Adsorption and surface mobility of proteins and colloids

Exploring the mechanisms of adsorption and ordering of proteins at interfaces can provide information applicable to many technological concerns. The goal of this thesis is to study the adsorption behavior of proteins at molecular scale, and to elucidate the mechanism of protein adsorption and self-assembly.; Atomic force microscopy (AFM) was used to obtain direct, high-resolution images of ferritin and catalase adsorbed at solid and fluid interfaces. The results showed a trend of increasing in surface coverage at low ionic strength, then decreasing at moderate values and increasing again at high values. The balance of protein-surface and protein-protein interaction is believed to be the cause of this trend, and the experimental results are compared with the theoretical calculation. The adsorbed protein molecules are distributed randomly on the solid substrates, whereas have some tendency to self-assemble into ordered arrays at the fluid interfaces, which suggests that surface mobility is important to protein ordered array formation.; Surface mobility of latex particles adsorbed on solid surfaces was measured by moving the particle with an AFM tip in lateral force microscopy mode. It was found that the effect of electrostatic interactions on the mobility of adsorbed particles is weak.; Mobility of proteins adsorbed at solid and fluid interfaces was measured by fluorescence recovery after photobleaching (FRAP). The concentration profiles of the adsorbed proteins after bleaching were calculated by solving the diffusion equation in cylindrical coordinates, and the lateral diffusion coefficients were obtained by fitting the experimental data to the calculated profiles. The lateral diffusion coefficients were estimated to be on the order of 10 –7 cm2/s for proteins adsorbed at liquid interfaces, and <10–10 cm2/s for those at solid interfaces, which demonstrates the higher surface mobilities of proteins at fluid-liquid interfaces.