Immobilization of Mie-Resonant Silicon Nanospheres on a Silica Substrate for Surface-Enhanced Fluorescence

A process to immobilize Mie-resonant silicon nanospheres (Si NSs) on a large area substrate is developed for the application of surface-enhanced fluorescence (SEF) biosensors. The surface of size-purified Si NSs having the low-order Mie resonances in the visible to near-infrared range is functionalized with the epoxy group, and the Si NSs are immobilized on the surface of an amino-terminated silica (SiO₂) substrate 1 × 1 cm ² in size by a fully wet process. The produced substrate exhibits a clear Mie resonant color. The wavelength of the reflectance maximum is controlled by the size of Si NSs, and the highest reflectance value reaches over 40%. In order to study the capability of the developed substrate as an SEF substrate, Lucifer Yellow CH dipotassium salt dye (LY) molecules are directly placed on the substrate and the photoluminescence (PL) properties are studied. The PL intensity is enhanced ≈14-fold on a substrate on which Si NSs 129 nm in average diameters are immobilized. Theoretical calculations by taking into account the size distribution of Si NSs explain the observed size dependence of the enhancement factor.