Self-assembled epoxy-modified polymer coating on a poly(dimethylsiloxane) microchip for EOF inhibition and biopolymers separation

Abstract

A straightforward approach to generate a stable and protein-resistant poly(dimethylsiloxane) (PDMS) surface using self-assembled hydrophilic polymers is demonstrated in this work. Epoxy-modified polymers were directly adsorbed from aqueous solution onto plasma oxidized PDMS based on H-bond interaction, and epoxies of polymer and silanols on oxidized PDMS surface were crosslinked by heating at 110 °C. The coating process could be completed within half hour. Poly(dimethylacrylamide-co-glycidyl methacrylate) (PDMA-co-GMA), poly(vinyl pyrrolidone)-g-glycidyl methacrylate (PVP-g-GMA) and poly(vinyl alcohol)-g-glycidyl methacrylate (PVA-g-GMA) (D. P. Wu, B. X. Zhao, Z. P. Dai, J. H. Qin and B. C. Lin, Lab Chip, 2006, 6, 942) were employed as examples here. Unlike PDMA, PVP, and PVA themselves, these epoxy-modified hydrophilic polymers could be directly used as static surface coatings on oxidized PDMS, and inhibited electroosmotic flow (EOF) within pH 3–11. It was also found that hard baking of PDMS at 150 °C for 24 hours before surface coating could greatly retard surface hydrophobicity recovery after oxygen plasma exposure, which strengthened epoxy-modified polymer coatings on oxidized PDMS surface, and resulted in EOF less than 0.2 × 10⁻⁴ cm² V⁻¹ s⁻¹ (pH 9.0) within two weeks. On epoxy-modified polymer coated PDMS microchips, basic proteins, peptides and DNA fragments could be separated satisfactorily, in which more than 2 × 10⁴ plates per 2 cm and less than 3% RSD (>8 runs) for migration time were obtained for lysozyme.