Electroanalytical properties of cytochrome c with direct electron transfer on graphene/gold nanoparticleschitosan modified glass carbon electrode

Abstract

A nitrite (NO₂⁻) sensor has been fabricated by immobilizing cytochrome c (Cyt c) on a graphene/gold nanoparticle-chitosan (Gra/Au NPs–Chit) modified glass carbon electrode (GCE). Graphene/gold nanoparticles (Gra/Au NPs) nanocomposite was prepared by dispersing graphene in an aqueous solution of β-cyclodextrin (β-CD) and hydrogen tetrachloroaurate and followed by NaBH₄ reduction. An aliquot of Gra/Au NPs in a 0.50 wt% chitosan solution was drop-coated on the surface of a GCE to form a Gra/Au NPs–Chit/GCE which was subsequently adsorbed with Cyt c. The Cyt c–Gra/Au NPs–Chit/GCE shows a quasi-reversible cyclic voltammetric redox couple at a formal potential of −0.037 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffer solution, suggesting that Gra/Au NPs–Chit film offers a biocompatible microenvironment for the Cyt c. It was found that the Cyt c–Gra/Au NPs–Chit sensor displays good electrocatalytic activity for NO₂⁻ oxidation at a relatively low working potential. The sensor possesses a linear response range of 10.0–420.0 μM NO₂⁻ with a correlation coefficient of 0.9989 and a sensitivity of 110.0 μA mM⁻¹. The limit of detection is determined as 2.46 μM NO₂⁻ based on a signal-to-noise ratio of 3. The proposed sensor has been applied successfully to the determination of NO₂⁻ in spiked and real water samples.