Fabrication of optomicrofluidics for real-time bioassays based on hollow sphere colloidal photonic crystals with wettability patterns

Abstract

An optomicrofluidic device was developed by introducing 3D wettability patterns into hollow SiO₂ sphere colloidal photonic crystals. Aqueous liquids flow through the superhydrophilic channel due to the surface tension confinement effect. Based on the significant fluorescence enhancement from photonic band gap (PBG) effects in these channels, real-time specific bioassays with high sensitivity were realized. To demonstrate this strategy, with two complementary single stranded DNA molecules acting as a target (fluorophore labeled) and a probe respectively, a 150-fold enhancement of fluorescence was observed compared with a similar device on a standard glass plate. This enhancement results from the strong PBG effect in an aqueous environment for these structures. While the PBG effect diminishes from refractive index matching in conventional solid sphere colloidal photonic crystals with water infiltrated, it is effectively enhanced in hollow sphere colloidal photonic crystals. This is because the dense shell of the hollow spheres prevents water from infiltrating into the inner air cavity of the hollow spheres, while water fills the voids between spheres. This creates a larger refractive index contrast, resulting in a pronounced PBG effect and strong fluorescence enhancement.