Abstract
Human exhaled methane (CH4) has essential significance in detecting intestinal flora. In this study, a high-precision quartz tuning fork (QTF) based light-induced thermoelastic spectroscopy (LITES) system was developed, a mid-infrared interband cascade laser (ICL) and a QTF detector coated with polydimethylsiloxane (PDMS) and reduced graphene oxide (rGO) were employed for the CH4 detection. Experimental results indicate that the composite coating resulted in a 3-fold increase in 2f signal amplitude and signal-to-noise ratio (SNR), when compared to the bare QTF detector. The system has achieved a minimum detection limit (MDL) of 58.65 ppbv (part per billion volume) and a normalized noise equivalent absorption coefficient (NNEA) of 2.069 × 10−10 cm−1·W·Hz−1/2, Allan deviation analysis indicates that the optimal measurement accuracy is 36.85 ppbv. 24 healthy college students and 10 overweight/obese students were recruited to measure the CH4 concentration in the exhaled breath. The results show that exhaled CH4 concentrations of healthy individuals range from 0.5 to 3 ppmv (part per million volume), with slightly higher levels in males than females, and higher levels in the obese individuals than those in the normal individuals. The mid-infrared LITES CH4 measurement system holds promise as a new non-invasive method for assessing human metabolic states, with potential applications in medical and life sciences.
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