore, there is often a time lag associated with obtaining ex vivo pH measurements, which can mean that significant health effects have already occurred before pH dysregulation is recognized.

[0010] It may be desirable to measure pH values ​​in vivo, especially over long measurement times using a single implanted sensor, but the nature of conventional pH measurements makes this task difficult. First of all, conventional pH measurements are typically performed using glass electrodes or ion-sensitive field effect transistors (ISFETs). Both types of devices are very sensitive to surface contamination, which can affect the measured surface potential and therefore the measured pH. Secondly, reference electrodes used in conjunction with pH measurements can drift, especially in vivo, which is an additional source of measurement error. In contrast, reference electrodes for in vivo measurements of analytes such as glucose, for example, are amperometrically operated at a plateau potential and are much less susceptible to drift effects. Therefore, conventional approaches are not well suited to measuring pH values ​​in vivo, especially when measurements are over long periods of time.

[0011] The following figures are included to illustrate certain aspects of the invention and should not be considered as exclusive embodiments. The disclosed subject matter is capable of considerable modification, substitutions, combinations and equivalents in form and function without departing from the scope of the invention. [Brief description of the drawings]

[0012] [Figure 1A] FIG. 2 illustrates an exemplary configuration of a pH sensor having two working electrodes and one counter / reference electrode, according to various embodiments described herein. [Figure 1B]FIG. 2 illustrates an exemplary configuration of a pH sensor having two working electrodes and one counter / reference electrode, according to various embodiments described herein. [Diagram 2] FIG. 2 illustrates an exemplary configuration of a pH sensor having two working electrodes, a reference electrode, and a counter electrode, according to various embodiments described herein. [Diagram 3] FIG. 2 illustrates an exemplary sensing system that is wearable and configured to measure pH based on receiving signals from first and second working electrodes, according to various embodiments described herein. [Figure 4] Graph showing plots of aggregate cyclic voltammograms at various pH values ​​for a working electrode containing toluidine blue bound to a polymer. [Diagram 5] FIG. 13 shows corresponding plots of aggregation cyclic voltammograms at various pH values ​​for a working electrode containing a polymer-bound osmium complex. [Figure 6] Graph showing a calibration curve corresponding to the voltage difference data vs. pH in Table 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention generally describes sensors and methods for measuring pH, and more particularly, sensors and methods that are particularly suited for measuring pH values ​​in vivo. As mentioned above, the electrochemical measurement of pH value in the body can be complicated by drift and surface fouling of one or more electrodes or similar pH measuring devices. The above problems can be particularly problematic in the body, but can also be encountered when measuring pH value in vitro or in a laboratory setting. In the absence of provisions for accurate measurement of pH value in the body, it is difficult to assess physiological conditions in real time or substantially in real time. Furthermore, the nature of the sensing corresponding to the measurement of the concentration of a particular analyte may be dependent on pH, and an inaccurate measurement of the concentration of the analyte may be due to a failure to measure pH with sufficient accuracy.

[0014] Described herein is a pH sensor that may overcome the above challenges and provide further advantages. In particular, the pH sensor of the present invention is largely unaffected by the effects of surface fouling and drift. The pH sensor of the present invention employs two different working electrodes, with the active portion of each working electrode exhibiting different electrochemical performance. As used herein, the term "active portion" refers to a layer or spot disposed on a portion of the working electrode where a desired electrochemical reaction occurs. That is, in the pH sensor of the present invention, the active portion disposed on the first working electrode includes a material having a pH-dependent redox property, and the active portion disposed on the second working electrode includes a material having a redox property that is nearly invariant with respect to pH. According to some embodiments, the material located on the active portion of the first working electrode includes a material that changes its protonation state during the course of the redox reaction, although this is not required. The potential at which the oxidation state changes can be determined during a voltammetric sweep of the first working electrode. According to some or various other embodiments, the material located on the active portion of the second working electrode does not necessarily have a completely invariant potential measured during a voltammetric sweep over a given pH range of interest. The change in the measured voltage may be less than a predetermined suitable value in a given pH range, for example, less than about 100 mV variation in a given pH range of interest, or less than about 50 mV variation, or less than about 10 mV variation. The variation may be determined by subtracting the minimum voltage from the maximum voltage observed in a voltage sweep between the two extreme values ​​of the useful pH range. The amount of acceptable variation may be determined based on how accurate the pH measurement needs to be. According to some embodiments, the material located at the active portion of the second working electrode may maintain (not change) its protonation state in the course of undergoing a redox reaction, although this is not required.

[0015] To calculate a pH value of a fluid in contact with the pH sensor, signals are received from the first and second working electrodes. In particular, an observed pH value of the fluid can be calculated based on the difference between the first and second signals. The signal difference can be correlated with a pH value by reference to a look-up table, a calibration curve, or the like (e.g., using a suitable processor or manually).

[0016] The pH sensors disclosed herein include a reference electrode and a counter electrode, or one counter / reference electrode, but do not need to receive, reference, utilize, or process a signal from the reference electrode or counter / reference electrode to determine a pH value. That is, the first working electrode and the second working electrode are individually referenced to the reference electrode or counter / reference electrode, so that the corrections applied to the first signal and the second signal are cancelled out when determining the signal difference. In other words, the first working electrode and the second working electrode are internally referenced to each other. Thus, the pH sensors described herein overcome the drift problems associated with conventional pH sensors by eliminating the need to correct the signal with a reference electrode or counter / reference electrode. Furthermore, given that a reference electrode is not required for signal correction, some embodiments of the pH sensors described herein may lack a reference electrode entirely. In such embodiments, the second working electrode can be considered a reference electrode for the first working electrode, or vice versa, and a suitable counter electrode can be present to form a closed electrical circuit.

