Sensors and methods for measuring pH

Abstract

Measuring in vivo pH using current electrochemical sensors can be particularly difficult due to sensor drift and fouling of the sensor surface. A sensor suitable for measuring pH, particularly in vivo pH, can include: a sensor tail comprising a first working electrode, a second working electrode, and at least one other electrode; a first active portion located on the first working electrode, the first active portion comprising a species having a pH-dependent redox chemistry; and a second active portion located on the second working electrode, the second active portion comprising a species having a substantially pH-independent redox chemistry. The difference between a first signal from the first active portion and a second signal from the second active portion can be correlated to the pH value of the fluid.

Description

[0001] background

[0002] Detection of various analytes within an individual can sometimes be crucial to monitoring their health and well-being. Deviations from normal analyte levels can often be an indicator of an underlying physiological condition, such as a metabolic condition or disease.

[0003] Analyte monitoring in an individual can be performed periodically or continuously over a period of time. Periodic analyte monitoring can be performed by extracting body fluids such as blood samples at set time intervals and analyzing them in vitro. Continuous analyte monitoring can be performed using one or more sensors that remain at least partially implanted in an individual's tissue, such as the dermis, subcutaneous tissue, or intravenously, so that analysis can be performed in vivo. The implanted sensor can collect analyte data at any prescribed rate, depending on the individual's specific health needs and / or previously measured analyte levels.

[0004] Regular in vitro analyte monitoring can be sufficient to determine the physiological status of many individuals. However, in vitro analyte monitoring can be inconvenient or painful for some people. In addition, if the analyte measurement results are not obtained at the appropriate time, the lost data cannot be recovered.

[0005] Continuous analyte monitoring using an implanted sensor may be a more desirable approach for individuals with severe analyte regulation disorders and / or rapidly fluctuating analyte levels, although it may also be beneficial for other individuals. Although continuous analyte monitoring using an implanted sensor may be advantageous, there are still challenges associated with these types of measurements. Intravenous analyte sensors have the advantage of providing analyte concentrations directly from blood, but they are invasive and can sometimes be painful for individuals to wear, particularly over extended periods of time. Subcutaneous, interstitial or dermal analyte sensors can often be less painful for individuals to wear, and can provide sufficient measurement accuracy in many cases.

[0006] Any analyte can be suitable for in vivo analysis, provided that a suitable chemistry can be determined to sense the analyte. Indeed, in vivo amperometric sensors configured to measure glucose have been developed and refined in recent years. Other analytes that may be similarly desirable for monitoring and that are often subject to physiological dysregulation include, but are not limited to, lactate, oxygen, pH, A1C, ketones, drug levels, and the like.

[0007] In order to bring into play normal biological function, pH level in vivo is typically maintained within a fairly narrow range. Normal blood pH is, for example, about 7.4, and a blood pH value less than 6.9 or greater than 7.6 can be life-threatening. The consequences of biological pH regulation abnormalities include, but are not limited to, in vivo precipitation of one or more components in the biological fluid, enzyme activity reduction or excessive activity, altered biofilm permeability, a tendency for some types of cancer, and other undesirable conditions. Some examples of conditions that can cause pH measurement results to shift include respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. About acidosis, respiratory acidosis can be especially caused by chest deformity or injury, chronic lung and airway disease, excessive use of sedatives, or obesity. Metabolic acidosis can be especially caused by long-term exercise, hypoxia, some drugs (including salicylates), hypoglycemia, alcohol, seizures, liver failure, some cancers, nephropathy, severe dehydration, and poisoning (such as methanol poisoning). Regarding alkalosis, respiratory alkalosis can be caused by, among others, hypoxia, fever, lung disease, liver disease, and salicylate poisoning. Metabolic alkalosis is rare but can be caused by, among others, severe dehydration, cystic fibrosis, and overdose of alkalotic agents such as antacids.

[0008] In addition to the health consequences directly attributable to malregulation of pH in the body, sensing chemicals associated with certain analytes can also be affected by changes in the local pH environment and / or local pH environment. For example, urea detection can be based on the pH changes that occur when a biological fluid interacts with urease to produce ammonia as a product. Ammonia changes the local pH environment, and pH measurements can allow for determination of urea concentrations. However, in the absence of an accurate way to measure pH, obtaining reliable concentration measurements of urea and similar analytes can be difficult, even when the pH level in the body does not directly affect the analyte concentration itself.

[0009] Measurement of pH levels in individuals is typically performed by withdrawing samples of biological fluid at set intervals and analyzing them in vitro. While this approach may be acceptable in some situations, in situations where pH levels are changing rapidly, it can be difficult to measure pH levels quickly enough to determine that a pH dysregulation has occurred. Furthermore, because there is often a time lag associated with obtaining in vitro pH measurements, significant health consequences may not occur until it becomes apparent that a pH dysregulation has occurred.

[0010] While it is desirable to measure pH levels in vivo, particularly over extended measurement times using a single implanted sensor, the nature of conventional pH measurements makes this task difficult. First, conventional pH measurements are typically performed using glass electrodes or ion sensing field effect transistors (ISFETs). Both types of devices are extremely sensitive to surface fouling, which can affect the measured surface potential and, therefore, the measured pH. Second, the reference electrode used in conjunction with measuring pH is subject to drift, particularly in vivo, which leads to additional sources of measurement error. In contrast, reference electrodes used for measuring analytes such as glucose in vivo can be operated in an amperometric manner at a plateau potential and are significantly less subject to drift effects. Therefore, conventional approaches are not particularly well suited for measuring pH values in vivo, particularly over extended measurement times. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following figures are included to illustrate certain aspects of the present disclosure and should not be construed as exclusive embodiments. The disclosed subject matter is capable of considerable modification, variations, combinations, and equivalents in form and function without departing from the scope of the present disclosure.

