QCM-D Study on Relationship of PEG Coated Stainless Steel Surfaces to Protein Resistance

Nonspecific protein adsorption generally occurs on any solid surfaces and usually has adverse consequences. Adsorption of proteins onto a solid surface is believed to be the initial and controlling step in biofouling. Surfaces modified with end-tethered poly(ethylene glycol) (PEG) have been shown to be protein-resistant to some degree. In this study, the adsorption of β-casein and lysozyme was performed on 6 different types of surfaces where PEG was tethered onto stainless steel by polyethylene imine (PEI) through either OH or NHS end groups. Protein adsorption was also performed on the bare stainless steel surface as a control. The adsorption was conducted at 23 °C and pH 7.2. In situ QCM-D was used to determine PEG adsorption kinetics, plateau PEG chain densities, protein adsorption kinetics and plateau protein adsorbed quantities. PEG grafting density was the highest for a NHS coupled chain, around 0.5 chains / nm. Interestingly, lysozyme which has smaller size than β-casein, appeared to adsorb much less mass than that of βcasein. Overall, the surface with high PEG grafting density exhibited a good protein rejection. Keywords—QCM-D, PEG, stainless steel, β-casein, lysozyme.