WO2024105528A1

WO2024105528A1 - Electropolymerization of pyrrole on gold (au) electrode

Info

Publication number: WO2024105528A1
Application number: PCT/IB2023/061417
Authority: WO
Inventors: Esma DERVISEVIC; Rita ROSHNI; Victor Javier Cadarso Busto; Sahan RANAMUKHAARACHCH
Original assignee: Proton Intelligence Inc.
Priority date: 2022-11-15
Filing date: 2023-11-12
Publication date: 2024-05-23

Abstract

A method of forming a polymerized transducer layer on an electrode and an electrode having a polymerized transducer layer. The electrodes are suitable for use in ion-selective applications. The method includes the steps of (i) forming a combination of an electrode having gold and an electropolymerization mixture. The electropolymerization mixture includes a doping agent and a monomer. The doping agent includes a benzenesulfonic acid having a benzene ring having an amine, a hydroxyl, and/or a methyl functional group, and/or a derivative of the benzenesulfonic acid. The monomer comprises a ring structure containing at least four Carbons (C) and at least one Nitrogen (N), Sulfur (S), and/or Oxygen (O). The method also includes the step of (ii) treating the combination formed in step (i) under electropolymerization conditions sufficient to oxidize the monomer and form polymer on the electrode.

Description

Title:

Electropolymerization of Pyrrole on Gold (Au) Electrode

Cross-Reference to Related Applications:

The present application claims priority to US Prov. Pat. App. Ser. No. 63/425,658 filed on November 15, 2022, is related to PCT/US2022/037198, and is related to PCT/US2022/052927, which are all incorporated herein by reference for all purposes.

Background of Invention:

Various polymers are reported for use in transducer layers for electrochemical sensors. Polypyrrole (PPy) is often selected due to its preferred properties which include high electrical conductivity, high stability at ambient conditions and high temperatures, and good redox properties. A number of electropolymerization methods in combination with different electropolymerization mixtures and different electrode materials are reported. The working electrode material affects the formation kinetics and adhesion of PPy film. Gold (Au) working electrodes have been found particularly troublesome. Improvements in this area are desired.

Summary of the Invention:

The present invention provides a method of forming a polymerized transducer layer on an electrode. The resulting electrodes are suitable for use in ion-selective applications such as ion-selective electrodes and/or sensors. The method includes the steps of forming a combination of an electrode having gold and an electropolymerization mixture. The electropolymerization mixture includes a doping agent and a monomer. The doping agent includes a benzenesulfonic acid wherein the benzene ring has an amine, a hydroxyl, and/or a methyl functional group, and/or a derivative of the benzenesulfonic acid. The monomer comprises a ring structure having at least four carbons (C) and at least one nitrogen (N), sulfur (S), and/or oxygen (O). The method also includes the step of treating the combination formed in step (i) under electropolymerization conditions sufficient to oxidize the monomer and form polymer on the electrode. An electrode formed from such methods is also provided preferably wherein the transducer layer comprises a detectable level of doping agent. Brief Description of the Figures:

Fig. 1 shows an overall reaction scheme of electrochemical polymerization of /?-TS doped PPy on a Au substrate.

Fig. 2 shows CV data from the examples of the invention.

Fig. 3 shows optical images of microelectrodes modified with p-TS-PPy shortly after the polymer deposition (fresh electrode) and 1 min after drop-casting THF (after THF exposure).

Fig. 4 shows optical images of microelectrodes modified with p-TS-PPy shortly after the polymer deposition (fresh electrode) and after exposing the electrode to a sticky tape (after sticky tape test).

Fig. 5 shows optical images of Au rod electrode (e.g. a macroelectrode (Au-RD)) modified with p-TS-PPy using our solution and three different methods shortly after polymer deposition (fresh electrode) and 1 min after drop-casting THF (after THF exposure).

