Electrocatalytic Oxidation of Hypoxanthine on a Nafion/Lead-Ruthenium Oxide Pyrochlore Modified Electrode

An enzymeless sensor based on a Nafion/lead-ruthenium oxide pyrochlore modified electrode (NPME) is described for the sensitive estimation of hypoxanthine (Hx) using square-wave voltammetry. The NPME showed a marked catalytic activity towards the oxidation of Hx. The quasi-steady-state oxidation current for Hx on the NPME provided a crucial mechanistic indication that the process follows the Michaelis-Menten kinetics. In brief, the process involves the formation of a substrate-catalyst complex that subsequently decomposes to form product and precatalyst; the latter can afterwards be regenerated electrochemically. The Michaelis-Menten constant (Km), catalytic rate constant (kc), heterogeneous electrochemical rate constant (ke′), and the reaction order (m) were evaluated. The experimental parameters were optimized for analytical estimation of Hx and the detection limit (S/N=3) was found to be as low as 0.75 µM. The use of the proposed sensor to estimate the fish freshness is demonstrated with very good reproducibility with a relative standard deviation of 2.4 % for ten successive measurements.