Highly Stable Porous Silicon–Carbon Composites as Label-Free Optical Biosensors

A stable, label-free optical biosensor based on a porous silicon–carbon (pSi–C) composite is demonstrated. The material is prepared by electrochemical anodization of crystalline Si in an HF-containing electrolyte to generate a porous Si template, followed by infiltration of poly(furfuryl) alcohol (PFA) and subsequent carbonization to generate the pSi–C composite as an optically smooth thin film. The pSi–C sensor is significantly more stable toward aqueous buffer solutions (pH 7.4 or 12) compared to thermally oxidized (in air, 800 °C), hydrosilylated (with undecylenic acid), or hydrocarbonized (with acetylene, 700 °C) porous Si samples prepared and tested under similar conditions. Aqueous stability of the pSi–C sensor is comparable to related optical biosensors based on porous TiO<sub>2</sub> or porous Al<sub>2</sub>O<sub>3</sub>. Label-free optical interferometric biosensing with the pSi–C composite is demonstrated by detection of rabbit IgG on a protein-A-modified chip and confirmed with control experiments using chicken IgG (which shows no affinity for protein A). The pSi–C sensor binds significantly more of the protein A capture probe than porous TiO<sub>2</sub> or porous Al<sub>2</sub>O<sub>3</sub>, and the sensitivity of the protein-A-modified pSi–C sensor to rabbit IgG is found to be ∼2× greater than label-free optical biosensors constructed from these other two materials.