[0012] Figure 1A and 1B Shown is an exemplary configuration of a pH sensor having two working electrodes and a counter / reference electrode according to various embodiments described herein.

[0013] Figure 2 Shown are exemplary configurations of a pH sensor having two working electrodes, a reference electrode, and a counter electrode according to various embodiments described herein.

[0014] Figure 3 A diagram is shown of an exemplary sensing system adapted to be worn on the body and capable of measuring pH based on signals received from first and second working electrodes, according to various embodiments described herein.

[0015] Figure 4 Shown are plots of ensemble cyclic voltammograms of a working electrode containing polymer-bound toluidine blue at various pH values.

[0016] Figure 5 The corresponding plots of the ensemble cyclic voltammograms at various pH values are shown for a working electrode containing a polymer-bound osmium complex.

[0017] Figure 6 Calibration curves corresponding to the pH versus voltage difference data shown in Table 1 are shown.

[0018] Details

[0019] This disclosure generally describes sensors and methods for measuring pH, and more particularly, sensors and methods that are particularly well-suited for measuring pH values in vivo.

[0020] As discussed above, in vivo electrochemical measurement of pH can be complicated due to surface fouling and drift of one or more electrodes or similar pH measuring devices. While these problems can be particularly problematic in vivo, it will be appreciated that these problems are sometimes also encountered when measuring pH in vitro or in laboratory settings. Without the ability to accurately measure pH in vivo, it can be difficult to assess an individual's physiological condition in real time or near real time. Furthermore, the sensing chemistry associated with measuring certain analyte concentrations can be pH-dependent, and inaccurate analyte concentration measurements can result from an inability to measure pH with sufficient accuracy.

[0021] The present disclosure describes a pH sensor that overcomes the challenges mentioned above and may also provide additional benefits. In particular, the pH sensor of the present disclosure is largely unaffected by surface fouling and drift effects. The pH sensor of the present disclosure utilizes two different working electrodes, wherein the active portion of each working electrode exhibits different electrochemical properties. As used herein, the term "active portion" refers to a layer or one or more points located on a portion of a working electrode where a desired electrochemical reaction occurs. That is, in the pH sensor of the present disclosure, the active portion located on the first working electrode comprises a substance having a pH-dependent oxidation-reduction chemistry, and the active portion located on the second working electrode comprises a substance having an oxidation-reduction chemistry that is substantially invariant with pH. According to some embodiments, the substance located in the active portion of the first working electrode may comprise a substance that changes its protonation state during the oxidation-reduction reaction, although this is not required. The potential at which the oxidation state changes can be measured during a voltammetric scan of the first working electrode. According to some or various other embodiments, the substance located in the active portion of the second working electrode does not necessarily have a completely constant measured potential during a voltammetric scan within a given pH range of interest. It will be understood that the change in voltage measured in a given pH range can be less than a predetermined suitable value, such as less than about 100mV variability or less than about 50mV variability, or less than about 10mV variability in a given pH range of interest. The change can be determined by subtracting the minimum voltage from the maximum voltage observed in the voltage sweep between the extremes of the useful pH range. An acceptable amount of variation can be determined based on how much accuracy the pH measurement requires. According to some embodiments, the substance in the active portion of the second working electrode can maintain (not change) its protonation state during the oxidation-reduction reaction, but this is also not necessary.

[0022] Signals can be received from the first working electrode and the second working electrode to calculate the pH value of a fluid in contact with the pH sensor. In particular, the pH value of the observed fluid can be calculated based on the difference between the first signal and the second signal. This signal difference can be correlated to a pH value by consulting a lookup table, a calibration curve, or the like (e.g., using a suitable processor or manually).

[0023] Although the pH sensor disclosed herein may include a reference electrode and a counter electrode or a counter / reference electrode, it is not necessary to receive, reference, utilize, or otherwise process the signal from the reference electrode or the counter / reference electrode to determine the pH value. That is, since the first working electrode and the second working electrode are separately referenced to the reference electrode or the counter / reference electrode, the corrections for the first and second signals are offset when the signal difference is determined. In other words, the first working electrode and the second working electrode are internally referenced to each other. Therefore, the pH sensor described herein overcomes the drift problem associated with conventional pH sensors by eliminating the need for signal correction using a reference electrode or a counter / reference electrode. In addition, considering that a reference electrode is not required for signal correction, some embodiments of the pH sensor described herein may completely lack a reference electrode. In such an embodiment, the second working electrode can be considered as a reference to the first working electrode, and vice versa, and a suitable counter electrode can be present to provide a closed circuit.

[0024] Furthermore, the pH sensor described herein addresses the problem of surface fouling, a problem with conventional electrochemical pH sensors. Specifically, the active portions of the first and second working electrodes comprise a relatively thick polymer layer or one or more spots, wherein the sensing chemistry occurs throughout the polymer layer or one or more spots, rather than solely on its surface. The passage of electrons through the polymer layer to the first and second electrodes allows the oxidation-reduction chemistry to occur throughout the active portion, rather than solely on the surface. Consequently, surface fouling effects can be limited in the pH sensor disclosed herein. Furthermore, because the oxidation-reduction reaction is not confined to the surface of the active portion in the pH sensor disclosed herein, a variety of mass-restricted or biocompatible membranes can be suitable for use in conjunction with the pH sensor, as the interface between the membrane and the active portion does not substantially affect the oxidation-reduction reaction occurring within the active portion. A variety of proton-permeable membranes can be suitable for use in conjunction with the pH sensor disclosed herein. Suitable proton-permeable membranes can be substantially impermeable to substances contained in the first and second active portions, thereby promoting the retention of those substances in the active portion, thereby maintaining pH sensing capability over extended measurement times.

