Full Paper Electrochemical Sensor for the Determination of Dopamine in Presence of High Concentration of Ascorbic Acid Using a Fullerene-C 60 Coated Gold Electrode Rajendra Nath Goyal,* Vinod Kumar Gupta, Neeta Bachheti, Ram Avatar Sharma Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247667, India *e-mail: rngcyfcy@iitr.ernet.in Received: August 6, 2007 Accepted: October 30, 2007 Abstract A fullerene-C 60 -modified gold electrode is employed for the determination of dopamine in the excess of ascorbic acid using square-wave voltammetry. Based on its strong catalytic function towards the oxidation of dopamine and ascorbic acid, the overlapping voltammetric response of both the biomolecules at the bare electrode is resolved into two well- defined voltammetric peaks with lowered oxidation potential and enhanced oxidation currents. Linear calibration curves for dopamine are obtained using square-wave voltammetry over the concentration range 1 nM –5.0 mM in 0.1 M phosphate buffer solution at pH 7.2 with a correlation coefficient of 0.9931 and the detection limit (3s) is estimated to be 0.26  10 9 M. The interference studies showed that the presence of physiologically common interferents (i.e. uric acid, citric acid, tartaric acid, glucose and sodium chloride) negligibly affects the response of dopamine. The practical analytical utility of the method is illustrated by quantitative determination of dopamine in commercially available pharmaceutical formulation and human body fluids, viz. urine and blood plasma, without any preliminary treatment. Keywords: Fullerene-C 60 , Gold electrode, Dopamine, Ascorbic acid, Human body fluids DOI: 10.1002/elan.200704073 1. Introduction Dopamine, one of the most important catecholamine neurotransmitters, plays a crucial role in the function of central nervous, hormonal, renal and cardiovascular systems [1, 2]. Besides modulating brain activity, controlling coor- dination and movement, regulation of flow of information to different areas of the brain, and having a stimulating effect on the heart, it is also vital in the development and persistence of addiction [3 – 7]. Changes in the concentra- tion of dopamine are related to several diseases, such as Parkinson)s disease and schizophrenia [8]. Therefore, the detection of concentration of dopamine in body fluids is of great significance in the field of clinical diagnostics. Being highly sensitive and simple, electrochemical meth- ods are widely used in the field of analytical chemistry and since dopamine is electroactive, the quantitative and qualitative determination of dopamine is of great signifi- cance using electrochemical methods. However, a major obstacle in monitoring dopamine using this technique is the coexistence of excess of ascorbic acid in human body fluids [9]. Ascorbic acid oxidizes at a potential close to that of dopamine at conventional electrodes, resulting in an over- lapping voltammetric response. To solve this problem, various chemically modified electrodes have been used since the modified electrode can lower the oxidation potential and also increase the sensitivity, thus improving the selectivity. Till now, a variety of modified electrodes have been proposed to determine the concentration of dopamine in the presence of excess of ascorbic acid, which include ruthenium oxide modified electrode, gold nano- particles distributed poly(4-aminothiophenol) modified electrode, carbon ionic liquid electrode, carbon ceramic electrode, RNA modified electrode, in-site functionalized self-assembled monolayer on gold electrode, glassy-carbon electrode modified with both polyaniline film and multi- walled carbon nanotubes with incorporated b-cyclodextrin, gold cysteamine self-assembled monolayers, Fe 3 O 4 nano- particles modified electrode, poly(4-(2-pyridylazo)-resorci- nol) modified glassy carbon electrode, nickel(II) complex polymer-modified electrodes and poly(p-nitrobenzenazo resorcinol) modified glassy carbon electrode [10 – 21]. However, improvement in the sensitivity and selectivity of the electrode towards dopamine is still an important issue among researchers. Since the discovery of fullerenes in 1985, buckminsterful- lerene (C 60 ) has fascinated a large number of scientists due to its remarkable electrochemical properties [22]. Recently, the electrochemical behavior of fullerene films in aqueous solutions has been investigated by many researchers and the most promising result of the studies is that the partially reduced fullerene films are sufficiently conductive such that they can be used to modify electrodes for various electro- chemical reactions, and they also show electrocatalytic properties [23, 24]. However, there are still few reports about these modified electrodes being applied as bimolec- 757 Electroanalysis 20, 2008, No. 7, 757 – 764 # 2008 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim