TW202311738A - Binder and salt system for solid contact ion selective electrode - Google Patents

Abstract

Aspects concern a layer structure for an ion selective electrode sensor, the layer structure comprising: a layer structure (100) for an ion selective electrode sensor (200), the layer structure (100) comprising: an ion selective membrane (110); a solid contact layer (120); an electrical conductor (130) disposed on an electrode (140), for connecting to an electronic circuit (150), wherein the solid contact layer (120) is disposed between the ion selective membrane (110) and the electrical conductor (130); wherein the ion selective membrane (110) and the solid contact layer (120) comprise a same organic salt (160); and wherein the solid contact layer (120) further comprises a matrix-polymer (170).

Description

Binder and Salt System for Solid Contact Ion Selective Electrode

Aspects of the invention relate to a layer structure for an ion selective electrode sensor. Aspects of the invention also relate to an ion-selective electrode sensor and a method of fabricating a layer structure for an ion-selective electrode sensor.

Ion selective electrode (ion selective electrode; ISE) is a convenient device for ion determination and measurement, and solid contact ISE (solid contact ISE; SC-ISE) provides convenience in its storage and use. However, since the SC layer is easily affected by solvent dissolution, the potential reproducibility between electrodes of SC-ISE with ion selective membrane (ion selective membrane; ISM) is poor.

Therefore, there is a need to provide an improved SC-ISE.

Various specific examples relate to a layer structure for an ion-selective electrode sensor, the layer structure comprising: an ISM; an SC layer; a conductor disposed on the electrode for connecting an electronic circuit; wherein the SC layer is disposed between the ISM and the conductor between bodies; wherein the ion-selective membrane and the solid contact layer comprise the same organic salt; and wherein the solid contact layer further comprises a matrix polymer.

Various embodiments relate to an ion selective electrode sensor comprising: a substrate; a layer structure as defined above disposed on a first portion of the substrate; a reference electrode disposed on a second portion of the substrate.

Various embodiments relate to a method of manufacturing a layer structure for an ion-selective electrode sensor as defined above, the method comprising: disposing an electrical conductor on an electrode; disposing a solid contact layer comprising the same organic salt and a matrix polymer On the electrical conductor; disposing an ion selective membrane comprising the same organic salt from a solution comprising an organic solvent and a membrane precursor on the disposed solid contact layer to form a layered structure.

The present invention relates to a layer structure 100 for an ion-selective electrode sensor 200 . Layer structure 100 includes ISM 110 . The layer structure 100 includes an SC layer 120 . The layer structure 100 includes an electrical conductor 130 arranged on an electrode 140 . The conductor 130 is disposed on the electrode 140 for connecting the electronic circuit 150 . The SC layer 120 is disposed between the ISM 110 and the electrical conductor 130 . The ion selective membrane 110 and the SC layer 120 include the same organic salt 160 . The SC layer 120 includes a matrix polymer 170 .

In conventional SC-ISE, a salt is introduced into the SC layer to generate a defined electrochemical potential between the SC layer and the ISM. If the composition of the SC layer and the ISM can be sufficiently controlled, the boundary potential E _PB between these two phases can be reproducibly established on a large number of identically fabricated electrodes. This results in SC-ISE showing a high reproducibility of its standard potential E ₁₀ ^when measured against a common reference electrode. Poor reproducibility between individual electrodes is a common phenomenon known in the art today. However, this issue remains unresolved since individual electrodes are usually calibrated before use. This standard procedure mitigates electrode-to-electrode variability since the calibration curve of individual electrodes is studied just before use. However, the calibration of individual SC-ISEs does not scale well if a large number of electrodes needs to be measured. Additionally, the calibration step increases the potential for operator error. Therefore, reproducible electrodes allow multiple measurements with reduced calibration. This simplifies measurement protocols, reducing the possibility or error and reducing operator training costs.

A cross-section of the potential distribution within the SC-ISE is shown in Figure 1 plot A. In order to achieve reproducible potentials with a standard deviation of 2 to 3 mV within a batch of electrodes, a uniform, defined interface potential between the electrodes should be formed between phases (1) and (2).

Salt is incorporated into the SC layer (2) and the ISM (1) as shown in Figure 1, Panel B. This results in the electrochemical potential between the SC and ISM phases being uniform across the electrodes. This is reflected in the potential reproducibility when readings are taken in sample solutions of the same concentration using a batch of electrodes.

