Lysozyme Adsorption Studies at the Silica/Water Interface Using Dual Polarization Interferometry

摘要

Lysozyme adsorption at the silica/water interface has been studied using a new analytical technique called dual polarization interferometry.This laboratory-based technique allows the build up or removal of molecular layers adsorbing or reacting on a lightly doped silicon dioxide(silica)surface to be measured in terms of thickness and refractive index changes with time.Lysozyme adsorption was studied at a range of concentrations from 0.03 to 4.0 g dm~(-3) and at both pH 4 and pH 7.Adsorbed layers ranging from 14 to 43 1 A in thickness and 0.21 to 2.36(+-)0.05 mg m~(-2) in mass coverage were observed at pH 4 with increasing lysozyme concentration,indicating a strong deformation of the monolayer over the low concentration range and the formation of an almost complete sideways-on bilayer toward the high concentration of 4 g dm~(-3).At pH 7,the thickness of adsorbed layers varied from 16 to 541 A with significantly higher surface coverage(0.74 to 3.29(+-)0.05 mg m~(-2),again indicating structural deformation during the initial monolayer formation,followed by a gradual transition to bilayer adsorption over the high concentration end.The pH recycling performed at a fixed lysozyme concentration of 1.0 g dm~(-3) indicated a broadly reversible adsorption regardless of whether the pH was cycled from pH 7 to pH 4 and back again or vice versa.These observations are in good agreement with earlier studies undertaken using neutron reflection although the fine details of molecular orientations in the layers differ subtly.