Ion-selective electrode having a sensor film covalently bonded to both an inert polymer substrate and a conductive carbon contact.

Abstract

An electrochemical sensor having an ion-selective membrane bonded by covalent chemical bonds to both an electrically non-conductive polymer substrate (electrode) and an underlying ion-electron converter.

Description

[Technical Field]

[0001] This disclosure relates to ion-selective electrodes (ISEs), and more particularly to solid-contact type ion-selective electrodes. [Background technology]

[0002] The use of ISEs (Insulated Ion Spectrometers) is of interest for many clinical, environmental, and industrial applications. However, prolonged exposure to aqueous samples, as well as under thermal and mechanical stress, often gradually weakens the adhesion between these films and their underlying substrates. Ultimately, this leads to the formation of a water layer at the interface with the underlying electron conductor and delamination of the film from the electrode. Both of these are major constraints on long-term monitoring.

[0003] Significant challenges remain in miniaturizing and extending the lifespan of ISEs (Insulator-Isolated Sensors). For example, pH glass electrodes (most commonly used for measuring pH) have high electrical resistance and are mechanically fragile. Furthermore, pH glass electrodes with internal solutions and conventional ionophore-based ISEs are difficult to miniaturize. Efforts to overcome these drawbacks often involve ionophore-doped sensor membranes with solid contacts to underlying electron conductors such as conductive polymers, high-surface-area carbon (e.g., nanographite or mesoporous carbon), and hydrophobic redox buffers. The lifespan of these sensors can be improved by using plasticizer-free polymers as the membrane matrix and by covalent bonding of ionophores or ionic sites to this matrix polymer. Another challenge that often limits the lifespan of such sensors is the formation of an aqueous layer at the interface between the sensor membrane and the underlying electron conductor, and delamination of the sensor membrane from the electrode body. To prevent such delamination, screw caps and other mechanical devices can be used, but this makes miniaturization more difficult and, in certain applications, may increase the risk of air bubble trapping and damage to the sensor membrane due to overtightening.

[0004] Because the physical adhesion between the sensor film and the underlying substrate is usually weak, several attempts have been made to covalently bond the ISE film to the underlying substrate. Harrison and collaborators used PVC films with hydroxyl groups and bonded them to a silicon oxide surface using SiCl4. T. Satchwill, DJ Harrison, Journal of Electroanalytical Chemistry 1986, 202, 75-81. Reinhoudt and collaborators functionalized the silicon oxide surface of an ion-selective field-effect transistor (ISFET) gate with a silylation reagent having terminal methacrylate groups, and then covalently bonded a photopolymerizable sensor film. EJR Sudholter, PD van der Wal, M. Skowronska-Ptasinska, A. van den Berg, DN Reinhoudt, Sensors and Actuators 1989, 17, 189-194. This method was later modified by incorporating a hydrogel layer between the gate and the sensor film. DN Reinhoudt, JFJ Engbersen, Z. Brzozka, HH van den Viekkert, GWN Honig, HAJ Hoiterman, UH Verkerk, Analytical Chemistry 1994, 66, 3618-3623;K. Kimura, T. Sunagawa, S. Yajima, S. Miyake, M. Yokoyama, Analytical Chemistry 1998, 70, 4309-4313; and EJR Sudholter, PD van der Wal, M. Skowronska-Ptasinska, A. van den Berg, P. Bergveld, DN Reinhoudt, Analytica Chimica Acta 1990, 230, 59-65.

[0005] However, this type of ISFET has never become widely available, likely because it was not possible to completely eliminate delamination of the sensor membrane in a satisfactory manner. Bobacka and his collaborators covalently bonded a polyacrylate-based sensor membrane to poly(3,4-ethylenedioxythiophene) by functionalizing the conductive polymer poly(3,4-ethylenedioxythiophene) with methacrylate groups. C. Ocana, N. Abramova, A. Bratov, T. Lindfors, J. Bobacka, Talanta 2018, 186, 279-285. Such bonding restricts the formation of a water layer between the sensor membrane and the conductive polymer, stabilizing the potentiometric response. Unfortunately, this does not prevent delamination of the membrane from the underlying electrode.

[0006] To prevent these problems without increasing the complexity of the design involving mechanical mounting, photo-induced graft polymerization is used to simultaneously covalently bond the sensor film to both high-surface-area carbon and inert polymer electrode materials (i.e., polypropylene and poly(ethylene-co-tetrafluoroethylene)) as ion-electron converters. The sensor has high reproducibility (E 0 It offers a standard deviation of 0.2 mV, long-term stability (potential drift of 7 μV / h for over 260 hours), and resistance to autoclaving (30 minutes at 121°C and 2.0 atm). In this study, to create a pH sensor with advantages over conventional pH glass electrodes, covalently bonded H + While a selective ionophore was used, the use of other ionophores would make this method suitable for ISE preparation for a variety of analytes.

[0007] Furthermore, the sensor films were chemically bonded to inert polymer sensor platform materials. Specifically, polyacrylate-based sensor films were covalently bonded to surface-modified poly(ethylene terephthalate) and poly(ethylene-co-cyclohexane-1,4-dimethanol terephthalate) by EL Anderson, SAChopade, B. Spindler, A. Stein, TPLodge, MAHillmyer, and P. Buhlmann. These sensors did not exhibit delamination of the film from the underlying substrate in either long-term measurements or severe mechanical stress tests; however, the surface modification of the substrate required multi-step synthesis, and the sensor films were not covalently bonded to the underlying electron conductors. [Overview of the project]

[0008] This disclosure describes an electrochemical sensor comprising an ion-selective film, an electrically nonconductive polymer substrate or electrode, and an underlying electron conductor, wherein the ion-selective film is covalently bonded to the electrically nonconductive polymer substrate or electrode and the underlying electron conductor.