However, during SC-ISE fabrication, the ISM is dissolved in an organic solvent such as tetrahydrofuran (THF). During the deposition of ISM in an organic solvent (ISM mixture; ISM cocktail) on the SC layer, the salt component contained in the SC layer can be easily dissolved into the ISM mixture. This can cause two problems. The first is that the enrichment of salts in ISM may negatively affect its properties. In the case of salts as cation exchangers, uncontrolled partitioning of such salts to the ISM disturbs the ratio of ion exchangers to ionophores in the ISM, resulting in worsening selectivity coefficients or lower detection limits. Furthermore, uncontrolled dissolution of part of the SC layer may introduce process dependence of SC-ISE since the speed and extent of dissolution may vary with environmental parameters. This results in reproducibility that may not be reproducible between batches or between laboratories, e.g. poor standard potential reproducibility of ±90 to 110 mV and 40±10 m V dec despite using similar components SC-ISE with bad slope of ^-1 . This effect is demonstrated in Example 8, illustrating the susceptibility of organic salts to organic solvents.

The layer structure 100 for ion-selective electrode sensors as described herein relieves each electrode by dissolving the same organic salt 160 in a matrix polymer 170 that is not only inert, but acts as a binder. poor reproducibility between. In particular, the mitigation of poor reproducibility between the various electrodes is believed to be a synergistic effect of the organic salt 160 with the matrix polymer 170 and the same organic salt 160 otherwise used in the SC layer 120 and the ISM 110 .

Specifically, an organic salt 160 (e.g. a lipophilic salt such as tetradecylammonium tetrakis(4-chlorophenyl)borate (ETH 500)) is completely dissolved in a matrix polymer 170 (e.g. a fluoropolymer such as PVDF) . Due to the solvent-resistant properties of the matrix polymer 170, the SC layer 120 resists dissolution by organic solvents during ISM cocktail deposition. Upon deposition, the reproducible potential is maintained until the time the deposited solvent evaporates into air.

Thus, when the SC layer 120 is used to fabricate a batch of SC-ISEs, the activity of free ions can be determined by matching the measured voltage to the activity on a calibration curve. It can be used when SC-ISE is placed in a solution containing some target ion activity. In addition, the calibration curve can be highly similar across electrodes, thereby reducing the need for calibration. By using it with an ISM composition containing the same organic salt 160, reproducible potentials for various ions can be obtained.

As used herein, "ion selective membrane (ISM)" refers to the ISM 110 that forms the outermost layer of the SC-ISE. ISM 110 controls sensitivity and selectivity to target ions. ISM 110 may include a polymer matrix, which may be hydrophobic. The polymer matrix can support additional components such as plasticizers, organic salts 160 and/or ionophores. The polymer matrix may comprise polyvinyl chloride, optionally in a weight percentage of about 1 wt % to about 50 wt % (relative to the total weight of the ISM 110 ), optionally in a weight percentage of about 10 wt % to about 40 wt %, Optionally about 20 wt % to about 35 wt %, optionally about 32.5 wt %. The ISM 110 may include a plasticizer, optionally in a weight percentage of about 50 wt% to about 90 wt%, optionally in a weight percentage of about 60 wt% to about 80 wt%, optionally in a range of about 65 wt% to about 70 wt% % by weight, optionally about 65% by weight. A non-limiting example of a plasticizer may be any suitable plasticizer compatible with polyvinyl chloride, such as DOS. Plasticizers increase diffusivity, thereby increasing the ionic conductivity of the ISM 110 .

ISM 110 may include ionophores. Ionophores can facilitate the selective diffusion of target ions in the sample into and/or out of the ISM 110, or the ionophores can be disposed in the ISM 110 where the ionophores can facilitate the selective diffusion of target ions in the sample into and/or out of the ISM 110 ISM 110. Ionophores may include, for example, valinomycin. Ionophores such as valinomycin may have a loading rate of about 1 wt% in the ISM 110. Ionophores can selectively bind target ions and can help transport them across the membrane to SC layer 120 .

As used herein, "organic salt" refers to a compound including cations and anions, wherein at least one of the cations or anions, preferably both, include or consist essentially of organic components. An organic component may refer to a component that includes at least one carbon-hydrogen covalent bond. Since the organic salt 160 includes an organic component, it may be lipophilic in nature, at least more lipophilic than the inorganic salt, which is typically a hydrophilic salt. Advantageously, when the same organic salt 160 is used in both the ISM 100 and the SC layer 120, the membrane charge transfer resistance can be reduced.

