SPR Studies of the Nonspecific Adsorption Kinetics of Human IgG and BSA on Gold Surfaces Modified by Self-Assembled Monolayers (SAMs)

The nonspecific binding of human immunoglobulin G (hIgG) and bovine serum albumin (BSA) was studied on gold surfaces modified by self-assembled alkyl thiol monolayers (SAMs) with the following terminal groups: CH3, C6H4OH, COO-, NH2, OH, and oligoethylene oxide (OEO). The kinetics of hIgG and BSA adsorption and desorption were monitored in real time utilizing the surface plasmon resonance (SPR) technique with a flow cell. The surface concentration of hIgG molecules adsorbed on the SAMs decreased in the order: CH3 > C6H5OH > COO- > NH2 > OH > OEO SAM surfaces. Binding of BSA to the SAM surfaces decreased in the order: C6H5OH > CH3 > COO- > NH2 > OH > OEO. The results show that on the OEO SAM, the surface concentration of these proteins was less than 0.5 ng/cm2 (the detection limit of our SPR device) and approximately 10(3) times less than that on the hydrophobic CH3-terminated SAM surfaces. The kinetics of the binding curves for the adsorption of the proteins are described in terms of multiple states of adsorbed proteins that involve multipoint hydrophobic, electrostatic, and hydrogen bond interactions for the different surfaces and protein lateral interactions caused by the unfolding of adsorbed proteins.