Spatially Resolved Adsorption Kinetics of Immunoglobulin G onto the Wettability Gradient Surface

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Abstract
Total internal reflection fluorescence (TIRF) was combined with charge-coupled-device (CCD) photon detection in measuring spatially resolved protein adsorption kinetics along one of the linear dimensions of a flat surface. The experimental method was designed to study the kinetics of binding of fluorescein-labeled immunoglobulin G (FITC-IgG) onto the surfaces with the wettability gradient. Protein was adsorbed from a flowing buffer solution. The buffer solution contained either only fluorescein-labeled immunoglobulin G or FITC-IgG and two other unlabeled proteins: albumin and fibrinogen. The concentrations of proteins were 1/1000 of the respective protein concentrations in plasma. Adsorption of FITC-IgG was dependent on the wettability of the surface as well as on the presence of other proteins in the adsorbing solution. The exchange of surface-bound FITC-IgG with other proteins was observed along the wettability transition region of the gradient surface but not at either the hydrophobic or the hydrophilic sides. The amphiphilic interface between the microscopic hydrophobic and hydrophilic domains in the wettability transition region of the gradient surface was proposed to explain the adsorption behavior of FITC-IgG. The spatially resolved TIRF-CCD method has the potential of detecting the fast protein adsorption, desorption, and exchange processes from complex protein mixtures, such as serum and plasma.