[0009] The disclosure further describes the sensor characterized by the covalent chemical bond being photoinitiated surface functionalization and subsequent photoinitiated graft polymerization or thermally initiated graft polymerization.

[0010] The disclosure further describes a sensor in which the covalent chemical bonds between the ion-selective film, the inert polymer electrode material, and the underlying electron conductor are characterized by the generation of radicals by plasma.

[0011] The present disclosure further describes the sensor generated by the plasma treatment including pretreatment of the electrically non-conductive polymer substrate or electrode body, and the underlying electron conductor, wherein the radical is any of argon, helium, oxygen, hydrogen peroxide, hydrogen, chlorine, BCl3, HBr, tetrafluoromethane, fluoroform, CO2, SF6, fluorocarbon or a mixture of two of these.

[0012] The present disclosure further describes the sensor in which peroxide functional groups and hydroperoxide functional groups are formed on the surfaces of the electrically non-conductive polymer substrate or electrode body, and the underlying electron conductor by exposure to oxygen or the ambient atmosphere.

[0013] The present disclosure further describes the sensor, wherein the covalent chemical bond is characterized by graft polymerization formed by the gas phase of the monomer introduced into the plasma and formed in the polymer, and the polymer is covalently bonded to the electrically non-conductive polymer substrate or electrode body and the underlying electron conductor.

[0014] The present disclosure includes that the ion-selective membrane is (i) selective for H + and contains an ionophore including a heterocyclic aromatic hydrocarbon which is any of a primary amine, a secondary amine or a tertiary amine, or pyridine, quinoline or phenanthrene, or (ii) doped with any of ionophores having selectivity for monovalent or polyvalent ions which are any of Li + 、K + 、Na + 、Mg 2+ 、Ca 2+ 、Cl - 、SO4 2- 、carbonate or phosphate. The sensor is further described.

[0015] The present disclosure further describes the sensor, wherein the ion exchange ability of the ion-selective membrane is characterized in that an ionic site containing a tetraphenylborate group, a sulfonate group, or a sulfonylimide group is doped.

[0016] The present disclosure further describes the sensor, wherein the ion-selective membrane contains no crosslinking agent or contains a crosslinking agent, and includes an alkyl methacrylate homopolymer, an alkyl acrylate homopolymer, or a copolymer of two or more alkyl methacrylates or alkyl acrylates.

[0017] The present disclosure further describes the sensor, which is characterized by not showing an aqueous layer effect.

[0018] The present disclosure further describes the sensor, wherein the ion-selective membrane contains a polymer material, and the polymer material includes polycarbonate, polystyrene, polyurethane, polyolefin, silicone, polyamide, polyester, polyether, polyimide, polysulfide, polycarbonate, polyacetal, polymethacrylate or polyacrylate, polyphenylene sulfide, polypropylene, polyethylene, poly(ethylene-co-tetrafluoroethylene), poly(tetrafluoroethylene), poly(vinyl chloride), polyvinylidene chloride, polyvinyl acetate, polyacrylonitrile, polyvinyl fluoride or polyvinylidene fluoride.

[0019] The present disclosure further describes a reference electrode, which includes an ionic liquid doped reference membrane, an inert plastic substrate, and a lower layer electronic conductor, and the ionic liquid doped reference membrane is bonded to both the inert plastic substrate and the lower layer electronic conductor by a covalent chemical bond.

[0020] The present disclosure further describes a reference electrode, wherein the covalent chemical bond is characterized by photoinitiated graft polymerization.

[0021] The disclosure further describes a reference electrode in which the covalent chemical bond is characterized by radicals formed by a plasma.

[0022] The disclosure further describes a reference electrode characterized by pre-treating the inert plastic substrate and the underlying electron conductor with argon plasma, helium plasma, or oxygen plasma, and subsequently exposing them to oxygen or an ambient atmosphere to form peroxide functional groups and hydroperoxide functional groups on their surfaces.

[0023] The disclosure further describes a reference electrode in which the ionic liquid-doped reference film comprises a polymer formed by the plasma, and the plasma comprises other gases which are converted into monomers and / or reactive fragments in the gas phase of the plasma to form the covalent chemical bond.

[0024] The disclosure further describes a reference electrode in which the covalent chemical bond is characterized by radicals formed by thermal polymerization.

[0025] The disclosure further describes a reference electrode in which the ionic liquid-doped reference membrane comprises a polymer material, wherein the polymer material comprises polycarbonate, polystyrene, polyurethane, polyolefin, silicone, polyamide, polyester, polyether, polyimide, polysulfide, polycarbonate, polyacetal, polymethacrylate or polyacrylate, polyphenylene sulfide, polypropylene, polyethylene, poly(ethylene-co-tetrafluoroethylene), poly(tetrafluoroethylene), poly(vinyl chloride), polyvinylidene chloride, polyvinyl acetate, polyacrylonitrile, polyvinyl fluoride, or polyvinylidene fluoride.

[0026] This disclosure further describes a reference electrode characterized by not exhibiting a water layer effect. [Brief explanation of the drawing]

[0027] [Figure 1] Figure 1 is a graph showing the initial emf response (square) and the response after 6 months (circle) to pH for an ISE with a PDMA membrane (doped with ionophores and ionic sites).

[0028] [Figure 2] Figure 2 is a graph of the aqueous layer test for ionophore-based ISEs with nanographite solid contacts.