[0017] Furthermore, the pH sensors described herein address the issue of surface fouling, which can be problematic for conventional electrochemical pH sensors. That is, the active portion of the first and second working electrodes includes a relatively thick polymer layer or spot, and the sensing chemical reaction occurs throughout the polymer layer or spot, not just on the surface. By passing electrons through the polymer layer to the first and second electrodes, the redox reaction occurs throughout the active portion, not just on the surface. Thus, the effect of surface fouling can be limited with the pH sensors disclosed herein. Furthermore, since the redox reaction is not limited to the surface of the active portion of the pH sensors disclosed herein, and the interface between the membrane and the active portion does not substantially affect the redox reaction occurring inside the active portion, various mass-limited or biocompatible membranes can be suitably used in combination with the pH sensors. Various proton-permeable membranes can be suitable for use in combination with the pH sensors disclosed herein. A suitable proton-permeable membrane is substantially impermeable to the substances contained within the first and second active portions, thereby promoting retention of those substances in the active portions, such that pH sensing capability is maintained over extended measurement times.

[0018] Finally, the pH sensor of the present invention is desirably operated by performing a voltammetric sweep (e.g., cyclic voltammetry, differential pulse voltammetry, pulse wave voltammetry, square wave voltammetry, etc.) of the sensing reaction within a given pH measurement range of interest. The potential measured at a given position of the voltammetric sweep using the above techniques is substantially insensitive to the geometry of the electrodes, such as the thickness and area of ​​the active portion on each working electrode. Thus, manufacturing variations in the active portions have minimal impact. In some embodiments, the active portion includes a sensing spot having an arc-shaped shape, such as that described in U.S. Patent Application Publication No. 2012 / 015005 and incorporated herein by reference. Thus, the measured potential is indicative of the chemical reaction nature of each active portion at a given pH. This feature may facilitate calibration of the pH sensor. The measured potential may be, for example, an anodic peak potential, a cathodic peak potential, a half-wave potential, etc., according to one or more embodiments. According to more specific embodiments, the potentials measured at each working electrode may be of the same type of measurement (e.g., anodic peak potential, cathodic peak potential, or half-wave potential of both the first and second working electrodes) in order to calculate the signal difference.

[0019] Thus, the pH sensor of the present disclosure includes a sensor tail including a first working electrode, a second working electrode, and at least one further electrode, a first active moiety disposed on the first working electrode, the first active moiety containing a substance having a pH-dependent redox property, and a second active moiety disposed on the second working electrode, the second active moiety containing a substance having a redox property that is substantially invariant with pH. Suitable redox chemistries for the first and second active moieties are described in further detail below.

[0020] As described below with reference to the drawings, various configurations are possible for pH sensors that include two working electrodes. At least one other electrode in the pH sensors disclosed herein includes, according to some embodiments, a counter electrode, or a counter electrode and a reference electrode, and in other embodiments, a counter / reference electrode. Thus, according to various embodiments, the pH sensors described herein include a total of at least three or at least four electrodes. Before describing the four-electrode configuration, the three-electrode configuration will first be described.

[0021] 1A and 1B show an exemplary configuration of a pH sensor having two working electrodes and one counter / reference electrode according to various embodiments described herein. As shown in FIG. 1A, the working electrodes 104, 106 are disposed on a substrate 102 in the pH sensor 100. An active portion 110 is disposed on the surface of the working electrode 104, and an active portion 112 is disposed on the surface of the working electrode 106. One of the active portions 110, 112 includes a material having a pH-dependent redox property, and the other includes a material having a redox property that is substantially invariant to pH. The counter / reference electrode 120 is electrically insulated from the working electrode 104 by a dielectric layer 122. Although the counter / reference electrode 120 is shown disposed on the working electrode 104, in some embodiments, the counter / reference electrode 120 may alternatively be disposed on the working electrode 106. Outer dielectric layers 130, 132 are disposed on the working electrode 106 and the counter / reference electrode 120. It should be understood that the length of each layer may vary from that depicted.The active moieties 110, 112 are exposed so that they can interact with the analyte.

[0022] According to various embodiments, the membrane 140 covers one or both of the active portions 110, 112. According to the present invention, the membrane 140 contains a polymer that is biocompatible and / or capable of restricting the flux of analytes (i.e., protons) to the active portions 110, 112. It may be desirable to restrict the flux of analytes to prevent saturation of the sensor. According to various embodiments, the thickness of the membrane 140 can vary the flux of analytes. The thickness of the membrane 140 can vary or be constant along the length of the sensor. In various embodiments, the thickness of the membrane 140 ranges between about 1 micron and about 100 microns, between about microns and about 50 microns, or between about 20 microns and about 90 microns. One or both sides of the pH sensor 100, or the entire pH sensor 100, are covered with the membrane 140.

[0023] As shown in Figure 1A, working electrodes 104, 106 are disposed on opposite sides of substrate 100. In an alternative configuration shown in Figure 1B, working electrodes 104, 106 are disposed on the same side of substrate 102 within pH sensor 101 and are separated by dielectric layer 122. Other alternative configurations are within the scope of the present invention.

