Name: electrochemical preparation of poly(3,4-ethylenedioxythiophene) layers on gold microelectrodes for uric acid-sensing applications
Uploaded: 2021-07-28T15:00:00
Description: Watch this Scientific Journal Video about Electrochemical Preparation of Poly3,4-Ethylenedioxythiophene Layers on Gold Microelectrodes for Uric Acid-Sensing Applications at JoVE.com

Thanks to the funding provided by the New Zealand Ministry of Business, Innovation and Employment (MBIE) within the &#34;High Performance Sensors&#34; program.

1. Preparing analytical solutions
<ol>
	<li>Preparing 0.1 M EDOT in an organic solution
	<ol>
		<li>Weigh out 0.213 g of LiClO4 and transfer it into a 20 mL volumetric flask.</li>
		<li>Use a measuring cylinder to take 20 mL of PC from the bottle.</li>
		<li>Add PC to the 20 mL volumetric flask containing LiClO4. Mix the solution by placing the flask in an ultrasonic bath for 30 min. Transfer the solution to a 20 mL glass vial.</li>
		<li>Cover the vial with aluminum foil and insert a long needle ...

<ol>
	<li>Guimard, N. K., Gomez, N., Schmidt, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conducting+polymers+in+biomedical+engineering.">Conducting polymers in biomedical engineering.</a> Progress in Polymer Science. 32 (8), 876-921 (2007).</li><li>Cui, X., Martin, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+deposition+and+characterization+of+poly(3,4-ethylenedioxythiophene)+on+neural+microelectrode+arrays.">Electrochemical deposition and characterization of poly(3,4-ethylenedioxythiophene) on neural microelectrode arrays.</a> Sensors and Actuators B: Chemical. 89 (1), 92-102 (2003).</li><li>Hong, S. Y., Marynick, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+conformational+stability+and+electronic+structures+of+modified+polymers+based+on+polythiophene.">Understanding the conformational stability and electronic structures of modified polymers based on polythiophene.</a> Macromolecules. 25 (18), 4652-4657 (1992).</li><li>Kundu, K., Giri, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+of+the+electronic+structure+of+cyclic+polythiophene+upon+bipolaron+doping.">Evolution of the electronic structure of cyclic polythiophene upon bipolaron doping.</a> Journal of Chemical Physics. 105 (24), 11075-11080 (1996).</li><li>Thomas, C. A., Zong, K., Schottland, P., Reynolds, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(3,4-alkylenedioxypyrrole)s+as+highly+stable+aqueous-compatible+conducting+polymers+with+biomedical+implications.">Poly(3,4-alkylenedioxypyrrole)s as highly stable aqueous-compatible conducting polymers with biomedical implications.</a> Advanced Materials. 12 (3), 222-225 (2000).</li><li>Yamato, H., Ohwa, M., Wernet, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stability+of+polypyrrole+and+poly(3,4-ethylenedioxythiophene)+for+biosensor+application.">Stability of polypyrrole and poly(3,4-ethylenedioxythiophene) for biosensor application.</a> Journal of Electroanalytical Chemistry. 397 (1-2), 163-170 (1995).</li><li>Latonen, R. -. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(3,4-ethylenedioxythiophene)+based+enzyme-electrode+configuration+for+enhanced+direct+electron+transfer+type+biocatalysis+of+oxygen+reduction.">Poly(3,4-ethylenedioxythiophene) based enzyme-electrode configuration for enhanced direct electron transfer type biocatalysis of oxygen reduction.</a> Electrochimica Acta. 68, 25-31 (2012).</li><li>Liu, K., Xue, R., Hu, Z., Zhang, J., Zhu, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+synthesis+of+acetonitrile-soluble+poly(3,4-ethylenedioxythiophene)+in+ionic+liquids+and+its+characterizations.">Electrochemical synthesis of acetonitrile-soluble poly(3,4-ethylenedioxythiophene) in ionic liquids and its characterizations.