[0029] [Figure 3] Figure 3 is a graph showing the long-term stability of the PDMA membrane.

[0030] [Figure 4] Figure 4 is a graph of the IR spectra of a polypropylene sheet and a poly(ethylene-co-tetrafluoroethylene) film.

[0031] [Figure 5] Figure 5 is a cross-sectional view of an example of a polypropylene-based electrode.

[0032] [Figure 6] Figure 6 is an image of the PDMA sensor film.

[0033] [Figure 7] Figure 7 is an image of the PDMA sensor film.

[0034] [Figure 8] Figure 8 is an image of the PDMA sensor membrane.

[0035] [Figure 9] Figure 9 is an image of the PDMA sensor membrane.

[0036] [Figure 10] Figure 10 is a graph showing the results of the aqueous layer test for gold / nanographite / PDMA ISE.

[0037] [Figure 11] Figure 11 is a graph showing the results of the aqueous layer test for gold / nanographite / PDMA. [Modes for carrying out the invention]

[0038] This disclosure describes the covalent bonding of an ISE film to both an inert polymer electrode and an underlying carbon conductor simultaneously. While there are precedents for covalent bonding of sensor films to conductive polymers as electron conductors and to inert polymer substrates, covalent bonding of sensor films to both inert polymers and ion-electron converters has not been shown until now. As an example, nanographite (surface area 250 m²) 2 Both poly(b) and glassy carbon are used as electronic conductors, and both polypropylene and poly(ethylene-co-tetrafluoroethylene) are used as electrode materials. The use of other polymers is within the scope of this disclosure. In particular, these electrode materials are not only widely used in industry but also possess good mechanical resistance, temperature resistance and chemical resistance suitable for industrial-grade sensor bodies. Further electrode materials suitable for use as electrode materials include, but are not limited to, polycarbonate, polystyrene, polyurethane, polyolefin, silicone, polyamide, polyester, polyether, polyimide, polysulfide, polycarbonate, polyacetal, polymethacrylate or polyacrylate, polyphenylene sulfide, poly(tetrafluoroethylene), poly(vinyl chloride), polyvinylidene chloride, polyvinyl acetate, polyacrylonitrile, polyvinyl fluoride, or polyvinylidene fluoride.

[0039] Both surface modification and graft polymerization were achieved by ultraviolet (UV) irradiation. In the first step (step 1), a THF solution of 2,2-dimethoxy-2-phenylacetophenone, a photopolymerization initiator, was deposited on the carbon-based conductor surface and the inert polymer of the adjacent electrode body. During UV irradiation, a photoreduction reaction (hydrogen abstraction) between the photopolymerization initiator and the surface CH bonds of polypropylene or poly(ethylene-co-tetrafluoroethylene) generates surface-localized radicals, which then combine with benzoyl radicals formed from the photopolymerization initiator, thereby forming benzoyl groups on these surfaces. In the case of carbon-based conductors, sp 2 The direct reaction of benzoyl radicals with hybrid carbon is likely the main reaction. In the second step (step 2), a solution containing decyl methacrylate and a crosslinking agent in addition to the photopolymerization initiator is deposited on the functionalized surface. Subsequent UV irradiation homolytically cleaves the bonds between benzoyl groups bonded to the surface, initiating graft polymerization of decyl methacrylate and generating polymer chains that are chemically bonded to the substrate. The success of this photo-induced graft polymerization is supported by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, contact angle, gravimetric measurements, and peel tests, as discussed below.

[0040] The following photo-induced surface modification of polypropylene: Step 1: Bonding of a photopolymerization initiator to the surface. Step 2: Grafting of monomers. [ka]

[0041] ATR-FTIR spectra for both polypropylene and poly(ethylene-co-tetrafluoroethylene) modified by surface photografting show characteristic C=O stretching vibrations of the ester group of poly(decyl methacrylate) (PDMA)

[40] (see Figure 4). Surface photografting was also confirmed by contact angle, which was 113° and 107° for unmodified polypropylene and poly(ethylene-co-tetrafluoroethylene) substrates, respectively, but decreased to 76° for both substrates after photografting of the PDMA film (see Table 2). This is consistent with the higher hydrophilicity of the methacrylate polymer due to the ester group. Incorporation of the crosslinking agent into the grafted PDMA was evident from differential scanning calorimetry (DSC). Compared with the uncrosslinked PDMA film, the glass transition temperature of the crosslinked PDMA film was 77°C higher, from -65°C to 12°C, which is as expected when the crosslinking agent is incorporated into polymethacrylate.

[0042] The efficiency of graft polymerization was calculated as the ratio of the experimental weight of the graft film to the total amount of polymerizable film components (i.e., decyl methacrylate monomer, crosslinking agent, and, where applicable, ionophores) used for its preparation. As shown in Table 1, a high graft polymerization efficiency of 81% can be achieved with minor optimization. The remaining polymerizable components are lost (in the form of monomers or oligomers) by evaporation during photopolymerization or when washing the film with a solvent (1 mL of THF or methanol) after polymerization.

[0043] Importantly, H2 is added to the solution of decyl methacrylate and the crosslinking agent. + 2-(diisopropylamino)ethyl methacrylate, a selective and polymerizable ionophore, and the ionic moiety (K + The addition of tetrakis(pentafluorophenyl)borate in salt form did not hinder photoinitiated polymerization (see Table 1) or covalent bonding to the underlying substrate. Suitable ionophores include, but are not limited to, (i)H +(ii)Li + , K + kaNa + Mg 2+ Ca 2+ Cl - SO4 2- Examples include ionophores that have selectivity for monovalent or polyvalent ions, which are either carbonates or phosphates. Electrical neutrality in the ion-selective membrane may be achieved by doping with ionic moieties containing tetraphenylborate groups, sulfonate groups, or sulfonylimide groups.

