Protein exclusion is preserved by temperature sensitive PEG brushes

Poly(ethylene glycol) (PEG) is widely used in biotechnology-related applications yet its temperature-dependent functionality is not well understood. Here, we use bovine serum albumin (BSA) monomers and cross-linked dimers to directly probe the height of strongly stretched PEG brushes using surface plasmon resonance (SPR) in aqueous solution. Our results show that PEG brush height follows a smooth decrease as a function of increasing temperature commencing near room temperature. Measurements obtained by BSA monomers and dimers are comparable and suggest that BSA effectively probes the leading edge of the brush with minimal penetration into its interior being supported by SPR reflectivity calculations. Further, the BSA-PEG interaction remains largely inert over the entire temperature range. Overall, PEG brushes undergo a smooth conformational transition while fully preserving its protein excluding properties far from the lower critical solution temperature