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Abstract:
Breath gas analysis is a novel powerful technique for
noninvasive, early-stage diagnosis of metabolic disorders or diseases.
Molecular hydrogen and methane are biomarkers for colonic
fermentation, because of malabsorption of oligosaccharides (e.g., lactose
or fructose) and for small intestinal bacterial overgrowth. Recently, the
presence of these gases in exhaled breath was also correlated with
obesity. Here, we report on the highly selective and sensitive detection of
molecular hydrogen and methane within a complex gas mixture
(consisting of H2, CH4, N2, O2, and CO2) by means of fiber-enhanced
Raman spectroscopy (FERS). An elaborate FERS setup with a
microstructured hollow core photonic crystal fiber (HCPCF) provided
a highly improved analytical sensitivity. The simultaneous monitoring of
H2 with all other gases was achieved by a combination of rotational (H2)
and vibrational (other gases) Raman spectroscopy within the limited spectral transmission range of the HCPCF. The HCPCF
was combined with an adjustable image-plane aperture pinhole, in order to separate the H2 rotational Raman bands from the
silica background signal and improve the sensitivity down to a limit of detection (LOD) of 4.7 ppm (for only 26 fmol H2). The
ability to monitor the levels of H2 and CH4 in a positive hydrogen breath test (HBT) was demonstrated. The FERS sensor
possesses a high dynamic range (∼5 orders of magnitude) with a fast response time of few seconds and provides great potential
for miniaturization. We foresee that this technique will pave the way for fast, noninvasive, and painless point-of-care diagnosis of metabolic diseases in exhaled human breath.