Advantageously, because organic salt 160 is substantially lipophilic, at least one process step during SC-ISE equilibration can be avoided, saving time. In particular, the preparation of electrodes usually includes an equilibration process in solution before taking measurements. Many processes can occur before the electrodes are considered sufficiently balanced. In these processes, saturation of the electrodes (for those with hydrophilic salts) with water is the only requirement. Therefore, SC-ISE with organic salts can bypass this requirement, which is useful in cases where water saturation is the limiting step. In contrast, in more detail, when a hydrophilic salt is mixed in the SC layer, the electrode absorbs water through the ISM when the SC-ISE is in contact with an aqueous sample. Water absorption has been found to be necessary to obtain stable and reproducible potentials across multiple devices. This occurs when water passes through the ISM and seeps into the hydrophilic regions within the SC layer. When this happens, a state of equilibrium can be reached due to the entry of water within the SC-ISE resulting in a supersaturated solution of primary ions in the SC layer. The concentration of primary ion salts within the SC layer at the solubility limit forms a controlled boundary potential with the ISM which also has a defined primary ion concentration depending on the concentration and ratio of ionophores and cation or anion exchangers it contains . However, to achieve this state, the SC-ISE needs to be immersed in an aqueous solution for a period of time before reaching equilibrium. This is attributed to the SC layer needing to be saturated with water. The use of primary ion salts also means that if the SC-ISE is ion-exchanged with the sample solution for a long time, the equilibrium state may change. This is because if the primary ions in the SC layer are depleted, the long-term exchange may cause its overall composition to change.

According to various embodiments, organic salt 160 may include an alkyl chain, such as a carbon-containing moiety. These carbon-containing moieties may be linear or branched, substituted or unsubstituted, and are derived from hydrocarbons, typically by replacing one or more carbon atoms with other atoms, such as oxygen, nitrogen, sulfur, phosphorus, or Functional groups of oxygen, nitrogen, sulfur and phosphorus. The carbon-containing moiety may comprise any number of carbon atoms, but preferably has a molecular weight above 500 g/mol or above 800 g/mol.

In a preferred embodiment, the carbon-containing moiety can be a linear or branched, substituted or unsubstituted alkyl group with 5 to 20 carbon atoms; a linear or branched chain with 5 to 20 carbon atoms , substituted or unsubstituted alkenyl; straight or branched, substituted or unsubstituted alkynyl having 5 to 20 carbon atoms; straight or branched or branched, substituted or unsubstituted alkynyl having 5 to 20 carbon atoms Substituted or unsubstituted alkoxy; substituted or unsubstituted cycloalkyl having 5 to 20 carbon atoms; substituted or unsubstituted cycloalkenyl having 5 to 20 carbon atoms; having 5 substituted or unsubstituted aryl groups having up to 20 carbon atoms; and substituted or unsubstituted heteroaryl groups having 5 to 20 carbon atoms. Advantageously, when the number of carbon atoms in the alkyl chain is very high, the lipophilicity can be very high, which is more favorable for SC-ISE for reasons detailed above.

The organic moiety may also be a combination of any of the groups defined above, including, but not limited to, alkylaryl, aralkyl, alkylheteroaryl, etc., to name a few, all of which may be substituted or unsubstituted. In general, organic salt 160 can be any substantially lipophilic salt that exhibits solubility in both SC layer 120 and ISM 110 . For example, it may also be a cation or anion exchanger, or similar salts containing bulky cations and anions may also be incorporated into the SC layer 120 . The organic salt 160 should be sufficiently lipophilic so that the presence of ionophores in the ion-selective membrane does not cause exchange of the charged salt with primary ions from the aqueous sample when ions from the sample enter the membrane through the sensing process. This will maintain the long-term functionality of the system.

In some embodiments, organic salt 160 may have a molecular weight greater than 500 g/mol, preferably greater than 1000 g/mol, and optionally up to 5000 g/mol. Advantageously, when the molecular weight is very high, the lipophilicity can be very high because more "organic matter" is provided relative to the charge of the organic salt 160 . For the reasons detailed above, high lipophilicity is more favorable for SC-ISE as described above. In one example, Organic Salt 160 is ETH 500.

Matrix polymer 170 is a highly dense, crystalline polymer and exhibits resistance to solvent attack. The matrix polymer 170 may function to stabilize the potential, contrary to the behavior of an inert adhesive. The advantages of this additional functionality were mentioned earlier in this article. Matrix polymer 170 may comprise a polymer such as polyetheretherketone, polyacrylate that is additionally crosslinked after being deposited, or the like.

According to various embodiments, the matrix polymer 170 may be a fluoropolymer. A fluoropolymer may be any polymer containing elemental fluorine. Fluorine can be covalently bonded to the carbon backbone. Fluoropolymers may comprise interpolymerized monomeric units. Units may be derived from monomers. The monomer may include fluorine. The monomers may be selected from tetrafluoroethylene, difluoroethylene or combinations thereof. In one embodiment, the fluoropolymer is PVDF.

