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 ...

By modifying the gold microelectrode surface with a thin layer of PEDOT made in an organic solvent, we can get a higher surface area and boost the sensor sensitivity. The microelectrode procedure is a rapid analysis of antioxidants in various media. This can be applied to different contexts, ranging from monitoring beverages through to an immediate assessment of the status of hospitalized patients.Use a suitable potentiostat to run cyclic voltammetry as the electrochemical technique of interest. Turn on the potentiostat and the computer attached to it. To test the communication between the computer and the instrument, start the software, then under the setup menu, select the hardware test command.After hearing some sounds from the potentiostat, the hardware test results are shown in a separate window. Click OK and continue running the experiment. Sometimes by clicking the hardware test command, a link failed error appears.Check the connection and port settings. After testing the connections, click on the setup menu, choose technique, and from the opening window, choose the cyclic voltammetry method. Then go back to the setup menu and click on parameters to enter the appropriate experimental parameters.For example, to run 0.1 molar EDOT electropolymerization in an organic electrolyte on the bare gold microelectrode, set the initial potential to negative 0.3 volts, final potential to negative 0.3 volts, high potential to 1.2 volts, number of segments to eight, scan rates to 100 millivolts per second, and direction to positive. After entering the appropriate cyclic voltammetry parameters, prepare three electrode setups in a glass electrochemical cell, including a working electrode, a reference electrode, and a platinum wire counter electrode. Pass these clean and dried electrodes through the holes of an electrode holder attached to a stand, then place the holder above the electrochemical cell to insert the electrodes in the target solution or sample.Ensure that there are no bubbles on the electrode surfaces. If there are bubbles, remove the electrodes, rinse them with deionized water again, and pat dry with a tissue. Then place the electrodes back into the stand holder and in the solution.If there are bubbles around the reference electrode, tap the tip gently. If there are bubbles around the counter electrode after starting the scan, clean the counter electrode. If the cyclic voltammetry scan becomes noisy, clean the electrode surface and check the system connections, wires, and clips.After ensuring that all the three wire connections for reference, working, and counter electrodes are correctly connected, start the experiment by clicking on run. To pretreat the gold microelectrode, polish it for 30 seconds with Alumina Slurry on an Alumina polishing pad placed on a glass polishing plate applying circular and eight-shaped hand motions, then rinse the microelectrode with deionized water. Insert it in a glass vile containing 15 milliliters of absolute ethanol and ultra sonicate for two minutes.Next, rinse the microelectrode with ethanol and water and ultra sonicate it again for four minutes in deionized water to remove excess Alumina from the electrode surface. Finally, remove additional impurities by cycling in 0.5 molar sulfuric acid for 20 segments between negative 0.4 and positive 1.6 volt potentials at a scan rate of 50 millivolts per second. Ensure there are two clear peaks due to the formation and reduction of gold oxide at consistent anodic and cathodic potentials each time the electrode is cleaned in sulfuric acid.To prepare 0.1 molar EDOT in an organic solution, first transfer one milliliter of the prepared 0.1 molar lithium perchlorate solution into an electrochemical cell. Then using a micropipette, add 10.68 microliters of the EDOT monomer to the electrochemical cell. To electropolymerize EDOT on the bare gold microelectrode surface, insert all electrode setups in the solution and run cyclic voltammetry.Then using scanning electron microscopy, characterize the surface of this modified electrode. Rinse the electrodes with deionized water and dry them with a tissue. Then to use this PEDOT modified gold microelectrode for sensing purposes, acclimatize its surface to an aqueous solution by immersing the electrode in a 0.1 molar sodium perchlorate solution and running cyclic voltammetry scans.Then after rinsing with deionized water, immerse this organically PEDOT-modified and acclimatized microelectrode in a phosphate buffer solution and run cyclic voltammetry to generate a background scan. Finally, take the electrode out of the buffer solution and without rinsing, immediately insert it into uric acid or milk solutions for running cyclic voltammetry scans. Next, to prepare 0.01 molar EDOT in an aqueous acetonitrile solution, use a micropipette and add 10.68 microliters of EDOT to one milliliter of acetonitrile in a glass vial, then add nine milliliters of deionized water to the vial to prepare 10 milliliters of 0.01 molar EDOT solution.Add 110 milligrams of lithium perchlorate powder to the prepared EDOT solution to obtain a 0.1 molar lithium perchlorate solution and mix gently. Transfer the prepared solution to the electrochemical cell. Insert the electrodes in the aqueous acetonitrile solution and electropolymerize 0.01 molar EDOT on the electrode surface by running cyclic voltammetry, then characterize the surface of this modified electrode by scanning electron microscopy.Analysis of uric acid content in regular fresh milk using the PEDOT sensor synthesized in the organic solution resulted in a 28.4 nano ampere anodic peak current at 0.35 volts, which is equivalent to a concentration of 82.7 micromoles. The second large oxidation peak in the cyclic voltammetry scan of regular milk at 0.65 volts is related to oxidizable compounds including electroactive amino acids such as cysteine, tryptophan, and tyrosine. The cyclic voltammetry scans obtained for caramel and white chocolate milk samples show a clear peak at 0.36 volts for uric acid, along with an additional peak at 0.5 volts that can be related to the presence of vanillic acid, one of the ingredients of flavored milk.Cyclic voltammetry of the Belgian chocolate milk sample demonstrates a catechin oxidation peak at 0.26 volts and a catechin reduction peak at 0.22 volts. The 0.3 volts peak current appearing as a sharp peak at the tail of the catechin peak is due to uric acid oxidation. Cyclic voltammetry of Colombian espresso milk sample exhibits broad anodic and cathodic peak currents at 0.35 volts and 0.23 volts respectively due to the major phenolic antioxidants in coffee, namely chlorogenic and caffeic acids.Cleaning and perturating the electrode is the most important part of this experiment that can affect the obtained current signals. The more detailed analysis of antioxidant compounds is needed, then we can turn to chromatographic methods such as LCMS. However, this is time consuming and is not needed for every sample.