Detailed Description of Invention:

It has herein been found that the material of the working electrode affects the electrochemical polymerization kinetics and adhesion of films containing specific polymers such as PPy. Gold working electrodes have been found to be troublesome and to resist formation of a thick and mechanically stable polymer layer (e.g. PPy). Without being bound by a particular mechanism of action this is believed to be due to: the low interfacial adhesion of polymers such as PPy to the underlying gold substrate, inability of the reaction mixture to covalently bond with the Au substrate, low surface energy of gold, and/or electrostatic interaction between the polymer (e.g. PPy) and the substrate. Prior art solutions to enhance adhesion via covalent bonding, such as adding functional groups like thiol to the reaction mixture [1] are not acceptable for certain electropolymerization methods since electrochemical cycling causes instability of the thiol functional groups. In addition, adherence improvement has been found to be dependent on the anion employed where the initial adsorption of counterions on the underlying electrode substrate appears to affect the nucleation process.

The present invention solves the above-identified problems and provides a method and electropolymerization reaction mixture that allows for robust formation of a conductive polymer (e.g. PPy) film with superior performance and adhesion properties on electrode surfaces, where the electrode comprises Au. In particular, the present Inventors have unexpectedly discovered that the electropolymerization of a Au-containing electrode in combination with specific polymerization mixtures which contain specific monomers and specific doping agents produce an electrode with robust and superior properties compared to those electropolymerized without the specific combination of monomer/doping agent. In particular, in the absence of specific doping agents, the resulting polymer film has less electrical conductivity and does not satisfactorily adhere to the Au-containing electrode when exposed to a tetrahydrofuran (THF) or to a sticky tape test. Furthermore, it has unexpectedly been found that the size of the working electrode affects adhesion characteristics of the resulting conductive polymer film. For example, when microelectrodes are used, the specific polymer film (e.g. p-TS-PPy film) is resistant to THF exposure whilst when a macroelectrode is used specific polymer films (e.g. p-TS-PPy) obtained using chronoamperometry (CA) and chronopotentiometry (CP), and not that obtained with cyclic voltammetry (CV), can resist the THF test.

Definitions:

As used in the specification and claims of this application, the following definitions, should be applied.

"a", "an", and "the" as an antecedent refer to either the singular or plural. For example, "a compound", “a polymer”, “a monomer”, etc. refers to either a single species or a mixture of like and/or unlike species unless the context indicates otherwise.

The electrode preferably comprises, consists of, or consists essentially of gold. Gold may be present in/on the electrode as a surface coating optionally combined with other materials and/or disposed a similar or dissimilar conductive material(s), and/or the entirety of the electrode may be formed of gold such as a gold rod or wire etc.

The reaction mixture described herein may be present in the form of a mixture or more preferably as a solution. The reaction mixture comprises a monomer to be polymerized and a doping agent. The reaction mixture may also comprise additional components known in the art for facilitating the chemical reactions or modifying properties of the resulting polymer or reaction substrate. These additional components are not limited herein and contain such things as catalyst, pH modifiers, electrolytes and/or salts (e.g. KC1, NaCl or the like), polymer characteristics modifiers, and the like.

The “monomer” comprises a chemical having a ring structure containing at least four carbons (C) and at least one nitrogen (N), and/or sulfur (S), and/or oxygen (O), and/or the like. The monomer is present in a positively charged oxidized form during electropolymerization process. The preferred monomers of the present application are useful for forming polymers such as polypyrrole, polyaniline, polythiophene, and poly(3,4- ethylenedi oxy thiophene). These monomers include without limitation pyrrole, aniline, thiophene, and 3, 4-ethylenedi oxythiophene.

The “doping agent” (e.g. preferably /?-TS) comprises a benzenesulfonic acid, or a derivative thereof (e.g. a benzenesulfonic acid in salt and/or polymer forms etc.). The benzenesulfonic acid preferably includes a chemical having a benzene ring which preferably contains any, or a combination of, functional groups such as amine, hydroxyl, or methyl. In preferred embodiments, the doping agent comprises /?-toluenesulfonic acid (/?-TS) and is present in the result polymer as /?-toluenesulfonic acid (/?-TS).

