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

• Electrochemical etching was used to make cascaded nano-porous silicon for chemical/biosensing.
• High sensitivity and low LOD were obtained, thanks to large area and high volume.
• Low LOD was enhanced with cascaded structures.
• FTIR spectrometry was used to identify functional groups of bio substances.
• The sensors were applied to detect d-(+)-glucose and Cy5-conjungated Rabbit Anti-Mouse IgG.

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 0.001 Ω cm and 0.005 Ω cm. The stacked porous layers of various porosities (20–80%) and thicknesses (5–9 μm) 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 50 cm−1/mM obtained for d-(+)-glucose and 96 cm−1/μg/mL for Cy5-conjungated Rabbit Anti-Mouse IgG. The lowest detectable concentration of glucose was 80 μM (1.4 mg/mL) with PS porosity of 40% and thickness of about 9 μm while it was 40 ng/mL for Cy5-conjugated Rabbit Anti-Mouse IgG which is 2.5×105 folds better than those in literature.