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 × 10 −5 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 × 10 −6 to 2.21 × 10 −4 mol L −1 and the detection limit was 4.78 × 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 × 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.