Fluorescence amplification using colloidal photonic crystal platform in sensing dye-labeled deoxyribonucleic acids

We applied self-assembled silica colloidal photonic crystals (CPCs) for a biosensing platform. Thin-film CPCs were tested for detecting dye-labeled deoxyribonucleic acid hybridization reactions. Due to the high porosity and large internal surface area, we observed a fluorescence signal enhanced by two orders of magnitude from CPC films composed of tens of silica sphere layers in the [1 1 1]-direction. This observation agrees with the theoretical enhancement factor of 2π/3 per silica sphere layer. The proof-of-the-concept experiment on fluorescence amplification was then followed by other complementary experiments that clarified the concerns regarding the practicality of the CPC sensor platform, such as film thickness dependence, and the effect of non-hybridized DNAs. We also learned that the silica sphere size should be chosen carefully, since the L-point photonic bandgap of the CPC may suppress the dye fluorescence.