[0024] A sensor configuration having both a counter electrode and a reference electrode is similar in structure to that shown in FIGS. 1A and 1B, except for the inclusion of an additional electrode. FIG. 2 illustrates an exemplary configuration of a pH sensor having two working electrodes, one reference electrode, and one counter electrode. As shown, working electrodes 204, 206 are disposed on a substrate 202 in a pH sensor 200. An active portion 210 is disposed on the surface of the working electrode 204, and an active portion 212 is disposed on the surface of the working electrode 206. One of the active portions 210, 212 includes a substance having a pH-dependent redox property, and the other includes a substance having a substantially pH-invariant redox property. The counter electrode 220 is electrically insulated from the working electrode 204 by a dielectric layer 222, and the reference electrode 221 is electrically insulated from the working electrode 206 by a dielectric layer 223. Outer dielectric layers 230, 232 are disposed on the reference electrode 221 and the counter electrode 220, respectively. In various embodiments, the membrane 240 covers at least the active portions 210, 212. One or both sides of the pH sensor 200, or the entire pH sensor 200, are covered with the membrane 240, as shown in Figures 1A and 1B.

[0025] The arrangement of the counter electrode 220 and the reference electrode 221 can be reversed from that shown in Figure 2. Furthermore, the working electrodes 204, 206 do not necessarily have to be on opposite sides of the substrate 202 as shown in Figure 2. One or both sides of the pH sensor 200, or the entire pH sensor 200, is covered with a membrane 240, as shown in Figures 1A and 1B.

[0026] As noted above, one of the active moieties comprises a substance having pH-dependent redox properties. Suitable substances having pH-dependent redox properties include, for example, quinones, redox indicator compounds, or any combination thereof.

[0027] As quinones are protonated or deprotonated with changes in pH, they exhibit changes in redox properties and associated differences in peak positions observed during voltammetric sweeps. At low pH values, the phenol form predominates. As the pH is increased and deprotonation of the phenol begins to occur, oxidation to the quinone form is promoted. Suitable quinones may include, but are not limited to, benzoquinone, naphthoquinone, anthraquinone, 1,10-phenanthrolinequinone, tetrachlorobenzoquinone (chloranil), dichlorodicyanobenzoquinone (DDQ), and the like, functionalized variants thereof, and any combination thereof. In some embodiments, there may be additional functional groups that can be covalently attached to the working electrode and / or the polymer of the active portion. Suitable quinones with additional functionality may include, but are not limited to, lawsone, alizarin, naphthazirin, and the like, and any combination thereof. Additional functional groups that can be covalently attached to the working electrode and / or polymer may be located directly on the quinone ring or spaced therefrom by one or more spacer atoms, such as an alkylene group, an oxyalkylene group, or a carboxylic acid derivative. In some embodiments, a suitable quinone has the structure shown in Formula 1:

[0028] [ka]

[0029] In Formula 1, Zn represents any functional group (n=14), and A is a spacer group that is covalently attached to the polymer that constitutes the first active portion. In certain embodiments, A is, for example, -(CH2) m -, -C(=O)-NH-, -C(=O)-O-, -O(CH2) m , or -(CH2) m and m is a positive integer ranging between 1 and about 20.

[0030] Redox indicator compounds include substances used in redox titrations based on their property of changing color at a particular electrode potential. Specific redox indicator compounds suitable for use herein include, but are not limited to, redox indicator compounds whose redox reaction is pH-dependent. Specific examples include, but are not limited to, indophenol compounds, indigo dyes, phenazines, thiazines, and the like, and any combinations thereof. Specific examples of redox indicator compounds having pH-dependent redox properties include, but are not limited to, indophenol, 2,6-dibromophenol-indophenol sodium, 2,6-dichlorophenol-indophenol sodium, o-cresol-indophenol sodium, thionine, methylene blue (methylthioninium chloride), toluidine blue, indigo tetrasulfonic acid, indigo trisulfonic acid, indigo disulfonic acid (indigo carmine), indigo monosulfonic acid, safranine, phenosafranine, neutral red, and the like, and any combinations thereof. Additional functional groups that can be covalently attached to the working electrode and / or polymer can be located directly on the redox indicator compound or spaced therefrom by one or more spacer atoms, such as an alkylene chain.

[0031] According to some embodiments, a polymer may be present in the first and second active portions. Suitable polymers for inclusion in the first and second active portions include, but are not limited to, polyvinylpyridine (e.g., poly(4-vinylpyridine)), polyimidazole (e.g., poly(1-vinylimidazole)), any copolymers thereof, and the like, and any combinations thereof. Suitable exemplary copolymers include, but are not limited to, copolymers including monomer units such as styrene, acrylamide, methacrylamide, acrylonitrile, and the like, and any combinations thereof.

[0032] In more specific embodiments, the first active moiety comprises a polymer covalently attached to a substance having pH-dependent redox properties. In some embodiments, the second active moiety similarly comprises a polymer covalently attached to a substance having redox properties that are substantially invariant with respect to pH. The manner in which the substances of the first and second active moieties are covalently attached is not believed to be particularly limiting and may depend on the type of polymer or copolymer present in the first and second active moieties. In some embodiments, the substance is covalently attached to the polymer by quaternizing a heterocycle (e.g., a pyridine nitrogen atom) in the polymer.