[0025] Finally, the pH sensor of the present disclosure can be desirably operated by performing a voltammetric scan (e.g., cyclic voltammetry, differential pulse voltammetry, pulse-wave voltammetry, square wave voltammetry, etc.) of the sensing chemistry within a given pH measurement range of interest. The potential measured at a given position of the voltammetric scan using these techniques does not substantially vary with the electrode geometry, such as thickness, and the area of the active portion on each working electrode. Therefore, manufacturing differences in the active portion have minimal results. In some embodiments, the active portion can include sensing points with precise geometry, such as those described in U.S. Patent Application Publication 2012 / 0150005, and incorporated herein by reference. Therefore, the measured potential is characterized by the chemistry in each active portion at a given pH. This feature can facilitate calibration of the pH sensor. According to one or more embodiments, the measured potential can be, for example, an anode peak potential, a cathode peak potential, a half-wave potential, etc. According to a more specific embodiment, the potential measured at each working electrode can include measurements of the same type (e.g., an anode peak potential, a cathode peak potential, or a half-wave potential of both the first working electrode and the second working electrode) to calculate the signal difference.

[0026] Thus, the pH sensor of the present disclosure can include a sensor tail comprising a first working electrode, a second working electrode, and at least one other electrode; a first active portion located on the first working electrode, the first active portion comprising a species having a pH-dependent redox chemistry; and a second active portion located on the second working electrode, the second active portion comprising a species having a substantially pH-independent redox chemistry. Suitable redox chemistries for the first and second active portions are discussed in further detail below.

[0027] Various configurations of pH sensors comprising two working electrodes are possible, as discussed below with reference to the accompanying figures. At least one other electrode in the pH sensors disclosed herein can, in some embodiments, comprise a counter electrode or a counter electrode plus a reference electrode, and in other embodiments can comprise a counter / reference electrode. Thus, in various embodiments, the pH sensors disclosed herein can comprise a total of at least three or at least four electrodes. Below, a three-electrode configuration is discussed first, before discussing a four-electrode configuration.

[0028] Figure 1A and 1B An exemplary configuration of a pH sensor having two working electrodes and a counter / reference electrode according to various embodiments described herein is shown. Figure 1AAs shown, working electrodes 104 and 106 are disposed on substrate 102 in pH sensor 100. Active portion 110 is disposed on the surface of working electrode 104, and active portion 112 is disposed on the surface of working electrode 106. One of active portions 110 and 112 contains a substance having a pH-dependent oxidation-reduction chemistry, and the other contains a substance having an oxidation-reduction chemistry that is substantially invariant with pH. Counter / reference electrode 120 is electrically isolated from working electrode 104 by dielectric layer 122. Although shown as being positioned on working electrode 104, it will be understood that in some embodiments, counter / reference electrode 120 can be alternately positioned on working electrode 106. Outer dielectric layers 130 and 132 are positioned on working electrode 106 and counter / reference electrode 120. It will be understood that the length of each layer can vary from that depicted. Active portions 110 and 112 can be exposed so that they can interact with the analyte.

[0029] According to various embodiments, film 140 can be coated with one or both of active parts 110 and 112. According to the disclosure of this paper, film 140 can include a polymer with biocompatibility and / or the ability to limit the flow of analyte (i.e. proton) to active parts 110 and 112. Restricting the flow of analyte can be desirable for avoiding being soaked into the sensor. According to various embodiments, the thickness of film 140 can change the flow of analyte. The thickness of film 140 can change or remain constant along the sensor length. In various embodiments, the thickness of film 140 can be approximately 1 micron to approximately 100 microns or approximately micron to approximately 50 microns, or approximately 20 microns to approximately 90 microns. One or two faces of pH sensor 100 or entire pH sensor 100 can be coated with film 140.

[0030] like Figure 1A As depicted, working electrodes 104 and 106 are positioned on opposing sides of substrate 100 . Figure 1B An alternative configuration is shown in which working electrodes 104 and 106 are positioned on the same side of substrate 102 in pH sensor 101 and are separated by dielectric layer 122. Other alternative configurations remain within the scope of the present disclosure.

[0031] The sensor configuration with both counter and reference electrodes can be similar in structure to Figure 1A and 1B Those shown, except including additional electrodes. Figure 2An exemplary configuration of a pH sensor having two working electrodes, a reference electrode, and a counter electrode is shown. As shown, working electrodes 204 and 206 are located on a substrate 202 in a pH sensor 200. An active portion 210 is located on the surface of the working electrode 204, and an active portion 212 is located on the surface of the working electrode 206. One of the active portions 210 and 212 contains a substance having a pH-dependent oxidation-reduction chemistry, and the other contains a substance having an oxidation-reduction chemistry that is substantially invariant with pH. The counter electrode 220 is electrically isolated from the working electrode 204 by a dielectric layer 222, and the reference electrode 221 is electrically isolated from the working electrode 206 by a dielectric layer 223. Outer dielectric layers 230 and 232 are positioned on the reference electrode 221 and the counter electrode 220, respectively. According to various embodiments, a membrane 240 may cover at least the active portions 210 and 212. As shown Figure 1A and 1B In that way, one or both sides of the pH sensor 200 , or the entire pH sensor 200 , may be covered with the membrane 240 .

[0032] The positioning of the counter electrode 220 and the reference electrode 221 can be Figure 2 In addition, the working electrodes 204 and 206 do not need to be Figure 2 The method shown in FIG is located on the opposite side of the substrate 202. Figure 1A and 1B In that way, one or both sides of the pH sensor 200 , or the entire pH sensor 200 , may be covered with the membrane 240 .

[0033] As mentioned above, one of the active moieties may contain a species with pH dependent redox chemistry. Suitable species with pH dependent redox chemistry include, for example, quinones, redox indicator compounds, or any combination thereof.

