Tunable Optical–Chemical Coupling in PVA/WO ₃ Nanocomposite Guided-Mode Resonance Sensors for Flexible VOC Detection

High Resolution Image Download MS PowerPoint Slide Flexible optical gas sensors that combine scalable fabrication with chemically tunable sensing layers remain underdeveloped for volatile organic compound (VOC) monitoring. Here, we report a poly(vinyl alcohol)/tungsten oxide (PVA/WO 3 ) nanocomposite guided-mode resonance (GMR) platform that enables tunable optical–chemical coupling for enhanced VOC vapor sensing. The device is fabricated on a polydimethylsiloxane (PDMS) substrate through a simple mold-casting process, forming a fully polymeric grating–waveguide architecture without requiring complex lithographic fabrication. Systematic composition control reveals that incorporating WO 3 nanoparticles increases the refractive index of the PVA matrix while simultaneously introducing optical loss, thereby establishing a structure–property trade-off that governs resonance performance. An optimal WO 3 loading of 10 wt % preserves distinct resonance characteristics while maximizing sensing sensitivity. Upon VOC exposure, the nanocomposite GMR sensor exhibits significantly enhanced optical responses, including an approximately 8-fold increase in resonance wavelength shift toward n -butanol compared with the pristine PVA-based device. This enhancement originates from coupled optical–chemical interactions, in which VOC adsorption and diffusion within the PVA/WO 3 grating–waveguide layer induce simultaneous changes in the effective refractive index and film thickness. Furthermore, oxygen-rich WO 3 surfaces promote stronger polar interactions and hydrogen bonding with alcohol molecules, thereby enhancing analyte uptake and amplified resonance shifts. This work demonstrates that nanocomposite-enabled optical–chemical coupling provides an effective and generalizable strategy for simultaneously tailoring optical transduction and analyte affinity in flexible photonic sensors, offering a pathway toward low-power, scalable, and application-specific VOC sensing platforms.