Analytical Sciences

In situ Monitoring of Lysozyme Adsorption onto Bare and Cysteine- or 1-Octadecanethiol-Modified Au Electrodes Using an Electrochemical Quartz-Crystal Impedance System

You-yu ZHANG, Qing-ji XIE,  An-hong ZHOU, and Shou-zhuo YAO

Chemical Research Institute, Hunan Normal University, Changsha 410081, P. R. China

The adsorption of lysozyme from phosphate-buffered saline (pH 7.4) onto bare and cysteine- or 1-octadecanethiol-modified Au electrodes was investigated in situ using an electrochemical quartz-crystal impedance system (EQCIS). The equivalent circuit parameters and resonant frequencies of the piezoelectric quartz-crystal (PQC) resonance, the value of half peak width of the electroacoustic conductance spectrum (Df_G1/2) as well as the electrical double-layer capacitance were obtained and analyzed. The adsorption kinetics was analyzed with a scheme of two consecutive reactions occurring at the interface. The amount of adsorbed lysozyme on a hydrophobic surface was greater than that on a hydrophilic one, and a more negative potential brought a larger amount of adsorbed lysozyme. The standard heterogeneous rate constants of ferricyanide/ferrocyanide before and after the lysozyme adsorption were evaluated.

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