[0044] To confirm that covalent bonding of the PDMA film to the underlying substrate and electrical contacts actually occurs through the two-step process for photografting, a peel test was performed (see Figures 6-9). As shown below, nanographite was used as the solid contact and electronic conductor for the fabrication of the potentiometer, but as shown below, nanographite was unsuitable for the peel test due to its powdery nature. Therefore, for this purpose, glassy carbon plates were used instead (Figure 6). These plates are perfectly flat and have a fully sp2-bonded fullerene-related structure that is chemically very similar to nanographite.

[0045] PDMA films were grafted onto polypropylene (Figure 7), poly(ethylene-co-tetrafluoroethylene) (Figure 8), and a glassy carbon plate placed on a polypropylene sheet (Figure 9) using two different methods. In one method, both were photografted using the complete two-step method described above. In the other method, a control was performed in which only decyl methacrylate, a crosslinking agent, and a photoinitiator were photopolymerized without pre-binding the photoinitiator to the surface, omitting the first step which involves binding the photoinitiator to the surface. Then, all four substrates thus obtained were immersed in phosphate buffer (pH=7.1). After 7 days, all PDMA films formed on unmodified polypropylene, unmodified poly(ethylene-co-tetrafluoroethylene), or unmodified glassy carbon (i.e., with the first step of the grafting method omitted) could be removed with minimal effort using tweezers. On the other hand, PDMA films bonded to polypropylene, poly(ethylene-co-tetrafluoroethylene), or glassy carbon using the complete two-step method could not be removed. This was consistent with the successful covalent bonding of the PDMA film to the two inert polymer substrates and the glassy carbon. Even when attempting to remove the PDMA very forcefully, only scratches occurred on the PDMA, and no delamination between film layers took place.

[0046] Since the covalent bonding of the sensor film to the polymer and carbon conductor was confirmed, a potentiometer was fabricated and its characteristics were determined. For this purpose, a gold-plated stainless steel rod was molded into a polypropylene body, and the gold-plated rod was exposed at the bottom of a cavity at one end of the polypropylene body, designed to hold the nanographite and ion-selective film. Figure 1 shows the initial emf response (square) and the response after 6 months (circle) to pH for an ISE with a polypropylene-based electrode body and a PDMA film (doped with ionophores and ionic sites) photografted onto a nanographite solid junction, compared to a free-flowing double junction reference electrode. The pH was adjusted by adding 1.0 M HCl or 1.0 M NaOH to 10 mM sodium phosphate buffer solution (pH 7.1). The pH shown on the x axis was measured using a pH glass electrode.

[0047] To prevent the sensor lifespan from being limited by ionophore leaching into the sample, 2-(diisopropylamino)ethyl methacrylate was included in the photograft solution. Due to its methacrylate group, this ionophore is incorporated into the PDMA polymer backbone during photoinitiated polymerization. The ionic moiety tetrakis(pentafluorophenyl)borate, necessary to impart membrane selective permeability to cations, was included in the photograft solution at a molecular ratio of 1-3 relative to the ionophore. Since ISEs with both ionophore and ionic moiety covalently bonded have been shown to exhibit higher electrical resistance and excessive response time, making them unsuitable for potentiometric analysis, no attempt was made to covalently bond the ionic moiety to the PDMA backbone.

[0048] After conditioning overnight in 10 mM sodium phosphate buffer at pH 7.1, the pH response of these electrodes was tested in 10.0 mM phosphate buffer solution by pH adjustment with aliquots of 1 M NaOH and HCl. Three similarly prepared electrodes showed a slope of -58.5 ± 1.2 mV / decade and an operating range of pH 1.4 to pH 9.7 (see Figure 1). The logarithmic selectivity coefficients of these membranes, log[K_(H,Na)^pot], log[K_(H,K)^pot], and log[K_(H,Li)^pot], were -10.4 ± 0.1, -9.8 ± 0.1, and -10.7 ± 0.1, respectively. These values ​​were similar to, but slightly different from, those previously reported for cases where the same ionophore is covalently bonded to the PDMA film, but the PDMA film is not covalently bonded to the inert polymer substrate and nanographite as a solid contact (see Table 3). The decrease in selectivity is due to K + The most significant difference was observed in log[K_(H,K)^pot], which increased from -10.7 to -9.8, while log[K_(H,Na)^pot] and log[K_(H,Li)^pot] increased by only 0.6 and 0.4, respectively. This difference may be related to the use of a photoinitiator in step 1 of film fabrication, where surface-bound benzoyl groups are formed, or to the higher photoinitiator concentration (1.5 wt%) used in step 2 of this study compared to our previous studies (0.9 wt%). Although there appears to be some room for optimization, this indicates that a well-functioning ISE can be obtained with a PDMA photoinitiated graft.

[0049] It is well known that the formation of a thin aqueous layer between the polymer film and solid contacts in ISEs leads not only to potential drift and reduced EMF reproducibility, but ultimately to delamination of the film. A well-established aqueous layer test was used to evaluate whether such an aqueous layer forms in the case of photografted PDMA films. (M. Fibbioli, WE Morf, M. Badertscher, NF De Rooij, E. Pretsch, Electroanalysis 2000, 12, 1286-1292; B. Hambly, M. Guzinski, B. Pendley, E. Lindner, Electroanalysis 2020, 32, 781-791). As shown in Figure 2(a), no such drift was observed for films covalently bonded to the electrode and nanographite solid contacts when using the two-step photografting method. On the other hand, when the first step of photografting was omitted and the PDMA film was not covalently bonded to the electrode and solid contacts, the presence of an aqueous layer was confirmed. This confirmed the importance of binding the photopolymerization initiator to these surfaces in the first step of the photografting process.