Advantageously, because the fluoropolymer includes fluorine, the fluoropolymer is substantially resistant to dissolution in a range of organic solvents including THF. Since the fluoropolymer is not easily soluble in organic solvents and supports the organic salt 160 as a binder or matrix, it may be beneficial to prevent the organic salt 160 from leaching from the SC layer 120 .

Since the matrix polymer 170 retains the organic salt in the SC layer 120, the amount of the organic salt 160 in the SC layer 120 can be reduced to less than 5 wt% of the total weight of the SC layer 120, or even less than the total weight of the SC layer 120. 1% by weight. It is advantageous to have a lower weight percent of organic salt 160 present in SC layer 120 because this further reduces the likelihood of organic salt 160 dissolving into the ISM mixture.

Although a lower weight percent of the organic salt 160 in the SC layer 120 is advantageous, the upper limit of the weight percent of the organic salt 160 in the SC layer 120 can be prevented by the solubility of the organic salt 160 in the matrix polymer 170 and the polymer during the manufacturing process. The ability to uncontrolled segregation into the ISM 110 is determined.

As shown in FIG. 2, the layer structure 100 may include three functional layers. According to some embodiments, these three layers may be disposed (eg, supported) on a substrate 210 , as shown in FIG. 3 , for forming the ion-selective electrode sensor 200 . In these embodiments, ISM 110 and substrate 210 may be the only portions of the sensor that are in contact with the sample solution. The electrical contact between the electrical conductor 130 and the electronic circuit 150 can be insulated, and the electronic circuit 150 can be an external potentiometer for measuring against a standard reference electrode.

The SC layer 120 can operate at near zero current (~10 ⁻¹² A) and can be capacitively coupled to the ISM 110 . The ionic current through the ISM 110 can be converted to an electronic current that can be measured by a standard potentiometer. The SC layer 120 may include polyaniline (PANI), poly-3-4-ethylenedioxythiophene polystyrene sulfonate (PEDOT:PSS), carbon material, poly(octylthiophene), polypyrrole, or combinations thereof. In one example, SC layer 120 includes a carbon material.

As used herein, the term "solid" has its normal meaning when used in the term "solid contact (SC) layer", thus including the resistance to exhibiting (significant) structural rigidity and to changes in shape or volume. A reference to a composition or substance (such as a non-flowing substance). In particular, the term "solid" may refer to a substance characterized by its resistance to penetration. The term "solid" is understood to exclude hydrogels.

The SC layer 120 may have a first main side and a second main side, wherein the second main side is opposite to the first main side. The first and second major sides of the SC layer 120 refer to the two largest surfaces of the layer. In particular, the layers typically extend in two directions (perpendicular to each other), while having a thickness in a direction perpendicular to the two directions in which the layers extend. The two surfaces extending into two directions are referred to herein as the first main side and the second main side. The distance between the two surfaces of the first main side and the second main side may refer to the thickness of the SC layer 120 .

The layer structure 100 according to the invention may be configured in such a configuration that the SC layer 120 faces (eg contacts) the porous ISM 110 with its first main side. The ISM|SC interface as used herein may thus be positioned on the first main side of the SC layer 120 . The SC layer 120 may have its second main side facing the electrical conductor 130 .

The SC layer 120 may have a thickness of about 0.1 μm (micrometer) to about 10 μm, or about 0.5 μm to about 5 μm, or about 0.8 μm to about 2 μm, or about 1 μm.

Conductor 130 may form an ohmic electrical contact between SC layer 120 and the wires to the potentiometer. The conductor 130 may include silver.

According to various embodiments shown in FIG. 3 , an ion-selective electrode sensor 200 is provided. The ion selective electrode sensor 200 includes a substrate 210 . Ion-selective electrode sensor 200 includes layer structure 100 disposed on a first portion of substrate 210 as described herein. The ion selective electrode sensor 200 includes a reference electrode 220 disposed on a second portion of the substrate 210 . The ion-selective electrode sensor 200 may not include an opposing electrode. Advantageously, an opposing electrode is not necessary for this ion-selective electrode sensor, since it operates at effectively zero current (10 ⁻¹² A). Only working and reference electrodes can be used.

The material for each electrode can be independently selected from, but not limited to, metals such as gold, silver, nickel, titanium, platinum. Alternatively, the material for each electrode can be independently selected from polymers, including poly(3,4-ethylenedioxythiophene), poly(thiophene), polyaniline, polypyrrole. Polymers may also be referred to as "conductive polymers". There are advantages when using conducting polymers as direct contact with ion selective membrane electrode materials due to their redox capacitance. In particular, the additional redox capacitance provided by the conducting polymer resists the polarization of the interface, thereby improving the stability of the electrode response. For metals to play a similar role in the robustness of processing conductive polymers, it may be beneficial to deposit a lipophilic monolayer prior to contact with the membrane, as this reduces water and gas interference.