A “microelectrode” is an electrode with a planar or three-dimensional surface typically having dimensions in the range of about 1 pm to 1000 pm, a thickness up to about 1000 pm, and a surface area in a range of about 1 pm² to 10⁶ pm². A microelectrode can be obtained by means of conventional thin film fabrication techniques on a substrate coated with an electrically insulating material, or on an electrically insulating substrate including magnetron sputtering, atomic layer deposition, pulsed laser deposition, chemical vapor deposition, electrospray deposition, electrochemical deposition, sol-gel deposition, molecular precursor-based deposition, and alike with or without an intermediate adhesion promotion layer between the substrate and Au such as Cr, Ti, or alike.

A “macroelectrode” is a planar or three-dimensional electrode typically having dimensions in the range of about 1000 pm to 10 cm and a surface area in the range of about 0.01 cm² to 100 cm². A macro-electrode can be a piece of pure Au mounted on a conductive metal and embedded in an electrically insulating material such as polycarbonate, teflon, and alike.

Reference throughout the specification to “one embodiment,” “another embodiment,” “an embodiment,” “some embodiments,” and so forth, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described element(s) and/or feature(s) of any embodiment may be combined in any suitable manner with any other described embodiments.

Numerical values in the specification and claims of this application reflect average values. Furthermore, unless indicated to the contrary, the numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

Electropolymerization and Reaction Mixture s Melhods:

Electrochemical polymerization (e.g. electropolymerization) is a well-known coating procedure where a conducting polymer is formed from a monomer-containing reaction mixture (e.g. polymerization reaction mixture) onto a conducting substrate. The applied potential is selected such that it is high enough to oxidize the monomer for polymerization, but low enough not to dissolve or corrode the conductive substrate. Electropolymerization is typically performed in an electrochemical cell having a combination of the substrate to be coated as a working electrode and an inert material(s) employed as counter electrode(s). The polymerization reaction mixture typically contains the monomer, a solvent, and a supporting electrolyte. There are at least three different electropolymerization techniques including potentiodynamic, galvanostatic, and potentiostatic electropolymerization.

In potentiodynamic electropolymerization (i.e. cyclic voltammetry, CV), a cyclic regular sweep of potential is performed between the limits of the monomer oxidation and the reduction of the polymerized conducting polymer. The growing polymer film continuously changes from a neutral state to a doped (or conducting) state as the potential is cycled back and forth. This process is accompanied by the continuous absorption and desorption of the electrolyte and the solvent to stabilize the growing film. Where polymerization is conducted via cyclic voltammetry the following conditions can be employed: an applied potential in a range of equal to or between -10.0 to +10.0 V, for example -2.0 to +2.0 V, more preferably - 1.0 to +1.5 V, for example, 0.0 to +1.0 V; a number of potential scanning cycles in the range of equal to or between 1 to 1000, more preferable 1 to 100, for example 3; and a potential scan rate in the range of equal to or between 1 to 300 mV/s, more preferably 10 to 200 mV/s, for example 100 mV/s.

In galvanostatic electropolymerization (chronopotentiometry, CP) constant current is applied to polymerize the conducting polymer at a constant rate. At the beginning of the electropolymerization, the potential rises for a short period and then decreases after a while. The initial increase in potential is brought about by the formation of the redox-active charged oligomers in front of the electrode. The subsequent decrease in the potential is brought about by the catalytic effect of the charged oligomers to oxidize the monomers. The measured potential also depends on the temperature — the measured potential decreases with decrease in temperature. This can be explained by the decrease of the volume of the solvent, which consequently increases the concentration of the monomer as the temperature decreases. Where polymerization is conducted via chronopotentiometry the following conditions can be employed: an applied current in the range of equal to or between 0 to 100 mA, more preferably 0 to 5 mA, for example 0.2 mA; and a current application time in the range of equal to or between 0 to 3600 s, more preferably 0 to 600 s, for example 10 s.

