| AVS 54th International Symposium | |
| Biomaterial Interfaces | Wednesday Sessions |
| Session BI-WeM |
| Session: | Nano-Engineered Biointerfaces |
| Presenter: | G.J. Leggett, University of Sheffield, UK |
| Authors: | G.J. Leggett, University of Sheffield, UK R.E. Ducker, University of Sheffield, UK M. Montague, University of Sheffield, UK K.S.L. Chong, University of Sheffield, UK |
| Correspondent: | Click to Email |
Photolithography is a convenient and rapid route to the fabrication of patterned self-assembled monolayers for the control of biological organisation. Alkanethiols may be photo-oxidised by exposure to light with a wavelength of 244 nm to yield soluble sulfonates which may be displaced by complementary thiols to yield clean, well-defined chemical patterns. Protein patterning is complicated by the problems of non-specific adsorption. Most proteins adhere to most surfaces, rendering protein patterning difficult. Oligo(ethylene glycol) (OEG) terminated self-assembled monolayers are attractive because they resist protein adsorption very effectively. Here we have explored the possibility of patterning OEG-terminated SAMs using photolithography. Rates of photo-oxidation of OEG-terminated thiols have been measured using contact angle goniometry, static SIMS and friction force microscopy. The kinetics observed appear to be different from those observed for other thiols. The mechanism appears to be complex. Over longer exposures, photo-oxidation of the head group occurs. Subsequent patterning through a mask yields well-defined structures that consist of either methyl or carboxylic acid terminated thiols in regions exposed to UV light, to which proteins may, respectively, be adsorbed or covalently bound, and protein-resistant OEG-terminated adsorbates over the rest of the surface. Exposure using a near-field scanning optical microscope (scanning near-field photolithography, SNP) yields nanometre scale structures. At short exposures, photodegradation of the OEG chain occurs leading to the formation of aldehyde groups that covalently bind proteins with high efficiency. This provides a very convenient single-step route to the introduction of a reactive functional group, in a spatially selective fashion, to a protein resistant OEG monolayer. The amount of streptavidin bound to such a photo-modified monolayer is nearly as great as that bound using well-established carbodiimide-based methods on carboxylic acid terminated monolayers. Significantly, the photodegradation of the OEG terminal groups in this process is much more rapid than the oxidation of the thiol head-group and is, moreover, capable of excitation at longer wavelengths, where photo-oxidation of the thiol sulfur atom is no longer a possibility. Photopatterning thus appears to be a simple and versatile route to protein patterning.