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 se rum albumin (BSA) was studied on gold surfaces modified by self-assemb led alkyl thiol monolayers (SAMs) with the following terminal groups: CH3, C6H4OH, COO-, NH2, OH, and oligoethylene oxide (OEO). The kinetic s of hIgG and BSA adsorption and desorption were monitored in real tim e utilizing the surface plasmon resonance (SPR) technique with a how c ell. The surface concentration of hIgG molecules adsorbed on the SAMs decreased in the order: CH3 > C6H5OH > COO- > NH2 > OH > OEO SAM surfa ces. 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/cm(2) (the detection limit of our SPR device) and approximately 10(3) times less than that on the hydrophobic CH3-terminated SAM surfaces. The ki netics of the binding curves for the adsorption of the proteins are de scribed 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. (C) 1997 Academic Press