[0034] Quinones can exhibit changes in redox chemistry and accompanying differences in peak positions observed during voltammetric scans as a result of becoming protonated or deprotonated as the pH changes. At low pH values, phenol forms the predominant species. As the pH increases and phenol deprotonation begins to occur, oxidation to the quinone form can become advantageous. Suitable quinones may include, but are not limited to, benzoquinone, naphthoquinone, anthraquinone, 1,10-phenanthroline quinone, tetrachlorobenzoquinone (chloranil), dicyanobenzoquinone dichloride (DDQ), and the like, functionalized variants thereof, and any combination thereof. In some embodiments, additional functional groups may be present that can become covalently bonded to the working electrode and / or polymer in the active moiety. Suitable quinones having additional functional groups may include, but are not limited to, iridium quinone, alizarin, naphthazarin, and the like, and any combination thereof. The additional functional groups that can become covalently bonded to the working electrode and / or polymer may be located directly on the quinone ring or separated therefrom by one or more spacer atoms, such as alkylene, oxyalkylene, or carboxylic acid derivatives. In some embodiments, a suitable quinone may have the structure shown in Formula 1, wherein

[0035]

[0036] Z n represents an optional functional group (n=1-4) and A is a spacer group covalently bonded to the first active portion comprising a polymer. In a particular embodiment, A can be a spacer group such as -(CH2) m -, -C(=O)-NH-, -C(=O)-O-, -O(CH2) m or -(CH2) m O-, where m is a positive integer from 1 to about 20.

[0037] Redox indicator compounds include substances that are used in redox titrations based on their ability to undergo a color change at a specific electrode potential. Specific redox indicator compounds suitable for use in the present disclosure include, but are not limited to, those whose redox chemistry is pH dependent. Specific examples include, but are not limited to, indophenol compounds, indigo dyes, phenazines, thiazines, and the like, and any combination thereof. Specific examples of redox indicator compounds with pH dependent redox chemistry include, but are not limited to, indophenol, 2,6-dibromophenol-sodium indophenol, 2,6-dichlorophenol-sodium indophenol, o-cresol-sodium indophenol, thionine, methylene blue (methylthionine chloride), thionine, thiophene ... ), toluidine blue, indigo tetrasulfonic acid, indigo trisulfonic acid, indigo disulfonic acid (indigo carmine), indigo monosulfonic acid, safranin, phenosafranin, neutral red, and the like, and any combination thereof. Additional functional groups capable of becoming covalently bonded to the working electrode and / or polymer may be located directly on the redox indicator compound or separated therefrom by one or more spacer atoms, such as an alkylene chain.

[0038] According to some embodiments, a polymer may be present in the first and second active moieties. Suitable polymers for inclusion in the first and second active moieties may 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 combination thereof. Suitable exemplary copolymers include, but are not limited to, copolymers containing monomeric units such as styrene, acrylamide, methacrylamide, acrylonitrile, and the like, and any combination thereof.

[0039] In more specific embodiments, the first active moiety may comprise a polymer covalently bonded to a substance having a pH-dependent redox chemistry. In some embodiments, the second active moiety may also comprise a polymer covalently bonded to a substance having a redox chemistry that is substantially invariant with pH. The manner in which the substances in the first and second active moieties become covalently bonded is not considered to be particularly limited and may depend on the type of polymer or copolymer present in the first and second active moieties. In some embodiments, the substances may be covalently bonded to the polymer by quaternizing a heterocyclic ring (e.g., a pyridinic nitrogen atom) in the polymer.

[0040] The covalent bonding of the substance with pH dependency redox chemistry to the first active part comprising polymer can be carried out via a suitable cross-linking agent. The cross-linking agent can be introduced by reacting with a suitable cross-linking agent. Suitable cross-linking agents for reacting with amino or hydroxyl groups in the substance with pH dependency redox chemistry can include but are not limited to polyepoxides such as polyethylene glycol diglycidyl ether (PEGDGE), cyanuric chloride, N-hydroxysuccinimide, imidoesters, epichlorohydrin, its derivative variants, etc. and any combination thereof. Suitable cross-linking agents for reacting with carboxylic acid groups in the substance with pH dependency redox chemistry can include but are not limited to carbodiimides.

[0041] The suitable material with the oxidation-reduction chemistry that does not change with pH basically is not considered to have special restriction, prerequisite is that described material demonstrates the response variability of enough limited degree in given pH range.According to various embodiments, described response variability can fluctuate about 100mV or less or about 50mV or less or about 10mV or less, or demonstrates basically no fluctuation in the given pH range of interest.In more specific embodiment again, described response variability can fluctuate in the 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 in the above-mentioned limit.

[0042] In a more specific embodiment, the second active portion has a material with substantially no pH variability in the redox chemistry and can include a transition metal complex such as an osmium complex, which is disclosed in, for example, U.S. Patents 6,134,461 and 6,605,200, which are incorporated herein by reference in their entirety. The transition metal complex can promote the transmission of electrons to the second working electrode during the redox reaction, wherein the pH may or may not change. Suitable transition metal complexes can include electroreducible and electrooxidizable ions, complexes or molecules with a redox potential that is several hundred millivolts higher or lower than the redox potential of a standard calomel electrode (SCE). Other suitable materials for inclusion in the second active portion can include, for example, a complex of ruthenium, iron (e.g., polyvinyl ferrocene) or cobalt. Suitable ligands for any of the transition metal complexes can include, but are not limited to, bidentate or more polydentate ligands such as dipyridine, diimidazole, phenanthroline, pyridyl (imidazole), etc. 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. Any combination of monodentate, bidentate, tridentate, quadridentate, or higher dentate ligands may be present in the metal complex to achieve a complete coordination sphere. One or more ligands in the metal complex may also be covalently bonded to the polymer in the second active moiety.

[0043] In other embodiments, the material with the oxidation-reduction chemistry with respect to pH being substantially immutable in the second active part 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 sulfate iron complex, N-ethoxy orange red (N-ethoxychysoidine), 5,6-dimethylphenanthroline iron, o-dianisidine, sodium diphenylamine sulfonate, diphenylbenzidine, diphenylamine and viologen. Other materials with oxidation-reduction chemistry that are substantially free of pH variability can include any material that does not undergo protonation or deprotonation within the pH range of interest, provided that the oxidation-reduction reaction is reversible.

