Membrane-based cavity ringdown spectroscopy for enhanced sensitivity of isoprene detection

Cavity ringdown spectroscopy (CRDS) is a laser absorption technique that quantifies endogenous volatile organic compounds (VOCs) associated with diseases or metabolism. Accurately measuring breath isoprene at a wavelength of 226.56 nm via CRDS is challenging due to interference from high levels of exhaled acetone. In this work, an ultra-sensitive breath analysis system was developed that integrates gas separation membrane technology with CRDS for precise quantification of isoprene. Polyvinylidene fluoride (PVDF) hollow fiber membranes were dip-coated with polydimethylsiloxane (PDMS) to separate isoprene from acetone effectively. Proton transfer reaction mass spectrometry (PTR-MS) demonstrated that the optimal composite membrane coated with PDMS for 5 min (M5), retained 91.43 % of acetone. When a mixed gas sample (isoprene 500 ppbv, acetone 1000 ppbv) was directly introduced into the CRDS system, the detected concentration of isoprene was 545.24 +/- 18.73 ppbv. After M5 separation, the isoprene concentration decreased to 497.69 +/- 7.38 ppbv, reducing the relative error from 9.05 % to 0.46 % and enhancing the accuracy of isoprene detection. This study explores the integration of membrane separation with CRDS for real-time monitoring of simulated exhaled isoprene. The developed membrane-based CRDS system offers potential applications in biomarker validation, sensitive and accurate clinical diagnosis and long-term monitoring.