Interrelation of Elasticity, Isotherm of Adsorbed Proteins, and its Subsequent Displacement by a Surfactant

Abstract

Quartz crystal microbalance with dissipation (QCM-D) is used to study the adsorption characteristics of insulin, myoglobin, bovine serum albumin, and beta-galactosidase over amine and methyl surfaces. The water-based and D2O-based phosphate buffers are used for making protein solution. The kinetics of adsorption data, equilibrium adsorption data, and the elasticity of an adsorbed protein is obtained experimentally. A kinetic model of the adsorption of protein with surface phase is developed and fitted to experimental kinetic data. The kinetic parameter involving the first binding step with the surface depends on the surface and physical characteristics of the protein such as charge and component of the secondary structure. The experimental adsorption isotherm data are fitted to a multilayer model with two equilibrium adsorption constants (K-s and K-L). The relative strength of adsorption over the bare surface is denoted by K-s, and the relative adsorption strength of protein over the adsorbed protein is denoted by K-L. A protein containing a higher amount of beta content has a higher K-s value during its adsorption on amine surface. The elastic component G’ of the viscoelastic properties of the adsorbed proteins is found to be high for the protein layer obtained through high K-s and low K-L values. The desorption kinetics of the adsorbed proteins using a surfactant solution is also investigated. The elastic properties of the adsorbed proteins and desorption characteristics of the adsorbed proteins by a surfactant (sodium dodecyl sulfate) are strongly related to the adsorption strengths determining factors K-s and K-L. An adsorbed protein obtained through a high K-s value is difficult to remove by the surfactant solution.