Fluorescence enhancement by a SiO₂-based monolithic waveguide structure for biomolecular detection

We have developed a fluorescence enhancement system for biomolecular detection using a monolithic waveguide sensing plate. The plate consists of a thermally grown amorphous SiO₂ layer, a Si single-crystal layer, and bulk amorphous SiO₂. Waveguide-mode excitation in this plate produces an enhanced electric field on the plate surface, and therefore, signals from analyte-labeling fluorescent dyes are enhanced. In the present paper, we elucidate the impact of the system from viewpoints of the electric field enhancement factor calculated numerically and the analysis of the limit of detection estimated from experimental results. Optimal layer thicknesses of the plates to achieve the highest sensitivity are also discussed. Further, an interesting phenomenon that accompanied the waveguide-mode excitation, namely, photoluminescence from the amorphous SiO₂ layer itself, is also reported.