Electrocatalytic oxidation of hypoxanthine on a Nafion/lead-ruthenium oxide pyrochlore modified electrode

An enzymeless sensor based on a Nafion/lead-ruthenium oxide pyrochlore modi fied electrode (NPME) is described for the sensitive estimation of hypoxant hine (Hx) using square-wave voltammetry. The NPME showed a marked catalytic activity towards the oxidation of Hx. The quasi-steady-state oxidation cur rent for Hx on the NPME provided a crucial mechanistic indication that the process follows the Michaelis-Menten kinetics. In brief, the process involv es the formation of a substrate-catalyst complex that subsequently decompos es to form product and precatalyst; the latter can afterwards be regenerate d electrochemically. The Michaelis-Menten constant (K-m), catalytic rate co nstant (k(c)), heterogeneous electrochemical rate constant (k(c)'), and the reaction order (m) were evaluated. The experimental parameters were optimi zed for analytical estimation of Hx and the detection limit (S/N = 3) was f ound to be as low as 0.75 mu M. The use of the proposed sensor to estimate the fish freshness is demonstrated with very good reproducibility with a re lative standard deviation of 2.4% for ten successive measurements.