[0050] H +Three tests were conducted to evaluate the improved long-term durability provided by the covalent bonding of the selective membrane. First, three electrodes were stored in pH buffer for six months. Then, the pH response and selectivity were measured, and the aqueous layer test was performed again. When stored in a 10 mM sodium buffer solution (pH 7.1) for six months, the three membranes exhibited a linear response range of pH 1.4 to 10.0 and maintained the theoretically predicted Nernst gradient (-58.4 mV ± 0.8 mV / decade) without change in the selectivity coefficient (see Table 3). Furthermore, the aqueous layer test demonstrated that no aqueous layer formed throughout this period (see Figure 10). In contrast, the PDMA membranes that were not covalently bonded to polypropylene and nanographite had already failed the aqueous layer test after being exposed to the buffer solution for five weeks, as shown in Figure 2. Figure 2 shows aqueous layer tests for ionophore-based ISEs with nanographite solid contacts: (a) PDMA film photografted onto polypropylene-based electrodes and nanographite solid contacts after autoclaving, and (b) PDMA film not covalently bonded to polypropylene-based electrodes and nanographite solid contacts after 5 weeks of exposure to buffer solution. In (a), the 0.1 M phosphate buffer solution (pH 7.1) was replaced with 0.1 M NaOH at t=1.01 hours, and in (b), at t=1.72 hours. In (a), the electrodes were returned to the 0.1 M phosphate buffer solution at t=3.36 hours, and in (b), at t=6.61 hours.

[0051] As a second test to evaluate the covalent bonding of the sensor membrane, the electrodes were exposed to high pressure (1500 Torr) and heat (121°C) in an autoclave. Commercial isotactic propylene melts in the range of 160-166°C, so the polypropylene-based electrode body would be damaged at considerably higher temperatures, but the cross-linked methacrylate does not melt and only decomposes at much higher temperatures.

[0052] In another experiment, the electrodes were also exposed to a 10% by weight ethanol solution for one day. The slope and selectivity of the response were the same for both autoclaving and ethanol treatment (see Table 3), and no aqueous layer was observed (see Figure 11). This confirms that covalent bonding of the sensor membrane to the electrode is attractive when the ISE is exposed to high temperatures or organic solvents during either measurement or cleaning.

[0053] The third durability test was a long-term EMF drift test. For this purpose, a capillary-based reference electrode was used to minimize the drift contributed by the reference electrode (fabricated as reported in EL Anderson, BK Troudt, P. Buhlmann, ACS Sensors 2021, 6, 2211-2217). As shown in Figure 3, all three electrodes fabricated by the two-step optical grafting process showed very low drift (7 μV / h). Consistent with the previous test, the aqueous layer was not detected after 260 hours, which is consistent with the other two tests. Furthermore, the y-intercept of the calibration curves of the three electrodes, E, was also shown. 0 The standard deviation was only ±0.2mV after the long-term stability test. In particular, the E of these electrodes 0 The small standard deviation (mV) and drift (μV / h) of the solid contact ISE are among the best observed to date.

[0054] Figure 3 shows the long-term stability of the underlying polypropylene-based electrode and the PDMA film directly bonded to the nanographite solid contact, measured against a capillary-based reference electrode in a 1.0 mM phosphate buffer solution within a temperature-controlled Faraday cage at 32°C.

[0055] In summary, a mechanically robust sensor exhibiting excellent long-term stability is provided by simultaneously bonding an ISE film to both a polymer electrode and an underlying electron conductor. The covalent photograft prevents delamination by inhibiting the formation of a water layer at the interface between the electrode and the sensor film, and also prevents EMF signal drift by preventing the formation of a water layer at the interface with the carbon solid contact. Within the scope of this disclosure, the method described herein can be applied to the detection of other ions by using different ionophores, provided that the ionophores are compatible with photopolymerization. This method is considered particularly suitable for wearable and implantable sensors that require long-term stability with little or no recalibration.

[0056] Plasma irradiation was also applied to graft sensor films onto both the electrode body and the solid contacts made of conductive carbon material. Plasma provided efficiency five times faster than ultraviolet (UV) treatment. Argon, helium, and oxygen plasmas generate radicals on the polymer surface. The newly generated radicals initiate monomer polymerization, and the grafted polymer chains chemically bond to the substrate. Other suitable plasmas, but not limited to, include hydrogen peroxide, hydrogen, chlorine, BCl3, HBr, tetrafluoromethane, fluoroform, CO2, SF6, fluorocarbons, or mixtures thereof.

[0057] Using one method, the components of the sensor film were deposited onto polypropylene and poly(ethylene-co-tetrafluoroethylene) platform substrates, which were then exposed to argon or helium plasma. The plasma generated radicals within the deposited sensor material and on the substrate surface, resulting in graft polymerization of the sensor film onto the substrate.

[0058] Alternatively, polymer substrates were pre-treated with argon, helium, or oxygen plasma, followed by exposure to oxygen or ambient atmosphere, to generate peroxide and hydroperoxide functional groups on their surfaces. The monomer components of the sensor film were then deposited onto these substrates, and the sensor film was graft-polymerized onto the substrates by inducing radical polymerization through UV irradiation or heat treatment. Plasma parameters (power, pressure, and flow rate) were used to control polymerization efficiency and the thickness of the resulting sensor film. High power values ​​could damage the ion-selective film and polymer electrode.

