Preparation of organic monolayers with azide on porous silicon via Si–N bonds

A series of azides have been synthesized and covalently linked to the silicon-hydride (Si–H) terminated porous silicon (PSi) via Si–N bonds by microwave irradiation in the presence of diacyl peroxide initiator. Two approaches were applied to covalently couple the amino-reactive linker, N-hydroxysuccinimide (NHS)-ester, on PSi. A stepwise synthesis includes the coupling of terminal carboxylic acid monolayers and their conversion to NHS-ester species. And a direct coupling method adopts the bulk synthesis of NHS-ester azides first and then the surface attachment. Finally, a protein of bovine serum albumin (BSA) was immobilized through amide bonds. Photo illumination of azide compounds in a 1,4-dioxane solvent was also examined for covalent grafting on PSi. Surface sensitive instruments such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), interferometric reflectance spectrometer, and field emission scanning electron microscopy (FESEM) were used to characterize the surface products. A reaction mechanism, involving the intermediate nitrene, is proposed for the surface reaction of azide on PSi.