Nanoporous Silicon

Silicon (the semiconductor material in computer chips) has begun to be utilized in biomedical applications. In particular, crystalline silicon has been utilized as a textured surface to guide cell alignment, to encapsulate cells for implantation, and as an electroactive substrate to stimulate excitable cells. In comparison, porous silicon, a nanocrystalline material generated by etching of crystalline silicon in hydrofluoric acid, has been less extensively investigated for biomedical applications. Its open pore structure and large surface area, combined with unique properties such as photo and electroluminescence have provided a platform for sensors for non-biological species (e.g., solvents, gases, and explosives) as well as biological species (DNA, proteins). In collaboration with M. Sailor (UCSD, Chemistry), we have explored the biocompatibility of this material with mammalian cells to develop a ‘smart petri dish' that will change its optical signature in response to cell death (Chin et al, 2001), the utility of encoded nanoporous silicon fragments for biomolecular screening (Cunin et al, 2002) and magnetic manipulation of microfluidic droplets (Dorvee, 2004), and its function as a template for polymer replicas that can deliver drugs while being monitored remotely (Li et al, 2003) . The figure below displays images of nanoporous silicon fragments used for biomolecular screening (note the encoded ‘colors'), and data showing the degradation of the infrared signature of a polymer replica as it releases caffeine into the solution.