Adsorption of lysozyme unto silica and polystyrene surfaces in aqueous medium

Abstract

The adsorption capacity of lysozyme (chicken egg white) from aqueous solutions unto silica and polystyrene interfaces was studied at varying lysozyme concentrations and ionic strength. The studies revealed an increase in adsorption capacity with increase in concentration and with maximum adsorption densities of 1.34 x10^-6 mol g^-1 and 1.57 x10^-6 mol g^-1 obtained for silica and polystyrene respectively at the maximum concentration studied. The observed adsorption isotherms on both surfaces were well fitted by the Langmuir adsorption isotherm model with maximum adsorption capacities (q_max) corresponding to monolayer coverage as 1.60 x 10^-6 and 2.72 x 10^-6 mol g^-1 respectively for silica and polystyrene. Fitting of the data into Langmuir-type isotherm suggested that chemisorption was the predominant mechanism in the adsorption process. Results presented in the limelight of varying ionic strength showed that adsorption capacity decreased with increase in ionic strength onto silica surface while showing no significant effect onto polystyrene surface, thus implying that electrostatic interaction may play a major role in lysozyme adsorption onto the silica surface.

Key words: Adsorption capacity, lysozyme, silica, polystyrene, Langmuir.