According to various embodiments, there is provided a method of fabricating a layer structure for an ion selective electrode sensor 300 as described herein. Method 300 includes step 310 of disposing electrical conductor 130 on electrode 140 . Method 300 includes a step 320 of disposing an SC layer including organic salt 160 and matrix polymer 170 on electrical conductor 130 . The method 300 includes a step 340 of disposing an ISM comprising an organic salt 160 on the disposed SC layer 120 from a solution comprising a solvent and a film precursor to form the layer structure 100 .

SC layer 120 may be prepared by dissolving matrix polymer 170 and organic salt 160 in a solvent system prior to disposing solid contact layer 120 on electrical conductor 130 . Fillers can be added to the solvent system. Advantageously, the filler can be conductive, which can facilitate an ohmic connection to the electrical conductor 130 . In particular, the filler may be one or more carbon materials, optionally selected from the group consisting of carbon black, carbon nanotubes, carbon fibers, graphene, graphene oxide, graphite, carbon mesosphere, and combinations thereof. After deposition on the electrical conductor 130 , relatively low temperatures (<100° C.) may be applied to cure the SC layer 120 . Additionally or alternatively, the temperature used may be as high as the thermal stability of any component. Accordingly, method 300 may include a step 330 of heating the disposed SC layer.

"Heating" refers to deliberately raising the temperature of a solution containing solvent and film precursor. Heating thus may involve raising the temperature above room temperature. In various embodiments, heat is dissipated from the oven. Heating may involve heating the disposed SC layer 120 to a temperature of at least 40°C. Heating may involve heating the disposed SC layer 120 to a temperature of at least 40°C, or to the boiling point of the solvent.

As used herein, "room temperature" refers to a temperature greater than 4°C, preferably in the range of 15°C to 40°C, or in the range of 15°C to 30°C, or in the range of 20°C to 30°C C range, or within the range of 15°C to 24°C, or within the range of 16°C to 21°C, or around 25°C. Such temperatures may include 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C and 25°C, each of which includes ±0.5°C.

The film precursor may have the same composition as previously described in the context of ISM 110 .

The electrode 140 may advantageously have a planar form so that the electrical conductor 130, the SC layer 120 and the ISM 110 can be easily disposed on the electrode 140 by drop casting or screen printing. Accordingly, each of the ISM 110, SC layer 120, and electrical conductors 130 are advantageously suitable for large-scale manufacturing methods, such as screen printing, and the SC-ISE can be printed on planar substrates. Additionally, electrodes 140 may be placed on the heating element for the heating step.

The solvent system may contain organic solvents. The solvent system may be capable of dissolving the matrix polymer 170, the organic salt 160 and the filler. The solvent of the solvent system may be selected from the group consisting of tetrahydrofuran, propylene carbonate, cyclohexanone, cyclopentanone, or combinations thereof.

Step 340 of disposing ISM 110 from solution may be repeated about 1 to 10 times, or 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 times.

The specific examples described in the context of the layer structure 100 or the ion-selective electrode sensor 200 are similarly valid for the method of fabricating the layer structure for the ion-selective electrode sensor 300 . Likewise, specific examples described in the context of a method of fabricating a layer structure for ion-selective electrode sensor 300 are similarly valid for layer structure 100 or ion-selective electrode sensor 200 , and vice versa.

Features described in the context of one embodiment can be correspondingly applied to the same or similar features in other embodiments. Features described in the context of an embodiment can correspondingly be applied to other embodiments even if not explicitly described in those other embodiments. In addition, additions and/or combinations and/or substitutions described for features in the context of specific examples can be correspondingly applied to the same or similar features in other specific examples.

The articles "a, an" and "the" used in reference to a feature or element in the context of various instances include reference to one or more features or elements.

As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. Example

Example 1 - Electrode selection:

Screen-printed carbon bonded to silver was chosen as the substrate electrode.

Purchase electrodes from commercial sources with the design shown in Figure 4. Both the working electrode and the dummy reference electrode are located on the same electrode.

The electrodes have a planar form factor that enables modification by drop casting or screen printing. The diameter of the working electrode is 4 mm, and only the working electrode is used for measurement.

