Photonic Crystal Film Preparation and Characterization for Chemical Sensing

Functionalized photonic crystal films were prepared for sensing small chemical molecules. First, silica nanospheres were self-assembled to form a colloidal crystal template within a mold. The interstitial space of this template was infiltrated by the hydrogel precursors, which were then allowed to polymerize. Upon removal of silica by hydrofluoric acid etching, a photonic crystal film, which produced a pink structural color, was formed. To add a chemical sensing functionality to the film, the molecules to be sensed were mixed with the hydrogel precursors for molecular imprinting; the amino acid proline was used for this purpose. Characterization of the functionalized photonic crystal film was conducted by optical reflectance measurements and imaging. The nanopores were imaged using SEM after cryogenic freezing of the film samples. Chemical sensing of proline was conducted on the film, with the reflectance peak shifting from 650 nm to