Covalent functionalizations of silicon surfaces and their application to biosensors

The silicon surface may be grafted with organic moieties through direct Si-C bonding. The covalent character of the Si-C bond provides the obtained surfaces with improved chemical stability in ambient as well as in aqueous medium. We here review recent work done in our group, dealing with the grafting of carboxyl-terminated aliphatic chains through hydrosilylation of ω-alkenoic acids, and subsequent activation of the carboxyl end groups, allowing for the covalent immobilisation of a biomolecule through an amino linker. Quantitative information on the composition of the functionalized surfaces and their properties in aqueous media has been obtained by using model (111)-Si surfaces as a benchmark. The optimised procedures have then been transferred to more realistic silicon surfaces, especially those of amorphous hydrogenated silicon and amorphous hydrogenated silicon/carbon alloys. The latter materials can be deposited in thin-film form on any substrate, which has allowed for their application to biochips. By designing appropriate structures, strong improvements in the performance of fluorescence, surface-plasmon, and localised-surfaceplasmon biochips have been obtained, in terms of sensitivity, stability and reliability.