Laser-based human breath analysis: D/H isotope ratio increase following heavy water intake

Partial Amplification of Octave-Spanning Supercontinuum in the Spectral Region of 1.5–2.2 μm

Octave-spanning supercontinuum conversion in three different rare-earth doped fiber amplifiers have been investigated. Using an erbium amplifier, it turned out to increase the output power to 445 mW with a spectral width of 1250 nm. For a thulium amplifier, an average output power of 390 mW and a spectral width of 569 nm was obtained. Additionally, for holmium, the average output power was 724 mW with a spectral width of 450 nm. For all cases, the output pulses envelope did not exceed 0.72 ns.

Analysis of the Stable Isotope Ratios (18O/16O, 17O/16O, and D/H) in Glacier Water by Laser Spectrometry

A compact isotope ratio sensor based on laser absorption spectroscopy at 2.7 μm was developed for high precision and simultaneous measurements of the D/H, ¹⁸O/¹⁶O and ¹⁷O/¹⁶O isotope ratios in glacier water. Measurements of the oxygen and hydrogen isotope ratios in glacier water demonstrate a 1σ precision of 0.3‰ for δ¹⁸O, 0.2‰ for δ¹⁷O, and 0.5‰ for δ²H, respectively. The δ values of the working standard glacier water obtained by the calibrated sensor system is basically identical to the IRMS measurement results with a very high calibration accuracy from 0.17‰ to 0.75‰. Preliminary results on the reproducibility measurements display a standard deviation of 0.13‰ for δ¹⁸O, 0.13‰ for δ¹⁷O, and 0.64‰ for δ²H, respectively.

All-chalcogenide single-mode optical fiber couplers

We demonstrate the fabrication of all chalcogenide single-mode optical fiber couplers including broadband couplers, wavelength division multiplexers, and polarization beamsplitters. The functionality of each coupler is engineered with a careful design of geometry. As a result, broadband couplers can be set to any arbitrary coupling ratio. Wavelength division multiplexers provide a coupling extinction ratio up to 35 dB, and polarization beamsplitters provide a polarization extinction ratio up to 18 dB.

Laser spectroscopy for breath analysis: towards clinical implementation

Detection and analysis of volatile compounds in exhaled breath represents an attractive tool for monitoring the metabolic status of a patient and disease diagnosis, since it is non-invasive and fast. Numerous studies have already demonstrated the benefit of breath analysis in clinical settings/applications and encouraged multidisciplinary research to reveal new insights regarding the origins, pathways, and pathophysiological roles of breath components. Many breath analysis methods are currently available to help explore these directions, ranging from mass spectrometry to laser-based spectroscopy and sensor arrays. This review presents an update of the current status of optical methods, using near and mid-infrared sources, for clinical breath gas analysis over the last decade and describes recent technological developments and their applications. The review includes: tunable diode laser absorption spectroscopy, cavity ring-down spectroscopy, integrated cavity output spectroscopy, cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, quartz-enhanced photoacoustic spectroscopy, and optical frequency comb spectroscopy. A SWOT analysis (strengths, weaknesses, opportunities, and threats) is presented that describes the laser-based techniques within the clinical framework of breath research and their appealing features for clinical use.

Measurement of Whole-Body CO2 Production in Birds Using Real-Time Laser-Derived Measurements of Hydrogen (δ(2)H) and Oxygen (δ(18)O) Isotope Concentrations in Water Vapor from Breath

The doubly labeled water (DLW) method is commonly used to measure energy expenditure in free-living wildlife and humans. However, DLW studies involving animals typically require three blood samples, which can affect behavior and well-being. Moreover, measurement of H (δ(2)H) and O (δ(18)O) isotope concentrations in H2O derived from blood using conventional isotope ratio mass spectrometry is technically demanding, time-consuming, and often expensive. A novel technique that would avoid these constraints is the real-time measurement of δ(2)H and δ(18)O in the H2O vapor of exhaled breath using cavity ring-down (CRD) spectrometry, provided that δ(2)H and δ(18)O from body H2O and breath were well correlated. Here, we conducted a validation study with CRD spectrometry involving five zebra finches (Taeniopygia guttata), five brown-headed cowbirds (Molothrus ater), and five European starlings (Sturnus vulgaris), where we compared δ(2)H, δ(18)O, and rCO2 (rate of CO2 production) estimates from breath with those from blood. Isotope concentrations from blood were validated by comparing dilution-space estimates with measurements of total body water (TBW) obtained from quantitative magnetic resonance. Isotope dilution-space estimates from δ(2)H and δ(18)O values in the blood were similar to and strongly correlated with TBW measurements (R(2) = 0.99). The (2)H and (18)O (ppm) in breath and blood were also highly correlated (R(2) = 0.99 and 0.98, respectively); however, isotope concentrations in breath were always less enriched than those in blood and slightly higher than expected, given assumed fractionation values between blood and breath. Overall, rCO2 measurements from breath were strongly correlated with those from the blood (R(2) = 0.90). We suggest that this technique will find wide application in studies of animal and human energetics in the field and laboratory. We also provide suggestions for ways this technique could be further improved.