</a> Journal of Nanoscience and Nanotechnology. 9 (4), 2364-2367 (2009).</li><li>Cui, X., Martin, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fuzzy+gold+electrodes+for+lowering+impedance+and+improving+adhesion+with+electrodeposited+conducting+polymer+films.">Fuzzy gold electrodes for lowering impedance and improving adhesion with electrodeposited conducting polymer films.</a> Sensors and Actuators A: Physical. 103 (3), 384-394 (2003).</li><li>Wilks, S. J., Richardson-Burn, S. M., Hendricks, J. L., Martin, D., Otto, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(3,4-ethylene+dioxythiophene)+(PEDOT)+as+a+micro-neural+interface+material+for+electrostimulation.">Poly(3,4-ethylene dioxythiophene) (PEDOT) as a micro-neural interface material for electrostimulation.</a> Frontiers in Neuroengineering. 2, 7 (2009).</li><li>Pranti, A. S., Schander, A., B&#246;decker, A., Lang, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+stable+PEDOT:PSS+coating+on+gold+microelectrodes+with+improved+charge+injection+capacity+for+chronic+neural+stimulation.">Highly stable PEDOT:PSS coating on gold microelectrodes with improved charge injection capacity for chronic neural stimulation.</a> Proceedings. 1 (4), 492 (2017).</li><li>&#352;tul&#237;k, K., Amatore, C., Holub, K., Marecek, V., Kutner, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microelectrodes:+Definitions,+characterization,+and+applications+(Technical+report).">Microelectrodes: Definitions, characterization, and applications (Technical report).</a> Pure and Applied Chemistry. 72 (8), 1483-1492 (2000).</li><li>&#352;tul&#237;k, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+solid+electrodes.">Activation of solid electrodes.</a> Electroanalysis. 4 (9), 829-834 (1992).</li><li>Motshakeri, M., Travas-Sejdic, J., Phillips, A. R. J., Kilmartin, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+electroanalysis+of+uric+acid+and+ascorbic+acid+using+a+poly(3,4-ethylenedioxythiophene)-modified+sensor+with+application+to+milk.">Rapid electroanalysis of uric acid and ascorbic acid using a poly(3,4-ethylenedioxythiophene)-modified sensor with application to milk.</a> Electrochimica Acta. 265, 184-193 (2018).</li><li>Motshakeri, M., Phillips, A. R. J., Travas-Sejdic, J., Kilmartin, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemical+study+of+gold+microelectrodes+modified+with+PEDOT+to+quantify+uric+acid+in+milk+samples.">Electrochemical study of gold microelectrodes modified with PEDOT to quantify uric acid in milk samples.</a> Electroanalysis. 32 (9), 2101-2111 (2020).</li><li>Motshakeri, M., Phillips, A. R. J., Kilmartin, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+cyclic+voltammetry+to+analyse+uric+acid+and+reducing+agents+in+commercial+milks.">Application of cyclic voltammetry to analyse uric acid and reducing agents in commercial milks.</a> Food Chemistry. 293, 23-31 (2019).</li></ol>

The CV method allows for fast and simple measurement of different analytes in foods, wine and beverages, plant extracts, and even biological samples. This technique produces a wide variety of data, including oxidation/reduction peak potentials, peak current values of the target analyte (proportional to concentration), and all other current and potential values after each CV run. Although using CV is relatively easy, the collected data sometimes need to be converted from Binary files to Text Comma format, depending on the...

