Amperometric sensor for hydrogen peroxide based on direct electron transfer of spinach ferredoxin on Au electrode

A protein-based electrochemical sensor for hydrogen peroxide (H2O2) was developed by an easy and effective film fabrication method where spinach ferredoxin (Fdx) containing [2Fe–2S] metal center was cross linked with 11-mercaptoundecanoic acid (MUA) on a gold (Au) surface. The surface morphology of Fdx molecules on Au electrodes was investigated by atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed to study the electrochemical behavior of adsorbed Fdx on Au. The interfacial properties of the modified electrode were evaluated in the presence of Fe(CN)63−/4− redox couple as a probe. From CV, a pair of well-defined and quasi-reversible redox peaks of Fdx was obtained in 10 mM, pH 7.0 Tris–HCl buffer solution at −170 and −120 mV respectively. One electron reduction of the [2Fe-2S]2+ cluster occurs at one of the iron atoms to give the reduced [2Fe-2S]+. The formal reduction potential of Fdx ca. −150 mV (vs. Ag/AgCl electrode) at pH 7.0. The electron-transfer rate constant, ks, for electron transfer between the Au electrode and Fdx was estimated to be 0.12 s−1. From the electrochemical experiments, it is observed that Fdx/MUA/Au promoted direct electron transfer between Fdx and electrode and it catalyzes the reduction of H2O2. The Fdx/MUA/Au electrode displays a linear increase in amperometric current for increasing concentration of H2O2.The sensor calibration plot was linear with r2 = 0.998 with sensitivity approximately 68.24 μAm M−1 cm−2. Further, the effect of nitrite on the developed sensor was examined which does not interfere with the detection of H2O2. Finally, the addition of H2O2 on MUA/Au electrode was observed which has no effect on amperometric current.