Bean sprout peroxidase biosensor based on L-cysteine self-assembled monolayer for the determination of dopamine

A new bean sprout peroxidase was immobilized on a gold electrode modified with self-assembled monolayers (SAM) Of L-cysteine for the determination of dopamine in pharmaceutical samples using square wave voltammetry. In the bean sprout-(SAM)-Au electrode, the peroxidase, in the presence of hydrogen Peroxide, catalyzes the oxidation of dopamine to the corresponding quinone, which is electrochemically reduced back to dopamine at +0.15 V vs. Ag/AgCl The performance and the factors influencing the response of this biosensor were studied in detail. The best performance was obtained using 0.1 mol L-1 phosphate buffer solution (pH 6.0), 6.0 x 10(-1) mol L-1 hydrogen peroxide, frequency of 100 Hz, pulse amplitude of 80 mV and scan increment of 4.0 mV. The analytical curve was linear for dopamine concentrations from 9.91 x 10(-6) to 2.21 x 10(-4) mol L-1 and the detection limit was 4.78 x 10(-7) mol L-1. The recovery of dopamine ranged from 98.0 to 111.8% and the relative standard deviation was 3.1% for a solution containing 1.30 x 10(-5) mol L-1 dopamine (n = 6). The lifetime of this biosensor was 15 days (at least 300 determinations). The results obtained for dopamine determination in pharmaceutical formulations using the proposed bean sprout-SAM-Au electrode were in agreement with those obtained with the standard method at the 95% confidence level. (C) 2008 Elsevier B.V. All rights reserved.