Cascaded nano-porous silicon for high sensitive biosensing and functional group distinguishing by Mid-IR spectra.

We present a chemical-biosensor in the Mid-IR range and based on cascaded porous silicon made on p- and n-type (100) silicon substrates of resistivities between 0.001Ωcm and 0.005Ωcm. The stacked porous layers of various porosities (20-80%) and thicknesses (5-9µm) are formed by successive electrochemical etchings with different current densities. Working with FTIR technique that possesses fast response, high sensitivity, and capability of detecting and identifying functional groups, the cascaded porous structures provided enhanced refractive index sensitivities and reduced detection limits in chemical and biodetection. The largest wavenumber shifts were 50cm(-1)/mM obtained for d-(+)-glucose and 96cm(-1)/µg/mL for Cy5-conjungated Rabbit Anti-Mouse IgG. The lowest detectable concentration of glucose was 80µM (1.4mg/mL) with PS porosity of 40% and thickness of about 9µm while it was 40ng/mL for Cy5-conjugated Rabbit Anti-Mouse IgG which is 2.5×10(5) folds better than those in literature.