Semipermeable poly(ethylene glycol) films: the relationship between permeability and molecular structure of polymer chains

Abstract

We describe size-selective semipermeable poly(ethylene glycol) (PEG) films which avoid the nonspecific absorption of large proteins but permit the passage of small target molecules. The size threshold for permeation through the PEG films on indium-tin oxide surfaces was characterised using cyclovoltammetry and redox-active probes of 0.3 and 0.6 nm diameter. The permeation was dependent on the molecular weight of PEG and the different conformational preferences of the polymer chains. PEG 5000 D with a looped and dynamically changing structure provided a porous and easily permeable meshwork for the passage of small molecules. In contrast, parallel aligned and helical PEG 500 chains represented a denser molecular sieve which is only permeable for small molecules 0.3 nm in size. By describing the relationship between the molecular structure and an important physiochemical property of surface-tethered PEG films, our findings on controllable semipermeable interfaces may be exploited for electrical sensor surfaces.