Highly sensitive cavity ring-down spectroscopy for exhaled carbon monoxide detection toward preclinical stroke monitoring

Rapid, noninvasive diagnosis is critical for stroke patient management. Conventional detection methods are often limited by slow turnaround and high costs. This work demonstrates a proof-of-concept, highly sensitive sensor for exhaled carbon monoxide (CO) to enable preclinical stroke monitoring in animal models. The system is based on near-infrared cavity ringdown spectroscopy (CRDS), in which birefringence noise in the high-finesse cavity is suppressed via polarization control, achieving a measurement sensitivity of 2.6 × 10 -12 cm −1 and a corresponding CO detection limit of 1.5 ppb. A novel scheme combining low-frequency large-amplitude laser current scanning for resonance acquisition, high-frequency small-amplitude dithering for continuous ring-down event recording, and stepwise PZT voltage adjustment, was developed to achieve efficient resonance locking and a tenfold improvement in spectral resolution. Additionally, a breath sampling and filtration device was designed to suppress interference from high concentrations of CO 2 and H 2 O in exhaled breath. The system enabled detection of exhaled CO in rat stroke models, providing a potential rapid and noninvasive screening approach for stroke in preclinical studies.