LAUSR

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 Cm+2EGn, 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 C10EGn were generally thicker than those from their corresponding homologues C11EGn, 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 A 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.