A Distributed Bragg Reflector Interface for Filter‐Free Fluorescence Spectro‐Microscopy With High Spectral Tunability

Fluorescence spectroscopy and microscopy are essential analytical methods, yet their miniaturization is constrained by the reliance on bulky excitation and emission filters. In this work, an all‐dielectric TiO 2 /SiO 2 distributed Bragg reflector (DBR) is engineered to function simultaneously as the sample substrate and the wavelength‐selective element, enabling filter‐free fluorescence spectro‐microscopy. The DBR, consisting of five high/low refractive‐index layer pairs, is designed through simulations informed by ellipsometry measurements to align the stopband with the excitation wavelength and the passband with the fluorophore emission. For ATTO532, the fabricated DBR exhibits a reflectance of ~0.015 at 532 nm and ~0.78 at 552 nm, providing strong suppression of excitation light and efficient reflection of fluorescence. Vapor‐phase APTES silanization of the TiO 2 surface yields an amine‐terminated interface for covalent NHS‐ester dye immobilization, confirmed by contact angle and atomic force microscopy (AFM) analysis. Spectral tunability is demonstrated by redesigning the DBR for Rhodamine B, where nanometer‐scale adjustments in TiO 2 thickness enable discrimination of fluorophores with closely spaced spectra. Fluorescence spectra and images are recorded without external filters using a compact confocal setup. High‐contrast imaging is achieved even for sub‐monolayer dye coverage. The platform establishes a tunable, substrate‐integrated filtering strategy for compact fluorescence sensing and imaging systems.