electrochemical-preparation-poly34-ethylenedioxythiophene-layers-on

Research

JoVE Journal

Chemistry

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Dynamic Electrochemical Measurement of Chloride Ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...

Simple Methods for the Preparation of Non-noble Metal Bulk-electrodes for Electrocatalytic Applications

The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and composition of the material was characterized via powder X-ray diffraction (PXRD), M&#246;ssbauer spectroscopy (MB), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and energy dispersive X-ray spectroscopy (EDX). Two preparation methods of pentlandite bulk electrodes are presented. In the first approach a piece of synthetic pentlandite rock is directly contacted via a wire ferrule. The second approach utilizes pentlandite pellets, pressed from finely ground powder, which is immobilized in a Teflon casing. Both electrodes, whilst being prepared by an additive-free method, reveal high durability during electrocatalytic conversions in comparison to common drop-coating methods. We herein showcase the striking performance of such electrodes to accomplish the hydrogen evolution reaction (HER) and present a standardized method to evaluate the electrocatalytic performance by electrochemical and gas chromatographic methods. Furthermore, we report stability tests via potentiostatic methods at an overpotential of 0.6 V to explore the material limitations of the electrodes during electrolysis under industrial relevant conditions.

A facile preparation method of electrodes using the bulk material Fe4.5Ni4.5S8 is presented. This method provides an alternative technique to conventional electrode fabrication and describes prerequisites for unconventional electrode materials including a straightforward electrocatalytic testing method.

The rock material pentlandite with the composition Fe4.5Ni4.5S8 was synthesized via high temperature synthesis from the elements. The structure and ...

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). ...

Gold Nanoparticle Modified Carbon Fiber Microelectrodes for Enhanced Neurochemical Detection

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into glass capillaries, pulled to a fine taper, and then sealed using an epoxy to create electrode materials that are used for fast scan cyclic voltammetry testing. The use of bare CFMEs has several limitations, though. First and foremost, the carbon fiber contains mostly basal plane carbon, which has a relatively low surface area and yields lower sensitivities than other nanomaterials. Furthermore, the graphitic carbon is limited by its temporal resolution, and its relatively low conductivity. Lastly, neurochemicals and macromolecules have been known to foul at the surface of carbon electrodes where they form non-conductive polymers that block further neurotransmitter adsorption. For this study, we modify CFMEs with gold nanoparticles to enhance neurochemical testing with fast scan cyclic voltammetry. Au3+ was electrodeposited or dipcoated from a colloidal solution onto the surface of CFMEs. Since gold is a stable and relatively inert metal, it is an ideal electrode material for analytical measurements of neurochemicals. Gold nanoparticle modified (AuNP-CFMEs) had a stability to dopamine response for over 4 h. Moreover, AuNP-CFMEs exhibit an increased sensitivity (higher peak oxidative current of the cyclic voltammograms) and faster electron transfer kinetics (lower &#916;EP or peak separation) than bare unmodified CFMEs. The development of AuNP-CFMEs provides the creation of novel electrochemical sensors for detecting fast changes in dopamine concentration and other neurochemicals at lower limits of detection. This work has vast applications for the enhancement of neurochemical measurements. The generation of gold nanoparticle modified CFMEs will be vitally important for the development of novel electrode sensors to detect neurotransmitters in vivo in rodent and other models to study neurochemical effects of drug abuse, depression, stroke, ischemia, and other behavioral and disease states.

