Sub-ppb-level sensitive hydrogen gas sensing based on PDMS-Pt enhanced microrod cavity

Hydrogen, as an important clean energy, requires highly sensitive and rapid detection to ensure safety during its production, transportation, and utilization. Whispering-gallery-mode (WGM) optical microcavities, owing to enhanced light-matter interaction and intrinsic spark-free characteristic, offer a highly sensitive and inherently safe sensing platform. However, due to hydrogen's small molecular weight, conventional microcavities present no responsiveness to hydrogen. Surface-functionalized optical microcavities have emerged as a promising solution. Here, we propose a high-quality-factor polydimethylsiloxane-platinum coated microrod resonator. Platinum (Pt) serves as a catalytic site to facilitate the oxidation of hydrogen, while polydimethylsiloxane (PDMS), acting as the encapsulating layer, preserves the microcavity's high Q factor. The large thermo-optic coefficient property of PDMS enables the device to sensitively respond to temperature changes, reflected as resonance shifting. By real-time monitoring of the transmission spectrum, hydrogen at 0.16 ppb was successfully detected. Moreover, selective detection with a dynamic range up to 100 ppm was achieved. This approach presents what we believe to be a novel optical strategy for hydrogen sensing and its practical applications.