Porous nanostructured encapsulation and immobilization materials for optical biosensors

In this paper, we review nanoporous materials, with meso/microscale pores, that provide a highly versatile and useful platform for immobilization and encapsulation of recognition elements for optical chemical and biological sensors. Specifically, we describe sol-gel process derived xerogels, electrochemical wet and dry-etched porous silicon, and holographically ordered porous polymer gratings (Bragg structures). These materials offer several advantages including low cost, ease of fabrication, high surface to volume ratio, biocompatibility, functionality with various recognition elements, and the ability to modify the material surface/volume properties and porosity. In addition, several optical sensing modalities can be employed using these materials including luminescence emission and lifetime sensing, diffraction, refractive index modulation, colorimetry, ratiometry, and reflection (or transmission). Finally, we review emerging techniques employing these materials that aim toward improving detection efficiency, sensitivity, and selectivity in optical sensors including plasmonics, photonic bandgap structures, and molecular imprinted materials.