[0033] The covalent attachment of the substance having pH-dependent redox properties to the polymer containing the first active moiety occurs via a suitable crosslinker. The crosslinker can be introduced by reaction with a suitable crosslinker. Crosslinkers suitable for reacting with amino or hydroxyl groups in the substance having pH-dependent redox chemistry can include, but are not limited to, polyethylene glycol diglycidyl ether (PEGDGE), cyanuric chloride, N-hydroxysuccinimide, imidoesters, polyepoxides such as epichlorohydrin, derivatized variants thereof, and the like, and any combination thereof. Crosslinkers suitable for reacting with carboxylic acid groups in the substance having pH-dependent redox properties can include, but are not limited to, carbodiimides.

[0034] Suitable substances having redox properties that are substantially invariant with pH are not believed to be particularly limited, provided that the substance exhibits a well-limited range of response variability over the given pH range. According to various embodiments, the response variability varies by about 100 mV or less, or by about 50 mV or less, or by about 10 mV or less, or shows substantially no variation over the given pH range of interest. In even more specific embodiments, the response variability varies within the above limits over a pH range of about 1 to about 14, or about 2 to about 12, or about 3 to about 7, or about 7 to about 12, or about 5 to about 8, or about 6.5 to about 8.5, or about 6.5 to about 8.

[0035] In even more specific embodiments, the substance having redox properties with substantially no pH variability in the second active portion may include transition metal complexes, such as osmium complexes, as disclosed in, for example, U.S. Patent Nos. 6,134,461 and 6,605,200, which are incorporated herein by reference in their entirety. The transition metal complexes may facilitate the transport of electrons to the second working electrode during the redox redox reaction, where the pH may or may not change. Suitable transition metal complexes may include electroreducible and electrooxidizable ions, complexes, or molecules that have a redox potential that is several hundred millivolts greater or less than the redox potential of a standard calomel electrode (SCE). Suitable substances for inclusion in the second active portion include, for example, complexes of ruthenium, iron (e.g., polyvinylferrocene), or cobalt. Suitable ligands for any of the transition metal complexes may include, but are not limited to, bidentate or higher dentate ligands, such as, for example, bipyridine, biimidazole, phenthroline, pyridyl (imidazole), and any combination thereof. Other suitable bidentate ligands may include, but are not limited to, amino acids, oxalic acid, acetylacetone, diaminoalkanes, o-diaminoarenes, and the like, and any combination thereof. To achieve a complete coordination sphere, any combination of monodentate, bidentate, tridentate, tetradentate, or higher dentate ligands may be present in the metal complex. One or more of the ligands in the metal complex may be covalently attached to the polymer of the second active moiety.

[0036] In another embodiment, the substance that has substantially no variability in redox reaction with respect to the pH of the second active portion can be a pH-independent redox indicator.Suitable pH-independent redox indicators can include, for example, 2,2'-bipyridine ruthenium, 2,2'-bipyridine iron, nitrophenanthroline, N-phenylanthranilic acid, 1,10-phenanthroline iron sulfate complex, N-ethoxyxoidine, 5,6-dimethylphenanthroline iron, o-dianisidine, sodium diphenylamine sulfonate, diphenylbenzidine, diphenylamine, and viologen.Other substances that have substantially no pH variability in redox properties can include any substance that does not undergo protonation or deprotonation over the pH range of interest, provided that the redox reaction is reversible.

[0037] The substances of the first and second active moieties may be covalently bound to the polymer in each active moiety, although other means of binding to the polymer may be suitable as well. In some embodiments, the substance is ionically or coordinatively bound to the polymer. For example, a charged polymer is ionically bound to an oppositely charged substance. In other embodiments, the substance may be physically incorporated into the polymer without being bound to the polymer.

[0038] According to various embodiments of the present disclosure, each of the working electrodes is configured to generate a signal, and the difference between the signals can be correlated to a pH value. Before further describing how the signal difference is determined and correlated to a pH value, a brief description is given of how the pH sensor communicates the signal to a user or processor for further analysis.

[0039] According to various embodiments, the pH sensor of the present invention is configured to be worn on the body and the sensor tail is configured to be inserted into tissue, particularly below the skin, subcutaneously, or interstitially. Figure 3 shows a diagram of an exemplary sensing system according to the present invention configured to be worn on the body and capable of measuring pH based on receiving signals from the first and second working electrodes. However, it should be understood that pH sensors having structures, configurations, and / or components different from or in addition to those explicitly described below may also be suitable for use in some embodiments of the present disclosure.

