Preparation, characterization, and protein-resistance of films derived from a series of α-oligo(ethylene glycol)-ω-alkenes on H–Si(111) surfaces

Abstract

A series of oligo(ethylene glycol) (OEG)-terminated monolayers were prepared by photo-activated grafting of OEG-alkenes with the general formula CH₂CH(CH₂)_m(OCH₂CH₂)_nOCH₃ (abbreviated as C_m+2EG_n, m = 8, 9; n = 3–7) on hydrogen-terminated silicon (111) surfaces using different deposition conditions. The films were characterized by contact-angle goniometry, ellipsometry, X-ray photoelectron spectroscopy (XPS) and tested for protein resistance. Films prepared under a higher vacuum showed a higher thickness and exhibited better protein resistance with increasing ethylene glycol (EG) units. Remarkably, the films prepared from C₁₀EG_n were generally thicker than those from their corresponding homologues C₁₁EG_n, and displayed better resistance to protein adsorption, which were probably due to the odd–even effect from the alkyl chain. Prepared under high vacuum conditions (∼10⁻⁵ mbar), the C₁₀EG₇ films with a thickness of 40 Å adsorbed <0.8% (the detection limit of N 1s XPS) monolayer of fibrinogen in a standard assay. The films remained protein-resistant (adsorbed <3% monolayer of fibrinogen) even after 28 days in phosphate buffered saline (PBS) at 37 °C or 17 days in MC3T3-E1 cell culture with 10% fetal bovine serum at 37 °C. Therefore, the C₁₀EG₇ films prepared under high vacuum conditions represent the most protein-resistant and stable films on non-oxidized silicon substrates.