[0044] While the substances in the first and second active moieties can be covalently bonded to the polymers in each active moiety, other means of association to the polymers may also be suitable. In some embodiments, the substances can be ionically or coordinatively associated with the polymers. For example, a charged polymer can be ionically associated with an oppositely charged substance. In still other embodiments, the substances can be physically entrained within the polymers without being bonded thereto.

[0045] According to various embodiments of the present disclosure, each working electrode is configured to generate a signal such that 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 of how the pH sensor can communicate the signal to a user or processor for further analysis is provided.

[0046] According to various embodiments, the pH sensor of the present disclosure may be adapted to be worn on the body such that the sensor tail is configured to be inserted into tissue, particularly the dermis, subcutaneous tissue, or interstitial tissue beneath the skin. Figure 3 A diagram of an exemplary sensing system suitable for wear on the body and capable of measuring pH based on signals received from first and second working electrodes according to the present disclosure is shown. However, it is understood that in some embodiments of the present disclosure, pH sensors having structures, configurations, and / or components other than or in addition to those explicitly described below may also be suitably used.

[0047] like Figure 3As shown, the sensing system 300 includes a sensor control device 302 and a reader device 320, which are configured to communicate with each other on a local or remote communication path or link, which can be wired or wireless, unidirectional or bidirectional, and encrypted or unencrypted. According to some embodiments, the reader device 320 can constitute an output media for observing pH and an alarm or notification determined by the sensor 304 or a processor associated therewith, and allowing one or more users to input. The reader device 320 can be a multi-purpose smart phone or a dedicated electronic reader instrument. Although only one reader device 320 is shown, more than one reader device 320 can exist in some cases. A plurality of reader devices 320 can communicate with each other (e.g., share and synchronize data). The reader device 320 can also communicate with a remote terminal 370 and / or a trusted computer system 380 via one or more communication paths / links 341 and / or 342, respectively, which can also be wired or wireless, unidirectional or bidirectional, and encrypted or unencrypted. The reader device 320 may also or alternatively communicate with a network 350 (e.g., a mobile phone network, the Internet, or a cloud server) via a communication path / link 351. The network 350 may be further communicatively coupled to a remote terminal 370 via a communication path / link 352 and / or to a trusted computer system 380 via a communication path / link 353. In some embodiments, the remote terminal 370 and / or the trusted computer system 380 may in turn communicate with the network 350. Alternatively, the sensor 302 may communicate directly with the remote terminal 370 and / or the trusted computer system 380 without the presence of an intervening reader device 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, as described in U.S. Patent Application Publication 2011 / 0213225, and incorporated herein by reference in its entirety. Any suitable electronic communication protocol may be used for each of the described communication paths or links, such as near field communication (NFC), radio frequency identification (RFID), or Low energy protocols, WiFi, etc. According to some embodiments, remote terminal 370 and / or trusted computer system 380 can be accessed by individuals other than the primary user. Reader device 320 can include a display 322 and an optional input component 321. According to some embodiments, display 322 can include a touch screen interface.

[0048] 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) can be communicatively coupled to the sensor 304 and physically located within the sensor housing 303 or reader device 320. According to some embodiments, the sensor 304 protrudes from the underside of the sensor housing 303 and extends through an adhesive layer 305 suitable for adhering the sensor housing 303 to a tissue surface, such as skin.

[0049] Sensor 304 is adapted to be at least partially inserted into a tissue of interest, such as beneath the skin. Sensor 304 can include a sensor tail having sufficient length to be inserted to a desired depth beneath the skin. According to one or more embodiments, the sensor tail can include a sensing region having two working electrodes according to the disclosure herein. In various embodiments of the present disclosure, the pH of any biological fluid of interest, such as dermal fluid, interstitial fluid, plasma, blood, lymph, synovial fluid, cerebrospinal fluid, saliva, bronchoalveolar lavage fluid, amniotic fluid, and the like, can be monitored.

[0050] An introducer may be temporarily present to facilitate the introduction of sensor 304 into the tissue. In exemplary embodiments, the introducer may comprise a needle. It is recognized that other types of introducers, such as cannulas or blades, may be present in alternative embodiments. More specifically, a needle or similar introducer may be temporarily present near sensor 304 prior to insertion and then withdrawn thereafter. While present, the needle or other introducer may facilitate insertion of sensor 304 into the tissue by opening an access path for sensor 304 to follow. For example, according to one or more embodiments, the needle may facilitate penetration of the epidermis into the dermis as an access path, allowing for implantation of sensor 304. After opening the access path, the needle or other introducer may be withdrawn to eliminate any sharp edges. In exemplary embodiments, the needle may be solid or hollow, beveled or non-beveled, and / or have a circular or non-circular cross-section. In more specific embodiments, the needle may be comparable to an acupuncture needle in cross-sectional diameter and / or tip design, and may have a cross-sectional diameter of approximately 250 microns. However, it is recognized that suitable needles may have a larger or smaller cross-sectional diameter if desired for a particular application.

[0051] In some embodiments, the needle tip (when present) may be angled on the end of the sensor 304 so that the needle first passes through the tissue and opens an access path for the sensor 304. In other exemplary embodiments, the sensor 304 may reside within a lumen or groove of the needle, and the needle similarly opens an access path for the sensor 304. In either case, after facilitating insertion, the needle is subsequently withdrawn.

[0052] Thus, in the pH sensor of the present disclosure, the first working electrode can be configured to generate a first signal and the second working electrode can be configured to generate a second signal, such that the difference between the first signal and the second signal can be correlated to pH. That is, according to various embodiments of the present disclosure, by subtracting the second signal from the first signal, the difference between the signal magnitudes can be correlated to pH. The signal difference can be calculated manually or automatically using a suitable processor. Similarly, once calculated, the signal difference can be correlated manually or automatically using a processor.

