Creation of a mixed poly(ethylene glycol) tethered-chain surface for preventing the nonspecific adsorption of proteins and peptides

Using a heterotelechelic poly(ethylene glycol) (PEG) possessing a mercapto group at one end and an acetal group at the other end (acetal-PEG-SH), the authors constructed a reactive PEG tethered-chain surface on a surface plasmon sensor (SPR) gold chip for biosensing with high sensitivity. Nonspecific bovine serum albumin adsorption on the PEG tethered-chain surface was significantly influenced by the density of the PEG chain, and was almost completely suppressed by increasing the PEG density through the repetitive treatment of the chip surface with acetal-PEG-SH. The PEG density was increased even more by adding an underbrushed layer made of shorter-PEG-SH-chain molecules (2 kDa, hereafter 2k) to the surface made of longer-PEG-SH-chain molecules (5 kDa, hereafter 5k). SPR measurement then gave an estimate of the adsorption of a series of proteins with varying sizes and isoelectric points on the PEG chain surface having an underbrushed layer (PEG5k/2k surface). As compared to other SPR surfaces, viz., a commercial carboxymethyl dextran and conventional PEG5k tethered-chain surface without an underbrushed layer, the mixed PEG5k/2k surface showed almost complete inhibition of the nonspecific adsorption not only of high-molecular-weight proteins but also of low-molecular-weight peptides.