In potentiostatic electropolymerization (e.g. chronoamperometry, CA) application of potential remains constant and the rate of polymerization is controlled depending on the applied potential. This method is similar to the galvanostatic electropolymerization and is different to potentiodynamic electropolymerization because no material is discharged from the deposited film during the coating procedure. Where polymerization is conducted via chronoamperometry the following conditions can be employed: an applied potential in the range of equal to or between -10.0 to +10.0 V, for example -2.0 to +2.5 V, more preferably 0.0 to +1.5 V, for example +0.8 V; and an potential application time in the range of equal to or between 0 to 3600 s, more preferably 0 to 600 s, for example 20 s.

Again, electropolymerization of specific monomers such as pyrrole (Py) can be facilitated by electrochemical methods where application of potential allows for the oxidation of monomers and their subsequent growth in the form of polymer on the anode surface (here on the electrode containing gold). The present Inventors have discovered however that, during the polymerization, a doping agent containing larger dopant anion molecules (e.g. such as sulfonates) can be added to the monomer reaction mixture, which unexpectedly decreases the distortion of polymer chains such as polypyrrole (PPy) and makes bipolaron movements easier and that addition of these doping agents to the reaction mixture allows for formation of a robust polymer transducer layer on electrodes containing gold.

Where the doping agent comprises -TS, which is resistant to overoxidation and can be used in electrode applications, a polymer such as /?-toluene sulfonic acid-doped polypyrrole (/?-TS-PPy) can be obtained facilitating excellent adhesion of the polymer thin film to the Au electrode. Fig. 1 shows the overall polymerization scheme of electrochemical polymerization of -TS doped PPy on a Au substrate.

Without being bound by a particular mechanism of action it is believed that during electrochemical polymerization, PPy along with a negatively charged doping agent (e.g. preferably /+TS) anion is formed. It is further believed that since the Au substrate is positively charged, this develops a strong electrostatic interaction between the negatively charged /?-TS anion which as a result promotes adhesion of PPy. The use of these doping agents (e.g. such as /?-TS) not only facilitates adhesion of /?-TS-PPy to Au substrate but also enhances the electron transfer kinetics of the resulting electrode surface.

The presence of the above-described doping agent (e.g. preferably /?-TS) within the reaction mixture and resulting polymer improves adhesion to Au electrode surface. Such benefits are not limited to reaction mixtures for polymerization of pyrrole for forming PPy but can include polymerization reaction mixtures containing other electropolymerized forms of monomers which contain a ring structure containing at least four carbons (C) and at least one nitrogen (N), and/or sulfur (S), and/or oxygen (O), and/or the like, which produces positively charged oxidized forms during electropolymerization process. Accordingly, additional reaction mixtures (e.g. polymerization mixtures) within the scope of the present application include monomers for forming polymers such as polyaniline, polythiophene, and poly (3 , 4-ethy 1 enedi oxy thi ophene) etc .

In a further embodiment, the resulting electrodes have gold and a polymerized transducer and are suitable for use in ion-selective monitoring and/or determination applications and preferably have an ion-selective membrane (ISM) disposed over and/or in contact with the transducer layer. In such embodiments, the method further comprises the step of forming an ion-selective membrane over the polymerized transducer layer on the electrode. Polymeric ion-selective membranes are incorporated in the solid-state ion- selective electrodes for the purpose of generating electrochemical signal caused by the selective ion transport through the ISM. The methods of forming and components of the ion- selective layer are not particularly limited and are preferably those as described in US Prov. App. Ser. No. 63/291,804, which is incorporated herein by reference for all purposes.