[0040] As shown in FIG. 3, the sensing system 300 includes a sensor controller 302 and a reader 320 configured to communicate with each other via a local or remote communication path or link, wired or wireless, unidirectional or bidirectional, and encrypted or unencrypted. According to some embodiments, the reader 320 configures an output medium for displaying the pH determined by the sensor 304 or its corresponding processor and for alerts or notifications, as well as for enabling one or more user inputs. The reader 320 may be a general-purpose smartphone or a dedicated electronic reader. Although only one reader 320 is shown in the figure, in certain examples, there may be multiple readers 320. The multiple readers 320 may communicate with each other (e.g., to share and synchronize data). The reader 320 may communicate with a remote terminal 370 and / or a trusted computer system 380 via communication paths / links 341, 342, respectively, which may also be wired or wireless, unidirectional or bidirectional, and encrypted or unencrypted communications. The reader 320 may also or alternatively communicate to a network 350 (e.g., a cellular network, the Internet, or a cloud server) via communication path / link 351. The network 350 is further communicatively connected to a remote terminal 370 via communication path / link 352 and / or to a trusted computer system 380 via communication path / link 353. In turn, in some embodiments, the remote terminal 370 and / or the trusted computer system 380 may communicate to the network 350. Alternatively, the sensor 302 may communicate directly to the remote terminal 370 and / or the trusted computer system 380 without an intervening reader 320. For example, according to some embodiments, the sensor 302 may communicate with the remote terminal 370 and / or the trusted computer system 380 via a direct communication link to the network 350, such as described in U.S. Patent Application Publication No. 2011 / 0213225, the entire contents of which are incorporated herein by reference.Any suitable electronic communication protocol may be used for each of the communication paths or links, such as Near Field Communication (NFC), Radio Frequency Identification (RFID), BLUETOOTH or BLUETOOTH low energy protocols, WiFi, etc. The remote terminal 370 and / or the trusted computer system 380, according to some embodiments, are accessible by individuals other than the primary user. The reader 320 may include a display 322 and optional input elements 321. According to some embodiments, the display 322 includes a touch screen interface.

[0041] The sensor control device 302 includes a sensor housing 303 that can house circuitry and a power source for operating the sensor 304. Optionally, the power source and / or active circuitry can be omitted. A processor (not shown) is communicatively connected to the sensor 304, the processor being physically located within the sensor housing 303 or the reader 320. According to some embodiments, the sensor 304 protrudes from an underside of the sensor housing 303 and extends through an adhesive layer 305 that is configured for adhering the sensor housing 303 to a tissue surface, such as skin.

[0042] The sensor 304 is configured to be at least partially inserted into a tissue of interest, such as beneath the skin. The sensor 304 includes a sensor tail of sufficient length to insert to a desired depth beneath the skin. According to one or more embodiments, the sensor tail includes a sensing region having two working electrodes as disclosed herein. In various embodiments of the present disclosure, pH is monitored in any biological fluid of interest, such as dermal fluid, interstitial fluid, plasma, blood, lymphatic fluid, synovial fluid, cerebrospinal fluid, saliva, bronchoalveolar lavage fluid, amniotic fluid, and the like.

[0043] An introducer may be temporarily present to facilitate the introduction of the sensor 304 into the tissue. In an exemplary embodiment, the introducer includes a needle. In alternative embodiments, another type of introducer, such as a sheath or blade, may be present. More specifically, a needle or similar introducer is temporarily present near the sensor 304 prior to insertion and is then withdrawn. While present, the needle or another introducer may facilitate the insertion of the sensor 304 into the tissue by opening an access path for the sensor 304 to follow. For example, according to one or more embodiments, the needle facilitates the penetration of the epidermis as an access path to the dermis to allow for the implantation of the sensor 304. After opening the access path, the needle or another introducer is withdrawn to eliminate the risk of sharps. In an exemplary embodiment, the needle is solid or hollow, beveled or non-beveled, and / or circular or non-circular in cross section. In a more specific embodiment, the needle corresponds in cross-sectional diameter and / or tip design to an acupuncture needle having a cross-sectional diameter of about 250 microns. However, it should be understood that suitable needles may have larger or smaller cross-sectional diameters as required for a particular application.

[0044] In some embodiments, the tip of the needle (while present) is angled above the tip of the sensor 304 so that the needle first penetrates the tissue to open an access path for the sensor 304. In another exemplary embodiment, the sensor 304 resides within a lumen or channel of the needle, which similarly opens an access path for the sensor 304. In either case, after facilitating insertion, the needle is then withdrawn.

[0045] Thus, in the pH sensor of the present invention, a first working electrode is configured to generate a first signal and a second working electrode is configured to generate a second signal, such that the difference between the first and second signals is correlated to pH. That is, according to various embodiments of the present invention, by subtracting the second signal from the first signal, the difference in signal magnitude can be correlated to pH. The signal difference can be calculated manually or automatically using a suitable processor. Once calculated, the signal difference can also be correlated manually or automatically with a processor.

[0046] In a more specific embodiment, a pH sensor of the invention includes a processor in signal communication with the first and second working electrodes. The processor is configured to receive a first signal from the first working electrode and a second signal from the second working electrode. The processor is further configured to calculate a difference between the first and second signals and correlate the difference between the signals to pH.

[0047] In some embodiments, the processor is configured to access a lookup table containing a plurality of pH values ​​and the difference between the corresponding first and second signals to calculate the pH. The lookup table is populated prior to measuring the unknown sample by analyzing a plurality of samples at known pH, measuring the first and second signals, and determining the difference between the two signals. The processor can, for example, determine which difference value in the lookup table is closest to that measured for the known sample and report the pH accordingly. In another embodiment, the processor can interpolate between the difference values ​​in the lookup table to determine the measured pH value. The interpolation may assume a linear distribution of pH between the reported difference values.

[0048] In another embodiment, the processor is configured to access a calibration curve of the difference between the corresponding first and second signals versus pH value to calculate the pH. Like a look-up table, the calibration curve may be determined by analyzing multiple samples at known pH, measuring the first and second signals, determining the difference between the two, and curve fitting the pH value versus the difference value to determine a calibration function before measuring the unknown sample. Determining the signal difference as a function of pH at the factory and assigning the look-up table or calibration curve to the pH sensor may allow for factory calibration at the lot level. Because no correction of the reference electrode for each signal is required, the signal difference at a particular pH range is invariant between sensors for the choice of materials for the first and second active moieties.

