Electrodeposited Cadmium Oxide Semiconductor Electrodes for Protein Redox Characterization

Abstract

Semiconductor films have previously shown promise for the measurement of protein reduction potentials.1,2 An advantage gained with semiconductor working electrodes is the ability to take measurements while adsorption phenomena that occur at bare metal electrodes are avoided, which denature the protein and make sample recovery impossible. This denaturation may also affect the redox potentials.3 Thus, an ability to measure redox potentials accurately while maintaining protein integrity can find many applications in bioanalytical systems. In this work we have synthesized and characterized cadmium oxide (CdO) working electrodes for electrochemical studies of native biomolecules in aqueous systems. Electrodeposited CdO films were generated through application of a constant current (4.5 mA/cm2) to an indium-doped tin oxide (ITO) working electrode immersed in a 0.1 M cadmium chloride (CdCl2) solution and subsequently annealed at 450 ˚C for 1.5 h. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy methods were employed to characterize deposited material. As proof of concept, cyclic voltammetry of redox dyes with CdO working electrodes was performed to determine their redox potentials. Azurin, a copper blue protein from Pseudomonas aerunginosa,and cytochrome c, a small heme protein purified from bovine heart, were among the metalloproteins investigated. A novel small volume (50 and 750 µL) cyclic voltammetry cell was employed that facilitates sample recovery. Cyclic voltammograms were recorded at 10 mV/s for each sample with a CdO working electrode, a saturated Ag/AgCl reference electrode (–0.044 V vs. SCE), and a platinum counter electrode in aqueous solutions containing 100 mM Tris buffer and 200 mM KCl.