The Transducer /Polymer Layer and Formed Electrode:

The resulting polymer layer formed from the herein described reaction mixtures and methods contains a detectable level of doping agent (e.g. preferably /?-Ts). For example, a 1/10 ratio of doping agent (e.g. /?-TS)/monomer (e.g. Py) in the electrochemical polymerization reaction mixture can produce doping agent-polymer film (e.g. /?-TS-PPy film) well-adhering to a Au electrode when containing ~2% mol ratio of doping agent to monomer (e.g. /?-TS over Py). Determination/estimation of these ratios can be performed using EDX. For example, the ratio of Sulphur (S) over Nitrogen (N) can be taken as reference given that each can only be present because of the incorporation of the doping agent and pyrrole monomer, respectively into the resulting polymer transducer layer. The doping agent/monomer (e.g. -TS/Py) molar range in the electropolymerization solution can be between 1/100 to 10/1 of -TS/Py. The detectable level of doping agent in the resulting polymer can be determined by known methods of evaluating of samples. In preferred embodiments, the detectable level of doping agent in the resulting polymer produced from a reaction mixture according to the present invention is determined by Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) Spectroscopy, UV absorption spectroscopy, energy dispersive X-ray (EDX or EDS), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, Gas Chromatography, Atomic Emission Spectrometry, Optical Emission Spectrometry, and Thermogravimetric Analysis (TGA).

The present invention provides a combination of a gold electrode and polymerization mixture containing specific monomers and specific doping agents. In the absence of the specific doping agent, the resulting polymer thin film has less electrical conductivity and does not adhere well to the Au working electrode when exposed to a tetrahydrofuran (THF) or to a sticky tape test. In addition, the size of the working electrode affects the adhesion of the resulting conductive polymer film. When microelectrodes are used, the /?-TS-PPy film is resistant to THF exposure whilst when a macroelectrode is used (large Au rod electrode), p- TS-PPy obtained using chronoamperometry (CA) and chronopotentiometry (CP), and not that obtained with cyclic voltammetry (CV), can resist the THF test.

In certain embodiments, the polymerized transducer layers can be removed in a solution containing ammonium hydroxide, hydrogen peroxide (active reagent), and water (1 :2: 10 mL, respectively) at 60 °C and not at room temperature.

Examples:

Without being bound by a particular mode of operation and without limiting the invention, the following examples are provided to illustrate the invention.

Electropolymerization solution:

PPy is conventionally obtained using a reaction mixture/solution containing Py monomer in the presence of a supporting electrolyte such as KC1 (potassium chloride) or NaCl (sodium chloride) or tetrabutylammonium perchlorate when in;

1. Distilled water or,

2. pH buffer solution such as phosphate-buffered saline or,

3. An organic solvent such as acetonitrile or,

4. A strong acid such as 1 M HC1. A preferred electropolymerization mixture/ solution contemplated by the present invention is aqueous and contains Py monomer, NaCl and the doping agent />-TS.

Method:

PPy is electrochemically formed using three electropolymerization techniques: potentiodynamic (cyclic voltammetry, CV); potentiostatic (chronoamperometry, CA); and galvanostatic (chronopotentiometry, CP). All three methods produce a -TS-PPy film well adhering to a gold microelectrode and the latter two techniques to a gold macro-electrode, when employing the preferred electropolymerization reaction mixture/solutions of the present invention.

Chemicals and electrodes:

1. Silver/Silver chloride (Ag/AgCl) pseudo-reference electrode (pRE) a. A Ag wire with 1 mm diameter was incubated in 0.25 M iron chloride (FeCh) containing 0.20 M hydrochloric acid (HC1) for 16 h.

2. Working electrode a. A 100 nm thick Au microelectrode was obtained via standard photolithography method with a 10 nm Chromium (Cr) adhesive layer. The width and length of the working electrode is 55 pm and 500 pm, respectively. Surface area: 0.0275 mm². b. The macro-electrode used is Au rod electrode (Au-RD) with a circular working electrode area of 3 mm in diameter. Surface area: 28.3 mm². c. Prior to use, the working electrode was electrochemically cleaned in 0.5 M (sulfuric acid) H2SO4.