[0049] Thus, the disclosed method of measuring pH includes exposing a pH sensor to a fluid having a constant pH value, the pH sensor including a first working electrode, a second working electrode, and at least one other electrode, measuring a first signal corresponding to the first working electrode, measuring a second signal corresponding to the second working electrode, calculating a difference between the first and second signals, and correlating the difference between the first and second signals to a pH value. In a more specific embodiment, the fluid is a biological fluid, and the pH sensor is exposed to the biological fluid within the body.

[0050] According to some embodiments, each of the first signal and the second signal includes a voltammetric peak potential. The voltammetric peak potential can be determined by cyclic voltammetry, differential pulse voltammetry, pulse wave voltammetry, square wave voltammetry, etc. Depending on the type of voltammetric sweep performed, the appropriate location on the observed curve can be determined to determine the voltammetric peak potential for each substance. A person skilled in the art can make this determination based on the type of voltammetric sweep performed.

[0051] According to various embodiments, the first signal and the second signal are measured at the same time or at different times. Measuring at different times includes, for example, performing a voltammetric sweep of each working electrode separately without applying a potential to one of the working electrodes. According to some embodiments, the measurement in this manner can utilize a single channel. In another embodiment, the first signal and the second signal can be measured simultaneously by simultaneously monitoring each working electrode via the first channel and the second channel.

[0052] In a further embodiment, the method of the present disclosure may include accessing a lookup table including a plurality of pH values ​​and a difference between the corresponding first and second signals to calculate the pH. In another further embodiment, the method of the present disclosure may include accessing a calibration curve of the difference between the corresponding first and second signals versus the pH values ​​to calculate the pH. In either configuration, the processor is configured to receive the first and second signals, calculate the difference between the first and second signals, and access the lookup table or calibration curve. According to various embodiments, accessing the lookup table or calibration curve may include performing an electronic query.

[0053] Embodiments disclosed herein include the following: A. A sensor for measuring pH. The pH sensor comprises a sensor tail having a first working electrode, a second working electrode, and at least one other electrode, a first active portion disposed on the first working electrode, the first active portion containing a substance having a pH-dependent redox property, and a second active portion disposed on the second working electrode, the second active portion containing a substance having a redox property that is substantially invariant to pH.

[0054] B. A method for measuring pH, comprising exposing a pH sensor to a fluid having a constant pH value, the pH sensor comprising a sensor tail comprising a first working electrode, a second working electrode, and at least one other electrode, a first active portion disposed on the first working electrode, the first active portion containing a substance having a pH-dependent redox property, and a second active portion disposed on the second working electrode, the second active portion containing a substance having a redox property that is substantially invariant with pH, ​​to the fluid having a constant pH value, measuring a first signal corresponding to the first working electrode, measuring a second signal corresponding to the second working electrode, calculating a difference between the first and second signals, and correlating the difference between the first and second signals to the pH value.

[0055] Each of embodiments A and B may have one or more or all of the following additional elements in any combination: Element 1: The sensor tail is configured to be inserted into tissue.

[0056] Element 2: The substance having a pH-dependent redox chemistry includes a quinone, a redox indicator compound, or any combination thereof. Element 3: Materials having pH-dependent redox chemistry include redox indicator compounds including thiazines.

[0057] Element 4: The at least one other electrode includes a counter electrode and a reference electrode. Element 5: The pH sensor further includes a dielectric layer interposed between the at least one other electrode and at least one of the first working electrode and the second working electrode.

[0058] Element 6: A first dielectric layer is interposed between the first working electrode and the counter or reference electrode, and a second dielectric layer is interposed between the second working electrode and the counter or reference electrode. Element 7: The at least one other electrode includes one counter / reference electrode.

[0059] Element 8: The pH sensor further includes a dielectric layer interposed between the one counter / reference electrode and at least one of the first and second working electrodes. Element 9: A first working electrode is configured to generate a first signal and a second working electrode is configured to generate a second signal, a difference between the first signal and the second signal correlates to pH.

[0060] Element 10: The pH sensor further comprises a processor configured to receive a first signal from the first working electrode and a second signal from the second working electrode, the processor calculating a difference between the first signal and the second signal and correlating the difference to pH.

[0061] Element 11: The processor is configured to access a look-up table including a plurality of pH values ​​and corresponding differences between the first and second signals to calculate the pH.

[0062] Element 12: The processor is configured to access a calibration curve of the difference between the corresponding first and second signals versus pH value to calculate the pH. Element 13: A substance having pH-dependent redox properties and a substance having redox properties that are substantially invariant to pH are both covalently attached to the polymer in the first and second active moieties, respectively.

[0063] Element 14: The fluid is a biological fluid and the pH sensor is exposed to the biological fluid in vivo. Element 15: The method further includes accessing a lookup table including a plurality of pH values ​​and corresponding differences between the first and second signals to calculate the pH.

[0064] Element 16: The processor is configured to receive the first signal and the second signal, calculate a difference between the first signal and the second signal, and access the look-up table. Element 17: The method further includes accessing a calibration curve of the difference between the corresponding first and second signals versus pH value to calculate the pH.

[0065] Element 18: The processor is configured to receive the first signal and the second signal, calculate a difference between the first signal and the second signal, and access the calibration curve. Element 19: The first signal comprises a voltammetric peak potential of a substance having pH-dependent redox properties and the second signal comprises a voltammetric peak potential of a substance having redox properties that are substantially invariant with pH.