[0053] In a more specific embodiment, a pH sensor of the present disclosure can include a processor in signal communication with first and second working electrodes. The processor can be configured to receive a first signal from the first working electrode and a second signal from the second working electrode. The processor can be further configured to calculate a difference between the first signal and the second signal, and to correlate the difference between the signals to pH.

[0054] In some embodiments, the processor can be configured to access a lookup table comprising a plurality of pH values and the corresponding difference between the first signal and the second signal to calculate the pH. The lookup table can be filled by measuring a plurality of samples with known pH, measuring the first and second signals, and determining the difference between the two before measuring the unknown sample. The processor can, for example, determine which difference in the lookup table is closest to the difference measured by the known sample and then report the pH accordingly. In other embodiments, the processor can interpolate between the differences in the lookup table to determine the measured pH value. The interpolation can assume a linear change in the pH between the reported differences.

[0055] In other embodiments, the processor can be configured to access a calibration curve that compares pH values to the corresponding difference between the first signal and the second signal to calculate the pH. Like a lookup table, a calibration curve can be determined before measuring an unknown sample by measuring multiple samples with a known pH, measuring the first and second signals, determining the difference between the two, and curve fitting the pH and the difference to determine a calibration function. By determining the signal difference as a function of pH at the factory and assigning the lookup table or calibration curve to the pH sensor, factory calibration at the batch level can be possible. Since reference electrode calibration for each signal is not necessary, for a given selection of substances in the first active portion and the second active portion, the signal difference within a given pH range should be constant between different sensors.

[0056] Thus, the pH measurement method of the present disclosure may include: exposing a pH sensor to a fluid having a pH value, the pH sensor comprising a first working electrode, a second working electrode, and at least one other electrode, as described above; measuring a first signal associated with the first working electrode; measuring a second signal associated with the second working electrode; calculating a difference between the first signal and the second signal; and correlating the difference between the first signal and the second signal to a pH value. In more specific embodiments, the fluid may be a biological fluid, and the pH sensor may be exposed to the biological fluid in vivo.

[0057] According to some embodiments, the first signal and the second signal can each comprise 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 scan performed, a suitable position on the observed curve can be determined to determine the voltammetric peak potential for each substance. One of ordinary skill in the art will be able to make this determination based on the type of voltammetric scan to be performed.

[0058] According to various embodiments, the first signal and the second signal can be measured simultaneously or at different times. Measuring at different times can include, for example, performing a voltammetric scan of each working electrode respectively, and not applying potential to another working electrode. According to some embodiments, measurement in this way can use a single channel. In other embodiments, the first signal and the second signal can be measured simultaneously by monitoring each working electrode simultaneously via the first channel and the second channel.

[0059] In another embodiment, the method of the present disclosure may include accessing a lookup table comprising a plurality of pH values and the corresponding difference between the first signal and the second signal to calculate pH. In other further embodiments, the method of the present disclosure may include accessing a calibration curve of the pH value compared to the corresponding difference between the first signal and the second signal to calculate pH. In either configuration, the processor may be configured to receive the first signal and the second signal to calculate the difference between the first signal and the second signal and access a lookup table or calibration curve. According to various embodiments, accessing the lookup table or calibration curve may include performing an electronic query.

[0060] Embodiments disclosed herein include:

[0061] A. A sensor for measuring pH. The pH sensor comprises: a sensor tail comprising a first working electrode, a second working electrode, and at least one other electrode; a first active portion located on the first working electrode, the first active portion comprising a species having a pH-dependent redox chemistry; and a second active portion located on the second working electrode, the second active portion comprising a species having a substantially pH-independent redox chemistry.

[0062] B. A method of measuring pH. The method comprises: exposing a pH sensor to a fluid having a 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 located on the first working electrode, the first active portion comprising a species having a pH-dependent oxidation-reduction chemistry; and a second active portion located on the second working electrode, the second active portion comprising a species having an oxidation-reduction chemistry that is substantially invariant with pH; measuring a first signal associated with the first working electrode; measuring a second signal associated with the second working electrode; calculating a difference between the first signal and the second signal; and correlating the difference between the first signal and the second signal to a pH value.

[0063] Each of embodiments A and B may have one or more or all of the following additional elements in any combination:

[0064] Element 1: wherein the sensor tail is configured to be inserted into tissue.

[0065] Element 2: wherein the substance having pH-dependent oxidation-reduction chemistry comprises a quinone, a redox indicator compound, or any combination thereof.

[0066] Element 3: wherein the substance having pH-dependent redox chemistry comprises: a redox indicator compound containing thiazine.

[0067] Element 4: wherein the at least one other electrode comprises a counter electrode and a reference electrode.

[0068] Element 5: wherein the pH sensor further comprises: a dielectric layer sandwiched between the at least one other electrode and at least one of the first working electrode and the second working electrode.

[0069] Element 6: wherein a first dielectric layer is sandwiched between the first working electrode and the counter electrode or the reference electrode, and a second dielectric layer is sandwiched between the second working electrode and the counter electrode or the reference electrode.

[0070] Element 7: wherein the at least one other electrode comprises a counter / reference electrode.

[0071] Element 8: wherein the pH sensor further comprises: a dielectric layer sandwiched between the counter / reference electrode and at least one of the first working electrode and the second working electrode.

[0072] Element 9: wherein the first working electrode is configured to generate a first signal, and the second working electrode is configured to generate a second signal, and the difference between the first signal and the second signal is correlated to pH.

[0073] Element 10: Wherein 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; wherein the processor is further configured to calculate a difference between the first signal and the second signal and relate the difference to pH.

[0074] Element 11: wherein the processor is configured to access a lookup table comprising a plurality of pH values and corresponding differences between the first signal and the second signal to calculate the pH.