3. Redox mediator a. 5 mM of potassium hexacyanoferrate (III) (I<3[Fe(CN)<>]) prepared in 0.1 M KC1.

4. Pyrrole polymerization solution a. Our solution: 10 mM NaCl aqueous solution containing 100 mM pyrrole and 100 mM p-TS. b. i. Method for polymerization

1. Potentiostatic (CA): +0.8 V, 20 s.

2. Potentiodynamic (CV) [REF:, (-1.0 to +1.0 V), 3 cycles, scan rate 0.1 V/s scan rate. c. Comparative example solution 1 [REF : https://link.springer.eom/article/10.1023/A:10106224225611: lO mM NaCl solution containing 100 mM pyrrole. i. Method for polymerization

1. CA: +0.8 V, 20 s.

2. CV: (0.0 to +1.1 V), 3 cycles, 0.1 V/s scan rate. d. Comparative example solution 2 [REF : https://www.sciencedirect.com/science/article/abs/pii/S09277757120073887vi a%3Dihub]: 100 mM Py in 50 mM of phosphate-buffered solution (PBS), pH 7.0, with 0.1 M KC1. i. Method for polymerization

1. CV: (0.0 to +1.1 V), 3 cycles, 0.1 V/s scan rate, followed by CA at +0.8 V for 20 s.

2. CV: (0.0 to +1.1 V), 3 cycles, 0.1 V/s scan rate, followed by CA at +1.0 V for 1 s, repeated for 20 times. e. Comparative example solution 3 [REF : 100 mM Pyrrole in acetonitrile

containing 100 mM tetrabutylammonium hexafluorophosphate (TBAPFe), 1 % (v/v) HC1, and 1 % (wt/wt) water. i. Method for polymerization

1. CA: +0.8 V, 20 s.

2. CP: 200 pA, 10 s (200pA/2 mC).

Results:

Fig. 2 shows CV data collected with Au microelectrodes coated with a polymer when using our solution, or three different comparative example solutions in [Fe(CN)6]³'^/4‘ redox marker solution. The CV plot obtained with a bare Au microelectrode before and after electropolymerization is labeled as “a” and “b”, respectively.

Figure 2 A represents the chronoamperometric signal recorded during electropolymerization of -TS-PPy on Au microelectrode. The effect of deposited film on the electrochemical conductivity was analyzed using [Fe(CN)6]³'^/4‘ redox and CV technique. A significant increase in the oxidation and the reduction peak currents after electropolymerization are clearly observed in Figure 2B. The electrode surface turns into a black color after /?-TS-PPy deposition.

The use of our solution allows for the formation of an electrochemically conductive p- TS-PPy layer when using CV or CA or CP. The presence of /?-TS increases the amount of the hydrophilic groups (sulfonic acid) available at the electrode surface and hence an increased electron transfer rate can be obtained, results of which are presented in Figure 2A&B. Comparative example solution 1, regardless of the electropolymerization method, resulted in a significantly less electrochemically conductive PPy layer as shown in Figure 2C,D. It can be concluded that the use of comparative example solution 2 has created an electrically insulating layer given the decrease in the CV peak current levels, Figure 2E&F. The use of comparative example solution 3 has created an insulating layer when implementing CA (Figure 2G). The use of comparative example solution 3 with CP resulted in a PPy film with increased oxidation and reduction peak currents when compared to the bare Au microelectrode. However, the CV profile shown in Figure 2H indicates that the obtained PPy film has stored capacitive charge which results in a capacitive transducer layer. This type of transducer is not suitable for potentiometric ion-selective sensing applications.

Testing the adhesion of polypyrrole

THF is an organic solvent commonly used in the preparation of ion- selective membrane cocktails. Figure 3 shows an optical image of /?-TS-PPy-coated microelectrodes before and after drop-casting THF, and wiping the surface with a tissue. The -TS-PPy obtained when using CV or CA shows excellent adhesion properties after being exposed to THF. PPy film obtained in comparative example solution 3 also shows good adhesion properties when exposed to THF.

