Direct electrochemistry and electrocatalysis of myoglobin on redox-active self-assembling monolayers derived from nitroaniline modified electrode

The adsorption processes and electrochemical behavior of 4-nitroaniline (4-NA) and 2-nitroaniline (2-NA) adsorbed onto glassy carbon electrodes (GCE) have been investigated in aqueous 0.1 M nitric acid (HNO3) electrolyte solutions using cyclic voltammetry (CV). Nitroaniline adsorbs onto GCE surfaces and upon potential cycling past -0.55 V is transformed into the arylhydroxylamine (ArHA), which exhibits a well-behaved pH dependent redox couple centered at 0.32V (pH 1.5). This modified electrode can be readily used as an immobilization matrix to entrap proteins and enzymes. In our studies, myoglobin (Mb) was chosen as a model protein for investigation. A pair of well-defined reversible redox peaks for Mb(Fe(III)-Fe(II)) was obtained at the Mb/arylhydroxylamine modified glassy carbon electrode (Mb/HAGCE) by direct electron transfer between the protein and the GCE. The formal potential (E-0'), the surface coverage (Gamma) and the electron transfer rate constant (k(s)) were calculated as -0.317 V, 4.15 +/- 0.5 x 10(-11) mol/cm(2) and 5115 s(-1), respectively. Dramatically enhanced biocatalytic activity was exemplified at the Mb/HAGCE for the reduction of hydrogen peroxide (H2O2), trichloroacetic acid (TCA) and oxygen (O-2). The Mb/ArHA film was also characterized by UV-vis spectra, scanning electron microscope (SEM) indicating excellent stability and good biocompatibility for protein in the film. The applicability of the method to the determination of H2O2 (similar to 3%) in a commercial antiseptic solution and soft-contact lenses cleaning solutions were demonstrated. This new Mb/HAGCE exhibited rapid electrochemical response (with in 2 s) with good stability in physiological condition. (c) 2007 Elsevier B.V. All rights reserved.