Electrically conducting polymers are organic materials widely used in bioelectronic devices to improve interfaces. Similar to conventional polymers, conducting polymers are easy to synthesize and are flexible during processing1. Conducting polymers can be synthesized using chemical and electrochemical methods; however, electrochemical synthesis approaches are particularly favorable. This is mainly due to their ability to form thin films, allow simultaneous doping, capture molecules in the conducting polymer, and most importantly, the simplicity of the synthesis process1. In addition, conducting polymers form uniform, fibrous, and bumpy nanostructures, firmly adherent to the electrode surface, which increases the active surface area of the electrode2.
In the 1980s, certain polyheterocycles, such as polypyrrole, polyaniline, polythiophene, and PEDOT, were developed that showed good conductivity, ease of synthesis, and stability3,4. Although polypyrrole is better understood than other polymers (e.g., polythiophene derivatives), it is prone to irreversible oxidation5. Thus, PEDOT has certain advantages over the rest as it has a much more stable oxidative state and retains 89% of its conductivity compared to polypyrrole under similar conditions6. In addition, PEDOT is known for high electroconductivity (~500 S/cm) and a moderate band gap (i.e., band gaps or energy gaps are regions with no charge and refer to the energy difference between the top of a valence band and the bottom of a conduction band)7.
Furthermore, PEDOT has electrochemical properties, needs lower potentials to be oxidized, and is more stable over time than polypyrrole after being synthesized7. It also has good optical transparency, which means its optical absorption coefficient, especially in the form of PEDOT-polystyrene sulfonate (PEDOT-PSS), is in the visible region of the electromagnetic spectrum at 400-700 nm7. In the formation of PEDOT electrochemically, EDOT monomers oxidize at the working electrode to form radical cations, which react with other radical cations or monomers to create PEDOT chains that deposit on the electrode surface1.
Different controlling factors are involved in the electrochemical formation of PEDOT films, such as electrolyte, electrolyte type, electrode setup, deposition time, dopant type, and solvent temperature1 PEDOT can be generated electrochemically by passing current through an appropriate electrolyte solution. Different electrolytes such as aqueous (e.g., PEDOT-PSS), organic (e.g., PC, acetonitrile), and ionic liquids (e.g., 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4)) can be used8.
One of the advantages of PEDOT coatings is that it can significantly decrease the impedance of a Au electrode in the 1 kHz frequency range by two or three orders of magnitude, which makes it helpful to increase the sensitivity of direct electrochemical detection of neural activity9. Moreover, the charge storage capacity of the PEDOT-modified electrodes increases and results in faster and lower potential responses when stimulation charge is transferred through PEDOT10. In addition, when polystyrene sulfonate (PSS) is used as a dopant for PEDOT formation on Au microelectrode arrays, it creates a rough, porous surface with a high active surface area, lower interface impedance, and higher charge injection capacity11. For the electropolymerization step, EDOT-PSS usually makes a dispersion in an aqueous electrolyte.
However, EDOT is soluble in chloroform, acetone, ACN, and other organic solvents such as PC. Therefore, in this study, a mixture of water was used with a small volume of ACN in a 10:1 ratio to make a soluble EDOT solution before electropolymerization starts. The purpose of using this aqueous electrolyte is to omit the acclimatization step in the preparation of PEDOT-modified microelectrode and shorten the steps. The other organic electrolyte used to compare with the aqueous/ACN electrolyte is PC. Both electrolytes contain LiClO4 as a dopant to help in oxidizing the EDOT monomer and forming the PEDOT polymer.
Microelectrodes are voltammetric working electrodes with smaller diameters than macroelectrodes, approximately tens of micrometers or less in dimension. Their advantages over macroelectrodes include enhanced mass transport from the solution toward the electrode surface, generating a steady-state signal, a lower ohmic potential drop, a lower double-layer capacitance, and an increased signal-to-noise ratio12. Similar to all solid electrodes, microelectrodes need to be conditioned before analysis. The appropriate pretreatment or activation technique is mechanical polishing to obtain a smooth surface, followed by an electrochemical or chemical conditioning step, such as potential cycling over a particular range in a suitable electrolyte13.