Figure 3 shows optical images of microelectrodes modified with /?-TS-PPy shortly after the polymer deposition (fresh electrode) and 1 min after drop-casting THF (after THF exposure).

The second adhesion test was performed by visually inspecting the PPy films after a sticky tape was placed on, and removed from, the microelectrode surface. /?-TS-PPy film was the only polymer film which remained 100% intact after the sticky tape test as shown in Figure 4, in contrast to the -30% remaining intact CA-based PPy film obtained using comparative example solution 3. Figure 4 shows optical images of microelectrodes modified with /?-TS-PPy shortly after the polymer deposition (fresh electrode) and after exposing the electrode to a sticky tape (after sticky tape test).

Effect of working electrode size on p-TS-PPy adhesion

The effect of the working electrode size on the adhesion of the -TS-PPy was investigated using a Au rod electrode (Au-RD, diameter of 3 mm) and three electropolymerization methods (CV, CA, CP). When using a microelectrode, both CV and CA-based depositions result in a THF-resistant polymer film on Au microelectrodes. However, when the working electrode surface area increases to 28.3 mm², the use of only CA and CP produces a THF-resistant /?-TS-PPy film with -99% and -97% post THF exposure surface coverage rate, respectively. CV-based -TS-PPy formation was not strong enough to resist THF exposure resulting in -50% /?-TS-PPy film removal after the THF exposure as shown in Figure 5.

Conventionally, increasing electrode surface area is expected to increase surface roughness and hence polymer adhesion. However, the THF adhesion test conducted with Au macro-electrode indicates that /?-TS-PPy obtained using CV does not adhere as well as that formed on a Au microelectrode. This might be attributed to lower film thickness obtained with the same number of CV cycles and therefore lower /?-TS ratio per surface area. The number of applied CV scans can be inversely correlated with the polymer film adhesion. This is due to reducing the polymer back to its initial state during reverse scan, which has poorer electrostatic interaction with negatively charged -TS and thus adhesion to the Au surface.

Conclusion:

The overall conclusion is that the proposed method when combined with the proposed electropolymerization solution allows the formation of a conductive -TS-PPy film with outstanding adhesion properties on Au micro- and macro-electrode.

REFERENCES:

The following references are incorporated herein by reference for all purposes.

[1] Robert J. Willicut and Robin L. McCarley. Electrochemical Polymerization of Pyrrole- Containing Self-Assembled Alkanethiol Monolayers on Au J. Am. Chem. SOC. 1994,116, 10823- 10824.

Claims

CLAIMS:

1. A method of forming a polymerized transducer layer on an electrode:

(i) forming a combination of an electrode and an electropolymerization mixture, wherein: the electrode comprises gold (Au), the electropolymerization mixture comprises a doping agent and a monomer, the doping agent comprises a benzenesulfonic acid having a benzene ring having an amine, a hydroxyl, and/or a methyl functional group, and/or a derivative of the benzenesulfonic acid, and the monomer comprises a ring structure containing at least four Carbons (C) and at least one Nitrogen (N), Sulfur (S), and/or Oxygen (O), and

(ii) treating the combination formed in step (i) under electropolymerization conditions sufficient to oxidize the monomer and form polymer on the electrode, thereby forming a polymerized transducer layer on the electrode.

2. The method of claim 1, further comprising the step of:

(iii) forming an ion-selective membrane over the polymerized transducer layer on the electrode.

3. The method of any one of claims 1 or 2, wherein the monomer is selected from the group consisting of pyrrole, aniline, thiophene, 3, 4-ethylenedi oxythiophene.

4. The method of any one of claims 1 to 3, wherein the doping agent comprises /?-TS, the monomer comprises pyrrole, and the polymer comprises polypyrrole.