Example 2 - ISM Choice:

The choice of ISM material was about 33 wt% PVC and 66 wt%/film weight composition. More specifically, the ISM composition was selected for the K ⁺ membrane: 32.5 wt% PVC, 1 wt% valinomycin, 65.1 wt% DOS, 1 wt% ETH 500, 0.5 wt% tetrakis (4-chlorophenyl) Potassium borate, 1 wt% valinomycin. The composition of the ISM was selected for the H ⁺ membrane: 31.6 wt% PVC, 65.3 wt% DOS, 1.2 wt% potassium tetrakis (4-chlorophenyl) borate (KtClPB), 3.9 wt% tridodecylamine. The ISM composition was selected for anion selective membrane: 33 wt% PVC, 65 wt% DOS, 1 wt% ETH 500, 1 wt% tridodecylmethylammonium chloride.

For the H ⁺ membrane composition without ETH 500, the cation exchanger KtClPB contains a common anion, tetra(4-chlorophenyl) borate, which also leads to a defined interfacial potential.

As a model system, a film mixture of K ⁺ ISM was used to show the reproducibility of the potential between electrodes during the casting process. The ISM component was dissolved in the solvent THF at 200 mg of the membrane component per mL of solvent. When a batch of three bare SC layers was inserted, the potential measured against the Ag/AgCl line showed a standard deviation of 2.6 mV, maintaining high reproducibility, as shown in FIG. 5 .

For each membrane mixture, the concentration of the membrane components in THF was maintained at 200 mg mL ⁻¹ , and two 20 μL deposits were drop-cast on the bare SC layer.

Example 3-SC layer selection:

The SC layer consists of several components. Conductive filler for ohmic connection to electrical contacts, binder to resist solvent intrusion and maintain controlled lipophilic salt composition, and controlled concentration of lipophilic salt to form a defined boundary with the ISM potential.

During the preparation of the SC layer, the binder was first prepared by mixing 50 mg PVDF with 0.75 mL each of THF and propylene carbonate. It was mixed overnight in a glove box at a temperature of 70°C.

Then 250 mg graphite, 5 mg carbon black and 1.5 mg ETH 500 were added to the mixture and stirred at 70°C for 20 minutes. This was followed by a further 10 min stirring step at room temperature and the mixture was allowed to stand for 10 min.

4 μL of the supernatant was then aspirated and deposited on a silver screen-printed electrode with a diameter of 4 mm. The electrodes were then placed in an oven at 50 °C for 30 min, and then the temperature was raised to 70 °C for 60 min.

Example 4 :material selection

Carbon black and graphite were chosen as inexpensive, abundant fillers. The particulate nature of the filler also allows the manufacture of inks suitable for screen printing.

ETH 500 was chosen because it is soluble in the adhesive. This is shown in the differential scanning calorimetry results in Fig. 6, when ETH 500 was loaded into PVDF at 3 wt%, its melting peak disappeared, the same proportion as in the SC layer.

PVDF was chosen for the above reasons because of its ability to maintain its integrity in contact with DOS and THF. This resulted in high reproducibility of potentials when batches of electrodes with the proposed SC were inserted into a solvent containing 1 wt% ETH 500, as shown in Fig. 7A and Fig. 7B. Comparing Figures 12A and 12B, the SC layer with PVDF binder can maintain potential reproducibility in both DOS and THF compared to the SC layer with PVC binder in DOS only.

Example 5 : Selection of electrical contacts:

Silver is a proven conductive ink suitable for screen printing and is stable at the potentials and temperatures experienced during the measurements.

Example 6 : Minimum amount of lipophilic salt required for potential reproducibility

Figure 8 shows the minimum concentrations of organic salts in the A: ISM and B: SC layers required for good reproducibility of the potential in a batch of electrodes. For each potential trace, a batch of three electrodes was inserted into the DOS and their potential was measured against the Ag/AgCl wire. When ETH 500 in DOS was varied, SC contained 0.5 wt% of ETH 500, and when ETH 500 in SC was varied, DOS contained 1 wt% of ETH 500.

observe

Highly reproducible potentials with a standard deviation of less than 3 mV were observed for ETH 500 at ≥0.2 wt% in DOS and ≥0.5 wt% in the SC layer.

A batch of bare SC layers containing only carbon and binder without ETH 500 exhibited poor reproducibility with a standard deviation of >12 mV.

One batch of bare Ag electrodes measured in DOS resulted in interfacial blockage with little charge transfer. The high impedance of the system makes it susceptible to environmental electrical noise, resulting in oscillatory signals seen in the batch of electrodes.

discuss / in conclusion

From the reproducibility of the potential it can be deduced that ETH 500 can be switched between the proposed SC layer and the DOS phase of the contact. When sufficient ETH 500 is present in both DOS and SC, cations and anions become potential-determining species for the entire SC|DOS interface, resulting in reproducible potentials due to the controlled composition of ETH 500 in each phase. Comparing this with the results in Figure 5, the potential is preserved even though the surrounding matrix (THF) also contains other ions such as K ⁺ cation and Si[3,5-bis(trifluoromethyl)phenyl]borate anion. Reproducibility.

