Real-Time Monitoring of ¹³C- and ¹⁸O-Isotopes of Human Breath CO₂ Using a Mid-Infrared Hollow Waveguide Gas Sensor

Abstract

Real-time measuring CO 2 isotopes ( 13 CO 2 , 12 CO 2 , and 18 OC 16 O) in exhaled breath using a mid-infrared hollow waveguide (HWG) gas sensor incorporating a 2.73 μm DFB laser was proposed and demonstrated first time based on calibrationfree wavelength modulation spectroscopy (CF-WMS). The measurement precisions for δ 13 C and δ 18 O were respectively 0.26‰ and 0.57‰ for an integration time of 131 s by Allan variance analysis. These measurement precisions achieved in the present work were at least 3.5 times better than those reported using direct absorption spectroscopy (DAS) and 1.3 times better than those obtained by calibration-needed wavelength modulation absorption spectroscopy (CN-WMS). Continuous measurement of three isotopes in the breathing cycle was performed. Alveolar gas from the expirogram was identified, and the 13 C/ 12 C and 18 O/ 16 O ratios were found to be almost constant during the alveolar plateau, which enables optimization of breath sampling and providing accurate information on metabolic processes. The 13 C/ 12 C and 18 O/ 16 O isotope ratios at the alveolar plateau of five breath cycles were averaged, yielding δ 13 C and δ 18 O values of (-24.3±3.4) ‰ and (-30.7±2.6) ‰, respectively. This study demonstrates the feasibility of real-time analysis of 13 C and 18 O-isotopes of human breath CO 2 in clinical application and shows its potential for diagnosing respiratory-related diseases with high sensitivity, selectivity, and specificity.

Designing Mid-Infrared Gold-Based Plasmonic Slot Waveguides for CO2-Sensing Applications

“…Several gas sensors based on optical waveguides were designed and proposed, see e.g., [23,24]. In addition, some recent mid-IR waveguides based on CO 2 sensing have been proposed and demonstrated [25][26][27]. In comparison to conventional dielectric waveguides, plasmonic waveguides typically can be expected to feature smaller propagation lengths (i.e., intrinsic damping), which are related to the intrinsic losses within the used metals.…”

Simultaneous Sensitive Determination of δ13C, δ18O, and δ17O in Human Breath CO2 Based on ICL Direct Absorption Spectroscopy

“…Finally, to demonstrate the potential for disease diagnosis, similar precisions were obtained in realtime breath measurement. Compared with the gas sensor in recent work [24] mentioned in the introduction section, our system reaches a more than five times better precision on δ 13 C and δ 18 O measurements. The obtained results highlight the viability of the laser spectroscopic system in general and its potential for practical application in breath analysis.…”

“…These measurements at near infrared require the assistance of a high-finesse optical cavity or a multipath cell, which is usually accompanied by a larger volume of gas demand, so they are not really friendly for real-time online breath analysis, where the sample gas is usually limited. A hollow waveguide with a small volume was used by Zhou et al to achieve simultaneous measurement of δ 13 C and δ 18 O, and the minimum precisions were 0.26‰ and 0.57‰ for δ 13 C and δ 18 O, respectively, achieved by calibration-free wavelength modulation spectroscopy [24,25]. However, there is currently no measurement of δ 17 O in exhaled CO 2 , although studies have shown that 17 O isotopes in respiration can be used as a biomarker of brain oxygen metabolism [26,27].…”

Liquid Metal-Based Epidermal Flexible Sensor for Wireless Breath Monitoring and Diagnosis Enabled by Highly Sensitive SnS 2 Nanosheets

“…Figure S12: time-resolved photo response under blue (450 nm), green (532 nm), and red (650 nm) light of 1 mW/cm 2 . Figure S13: temporal photocurrent response under blue light of various power densities (1,3,5,10,20, and 40 mW/cm 2 ). Figure S14: fitting curve of photocurrent and power density under blue light illumination.…”

“…For example, Il-Doo Kim group fabricated colorimetric dye-loaded nanofiber yarn which is sensitive to ppm-level H 2 S and NH 3 biomarkers [15]. Zhou et al utilized a mid-infrared hollow waveguide gas sensor to realize real-time measuring of CO 2 isotopes [20]. Chen et al developed a breath analysis approach based on SERS sensor to detect fourteen volatile organic compound (VOC) biomarkers [16].…”