In this study, we modify carbon-fiber microelectrodes with gold nanoparticles to enhance the sensitivity of neurotransmitter detection.

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into ...

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 &#181;m diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries ...

Growth of Gold Dendritic Nanoforests on Titanium Nitride-coated Silicon Substrates

In this study, a high-power impulse magnetron sputtering system is used to coat a flat and firm titanium nitride (TiN) film on silicon (Si) wafers, and a fluoride-assisted galvanic replacement reaction (FAGRR) is employed for the rapid and easy deposition of gold dendritic nanoforests (Au DNFs) on the TiN/Si substrates. Scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy patterns of TiN/Si and Au DNFs/TiN/Si samples validate that the synthesis process is accurately controlled. Under the reaction conditions in this study, the thickness of the Au DNFs increases linearly to 5.10 &#177; 0.20 &#181;m within 15 min of the reaction. Therefore, the employed synthesis procedure is a simple and rapid approach for preparing Au DNFs/TiN/Si composites.

This study presents a feasible procedure for synthesizing gold dendritic nanoforests on titanium nitride/silicon substrates. The thickness of gold dendritic nanoforests increases linearly within 15 min of a synthesis reaction.

In this study, a high-power impulse magnetron sputtering system is used to coat a flat and firm titanium nitride (TiN) film on silicon (Si) wafers, and a ...

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We developed an asymmetric thermoelectrochemical cell (aTEC) for heat-to-electricity conversion under isothermal operation in the charging and discharging processes without exploiting the thermal gradient or the thermal cycle. The aTEC is composed of a graphene oxide (GO) cathode, a polyaniline (PANI) anode, and 1M KCl as the electrolyte. The cell generates a voltage due to the pseudocapacitive reaction of GO when heating from room temperature (RT) to a high temperature (TH, ~40-90 &#176;C), and then current is successively produced by oxidizing PANI when an external electrical load is connected. The aTEC demonstrates a remarkable temperature coefficient of 4.1 mV/K and a high heat-to-electricity conversion efficiency of 3.32%, working at a TH = 70 &#176;C with a Carnot efficiency of 25.3%, unveiling a new promising thermoelectrochemical technology for low-grade heat recovery.

Low-grade heat is abundant, but its efficient recovery is still a great challenge. We report an asymmetric thermoelectrochemical cell using graphene oxide as a cathode and polyaniline as an anode with KCl as the electrolyte. This cell works under isothermal heating, exhibiting a high heat-to-electricity conversion efficiency in low-temperature regions.

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We ...

Quantitative SERS Detection of Uric Acid via Formation of Precise Plasmonic Nanojunctions within Aggregates of Gold Nanoparticles and Cucurbit[n]uril

This work describes a rapid and highly sensitive method for the quantitative detection of an important biomarker, uric acid (UA), via surface-enhanced Raman spectroscopy (SERS) with a low detection limit of ~0.2 &#956;M for multiple characteristic peaks in the fingerprint region, using a modular spectrometer. This biosensing scheme is mediated by the host-guest complexation between a macrocycle, cucurbit[7]uril (CB7), and UA, and the subsequent formation of precise plasmonic nanojunctions within the self-assembled Au NP: CB7 nanoaggregates. A facile Au NP synthesis of desirable sizes for SERS substrates has also been performed based on the classical citrate-reduction approach with an option to be facilitated using a lab-built automated synthesizer. This protocol can be readily extended to multiplexed detection of biomarkers in body fluids for clinical applications.

Quantitative SERS Detection of Uric Acid via Formation of Precise Plasmonic Nanojunctions within Aggregates of Gold Nanoparticles and Cucurbit[n]uril

A host-guest complex of cucurbit[7]uril and uric acid was formed in an aqueous solution before adding a small amount into Au NP solution for quantitative surface-enhanced Raman spectroscopy (SERS) sensing using a modular spectrometer.

This work describes a rapid and highly sensitive method for the quantitative detection of an important biomarker, uric acid (UA), via surface-enhanced ...