Directly Imprinted Porous Titania Metasurfaces Supporting Guided Mode Resonance and Quasibound States in the Continuum

Resonant optical metasurfaces based on guided mode resonance (GMR) and quasibound states in the continuum (qBIC) offer compelling capabilities in sensing, structural color, and flat optics, but their fabrication typically requires multistep lithographic processing that limits scalability and practical deployment. Here, we demonstrate that direct nanoimprinting of mesoporous titania (pTiO 2 ) thin films using custom‐designed periodic grating stamps produces resonant metasurfaces in a streamlined two‐step deposition‐and‐imprint process requiring no conventionalol lithography, etching, or cleanroom environment. The resulting structures support sharp, pitch‐tunable GMR resonances observable in both transmission and reflection, with resonant wavelengths scaling linearly with grating pitch. Spatial arrangement of structures with systematically varied pitch and duty cycle enables pixel‐level structural color image encoding with contrast visible under both broadband and laser illumination. Exposure to aerosolized deionized water produces fully reversible spatial resonance shifts, demonstrating label‐free dynamic colorimetric vapor sensing. Finally, introduction of a lateral asymmetry parameter α into the grating unit cell activates qBIC resonances. These results establish directly imprinted pTiO 2 as a facile, scalable platform for visible‐wavelength resonant metasurface devices.