Due to the ability of ETH 500 to transfer between SC and DOS, it is expected that other charged species such as anion or cation exchangers may also exhibit similar transfer. Therefore, further optimization of the system may require finding an equilibrium concentration of all charged species in the SC and ISM to achieve a stable and reproducible potential between electrodes.

Example 7 : Reproducibility of calibration curves between batches of SC-ISE

Figure 9 shows the SC-ISE in response to K ⁺ , anions and H ⁺ made from the proposed SC layer containing 0.5 wt% ETH 500. High reproducibility of the standard potential _E0 was achieved over three or four electrode sets, as predicted by the evidence shown during testing of bare SC layers. The slopes recorded for K ⁺ and Cl ^- in the 10 ^-1 to 10 ^-4 M ion range show good linearity, extending the linear range to 10 ^- compared to the reduced high detection limit of SC-ISE proposed by the prior art ¹ M.

Example 8 : Explanation of common knowledge SC layer solvent sensitivity

Figure 11 depicts a conventional embodiment of a conventional SC layer 120a, showing a conventional ion selective electrode sensor 200a comprising a conventional SC layer 120a, a conventional electrical conductor 130a disposed on a conventional substrate 210a. Conventionally, ISMs are formed on SC-ISEs by depositing an ISM mixture on top of an existing SC layer. This ISM mixture consists of solid components dissolved in an organic solvent, usually tetrahydrofuran (THF). After deposition, the device was left to evaporate the solvent. During this time, solvent exposure of the SC layer may result in dissolution of some or all of the SC layer.

This phenomenon is shown in the case of an SC layer 120a composed of lipophilic salt ETH 500, polyvinyl chloride (PVC), graphite and carbon black.

Three identical electrodes were inserted into THF (Figure 12A) or DOS (Figure 12B) each containing 1 wt% ETH 500. The standard deviation of the potential measured for the Ag/AgCl wire was recorded within 600 seconds after immersion.

A clear difference in potential reproducibility between the two sets of electrodes can be seen. Electrodes in DOS showed higher reproducibility over time than electrodes in THF. The reproducibility of electrodes in THF also varies greatly over the time scale of the measurement. This is due to the interaction between PVC and two organic liquids. Although DOS is a plasticizer, it will not change the volume of PVC in a short contact time, but PVC is easily corroded by THF solvent.

While a stable ETH 500 composition in the electrode and surrounding matrix is sufficient to define the electrode|matrix boundary potential, this boundary potential cannot be observed if the electrode material is susceptible to solvent attack. If this happens, the electrodes may disintegrate, boundary potentials become difficult to define, and potentials between electrodes become difficult to reproduce.

For SC-ISEs with SC layers susceptible to solvent dissolution, the lack of defined interfacial potential due to dissolution of the SC layer by the ISM mixture results in poor inter-electrode potential reproducibility.

A set of SC layers (n = 4) presented in Fig. 11 shows poor potential reproducibility when these are used to fabricate a set of K ⁺ selective SC-ISEs. Calibration curves showing the response of the electrode in 10 ^-1 to 10 ^-4 M KCl solutions are shown in Figure 12C. According to the Nernst equation, an uncertainty of 1 mV corresponds to a 4% error in the determination of the ionic activity of a monovalent ion. Therefore, a change of ±8.8 mV introduces more error than is acceptable in many sensing use cases, and switching from one electrode to the other requires calibration.

Furthermore, the slope shows a significant deviation (>5% deviation) from the expected Nernstian response of 59.2 mV dec ^-1 , which may indicate that charge transfer within the SC-ISE is hampered by kinetic processes and does not fully respect the thermodynamic value.

While the invention has been particularly shown and described with reference to particular embodiments, it should be understood by those skilled in the art that changes may be made in the form and scope thereof without departing from the spirit and scope of the invention as defined by the appended claims. Various changes were made to the details. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

