THE ADSORPTION OF LYSOZYME TO HYDROPHILIC SILICON-OXIDE SURFACES - COMPARISON BETWEEN EXPERIMENTAL-DATA AND MODELS FOR ADSORPTION-KINETICS

The adsorption of lysozyme onto silicon oxide surfaces was investigate d using in situ ellipsometry. Both the adsorption kinetics and the des orption upon rinsing with buffer were followed and the experimental da ta obtained were compared to models for adsorption kinetics. The effec ts of concentration, time of adsorption, and ionic strength were studi ed. The adsorbed amount reached a semiplateau within an hour of adsorp tion and only partial desorption was observed upon rinsing. The adsorp tion was found to be affected by the ionic strength and the following parameters were seen to increase in buffers of low ionic strength: the amount adsorbed, the rate of initial adsorption, and the amount adsor bed irreversibly after rinsing with buffer. The amount adsorbed after 1 h did not reach a plateau within the concentration range investigate d, in spite of reaching levels above monolayer coverage. The fraction adsorbed irreversibly increased during the time interval studied(1 h). The experimental data could be fitted to a model involving lysozyme a dsorbed in three states. These include molecules adsorbed reversibly t o the surface, models adsorbed irreversibly to the surface, and molecu les adsorbed in a second layer. The second layer was considered to ads orb irreversibly to the molecules in the first layer. Furthermore, the rate constants were dependent on the surface coverage and the model a llowed for exchange between adsorbed molecules and those in solution. (C) 1995 Academic Press, Inc.