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

Summary

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.

Abstract

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.

Introduction

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, fib....

Protocol

1. Preparing analytical solutions

1. Preparing 0.1 M EDOT in an organic solution
   1. Weigh out 0.213 g of LiClO₄ and transfer it into a 20 mL volumetric flask.
   2. Use a measuring cylinder to take 20 mL of PC from the bottle.
   3. 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.
   4. Cover the vial with aluminum foil and insert a long needle .......

Discussion

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.......

Materials

Name	Company	Catalog Number	Comments
Acetonitrile	Baker Analyzed HPLC Ultra Gradient Solvent	75-05-8	HPLC grade
Alumina polishing pad	BASi, USA	MF-1040	tan/velvet color
Belgian chocolate milk	Puhoi Valley dairy company, Auckland, NZ	_	Buy from local supermarket
Caramel/white chocolate milk	Puhoi Valley dairy company, Auckland, NZ	_	Buy from local supermarket
CH instrument	CH instruments, Inc. USA	_	Model CHI660E
Counter electrode	BASi, USA	MW-1032	7.5 cm long platinum wire (0.5 mm diameter) auxiliary/counter electrode, 99.95% purity
Disodium hydrogen phosphate (Na2HPO4, 2H2O)	Scharlau Chemie SA, Barcelona, Spain	10028-24-7	Weigh 17.8 g
DURAN bottle	University of Auckland	_	The glasswares were made locally at the University of Auckland
Electrochemical cell	BASi, USA	MF-1208	5-15 mL volume, glass
Electrode Polishing Alumina Suspension	BASi, USA	CF-1050	7 mL of 0.05 µm particle size alumina polish
Espresso milk	Puhoi Valley dairy company, Auckland, NZ	_	Buy from local supermarket
3,4-Ethylenedioxythiophene (EDOT), 97%	Sigma-Aldrich	126213-50-1	Take 10.68 μL from bottle
FEI ESEM Quanta 200 FEG	USA	_	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.
Gold microelectrode	BASi, USA	MF-2006	Working electrode (10 μm diameter)
Lithium perchlorate, ACS reagent, ≥95%	Sigma-Aldrich	7791-03-9	Make 0.1 M solution
Micropipettes	Eppendorf	_	10-100 μL and 100-1000 volumes
MilliQ water	Thermo Scientific, USA	_	18.2 MΩ/cm at 25°C, Barnstead Nanopure Diamond Water Purification System
Propylene carbonate, Anhydrous, 99.7%	Sigma-Aldrich	108-32-7	Take 20 mL from bottle
Reference electrode	BASi, USA	MF-2052	Silver/silver chloride (Ag/AgCl) electrode to be kept in 3 M sodium chloride
Replacement glass polishing plate	BASi, USA	MF-2128	Glass plate as a stand to attach the polishing pad on it
Sodium dihydrogen phosphate  (NaH2PO4, 1H2O)	Sigma-Aldrich	10049-21-5	Weigh 13.8 g
Sodium hydroxide pearls, AR	ECP-Analytical Reagent	1310-73-2	Make 0.1 M solution
Sodium perchlorate, ACS reagent, ≥98%	Sigma-Aldrich	7601-89-0	Make 0.1 M solution
Sulfuric acid (98%)	Merck	7664-93-9	Make 0.5 M solution
Uric acid	Sigma-Aldrich	69-93-2	Make 1 mM solution
Whole milk	Anchor dairy company, Auckland, NZ		Blue cap milk, buy from local supermarket