[0059] By simultaneously bonding an ISE film to both the polymer electrode and the underlying electron conductor, a mechanically robust sensor exhibiting excellent long-term stability is provided. The covalent photograft or plasma graft prevents delamination by inhibiting the formation of a water layer at the interface between the electrode and the sensor film, and also prevents EMF signal drift by preventing the formation of a water layer at the interface with the carbon solid contact. It is clear that this method can be applied to detecting other ions by using different ionophores, provided that the ionophores are compatible with photopolymerization. This method is considered particularly suitable for wearable and implantable sensors requiring long-term stability with little to no recalibration.

[0060] Experiment details Reagents and materials. Magnesium sulfate, sodium chloride, lithium chloride, lithium hydroxide, 2,2-dimethoxy-2-phenylacetophenone, 1,6-hexanediol dimethacrylate, and 2-(diisopropylamino)ethyl methacrylate were purchased from Sigma Aldrich (St. Louis, Missouri, USA). Decyl methacrylate (97%) was purchased from Pfaltz & Bauer (Waterbury, Connecticut, USA). Potassium chloride, potassium hydroxide, basic alumina, sodium hydroxide, and tetrahydrofuran were purchased from Fisher Chemical (Waltham, Massachusetts, USA). Nanographite powder (GS-4827, BET surface area 250 m²) 2 We purchased potassium tetrakis(pentafluorophenyl)borate (KTPFB) (particle size distribution 0.10μm~10μm) from Graphitestore (Northbrook, Illinois, USA). We purchased potassium tetrakis(pentafluorophenyl)borate (KTPFB) from Alfa Aesar (Tewkesbury, Massachusetts, USA). We purchased polypropylene sheets and poly(ethylene-co-tetrafluoroethylene) (also known as Tefzel) membranes from McMaster-Carr (Chicago, Illinois, USA). We purchased glassy carbon plates (SPI-glas 11 grade, 50mm x 50mm) from SPI Supplies (Westchester, Pennsylvania, USA). For delamination testing, we used a rotary cutting wheel tool (Dremel, Mount Prospect, Wisconsin, USA) to cut the glassy carbon plates to 1 x 1 cm². 2 The samples were cut into sections. Decyl methacrylate, 1,6-hexanediol dimethacrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diisopropylamino)ethyl methacrylate, and inhibitor-free anhydrous tetrahydrofuran (THF) were each passed separately through a pipette column packed with basic alumina before use. All aqueous solutions were prepared using deionized and charred water (resistivity of 18.2 MΩ / cm) with a Milli-Q Plus reagent-grade water system (Millipore, Bedford, Massachusetts, USA).

[0061] Contact angle measurement. The contact angles of polypropylene substrates and poly(ethylene-co-tetrafluoroethylene) films before and after surface modification were measured using a droplet method with a contact angle goniometer (Erma, Tokyo, Japan) (R. Good, Journal of Adhesion Science and Technology 1992, 6, 1269-1302). The advance angle was measured using 5 μL, 10 μL, 15 μL, and 20 μL purified H2O droplets, followed by the receding angle by removing 5 μL aliquots from the droplets three times. The advance contact angles for 10 μL, 15 μL, and 20 μL droplets were within the same margin of error, but the advance angle for the 5 μL droplet was slightly larger, which was thought to be influenced by system errors due to the small volume of the droplet. The receding angles were within the same margin of error for all droplet volumes. Three advance angles were calculated for 10 μL, 15 μL, and 20 μL droplets, and three receding angles were calculated for 15 μL, 10 μL, and 5 μL droplets, as well as the average from three different sample surfaces.

[0062] DSC: For all DSC measurements, a TA Instrument Q1000 DSC (Newcastle, Delaware) differential scanning calorimeter with a liquid nitrogen cooling system was used. The capped sample dish was thermally equilibrated at 100°C for 1 minute. The sample was then scanned down to -90°C at a heating / cooling rate of 10°C / min, and then returned to 100°C for scanning. The glass transition temperature was determined from the midpoint of the transition region.

[0063] Other measurements: ATR-FTIR spectroscopy was performed using a UV-1800 spectrometer from Shimadzu Corporation (Canby, Oregon, USA). Electrodes were autoclaved using a 2340M manual sterilizer from Tuttnauer (Hoboge, New York). A 3UV lamp was purchased from Analytik Jena (Jena, Germany).

[0064] Bonding of surface initiator to a solid surface. A total of 30 μL of a methanol solution of 20 wt% THF or 2,2-dimethoxy-2-phenylacetophenone was drop-cast (in four separate additions of 10 μL, 10 μL, 5 μL, and 5 μL to avoid splashing of the liquid away from the nanographite) onto gold electrodes coated with nanographite and surrounding polypropylene. The electrodes were placed in a well-sealed box covered with a UV-transparent quartz glass plate, and the box was flashed with argon for 10 minutes. The photopolymerization initiator was then grafted onto the polypropylene and nanographite solid contacts by UV irradiation (peak power 365 nm, high power in the range of 350-390 nm) for 20 minutes. The electrodes were dried in air at room temperature for 1 hour.

[0065] Grafting of crosslinked PDMA onto functionalized inert polymers and solid contact carbon. This procedure was similar to the bonding of surface initiators to inert polymers or solid contact carbon, except that 1.5 wt% of a crosslinking agent and 15 wt% or 50 wt% of decyl methacrylate were used in addition to 2,2-dimethoxy-2-phenylacetophenone (see Table 1 for concentrations).