[0066] Element 20: The first signal and the second signal are measured at different times. Element 21: A first signal and a second signal are measured simultaneously via a first channel and a second channel.

[0067] By way of non-limiting example, illustrative combinations applicable to A and B include the following: Elements 1 and 2, Elements 1 and 3, Elements 1 and 4, Elements 1, 4 and 5, Elements 1, 4 and 6, Elements 1 and 7, Elements 1, 7 and 8, Elements 1 and 9, Elements 1 and 10, Elements 1, 10 and 11, Elements 1, 10 and 12, Elements 1 and 13, Elements 2 and 4, Elements 2, 4 and 5, Elements 2, 4 and 6, Elements 2 and 7, Elements 2, 7 and 8, Elements 2 and 9, Elements 2 and 10, Elements 2, 10 and 11, Elements 2, 10 and 12, Elements 3 and 4, Elements 3, 4 and 5, Elements 3, 4 and 6, Elements 3 and 7, elements 3, 7 and 8, elements 3 and 9, elements 3 and 10, elements 3, 10 and 11, elements 3, 10 and 12, elements 4 and 10, elements 4, 10 and 11, elements 4, 10 and 12, elements 7 and 10, elements 7, 10 and 11, elements 7, 10 and 12, elements 2 and 9, elements 3 and 9, elements 4 and 9, elements 7 and 9, elements 9, 10 and 11, elements 10 and 12, elements 10 and 13, elements 10, 11 and 13, or elements 10, 12 and 13. Elements 2 and 13, Elements 2 and 14, Elements 2 and 15, Elements 2, 15 and 16, Elements 2 and 17, Elements 2, 17 and 18, Elements 2 and 19, Elements 2 and 20, Elements 2 and 21, Elements 3 and 13, Elements 3 and 14, Elements 3 and 15, Elements 3, 15 and 16, Elements 3 and 17, Elements 3, 17 and 18, Elements 3 and 19, Elements 3 and 20, Elements 3 and 21, Elements 13 and 14, Elements 13 and 15, Elements 13, 15 and 16, Elements 13 and 17, Elements 13, 17 and 18, Elements 13 and 19, Elements 13 and 20, Elements 13 and 21, Method B combining elements 14 and 15, elements 14, 15 and 16, elements 14 and 17, elements 14, 17 and 18, elements 14 and 19, elements 14 and 20, elements 14 and 21, elements 15 and 16, elements 15 and 19, elements 15, 16 and 19, elements 15 and 20, elements 15, 16 and 20, elements 15 and 21, elements 15, 16 and 21, elements 17 and 19, elements 17, 18 and 19, elements 17 and 20, elements 17, 18 and 20, elements 17 and 21, elements 17, 18 and 21, elements 19 and 20, or elements 19 and 21.

[0068] To facilitate a better understanding of the embodiments described herein, the following examples of various representative embodiments are given and should not be construed as limiting or defining the scope of the invention.

[0069] Working Example Working electrode #1: A first carbon working electrode was coated with a polymer layer of toluidine blue (TOB). Prior to coating, the working electrode was preconditioned by periodically sweeping the potential from -0.8 V to 1.2 V at a sweep rate of 50 mV / s for 5 cycles in a solution containing 100 mM citric acid / 200 mM phosphate / 100 mM KCl (pH=4). Electrodeposition of TOB was performed by adding 5 mM TOB to the above solution and cycling the potential from -0.8 V to 1.2 V at a sweep rate of 50 mV / s for 60 cycles. The sensor was then rinsed with distilled water and air-dried.

[0070] Working Electrode #2: A second carbon working electrode was coated with a polymer having an osmium complex covalently attached thereto. The structure of the polymer, described in more detail in U.S. Pat. No. 6,605,200 and incorporated herein in its entirety, is shown below in Formula 2.

[0071] [ka]

[0072] A solution containing 45 mg / mL of the above polymer and 15 mg / mL of PEG400 was added to 10 mM Three 20 nL droplets of the above solution were placed on the electrode surface, each with a thickness of approximately 0.1 mm. 2 This produced three detection (active) layer spots with an area of ​​100 nm. The working electrodes were then cured overnight at 25° C. and 65% relative humidity.

[0073] Cyclic voltammetry was performed for each working electrode separately in a series of pH buffers with pH ranging from 2 to 12, at a scan rate of 50 mV / s, over the potential range of -0.8 to 1.2 V. A carbon counter electrode and an Ag / AgCl reference electrode were used for all measurements. Figure 4 shows plots of the aggregation cyclic voltammograms at various pH values ​​for the first working electrode (containing TOB). Figure 5 shows corresponding plots of the aggregation cyclic voltammograms at various pH values ​​for the second working electrode (containing the osmium complex bound to the polymer). Table 1 below summarizes the observed anodic peak potentials.

[0074] [Table 1]

[0075] The difference values ​​in the bottom row of Table 1 and the corresponding pH values ​​in the top row can form a look-up table. Alternatively, a calibration curve can be created by plotting the values. Figure 6 shows the calibration curve corresponding to the voltage difference vs. pH data shown in Table 1.

[0076] 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 expressly indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties contemplated to be obtained by embodiments of the invention. Without intending to limit the application of the doctrine of equivalents to the scope of the claims, at the very least, each numerical parameter should be construed in light of at least the number of significant digits disclosed and by applying ordinary rounding techniques.

