Direct electrochemistry of tyrosinase and biosensing for phenol based on gold nanoparticles electrodeposited on a boron-doped diamond electrode

Tyrosinase (Tyr)-based biosensors might be interesting devices for fast analytical screening of phenols, especially if gold nanoparticles (AuNPs) are used as mediators of the direct electron transfer (DET) reaction between enzyme and electrode substrate. Therefore, by immobilizing Tyr on AuNPs electrodeposited on a boron-doped diamond (BDD) electrode. The best conditions (applied potential and deposition time) to electrodeposit AuNPs on BDD were selected by factorial design; homogeneously distributed quasi-spherical AuNPs (33 nm average diameter) were obtained by applying -0.4 V vs. Ag/AgCl (3 M KCl) for 40 s. Then, Tyr was immobilized on AuNPs previously modified using cystamine and glutaraldehyde. The occurrence of DET between the electrode surface and the Tyr active site was verified by cyclic voltammetry. yielding the following parameter values: formal redox potential, 115 mV vs. Ag/AgCl (3 M KCl); transfer coefficient, 0.45; heterogeneous electron transfer rate constant, 0.032 s(-1). Using square-wave voltammetry (SWV), a sensitive electrochemical reduction of phenol was attained: concentration range, 0.10-11.0 mu M; detection limit, 0.07 mu M; intra-day and inter-day repeatability RSDs, 3.4% and 4.24%, respectively; reasonably good stability (only 15% response decrease after 30 days). Furthermore, the obtained apparent Michaelis-Menten kinetic constant for phenol (13.0 mu M) is quite good when compared to the ones reported in the literature. Hence, the developed Tyr-AuNPs/BDD biosensor exhibits good sensitivity, stability, and reproducibility for the determination of phenol by SWV. (C) 2012 Elsevier B.V. All rights reserved.