MACROPOROUS P-TYPE SILICON FABRY-PEROT LAYERS - FABRICATION, CHARACTERIZATION, AND APPLICATIONS IN BIOSENSING

We present in this paper that porous silicon can be used as a large su rface area matrix as well as the transducer of biomolecular interactio ns. We report the fabrication of heavily doped p-type porous silicon w ith pore diameters that can be tuned, depending on the etching conditi on, from approximately 5 to 1200 nm. The structure and porosity of the matrixes were characterized by scanning force microscopy (SFM) and sc anning electron microscopy (SEM), Brunnauer-Emmett-Teller nitrogen ads orption isotherms, and reflectance interference spectroscopy. The thin porous silicon layers are transparent to the visible region of the re flectance spectra due to their high porosity (80-90%) and are smooth e nough to produce Fabry-Perot fringe patterns upon white light illumina tion. Porous silicon matrixes were modified by ozone oxidation, functi onalized in the presence of idyldithiopropionamidobutyl)dimethylmethox ysilane, reduced to unmask the sulfhydryl functionalities, and coupled to biotin through a disulfide-bond-forming reaction. Such functionali zed matrixes display considerable stability against oxidation and corr osion in aqueous media and were used to evaluate the utility of porous silicon in biosensing. The streptavidin-biotin interactions on the su rface of porous silicon could be monitored by the changes in the effec tive optical thickness calculated from the observed shifts in the Fabr y-Perot fringe pattern caused by the change in the refractive index of the medium upon protein-ligand binding. Porous silicon thus combines the properties of a mechanically and chemically stable high surface ar ea matrix with the function of an optical transducer and as such may f ind utility in the fabrication of biosensor devices.