H2O2-Generating Peroxidase Electrodes as Reagentless Cyanide Sensors

Abstract

Inexpensive, reagentless, and simple (single-electrode) cyanide biosensors are developed using a pyrolytic graphite (PG) electrode on which horseradish peroxidase (HRP) is adsorbed. The electrode is poised at −300 mV vs Ag/AgCl for 40 s to reduce dissolved O₂ to H₂O₂ at the PG surface. The generated H₂O₂ accumulates in the diffusion layer. The potential is then stepped to 0 mV, at which the accumulated H₂O₂ is reduced, though the O₂ reduction does not proceed. Since the H₂O₂ reduction is catalyzed by HRP, the transient cathodic current is inhibited by cyanide. Therefore, the transient current is a function of the cyanide concentration. A HRP/PG electrode with saturated HRP coverage is reliable, and it can determine 10^-5−10^-3 M cyanide. On the other hand, the electrode with lower HRP coverage is less reliable, though it is so sensitive as to detect 2 × 10^-7 M cyanide because the system is under kinetic control.