Cooperative use of cytochrome cd1 nitrite reductase and its redox partner cytochrome c₅₅₂ to improve the selectivity of nitrite biosensing

In this work, a novel enzymatic biosensor for determination of nitrites constructed on an electrochemical transducing platform is proposed. The sensor is based on cytochrome-cd₁ (cyt-cd₁) nitrite reductase from Marinobacter hydrocarbonoclasticus strain 617 as biological recognition element, and its putative physiological redox partner cytochrome-c₅₅₂ (cyt-c₅₅₂), as electron mediator. The proteins were co-immobilized using a photopolymerizable polyvinyl alcohol (PVA) derivative, onto carbon paste screen printed electrodes (CPSPEs); the optimal modification conditions were 100μM cyt-cd₁/100μM cyt-c₅₅₂ and 50% PVA, after a 48h polymerization time. Electrochemical characterization of the mediator was carried out by cyclic voltammetry. The one-electron exchange between cyt-c₅₅₂ and the working electrode is a quasi-reversible process, without mass transport limitations. The formal potential of the mediator is 254±2mV vs NHE and the intermolecular electron transfer rate constant between cytochromes c₅₅₂ and cd₁ is 9.9×10³M^-1s^-1. The analytical parameters of the biosensor response to nitrite as assessed by amperometric measurements were: linear range from 10 to 200μM; detection and quantification limits of 7 and 24μM, respectively; sensitivity of 2.49±0.08Amol^-1cm²μM^-1. Catalytic profiles in the presence of possible interfering species were also investigated. The interference from competitive enzymatic reduction of dissolved oxygen could be overcome by tuning the cyclic voltammograms for faster sweep rates.