Adaptively laser-tagging optofluidic microcavity for single-molecule hydrogen detection across 9-decade concentration span

Optical microcavities are exceptional transducers for gas sensing, yet their performance is fundamentally constrained by the trade-off between sensitivity and dynamic range, degradation of quality factor ( Q ) upon integration with sensitive materials, and pervasive system noises. Here, we introduce a laser-tagging optofluidic microcavity that simultaneously overcomes these challenges for single-molecule hydrogen detection. Our architecture employs a hollow whispering-gallery-mode microcavity, functionally inner-coated with Pt/WO ₃ nanofilm. Gas detection is mediated through thermal phonon transfer, which prevents the sensitive film from perturbing the optical field. This mechanism preserves an ultrahigh intrinsic Q factor of 1.89 × 10 ⁹ even during sensing, therefore offers a unique tool to develop a laser-tagging method that dynamically locks the probe laser to the microcavity’s optimal operation point, enabling real-time resonance tracking. This approach suppresses phase noise by over three orders of magnitude and facilitates wide-bandwidth optoelectronic heterodyne demodulation. Consequently, we achieve a Hz-level frequency-shift resolution and a measurable resonance shift range of 1 GHz, breaking the conventional inverse relationship between accuracy and dynamic range. In single-shot measurement, our sensor achieves a minimum detectable concentration of 0.1 ppb and a maximum of 162 ppk, spanning 9 orders of magnitude. Moreover, after lock-in amplification, individual molecule dynamics are resolved. The integrated, centimetre-scale footprint of the device ensures robust ‘plug-and-play’ operation outside the laboratory, providing a universal strategy to advance optical microcavities towards a broad spectrum of ultra-precise metrology applications.