[0066] Preparation of pH sensor membrane precursor solution. A solution for the fabrication of a PDMA membrane with a covalently bonded ionophore was prepared by mixing 1.5 wt% 2,2-dimethoxy-2-phenylacetophenone (photopolymerization initiator), 93 wt% decyl methacrylate, 1.5 wt% 1,6-hexanediol dimethacrylate (crosslinking agent), 4 wt% potassium tetrakis(pentafluorophenyl)borate (ionic moiety), and 2-(diisopropylamino)ethyl methacrylate (300 mol% relative to the ionic moiety, equivalent to 18.2 mg relative to 694.7 mg of other membrane components), which is a covalently bondable ionophore. No additional solvent was used.

[0067] Grafting of pH sensor membranes onto functionalized inert polymers and solid contact carbon. This procedure was similar to the binding of surface initiators to inert polymers and solid contact carbon, except that the pH sensor membrane precursor solution contained ionophores, monomers, and crosslinking agents in addition to the 2,2-dimethoxy-2-phenylacetophenone solution (see previous paragraph). A total of 30 μL (divided into portions of 10 μL, 10 μL, 5 μL, and 5 μL) of the membrane precursor solution was drop-cast onto polypropylene regions and nanographite pre-activated with surface initiators.

[0068] Grafting degree / grafting efficiency, and film thickness. The grafting degree, film thickness, and grafting efficiency were calculated as follows. Graft degree = (W1 - W0) / A (1) d = (W1 - W0) / (A DM) (2) Graft efficiency = (W1 - W0) / W2 (3) Here, d is the thickness of the covalent PDMA film, W0 is the weight of the unmodified polymer sheet, W1 is the weight of the polymer sheet having the covalent PDMA film or ion-selective film, A is the surface area, DM is the monomer density, and W2 is the theoretical weight increase expected if all polymerizable components (i.e., monomers, crosslinking agents, and covalently bondable ionophores, where applicable) deposited for the formation of the PDMA film or ion-selective film polymerize with 100% efficiency.

[0069] Potentiometric measurements were performed on a double junction reference electrode (DX200, Mettler Toledo, Switzerland) with a 3.00 M AgCl saturated KCl reference electrolyte and a 1.0 M KCl bridge electrolyte, using an EMF16 high-impedance voltmeter (Lawson Labs, Malvern, Pennsylvania, USA) controlled by EMF Suite 1.03 software, in a stirred solution. A pH glass electrode (InLab201, Mettler Toledo, Columbus, Ohio, USA) was used to separately determine the pH of the aqueous solution. To measure the pH response of ISE, the pH of a 10 mM pH 7.1 sodium phosphate buffer solution was varied by adding aliquots of 1 M NaOH or 1 M HCl. + , K + and Li + The selectivity coefficient for was measured using the fixed interference method (FIM) (E. Bakker, E. Pretsch, P. Buhlmann, Analytical Chemistry 2000, 72, 1127-1133). Long-term drift tests were performed in a temperature-controlled Faraday cage at 32°C, using capillary-based electrodes in 1.0 mM sodium phosphate buffer solution (EL Anderson, BK Troudt, P. Buhlmann, ACS Sensors 2021, 6, 2211-2217) or Ag-Cl coated Ag wire in 1.0 mM NaCl solution.

[0070] Electrode body. A cylindrical polypropylene-based electrode body was fabricated by molding a gold-coated stainless steel rod inside polypropylene. The metal rod protrudes slightly from the bottom of the cavity at the end of the electrode body (see Figure 5). This design has several advantages. Firstly, the gold pins, which protrude from the cavity but are recessed from the outermost end of the inert electrode body, are designed to be easily coated with nanographite not only from the top but also from the exposed sides, thereby increasing the surface area of ​​the contacts. Furthermore, as the temperature rises, the recessed sensor film is mechanically pressed against the sidewall of the cavity, adding mechanical stability, and as the temperature falls, the sensor film is firmly held by the pins, again adding mechanical stability. This mechanical robustness reinforces the strength obtained from the covalent bonding of the sensor film to polypropylene and nanographite.

[0071] Table 1. Formation of poly(decyl methacrylate) on a polypropylene substrate in a two-step process: (1) A 2,2-dimethoxy-2-phenylacetophenone (photopolymerization initiator) solution in a tetrahydrofuran or methanol solution was drop-cast onto the substrate, irradiated with UV light, and dried until a constant weight was achieved. (2) A decyl methacrylate solution in tetrahydrofuran or methanol was drop-cast onto a polypropylene sheet, irradiated with UV light again, and dried until a constant weight was achieved. Grafting degree, film thickness, and grafting efficiency were calculated from the weight difference before and after photografting. These are given as functions of the concentration of the photopolymerization initiator and the decyl methacrylate or ion-selective film component in each solution. [Table 1] a. The photograft solution contained a photopolymerization initiator, decyl methacrylate, and a crosslinking agent. b. The photograft solution contained a photopolymerization initiator, decyl methacrylate, a crosslinking agent, an ionophore, and an ionic moiety.

[0072] Table 2 shows the contact angles of H2O on unmodified polypropylene sheets and unmodified poly(ethylene-co-tetrafluoroethylene) films, as well as the contact angles of H2O on PDMA films bonded to polypropylene and poly(ethylene-co-tetrafluoroethylene). [Table 2] [Table 3]

[0073] Table 3 shows a comparison of the initial potentiometric response with the potentiometric response after 6 months in a 10 mM sodium phosphate buffer solution (pH 7.1), and with the potentiometric response after exposure to heat and pressure using an autoclave (121°C, 2.0 atm for 30 minutes) or 1 day of exposure to 10% by weight ethanol. [Table 4] a. Here, the operating range is determined by the intersection of the Nernst (linear) region and the constant (flat) emf region at the lower or upper detection limit.

