Application of Near-Infrared Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) to the Detection of Ammonia in Exhaled Human Breath

Abstract

The qualitative and quantitative analysis to trace gas in exhaled human breath has become a promising technique in biomedical applications such as disease diagnosis and health status monitoring. This paper describes an application of a high spectral resolution optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) for ammonia detection in exhaled human breath, and the main interference of gases such as CO2 and H2O are approximately eliminated at the same time. With appropriate optical feedback, a fibered distributed feedback (DFB) diode laser emitting at 1531.6 nm is locked to the resonance of a V-shaped cavity with a free spectral range (FSR) of 300 MHz and a finesse of 14,610. A minimum detectable absorption coefficient of αmin = 2.3 × 10−9 cm−1 is achieved in a single scan within 5 s, yielding a detection limit of 17 ppb for NH3 in breath gas at low pressure, and this stable system allows the detection limit down to 4.5 ppb when the spectra to be averaged over 16 laser scans. Different from typical CEAS with a static cavity, which is limited by the FSR in frequency space, the attainable spectral resolution of our experimental setup can be up to 0.002 cm−1 owing to the simultaneous laser frequency tuning and cavity dither. Hence, the absorption line profile is more accurate, which is most suitable for low-pressure trace gas detection. This work has great potential for accurate selectivity and high sensitivity applications in human breath analysis and atmosphere sciences.

Study of a Mode Separation Due to Polarization Existing in a Cavity-Enhanced Absorption Spectroscopy

“…The addition of line polarizers allowed to improve the system, namely by preventing and eliminating the resonant mode separation phenomenon observed, leading to the observation of several absorption lines of residual water vapor in the cavity. A minimum detectable absorption coefficient of α min = 7.6 × 10 −9 cm −1 can be obtained in a single laser scan of 10 s. This trace gas detection sensor has a compact structure and potential to provide stable performance in breath applications according to our previous work [29]. Potential applications of this phenomenon are also proposed in our paper.…”

“…It also prevents the direct reflection light at the incident mirror from being fed back to the laser, causing oscillations in the laser output pattern. The folded-cavity is a classical cavity structure in the application of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) [29]. However, such a structure seems to make the cavity selective for the polarization of the incident laser.…”

Smelling the Disease: Diagnostic Potential of Breath Analysis

“…Exhaled breath analysis has the potential to be useful in a wide range of diagnostic studies. This necessitates a detector with high sensitivity and accurate selectivity that can detect many VOCs in ultralow concentrations in exhaled breath samples for qualitative and quantitative analysis [ 54 ]. VOCs in exhaled breath can be detected using a variety of analytical techniques (Fig.…”

“…A recent and the most promising technique for real-time trace gas detection, cavity-enhanced absorption spectroscopy (CEAS) is based on spectral distribution and line shape theories, which can detect gaseous components in low concentrations with high sensitivity and accurately identify them even in the presence of other interfering gases. The CEAS employs an optical frequency comb (OFC), a light source developed by the Ye group, to simultaneously detect several components [ 54 , 81 ]. Once a specific molecule linked with the disease has been identified, optical absorption can be used to diagnose the disease.…”

Selectivity in trace gas sensing: recent developments, challenges, and future perspectives

“…Apart from these well-known techniques, several variations of absorption spectroscopy have been used in recent years to detect trace gases and VOCs. Some notable examples are optical feedback cavity enhanced absorption spectroscopy (OF-CEAS), 119 tunable diode laser spectroscopy (TDLS), 24 photoacoustic spectroscopy (PAS), 24,161 quartz-enhanced PAS (QEPAS), 77,79,81,162 differential optical absorption spectroscopy (DOAS), 163–165 noise-immune cavity-enhanced optical heterodyne spectroscopy (NIC-EOHS), 166 two-tone frequency modulation spectroscopy (TTFMS), 167–169 and broadband cavity-enhanced spectroscopy (BB-CEAS). 46,170…”