[0075] Element 12: wherein the processor is configured to access a calibration curve of pH values compared to a difference between the first signal and the second signal to calculate the pH.

[0076] Element 13: wherein the substance having pH-dependent redox chemistry and the substance having substantially pH-independent redox chemistry are both covalently bound to polymers in the first active moiety and the second active moiety, respectively.

[0077] Element 14: wherein the fluid is a biological fluid and the pH sensor is exposed to the biological fluid in vivo.

[0078] Element 15: wherein the method further comprises: accessing a lookup table comprising a plurality of pH values and corresponding differences between the first signal and the second signal to calculate the pH.

[0079] Element 16: wherein 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 lookup table.

[0080] Element 17: wherein the method further comprises: accessing a calibration curve of pH values compared to the difference between the first signal and the second signal to calculate the pH.

[0081] Element 18: Wherein 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.

[0082] Element 19: wherein the first signal comprises a voltammetric peak potential of the species having a pH-dependent redox chemistry, and the second signal comprises a voltammetric peak potential of the species having a redox chemistry that is substantially invariant with pH.

[0083] Element 20: wherein the first signal and the second signal are measured at different times.

[0084] Element 21: wherein the first signal and the second signal are measured simultaneously via a first channel and a second channel.

[0085] As non-limiting examples, exemplary combinations applicable to A and B include:

[0086] A pH sensor with elements 1 and 2; 1 and 3; 1 and 4; 1, 4 and 5; 1, 4 and 6; 1 and 7; 1, 7 and 8; 1 and 9; 1 and 10; 1, 10 and 11; 1, 10 and 12; 1 and 13; 2 and 4; 2, 4 and 5; 2, 4 and 6; 2 and 7; 2, 7 and 8; 2 and 9; 2 and 10; 2, 10 and 11; 2, 10 and 12; 3 and 4; 3, 4 and 5; 3 , 4 and 6; 3 and 7; 3, 7 and 8; 3 and 9; 3 and 10; 3, 10 and 11; 3, 10 and 12; 4 and 10; 4, 10 and 11; 4, 10 and 12; 7 and 10; 7, 10 and 11; 7, 10 and 12; 2 and 9; 3 and 9; 4 and 9; 7 and 9; 10 and 11; 10 and 12; 10 and 13; 10, 11 and 13; and 10, 12 and 13 combined. Method B and elements 2 and 13; 2 and 14; 2 and 15; 2, 15 and 16; 2 and 17; 2, 17 and 18; 2 and 19; 2 and 20; 2 and 21; 3 and 13; 3 and 14; 3 and 15; 3, 15 and 16; 3 and 17; 3, 17 and 18; 3 and 19; 3 and 20; 3 and 21; 13 and 14; 13 and 15; 13, 15 and 16; 13 and 17; 13, 17 and 18; 13 and 19; 13 and 20; 13 and 2 1; 14 and 15; 14, 15 and 16; 14 and 17; 14, 17 and 18; 14 and 19; 14 and 20; 14 and 21; 15 and 16; 15 and 19; 15, 16 and 19; 15 and 20; 15, 1 6 and 20; 15 and 21; 15, 16 and 21; 17 and 19; 17, 18 and 19; 17 and 20; 17, 18 and 20; 17 and 21; 17, 18 and 21; 19 and 20; and 19 and 21 combination.

[0087] To facilitate a better understanding of the embodiments described herein, the following examples of various representative embodiments are given.The following examples should in no way be read as limiting or defining the scope of the invention. Example

[0088] Working Electrode #1: The first carbon working electrode was coated with a polymeric layer of toluidine blue (TOB). Prior to coating, the bare working electrode was preconditioned in a solution containing 100 mM citric acid / 200 mM phosphate / 100 mM KCl (pH 4) by cycling from -0.8 V to 1.2 V for 5 cycles at a scan rate of 50 mV / s. Electrodeposition of TOB was performed by adding 5 mM TOB to the solution and cycling from -0.8 V to 1.2 V for 60 cycles at a scan rate of 50 mV / s. The sensor was then rinsed with distilled water and air-dried.

[0089] Working Electrode #2: A second carbon working electrode is coated with a polymer having an osmium complex covalently attached thereto. The structure of the polymer is shown below in Formula 2, which is described in further detail in US Patent 6,605,200, and is incorporated herein in its entirety.

[0090]

[0091] A solution of 45 mg / mL of the above polymer and 15 mg / mL of PEG400 was freshly prepared in 10 mM HEPES buffer (pH = 8). Three 20 nL aliquots of the solution were applied to the electrode surface to create three sensing (active) layer spots, each with a 0.1 mm 2 The working electrode was then cured overnight at 25°C under 65% relative humidity.

[0092] Cyclic voltammetry was performed on each working electrode in a series of pH buffers ranging from pH 2 to 12 at a scan rate of 50 mV / s from -0.8 V to 1.2 V. A carbon counter electrode and an Ag / AgCl reference electrode were used in all measurements. Figure 4 Shown is a plot of the integrated cyclic voltammograms of the first working electrode (which contains TOB) at various pH values. Figure 5 The corresponding plots of the integrated cyclic voltammograms at various pH values are shown for the second working electrode (which contains the polymer-bound osmium complex).Table 1 below summarizes the observed anodic peak potentials.

[0093] Table 1

[0094]

[0095] A look-up table can be constructed from the differences in the last row of Table 1 and the corresponding pH values in the first row. Alternatively, a calibration curve can be constructed by plotting the values. Figure 6 A calibration curve corresponding to the pH versus voltage difference data shown in Table 1 is shown.

[0096] Unless otherwise indicated, all numbers expressing quantities and the like in this specification and the associated 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 the appended claims are approximate and may vary depending upon the desired properties sought to be obtained by embodiments of the present invention. Initially, 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 reported significant digits and by applying ordinary rounding techniques.

