Tunable optical filters with hybrid plasmonic-dielectric thin-films for fluorescence sensing

Abstract

Hyperspectral imaging and fluorescence sensing are widely used technologies in many applications in biomedical sciences. The key component in such techniques is the wavelength optical tunable filter that covers a wide range of excitation and emission spectrums of fluorophores. The detection sensitivity and specificity are highly dependent on the spectral filtering method’s characteristics and performance. Acousto-optic tunable filters (AOTF) and liquid crystal tunable filters (LCTF) are widely used spectral filtering methods for microscopy systems. Due to the complexity of these filters’ structures, they lack the integrability in miniaturized systems. Miniaturization allows portability, lower cost due to the possibility of mass production along with small amounts of samples and reagents needed to perform the analysis. Herein, we introduce a plasmonic tunable optical filter based on hybrid dielectric and plasmonic thin films of TiO₂, SiO₂ and Ag respectively, with a tunable air gap. The simplicity of the structure fabrication allows its integrability in lab-on-chip systems. The gap thickness can be changed by a micro-actuator, which translates to a tunable range of central wavelengths that exceeds 300 nm covering several types of fluorophores’ excitation and emission ranges. The peak's maximum transmittance is above 70% for all colors, and can even be up to 85% for some colors, with a rejection band over the rest of the visible range. The same filter structure could be tuned to cover different bands in the visible range by changing the film's thicknesses and materials.