Chemical modification of porous silicon mirror for biosensing applications
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abstract
Porous silicon (PSi) nanostructures have remarkable optical properties that can be used for biosensing applications. In this paper we report first on the fabrication of heavily doped p-type PSi with pore diameters in the range of 400-4000 nm. The nonspecific and specific binding of the Glucose Oxidase protein (GOX) was then studied onto the PSi mirror-like substrate. Adsorption of GOX was tuned by the pH of the protein solution (pI = 4.2) depending of the surface charge. PSi matrixes were first stabilized by thermal oxidation and GOX adsorption was performed once directly on the oxidized PSi surface, and also on previously functionalized PSi surfaces. In the latter case the GOX was coupled to the PSi via the S-H group of the 3-(mercaptopropyl)trimethoxysilane (MPTS). The silane-GOX and GOX interactions on the PSi surface were monitored by the Fourier Transformed Infrared spectra that display characteristic bands of the linked molecules. The interference spectrum shows a large blue shift in the Fabry- Perot interference pattern caused by the change in the refractive index of the medium implying a decrease in the effective optical thickness. Quantitative analysis shows that chemically modified PSi samples admit approximately 24%25 of GOX. Activity assay proved that the protein preserves its catalyst properties under these adsorption conditions.