[0097] One or more exemplary embodiments of various features are proposed herein. For the sake of brevity, all features of physical implementation are not described or shown in this application. It is to be understood that in the development of physical implementations of the embodiments of the present invention, many implementation-specific decisions must be made to achieve the developer's goals, such as meeting system-related, business-related, government-related and other constraints that vary and change over time due to implementation. Although the developer's efforts may be time-consuming, such efforts are routine work for those of ordinary skill in the art who benefit from this disclosure.

[0098] 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" the various components and steps.

[0099] As used herein, the phrase "at least one" preceding a list of items, using the terms "and" or "or" to separate any of the items, alters the list as a whole, rather than each element of the list (i.e., each item). The phrase "at least one" allows for a meaning that includes 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. As an example, the phrase "at least one of A, B, and C" or "at least one of A, B, or C" each refers to only A, only B, or only C; any combination of A, B, and C; and / or at least one of each of A, B, and C.

[0100] Therefore, the disclosed systems, tools, and methods are particularly well-suited to achieving the results and advantages mentioned, as well as those inherent therein. The specific embodiments disclosed above are exemplary only, as the teachings of this disclosure may be modified and practiced differently, but equivalents will be apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitation is intended to the details of construction or design shown herein other than as described in the claims below. It is therefore apparent that the specific exemplary embodiments disclosed above may be altered, combined, or modified, and all such variations are considered to be within the scope of this disclosure. The systems, tools, and methods exemplarily disclosed herein may be suitably implemented in the absence of any element not specifically disclosed herein and / or in the absence of any optional element disclosed herein. Although systems, tools, and methods are described as "comprising," "containing," or "including" various components or steps, the systems, tools, and methods may also be "consisting essentially of" or "consisting of" the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, each range of values disclosed herein (in the form of "about a to about b," or equivalently "approximately a to b," or equivalently "approximately a b") is to be understood as reciting each number and range encompassed within the broader range of values. Likewise, the terms in the claims have their plain, everyday meaning unless otherwise expressly and clearly defined by the patentee. In addition, the indefinite articles "a" or "an" used in the claims are defined herein to mean one or more than one element that it introduces. If there is any conflict in the use of a word or term in this specification and in one or more patents or other documents that may be incorporated by reference herein, the definition consistent with this specification shall apply.

Claims

1. A pH sensor comprising: a substrate having a first opposing side and a second opposing side, a first working electrode, a second working electrode, and at least one other electrode; a first active moiety located on the first working electrode, the first active moiety comprising a first polymer and a species having a pH-dependent redox chemistry covalently bound to the first polymer; a second active portion located on the second working electrode, the second active portion comprising a second polymer and a species having substantially pH-independent redox chemistry covalently bound to the second polymer, wherein the second active portion comprises a sensing site throughout which redox chemistry occurs; and a first dielectric layer covering the first working electrode except for a distal end of the first working electrode where the first active portion is exposed; a second dielectric layer covering the second working electrode except for a distal end of the second working electrode where the second active portion is exposed; a membrane overlying the first opposing side and the second opposing side of the substrate, wherein the membrane is capable of restricting the flow of analyte to both the first active portion and the second active portion; wherein the material having a substantially pH-independent redox chemistry exhibits a measured voltage change of 50 mV or less over a pH range of 5-8, wherein the first working electrode is configured to generate a first signal and the second working electrode is configured to generate a second signal, and the difference between the first signal and the second signal is related to pH, and Wherein the sensor is configured to be at least partially inserted into subcutaneous tissue. 2 . The pH sensor of claim 1 , wherein the substance having pH-dependent oxidation-reduction chemistry comprises a quinone, a redox indicator compound, or any combination thereof.

3. The pH sensor of claim 2, wherein the substance having pH-dependent redox chemistry comprises a thiazine-containing redox indicator compound. The pH sensor of claim 1 , wherein the at least one other electrode comprises a counter electrode and a reference electrode. 5 . The pH sensor of claim 1 , wherein the first dielectric layer is sandwiched between the first working electrode and at least one other electrode, and the second dielectric layer is sandwiched between the second working electrode and at least one other electrode. The pH sensor of claim 1 , wherein the at least one other electrode comprises a counter / reference electrode.

7. A pH sensor according to claim 6, wherein the first dielectric layer is sandwiched between the counter / reference electrode and the first working electrode; or wherein the second dielectric layer is sandwiched between the counter / reference electrode and the second working electrode; or wherein the first dielectric layer is sandwiched between the counter / reference electrode and the first working electrode and the second dielectric layer is sandwiched between the counter / reference electrode and the second working electrode.

8. 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, and the difference between the first signal and the second signal is related to pH.

9. The pH sensor according to claim 8, further comprising: a processor configured to receive the first signal from the first working electrode and the second signal from the second working electrode; Wherein the processor is further configured to calculate a difference between the first signal and the second signal and to relate the difference to pH.

10. The pH sensor of claim 9, wherein the processor is configured to access a lookup table containing a plurality of pH values and to correlate the difference between the first signal and the second signal to the pH value in the lookup table to calculate pH.

11. The pH sensor of claim 9, wherein the processor is configured to access a calibration curve of pH values and to correlate the difference between the first signal and the second signal to the pH value in the calibration curve to calculate pH.

12. The pH sensor of claim 1, wherein the second polymer has an osmium complex covalently bound thereto as a species having a substantially pH-independent redox chemistry.

13. The pH sensor of claim 1, wherein the second polymer has a structure of Formula 2: Formula 2.

14. The pH sensor of claim 1, wherein the first polymer comprises polyvinylpyridine, polyimidazole, a copolymer thereof, or any combination thereof.

15. The pH sensor of claim 1, wherein the second polymer comprises polyvinylpyridine, polyimidazole, a copolymer thereof, or any combination thereof.

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