[0077] One or more exemplary embodiments incorporating various elements are presented herein. For the sake of brevity, not all elements of a physical implementation are described or shown herein. In developing a physical embodiment incorporating an embodiment of the present invention, it will be understood that numerous implementation-specific decisions must be made to achieve the developer's goals, including system-related, business-related, political-related and other constraints, which will vary from implementation to implementation and from time to time. Although the developer's efforts will be time consuming, such efforts are routine for one of ordinary skill in the art and will have the benefit of the present invention.

[0078] Although various systems, tools, and methods are described herein in terms of "comprising" various components or steps, the systems, tools, and methods may also "consist essentially of" or "consist of" the various components and steps.

[0079] As used herein, the phrase "at least one" preceding a series of items, together with the term "and" or "or" separating any one of the items, modifies the entire list, not each member (each item) in the list. The phrase "at least one" allows for a meaning including 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 item. By way of example, the phrase "at least one of A, B, and C" or "at least one of A, B, or C" refers to a meaning of only A, only B, or only C, any combination of A, B, and C, and / or at least one of A, B, and C, respectively.

[0080] Thus, the disclosed systems, tools, and methods are well configured to achieve the objects and advantages mentioned, as well as those inherent therein. The specific embodiments of the present invention are illustrative only, as those skilled in the art having the benefit of the teachings disclosed herein may modify and practice in different but equivalent manners. Moreover, no limitation is intended to the details of construction or design shown herein, except as set forth in the following claims. Thus, it is apparent that the specific exemplary embodiments described above may be altered, combined, or modified, and all such variations are considered to be within the scope of the present invention. The systems, tools, and methods illustratively described herein may suitably be practiced in the absence of any elements not specifically disclosed herein and / or any elements disclosed herein. Although the systems, tools, and methods are described in terms of "including," "containing," or "comprising" various components or steps, the systems, tools, and methods may also "consist essentially of" or "consist of" various components and steps. All of the above numbers and ranges may vary somewhat. Whenever a numerical range with a lower and upper limit is disclosed, any number within that range and any included range is specifically disclosed. In particular, all range values ​​disclosed herein (in the form of "about a to about b," or equivalently, "about a to b," or equivalently, "about a to b") should be understood to refer to all numbers and ranges within the broader range of values. Moreover, the terms in the claims have their plain and ordinary meaning unless expressly and unambiguously defined by the patent owner. Moreover, the indefinite article "a" or "an" used in the claims is defined herein to mean one or more elements that it introduces. In the event of a discrepancy between the usage of a word or term in this specification and one or more patent documents or other documents that may be incorporated by reference herein, the consistent definition in this specification shall prevail.

Claims

1. a sensor tail including a first working electrode, a second working electrode, and at least one other electrode; a first active portion disposed on the first working electrode, the first active portion including a substance having pH-dependent redox properties; a second active portion disposed on the second working electrode, the second active portion including a substance having redox properties that are substantially invariant to pH; A pH sensor comprising:

2. The pH sensor of claim 1 , wherein the sensor tail is insertable into tissue.

3. 3. The pH sensor according to claim 1, wherein the substance having pH-dependent redox properties comprises a quinone, a redox indicator compound, or a combination thereof.

4. 4. The pH sensor of claim 3, wherein the substance having pH-dependent redox properties comprises a redox indicator compound containing thiazine.

5. The pH sensor of any one of claims 1 to 4, wherein the at least one further electrode includes a counter electrode and a reference electrode.

6. 6. The pH sensor of claim 5, further comprising a dielectric layer interposed between the at least one other electrode and at least one of the first working electrode and the second working electrode.

7. 7. The pH sensor of claim 6, wherein the first dielectric layer is disposed between the first working electrode and the counter or reference electrode, and the second dielectric layer is disposed between the second working electrode and the counter or reference electrode.

8. The pH sensor of any one of claims 1 to 7, wherein the at least one further electrode comprises a counter / reference electrode.

9. 10. The pH sensor of claim 8, further comprising a dielectric layer disposed between the counter / reference electrode and at least one of the first working electrode and the second working electrode.

10. 10. The pH sensor of claim 1, wherein the first working electrode is configured to generate a first signal and the second working electrode is configured to generate a second signal, a difference between the first and second signals being correlated to pH.

11. 11. The pH sensor of claim 10, further comprising a processor that receives a first signal from the first working electrode and a second signal from the second working electrode, calculates a difference between the first signal and the second signal, and correlates the difference to pH.

12. 12. The pH sensor of claim 11, wherein the processor is configured to access a lookup table containing a plurality of pH values ​​and corresponding differences between the first and second signals to calculate the pH.

13. 12. The pH sensor of claim 11, wherein the processor is configured to access a calibration curve of the difference between the corresponding first and second signals versus pH value to calculate pH.

14. A pH sensor according to any one of claims 1 to 13, wherein the substance having pH-dependent redox properties and the substance having redox properties that are substantially invariant to the pH are covalently bonded to a polymer in the first active portion and the second active portion, respectively.

15. 13. A method comprising exposing a pH sensor to a fluid having a pH value according to claim 1, measuring a first signal corresponding to the first working electrode, measuring a second signal corresponding to the second working electrode, calculating a difference between the first and second signals, and correlating the difference between the first and second signals to the pH value, wherein the fluid is a biological fluid and the pH sensor is exposed to the biological fluid in vivo.

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