In situ monitoring of lysozyme adsorption onto bare and cysteine- or 1-octadecanethiol-modified Au electrodes using an electrochemical quartz-crystalimpedance system

The adsorption of lysozyme from phosphate-buffered saline (pH 7.4) onto bar e and cysteine- or 1-octadecanethiol-modified Au electrodes was investigate d in situ using an electrochemical quartz-crystal impedance system (EQCIS). The equivalent circuit parameters and resonant frequencies of the piezoele ctric quartz-crystal (PQC) resonance, the Value of half peak width of the e lectroacoustic conductance spectrum (Df(G1/2)) as well as the electrical do uble-layer capacitance were obtained and analyzed. The adsorption kinetics was analyzed with a scheme of two consecutive reactions occurring at the in terface. The amount of adsorbed lysozyme on a hydrophobic surface was great er than that on a hydrophilic one, and a more negative potential brought a larger amount of adsorbed lysozyme. The standard heterogeneous rate constan ts of ferricyanide/ferrocyanide before and after the lysozyme adsorption we re evaluated.