Adsorption of human serum albumin: Dependence on molecular architecture ofthe oppositely charged surface

We contrast the adsorption of human serum albumin (HSA) onto two solid subs trates previously primed with the same polyelectrolyte of net opposite char ge to form one of two alternative structures: randomly adsorbed polymer and the "brush" configuration. These structures were formed either by the adso rption of quaternized poly-4-vinylpyridine (QPVP) or by end-grafting QPVP c hains of the same chemical makeup and the same molecular weight to surfaces onto which QPVP segments did not adsorb. The adsorption of HSA was quantif ied by using Fourier transform infrared spectroscopy in attenuated total re flection (FTIR-ATR). The two substrates showed striking differences with re gard to HSA adsorption. First, the brush substrate induced lesser perturbat ions in the secondary structure of the adsorbed HSA, reflecting easier conf ormational adjustment for longer free segments of polyelectrolyte upon bind ing with the protein. Second, the penetration of HSA into the brush substra te was kinetically retarded relative to the randomly adsorbed polymer, prob ably due to both pore size restriction and electrostatic sticking between c harged groups of HSA and QPVP molecules. Third, release of HSA from the ads orbed layer, as the ionic strength was increased from a low level up to the high level of 1 M NaCl, was largely inhibited for the brush substrate, but occurred easily and rapidly for the substrate with statistically adsorbed QPVP chains. Finally, even after addition of a strong polymeric adsorption competitor (sodium polystyrene sulfonate), HSA remained trapped within a br ush substrate though it desorbed slowly from the preadsorbed QPVP layer. Th is method to produce irreversible trapping of the protein within a brush su bstrate without major conformational change may find application in biosens or design. (C) 1999 American Institute of Physics. [S0021-9606(99)50120-7].