Adsorption of Lactoperoxidase on Hydrophilic and Hydrophobic Silicon Dioxide Surfaces: An Ellipsometric Study

Abstract

The kinetics and steady-state properties of films of lactoperoxidase adsorbing on hydrophilic and hydrophobic silicon dioxide surfaces were studied with ellipsometry. At steady state, the wavelength dependence of the refractive index for lactoperoxidase adsorbed on gold was measured with spectroscopic ellipsometry. The refractive index was found to be close to 1.5 for light in the visible region. Lactoperoxidase was found to have a very high surface affinity and a monolayer was formed at concentrations as low as 0.5 μg/ml. Thicker films (3.7 nm) were formed on hydrophilic surfaces than on hydrophobic surfaces (2.5 nm). The adsorption cannot be described with a classical adsorption model. Different models are discussed and a model involving different molecular orientations and exchange reactions is proposed.