CV is very commonly used in the electrochemical polymerization of PEDOT by inserting electrodes in a monomer solution that involves a suitable solvent and dopant electrolyte. This electrochemical technique is beneficial in providing direction information such as the reversibility of conducting polymer doping processes and the number of transferred electrons, diffusion coefficients of analytes, and the formation of reaction products. This paper describes how two different electrolytes used for the electropolymerization of PEDOT can generate thin nanostructure films with a potential sensing application that depends on the morphology and other intrinsic properties.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acetonitrile</td>
			<td>Baker Analyzed HPLC Ultra Gradient Solvent</td>
			<td>75-05-8</td>
			<td>HPLC grade</td>
		</tr>
		<tr>
			<td>Alumina polishing pad</td>
			<td>BASi, USA</td>
			<td>MF-1040</td>
			<td>tan/velvet color</td>
		</tr>
		<tr>
			<td>Belgian chocolate milk</td>
			<td>Puhoi Valley dairy company, Auckland, NZ</td>
			<td>_</td>
			<td>Buy from local supermarket</td>
		</tr>
		<tr>
			<td>Caramel/white chocolate milk</td>
			<td>Puhoi Valley dairy company, Auckland, NZ</td>
			<td>_</td>
			<td>Buy from local supermarket</td>
		</tr>
		<tr>
			<td>CH instrument</td>
			<td>CH instruments, Inc. USA</td>
			<td>_</td>
			<td>Model CHI660E</td>
		</tr>
		<tr>
			<td>Counter electrode</td>
			<td>BASi, USA</td>
			<td>MW-1032</td>
			<td>7.5 cm long platinum wire (0.5 mm diameter) auxiliary/counter electrode, 99.95% purity</td>
		</tr>
		<tr>
			<td>Disodium hydrogen phosphate (Na2HPO4, 2H2O)</td>
			<td>Scharlau Chemie SA, Barcelona, Spain</td>
			<td>10028-24-7</td>
			<td>Weigh 17.8 g</td>
		</tr>
		<tr>
			<td>DURAN bottle</td>
			<td>University of Auckland</td>
			<td>_</td>
			<td>The glasswares were made locally at the University of Auckland</td>
		</tr>
		<tr>
			<td>Electrochemical cell</td>
			<td>BASi, USA</td>
			<td>MF-1208</td>
			<td>&#160;5-15 mL volume, glass</td>
		</tr>
		<tr>
			<td>Electrode Polishing Alumina Suspension</td>
			<td>BASi, USA</td>
			<td>CF-1050</td>
			<td>7 mL of 0.05 &#181;m particle size alumina polish</td>
		</tr>
		<tr>
			<td>Espresso milk</td>
			<td>Puhoi Valley dairy company, Auckland, NZ</td>
			<td>_</td>
			<td>Buy from local supermarket</td>
		</tr>
		<tr>
			<td>3,4-Ethylenedioxythiophene (EDOT), 97%</td>
			<td>Sigma-Aldrich</td>
			<td>126213-50-1</td>
			<td>Take 10.68 &#956;L from bottle</td>
		</tr>
		<tr>
			<td>FEI ESEM Quanta 200 FEG</td>
			<td>USA</td>
			<td>_</td>
			<td>SEM equipped with a Schottky field emission gun (FEG) for optimal spatial resolution. The instrument can be used in high vacuum mode (HV), low-vacuum mode (LV) and the so called ESEM (Environmental SEM) mode.&#160;</td>
		</tr>
		<tr>
			<td>Gold microelectrode</td>
			<td>BASi, USA</td>
			<td>MF-2006</td>
			<td>Working electrode (10 &#956;m diameter)</td>
		</tr>
		<tr>
			<td>Lithium perchlorate, ACS reagent, &#8805;95%</td>
			<td>Sigma-Aldrich</td>
			<td>7791-03-9</td>
			<td>Make 0.1 M solution</td>
		</tr>
		<tr>
			<td>Micropipettes</td>
			<td>Eppendorf</td>
			<td>_</td>
			<td>10-100 &#956;L and 100-1000 volumes</td>
		</tr>
		<tr>
			<td>MilliQ water</td>
			<td>Thermo Scientific, USA</td>
			<td>_</td>
			<td>18.2 M&#937;/cm at 25&#176;C, Barnstead Nanopure Diamond Water Purification System</td>
		</tr>
		<tr>
			<td>Propylene carbonate, Anhydrous, 99.7%</td>
			<td>Sigma-Aldrich</td>
			<td>108-32-7</td>
			<td>Take 20 mL from bottle</td>
		</tr>
		<tr>
			<td>Reference electrode</td>
			<td>BASi, USA</td>
			<td>MF-2052</td>
			<td>Silver/silver chloride (Ag/AgCl) electrode to be kept in 3 M sodium chloride</td>
		</tr>
		<tr>
			<td>Replacement glass polishing plate</td>
			<td>BASi, USA</td>
			<td>MF-2128</td>
			<td>Glass plate as a stand to attach the polishing pad on it</td>
		</tr>
		<tr>
			<td>Sodium dihydrogen phosphate&#160; (NaH2PO4, 1H2O)</td>
			<td>Sigma-Aldrich</td>
			<td>10049-21-5</td>
			<td>Weigh 13.8 g</td>
		</tr>
		<tr>
			<td>Sodium hydroxide pearls, AR</td>
			<td>ECP-Analytical Reagent</td>
			<td>1310-73-2</td>
			<td>Make 0.1 M solution</td>
		</tr>
		<tr>
			<td>Sodium perchlorate, ACS reagent, &#8805;98%</td>
			<td>Sigma-Aldrich</td>
			<td>7601-89-0</td>
			<td>Make 0.1 M solution</td>
		</tr>
		<tr>
			<td>Sulfuric acid (98%)</td>
			<td>Merck</td>
			<td>7664-93-9</td>
			<td>Make 0.5 M solution</td>
		</tr>
		<tr>
			<td>Uric acid</td>
			<td>Sigma-Aldrich</td>
			<td>69-93-2</td>
			<td>Make 1 mM solution</td>
		</tr>
		<tr>
			<td>Whole milk</td>
			<td>Anchor dairy company, Auckland, NZ</td>
			<td></td>
			<td>Blue cap milk, buy from local supermarket</td>
		</tr>
	</tbody>
</table>