Measurement of the D/H, ¹⁸O/¹⁶O, and ¹⁷O/¹⁶O isotope ratios in water by laser absorption spectroscopy at 2.73 μm

A compact isotope ratio laser spectrometry (IRLS) instrument was developed for simultaneous measurements of the D/H, 18O/16O and 17O/16O isotope ratios in water by laser absorption spectroscopy at 2.73 μm. Special attention is paid to the spectral data processing and implementation of a Kalman adaptive filtering to improve the measurement precision. Reduction of up to 3-fold in standard deviation in isotope ratio determination was obtained by the use of a Fourier filtering to remove undulation structure from spectrum baseline. Application of Kalman filtering enables isotope ratio measurement at 1 s time intervals with a precision (<1‰) better than that obtained by conventional 30 s averaging, while maintaining a fast system response. The implementation of the filter is described in detail and its effects on the accuracy and the precision of the isotope ratio measurements are investigated.

Infrared spectroscopy on smoke produced by cauterization of animal tissue

In view of in vivo surgical smoke studies a difference-frequency-generation (DFG) laser spectrometer (spectral range 2900–3144 cm⁻¹) and a Fourier-transform infrared (FTIR) spectrometer were employed for infrared absorption spectroscopy. The chemical composition of smoke produced in vitro with an electroknife by cauterization of different animal tissues in different atmospheres was investigated. Average concentrations derived are: water vapor (0.87%), methane (20 ppm), ethane (4.8 ppm), ethene (17 ppm), carbon monoxide (190 ppm), nitric oxide (25 ppm), nitrous oxide (40 ppm), ethyne (50 ppm) and hydrogen cyanide (25 ppm). No correlation between smoke composition and the atmosphere or the kind of cauterized tissue was found.

Kalman filtering real-time measurements of H2O isotopologue ratios by laser absorption spectroscopy at 2.73 microm

Kalman adaptive filtering was applied for the first time, to our knowledge, to the real-time simultaneous determination of water isotopic ratios using laser absorption spectroscopy at 2.73 microm. Measurements of the oxygen and hydrogen isotopologue ratios delta(18)O, delta(17)O, and delta(2)H in water showed a 1-sigma precision of 0.72 per thousand for delta(18)O, 0.48 per thousand for delta(17)O, and 0.84 per thousand for delta(2)H, while sampling the output of the tuned Kalman filter at 1 s time intervals. Using a standard running average technique, averaging over approximately 30 s is required to obtain the same level of precision.

Cavity-enhanced direct frequency comb spectroscopy: technology and applications

Cavity-enhanced direct frequency comb spectroscopy combines broad bandwidth, high spectral resolution, and ultrahigh detection sensitivity in one experimental platform based on an optical frequency comb efficiently coupled to a high-finesse cavity. The effective interaction length between light and matter is increased by the cavity, massively enhancing the sensitivity for measurement of optical losses. Individual comb components act as independent detection channels across a broad spectral window, providing rapid parallel processing. In this review we discuss the principles, the technology, and the first applications that demonstrate the enormous potential of this spectroscopic method. In particular, we describe various frequency comb sources, techniques for efficient coupling between comb and cavity, and detection schemes that utilize the technique's high-resolution, wide-bandwidth, and fast data-acquisition capabilities. We discuss a range of applications, including breath analysis for medical diagnosis, trace-impurity detection in specialty gases, and characterization of a supersonic jet of cold molecules.

Breath analysis using laser spectroscopic techniques: breath biomarkers, spectral fingerprints, and detection limits

Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser spectroscopic techniques and laser sources have driven breath analysis to new heights, moving from laboratory research to commercial reality. Laser spectroscopic detection techniques not only have high-sensitivity and high-selectivity, as equivalently offered by the MS-based techniques, but also have the advantageous features of near real-time response, low instrument costs, and POC function. Of the approximately 35 established breath biomarkers, such as acetone, ammonia, carbon dioxide, ethane, methane, and nitric oxide, 14 species in exhaled human breath have been analyzed by high-sensitivity laser spectroscopic techniques, namely, tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS), cavity leak-out spectroscopy (CALOS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS). Spectral fingerprints of the measured biomarkers span from the UV to the mid-IR spectral regions and the detection limits achieved by the laser techniques range from parts per million to parts per billion levels. Sensors using the laser spectroscopic techniques for a few breath biomarkers, e.g., carbon dioxide, nitric oxide, etc. are commercially available. This review presents an update on the latest developments in laser-based breath analysis.