Claims

1. An electrochemical sensor comprising an ion-selective film, an electrically nonconductive polymer substrate or electrode, and an underlying electron conductor, wherein the ion-selective film is covalently bonded to the electrically nonconductive polymer substrate or electrode and the underlying electron conductor.

2. The sensor according to claim 1, wherein the covalent chemical bond is characterized by photoinitiated surface functionalization and subsequent photoinitiated graft polymerization or thermally initiated graft polymerization.

3. The sensor according to claim 1, wherein the covalent chemical bonds to both the electrically nonconductive polymer substrate or electrode and the underlying electron conductor are the result of polymerization initiated by radicals formed by plasma treatment.

4. The radicals include argon, helium, oxygen, hydrogen peroxide, hydrogen, chlorine, and BCl. ３ HBr, tetrafluoromethane, fluoroform, CO ２ SF ６ The sensor according to claim 3, which is produced by a plasma treatment comprising pretreatment of the electrically nonconductive polymer substrate or electrode body and the underlying electron conductor with a plasma containing, fluorocarbon, or a mixture of the two thereof.

5. The sensor according to claim 4, wherein peroxide functional groups and hydroperoxide functional groups are formed on the surfaces of the electrically nonconductive polymer substrate or electrode body and the underlying electron conductor by subsequent exposure to oxygen or the ambient atmosphere.

6. The sensor according to claim 3, wherein the covalent chemical bond is characterized by graft polymerization, in which monomers are formed into a polymer by the deposition of liquid monomers or by gas-phase monomers introduced into the plasma treatment, and the polymer is covalently chemically bonded to the electrically nonconductive polymer substrate or electrode and the underlying electron conductor.

7. The ion-selective membrane is (i) selective for H ＋ and contains an ionophore that is selective for a primary amine, secondary amine, or tertiary amine, or a heterocyclic aromatic hydrocarbon that is either pyridine, quinoline, or phenanthrene, or (ii) doped with any ionophore having selectivity for a monovalent or polyvalent ion that is either Li ＋ , K ＋ , Na ＋ , Mg ２＋ , Ca ２＋ , Cl － , SO ４ ２－ , carbonate, or phosphate. The sensor according to claim 1.

8. The sensor according to claim 1, characterized in that the ion exchange capacity of the ion-selective membrane is due to the doping of an ionic moiety containing a tetraphenylborate group, a sulfonate group, or a sulfonylimide group.

9. The sensor according to claim 1, wherein the ion-selective membrane comprises an alkyl methacrylate homopolymer, an alkyl acrylate homopolymer, or a copolymer of two or more alkyl methacrylates or alkyl acrylates, which either does not contain a crosslinking agent or contains a crosslinking agent.

10. The sensor according to claim 1, characterized in that it does not exhibit a water layer effect.

11. The electrochemical sensor according to claim 1, wherein the ion-selective membrane comprises a polymer material, and the polymer material comprises polycarbonate, polystyrene, polyurethane, polyolefin, silicone, polyamide, polyester, polyether, polyimide, polysulfide, polycarbonate, polyacetal, polymethacrylate or polyacrylate, polyphenylene sulfide, polypropylene, polyethylene, poly(ethylene-co-tetrafluoroethylene), poly(tetrafluoroethylene), poly(vinyl chloride), polyvinylidene chloride, polyvinyl acetate, polyacrylonitrile, polyvinyl fluoride, or polyvinylidene fluoride.

12. A reference electrode comprising an ionic liquid-doped reference film, an inert plastic substrate, and an underlying electron conductor, wherein the ionic liquid-doped reference film is covalently bonded to both the inert plastic substrate and the underlying electron conductor.

13. The reference electrode according to claim 12, wherein the covalent chemical bond is characterized by photoinitiated graft polymerization.

14. The reference electrode according to claim 12, wherein the covalent chemical bond is characterized by radicals formed by plasma.

15. The reference electrode according to claim 14, characterized by pre-treating the inert plastic substrate and the underlying electron conductor with argon plasma, helium plasma, or oxygen plasma, and subsequently exposing them to oxygen or an ambient atmosphere to form peroxide functional groups and hydroperoxide functional groups on their surfaces.

16. The reference electrode according to claim 14, wherein the ionic liquid-doped reference film comprises a polymer formed by the plasma, and the plasma comprises monomers and / or other gases that are converted into reactive fragments to form the covalent chemical bonds.

17. The reference electrode according to claim 14, wherein the covalent chemical bond is characterized by radicals formed by thermal polymerization.

18. The reference electrode according to claim 12, wherein the ionic liquid-doped reference membrane comprises a polymer material, and the polymer material comprises polycarbonate, polystyrene, polyurethane, polyolefin, silicone, polyamide, polyester, polyether, polyimide, polysulfide, polycarbonate, polyacetal, polymethacrylate or polyacrylate, polyphenylene sulfide, polypropylene, polyethylene, poly(ethylene-co-tetrafluoroethylene), poly(tetrafluoroethylene), poly(vinyl chloride), polyvinylidene chloride, polyvinyl acetate, polyacrylonitrile, polyvinyl fluoride, or polyvinylidene fluoride.

19. The reference electrode according to claim 12, characterized in that it does not exhibit a water layer effect.

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