Determination of Dopamine in Presence of Ascorbate in Ultrathin Carbon Nanoparticle Composite Film Electrodes

Mandana Amiri 1Saeed Shahrokhian Frank Marken 2

1. Sharif University of Technology, Azadi Avenue, Tehran 14588, Iran
2. University of Bath, Department of Chemistry, Claverton Down, Bath BA2-7AY, United Kingdom

Abstract

Carbon materials are widely used for modified electrodes in electroanalysis and in particular the recent development of a new range of nanocarbons has triggered many new developments in electrochemical sensing. In this report uniform carbon nanoparticles are employed in conjunction with a poly(diallyldimethylammonium chloride) or PDDAC binder. After suspension into water, the carbon nanoparticles with negative surface charge readily assemble onto surfaces which have been modified with PDDAC polycations. A layer-by-layer electrostatic assembly process is used to grow thin carbon nanoparticle films with ca. 5 to 6 nm average thickness increase per deposition layer at tin-doped indium oxide (ITO) substrates. Transparent and strongly adhering films of high electrical conductivity are formed and characterized in terms of their electrochemical reactivity. When immersed in aqueous 0.1 M phosphate buffer pH 7, each layer of CNP-PDDAC is adding an interfacial capacitance of ca. 10 mF cm-2. Absorption into the CNP–PDDAC nanocomposite film is dominated by the sites in the PDDAC cationomer and therefore anionic molecules such as indigo carmine are strongly bound and retained within the film (cationic binding sites per layer ca. 150 pmol cm-2). The characteristics of these ultrathin films as electrodes for adsorbed and for solution redox systems are explored and the selective determination of dopamine in the presence of ascorbate is highlighted as a potential sensor application. The determination of dopamine in the presence of ascorbateis a challenging problem for in vivo nerve cell investigations and it has led to new types of modified electrodes. For the mixed redox system ascorbate–dopamine in 0.1M phosphate buffer pH 7 cyclic voltammograms suggest a rapid and selective temporary poisoning process which causes the ascorbate oxidation to be suppressed in the second potential cycle. This effect is exploited for the detection of micromolar concentrations of dopamine in the presence of millimolar ascorbate.

References

[1] K.J. McKenzie, F. Marken, Langmuir 19 (2003) 4327.

 [2] R. L. McCreery, Electroanal. Chem. 1991, 17, 221.

 [3] C.W. Welch, R. G. Compton, Anal. Bioanal. Chem. 2006, 384, 601.

[4] G. Decher, J. B. Schlenoff, Multilayer Thin Films, Wiley VCH, Weinheim 2003.

 

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Presentation: Poster at SMCBS'2007 International Workshop, by Mandana Amiri
See On-line Journal of SMCBS'2007 International Workshop

Submitted: 2007-09-23 08:17
Revised:   2009-06-07 00:48