5. The method of any one of claims 1 to 4, wherein the mol ratio of doping agent/monomer (e.g /?-TS/pyrrole) in the polymerization mixture is in a range of equal to or between 1/100 and 10/1 preferably in a range of equal to or between 1/50 and 5/1, more preferably in a range of equal to or between 1/20 and 2/1, for example 1/10.

6. The method of any one of claims 1 to 5, wherein the electropolymerization conditions are selected from the group consisting of: potentiodynamic (cyclic voltammetry); potentiostatic (chronopotentiometry), and galvanostatic (chrono-amperometry).

7. The method of any one of claims 1 to 6, wherein the electrode has a surface area equal to or between 1 pm² to 10⁶ pm² (e.g. a micro electrode) or wherein the electrode has a surface area equal to or between 0.01 cm² to 100 cm².

8. The method of any one of claims 1 to 7, wherein the polymerization is conducted via cyclic voltammetry under the following conditions: an applied potential in a range of equal to or between -10.0 to +10.0 V, for example -2.0 to +2.0 V, more preferably -1.0 to +1.5 V, for example, 0.0 to +1.0 V; a number of potential scanning cycles in the range of equal to or between 1 to 1000, more preferable 1 to 100, for example 3; and a potential scan rate in the range of equal to or between 1 to 300 mV/s, more preferably 10 to 200 mV/s, for example 100 mV/s.

9. The method of any of claims 1 to 7, wherein the polymerization is conducted via chronoamperometry under the following conditions: an applied potential in the range of equal to or between -10.0 to +10.0 V, for example -2.0 to +2.5 V, more preferably 0.0 to +1.5 V, for example +0.8 V; and an potential application time in the range of equal to or between 0 to 3600 s, more preferably 0 to 600 s, for example 20 s.

10. The method of any of claims 1 to 7, wherein the polymerization is conducted via chronopotentiometry under the following conditions: an applied current in the range of equal to or between 0 to 100 mA, more preferably 0 to 5 mA, for example 0.2 mA; and a current application time in the range of equal to or between 0 to 3600 s, more preferably 0 to 600 s, for example 10 s.

11. The method of any of claims 1 to 7, wherein the electrode has a surface area equal to or between 0.01 cm² to 100 cm² and the polymerization conditions are selected from the group consisting of chronopotentiometry and chronoamperometry.

12. An electrode comprising a polymerized transducer layer, wherein the electrode is produced by the method of any one of claims 1 to 11.

13. An electrode comprising gold (Au) and a polymerized transducer layer having a detectable level of doping agent (e.g. /?-toluenesulfonic acid (/?-TS)).

14. The electrode of claim 12 or 13, wherein the polymerized transducer layer incorporates a mol ratio of doping agent (e.g. /?-TS) over the monomer (e.g. pyrrole) in a range of equal to or between 1/1000 to 1/10, more preferably 1/100 to 1/25, for example 1/50.

15. The electrode of any one of claims 12 to 14, wherein the polymerized transducer layer is resistant to mechanically removal using a sticky tape and/or to the exposure of organic and inorganic solvents selected from the group consisting of tetrahydrofuran, dimethyl sulfoxide, dimethyl formamide, ethanol, acetone, and isopropanol at ambient temperatures.

16. The electrode of any one of claims 12 to 15, further comprising: an ion-selective membrane disposed over the polymerized transducer layer on the electrode.

17. The electrode of any one of claims 12 to 16, wherein the polymer is selected from the group consisting of polypyrrole, polyaniline, polythiophene, poly3,4-ethylenedi oxythiophene.

18. The electrode of any one of claim 12 to 17, wherein the doping agent comprises /?-TS and the polymer comprises polypyrrole.

19. An ion-selective electrode comprising gold (Au), a polymerized transducer layer having a detectable level of doping agent (e.g. /?-toluenesulfonic acid (/?-TS)), and an ion-selective membrane disposed over the polymerized transducer layer on the electrode.