The present invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and accompanying drawings, wherein: [FIG. 1] is a schematic diagram showing: A: Segmented potential diagram of a SC-ISE with three layers , showing the potential of each layer of ISM (1), SC layer (2) and conductor (3); and B: a diagram showing the charge exchange between the three layers of SC-ISE, where organic salts (cations and anions) are in the SC layer and ISM, wherein I+ represents primary ions; [Fig. 2] is a side view of a layered structure according to some embodiments; [Fig. 3] is a side view of an SC-ISE architecture according to some embodiments; [Fig. 4] is Schematic diagram of screen-printed electrodes; [Fig. 5] is a graph showing the standard deviation of three electrodes immersed in a membrane mixture (cocktail) of K ⁺ ISM, in which the components were dissolved in THF at a concentration of 200 mg mL ^-1 ; [Fig. 6] is a graph showing comparative differential scanning calorimetry traces of polyvinylidene difluoride (PVDF) as a powder as it is, cast as a film, or loaded with 3 wt% ETH 500, including pure ETH 500 Traces; [Fig. 7A] is a graph showing the potential reproducibility of a set of (n=3) solid contacts in THF with 1 wt% ETH 500; [Fig. A graph of the potential reproducibility of a group (n=3) of solid contacts in dioctyl sebacate (DOS); [Figure 8A] shows the potential reproducibility of a batch (n=3) of bare solid contacts in DOS Figure 8, in which the concentration of ETH 500 in DOS was varied, so that the ETH 500 in the solid contact was kept at 0.5 wt%; [Fig. 8B] shows the potential reproducibility of batches (n=3) of bare solid contact in DOS Figure 9, wherein the concentration of ETH 500 in the solid contact is varied, and ETH 500 is kept at 1 wt% in DOS; [ ^Fig . - a graph of the ISE; [ FIG. 9B ] is a graph showing the SC-ISE in response to anions made with an SC layer according to some embodiments; [ FIG. 9C ] is a graph showing the response to anions made with an SC layer according to some embodiments. [ ^FIG . 10] is a flow chart illustrating a method for fabricating a layer structure for an ion-selective electrode sensor; [FIG. 11] showing the SC layer 120a of a conventional SC-ISE 200a , conductor 130a and substrate 210a; [FIG. 12A] is a graph showing the potential reproducibility of a group (n=3) of bare solid contacts in THF with 1 wt% ETH 500; [FIG. 12B] is a graph showing Graph showing the potential reproducibility of a set (n = 3) of bare solid contacts in DOS with 1 wt% ETH 500; and [Fig. 12C] showing a set (n = 4) of electrodes with the SC layer introduced in Fig. 11 A graph of the calibration curve of K ⁺ SC-ISE was made.

100: layer structure

110:ISM

120: SC layer

130: Conductor

Claims (12)

A layer structure (100) for an ion-selective electrode sensor (200), the layer structure (100) comprising: ion selective membrane (110); solid contact layer (120); an electrical conductor (130) disposed on an electrode (140) for connecting an electronic circuit (150), wherein the solid contact layer (120) is disposed between the ion selective membrane (110) and the electrical conductor (130); wherein the ion selective membrane (110) and the solid contact layer (120) comprise the same organic salt (160); and Wherein the solid contact layer (120) comprises a matrix polymer (170). The layer structure (100) of claim 1, wherein the same organic salt (160) has a molecular weight higher than 500 g/mol. The layer structure (100) of claim 1 or 2, wherein the matrix polymer (170) is a fluoropolymer. The layer structure (100) of claim 3, wherein the fluoropolymer (170) is a polymer of monomer units derived from the interpolymerization of monomers, the monomers comprising tetrafluoroethylene and/or difluoroethylene ( vinylidene difluoride). The layer structure (100) according to any one of claims 1 to 3, wherein the ion-selective membrane (110) comprises polyvinyl chloride. The layer structure (100) according to any one of claims 1 to 4, wherein the ion-selective membrane (110) comprises ionophores. The layer structure (100) of any one of claims 1 to 5, wherein the electrical conductor (130) comprises silver. An ion selective electrode sensor (200) comprising: substrate (210); a layer structure (100) according to any one of the preceding claims arranged on the first part of the substrate (210); and A reference electrode (220) is disposed on the second portion of the substrate (210). A method of manufacturing a layer structure according to any one of claims 1 to 7 for an ion-selective electrode sensor (300), the method comprising: (310) disposing the conductor (130) on the electrode (140); (320) disposing a solid contact layer (120) comprising the same organic salt (160) and matrix polymer (170) on the electrical conductor (130); and ( 340 ) Disposing an ion selective membrane ( 110 ) comprising the same organic salt ( 160 ) on the disposed solid contact layer from a solution comprising an organic solvent and a membrane precursor to form a layer structure ( 100 ). The method of claim 9, further comprising mixing the matrix polymer (170) with the same organic salt (160) and filler in a solvent system before disposing the solid contact layer (120) on the conductor. The method according to claim 10, wherein the filler comprises carbon material. The method according to any one of claims 9 to 11, wherein the step of disposing the ion-selective membrane (110) from solution is repeated for a number selected from 1 to 10 times.

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