A potential masking approach in the detection of dopamine on 3-mercaptopropionic acid capped ZnSe quantum dots modified gold electrode in the presence of interferences Peter M. Ndangili, Omotayo A. Arotiba, Priscilla G.L. Baker, Emmanuel I. Iwuoha * SensorLab, Department of Chemistry, University of the Western Cape, Bellville 7535, South Africa article info Article history: Received 16 December 2009 Received in revised form 2 March 2010 Accepted 8 March 2010 Available online 11 March 2010 Keywords: Dopamine Quantum dots Zinc selenide 3-Mercaptopropionic acid Uric acid Ascorbic acid abstract Electrochemical detection of dopamine in the presence of excess ascorbic acid and uric acid on a gold electrode modified with 3-mercaptopropionic acid capped zinc selenide quantum dots is presented. The synthesized quantum dots were immobilized on the surface of gold disk electrode by self assembly method in dark conditions for 24 h and electrochemically characterized. A surface coverage of 0.91 was calculated using electrochemical impedance spectroscopy. The quantum dot afforded the simultaneous detection of these three compounds with wide peak separations which allowed the interferences to be masked with applied potential. Using a potential window of 0–400 mV, where only dopamine was elec- troactive, a detection limit of 2.43  10 10 M and 5.65  10 10 M were calculated from square wave vol- tammetry and amperometry respectively. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Dopamine (DA) is one of the most important catecholamine neurotransmitters in mammals that play crucial roles in the functioning of cardiovascular, renal, hormonal and central nervous system [1]. Loss of DA is associated with neurological disorders such as Parkinson’s disease [2]. DA acts like a brain chemical to transmit messages to parts of the brain for coordination of body movement. Thus monitoring the DA levels can be an important marker for biomedical diagnosis. Among other methods which are based on spectroscopy and chromatography [3] for DA detection, electrochemical determination has an advantage owing due to the easy oxidizable nature of DA and cost. However, electrochemical detection has the challenge of eliminating interfering ascorbic acid and uric acid (also present in physiological fluid) because of the proximity in oxidation potential with DA [4]. At unmodified elec- trodes, dopamine, ascorbic acid (AA) and uric acid (UA) exhibit overlapping oxidation potentials while adsorption of oxidized products causes fouling [5]. Electrodes are modified to enhance re- sponse or selectivity towards a particular substrate. Materials such as redox polymers [6,7], dendrimers [8], nanoparticles [9,10] are commonly used to prepare modified electrodes. In the analysis of dopamine in particular, gold nano film [11] carbon electrode mod- ified with polyglycine [1], poly(acid chrome blue K) [2] and others [1,12,13] have recently been reported. In the preparation of modi- fied electrodes, a unique class of nanoparticles called quantum dots are now emerging. Quantum dots are semiconductor nanocrystals that range from 2 to 10 nm in size. They possess size-tunable optical and electronic properties. Their quantum size effects give rise to excellent electri- cal, optical and electrochemical properties, such as change of elec- trochemical potential of band edge [14]. Quantum dots have found potential applications in several areas, including catalysis, coatings, textiles, data storage, biotechnology, health care, biomedical, phar- maceutical industries and most recently, in bioanalytical chemistry [11]. When suitably functionalized with amphiphilic bifunctional molecules such as mercapto carboxylic acids [HS-(CH 2 )n-COOH, n = 1–15] [15], the small sizes of quantum dots can allow for rapid transfer of electrons to the surface of the target particles, resulting to a higher charge detaching efficiency [14]. Short chained capping agents such as mercaptopropionic acid (MPA) have been used for self assembly on gold electrode [16] and are associated with enhanced electrochemical signals of the quantum dots towards target analytes [17]. Most applications of quantum dots in analyt- ical purposes make use of their fluorescent properties [18,19]. Although quantum dots show excellent electrochemical properties when properly functionalized, their use in electrochemical systems for analytic purposes are at the onset [14,20,21]. ZnO semiconduc- tors electrodeposited on the surface of a glassy carbon electrode for determination of DA in presence of AA and UA with a detection limit of 0.50 lM have been reported [22]. A gold electrode 1572-6657/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2010.03.006 * Corresponding author. Tel.: +27 (0) 21 9593054; fax: +27 (0) 21 9591562. E-mail address: eiwuoha@uwc.ac.za (E.I. Iwuoha). Journal of Electroanalytical Chemistry 643 (2010) 77–81 Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem