We study fundamentals and applications of silicon-based nanomaterials. We focus on mesoporous silicon, harnessing its properties to answer fundamental questions in chemistry, materials science, biology, and medicine. Current research topics emphasize using tissue-specific peptide targeting groups and biologic (proteins and nucleic acid) drug payloads incorporated with porous silicon nanoparticles to help understand and treat conditions such as cancer, bacterial and viral infections, neuronal injuries, and diseases of the eye. We also use the porous nanostructures to encapsulate and enhance the performance of enzymes and other catalytic compounds for a range of medical, environmental remediation, and energy storage/harvesting applications. We explore luminescent silicon quantum dots as in-vitro and in-vivo imaging agents. We construct dielectric mesostructures such as photonic crystals for chemical/biochemical sensor applications. Trainees in our lab engage in these projects with a network of academic and industrial research collaborators from around the globe.