ABSTRACT
Horseradish peroxidase enzyme selectively oxidizes phenol to o-quinone that can be reduced electrochemically to catechol and generating a current response which is directly proportional to phenol concentration. In order to investigate the o-quinone enzymatic production and its electrochemical behavior, a 2-D model was developed for a nanochip biosensor in COMSOL Multiphysics. The oxidation rate of phenol to o-quinone was predicted by the developed model based on Michaelis-Menten equation. The diffusion coefficient of o-quinone was obtained 2.17 × 10-6 cm2 s-1 based on experimental chronoamperograms. The cathodic and anodic peak potentials for o-quinone/catechol redox couple are obtained experimentally 255 and 310 mV, respectively. The obtained results from simulation were compared with the experimental results to verify the validity of the model. By comparing the cyclic voltammograms from the simulation and experimental results, the heterogeneous rate constant, k°, and the transfer coefficient, α, were calculated 0.02 cm s-1 and 0.5, respectively. Then, using simulation results, chronoamperograms were drawn for the nanochip biosensors with different heights. Also, o-quinone concentration gradients were determined at the electrode surface, which can be used to estimate the thickness of the diffusion layer. Finally, a calibration plot was obtained based on the simulation results of the proposed nanochip as phenol biosensor with the following equation I (nA) = 0.1497 C (µM)-0.3521 and a linear range of 20.0-150.0 µM.