electrochemical preparation of poly(3,4-ethylenedioxythiophene) layers on gold microelectrodes for uric acid-sensing applications

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer in an aqueous and an organic solution. Cyclic voltammetry (CV) was used in the synthesis of PEDOT thin layers. Lithium perchlorate (LiClO4) was used as a dopant in both aqueous (aqueous/acetonitrile (ACN)) and organic (propylene carbonate (PC)) solvent systems. After the PEDOT layer was created in the organic system, the electrode surface was acclimatized by successive cycling in an aqueous solution for use as a sensor for aqueous samples. 
The use of an aqueous-based electropolymerization method has the potential benefit of removing the acclimatization step to have a shorter sensor preparation time. Although the aqueous method is more economical and environmentally friendly than the organic solvent method, superior PEDOT formation is obtained in the organic solution. The resulting PEDOT electrode surfaces were characterized by scanning electron microscopy (SEM), which showed the constant growth of PEDOT during electropolymerization from the organic PC solution, with rapid fractal-type growth on gold (Au) microelectrodes.

Cyclic voltammetry is an easy technique to form a thin PEDOT layer on a Au microelectrode surface to increase the electrode conductivity and sensitivity during electrochemical sensing of target analytes. This protocol demonstrates the method of electropolymerization of 0.1 M EDOT from an organic solution compared to 0.01 M EDOT from an aqueous electrolyte solution. Running 10 cycles in aqueous/ACN solution results in a moderate growth of PEDOT comparable to that observed with the 4 cycles in LiClO4/PC solution...

Watch this Scientific Journal Video about Electrochemical Preparation of Poly3,4-Ethylenedioxythiophene Layers on Gold Microelectrodes for Uric Acid-Sensing Applications at JoVE.com

Electrochemical Preparation of Poly3,4-Ethylenedioxythiophene Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

We describe aqueous and organic solvent systems for the electropolymerization of poly(3,4-ethylenedioxythiophene) to create thin layers on the surface of gold microelectrodes, which are used for sensing low molecular weight analytes.

Electrochemical Preparation of Poly(3,4-Ethylenedioxythiophene) Layers on Gold Microelectrodes for Uric Acid-Sensing Applications

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of ...

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