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.Peer reviewe

Simultaneous cavity-enhanced and cavity ringdown absorption spectroscopy using optical feedback

International audienceWe present a scheme of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) including a fast optical switch to produce cavity ringdown spectra (OF-CRDS) simultaneously. This also works as a dynamically adjustable variable attenuator allowing to compensate for reduced signal levels in correspondence with absorption lines. For this, an acousto-optic deflector is used in a double-pass configuration to eliminate the single-pass frequency shift, which is incompatible with optical feedback. This is probably the most effective device providing the required fast response and the high extinction ratio necessary to perform clean ringdown measurements. The resulting direct comparison of OF-CEAS and OF-CRDS shows that these produce almost equivalent spectral data, with 0.3 % maximal difference at the top of an absorption line having a signal-to-noise ratio (S/N) of 3,300. OF-CEAS is largely winning on the short-term noise level while OF-CRDS appears to be more immune from interference fringes, delivering cleaner spectra after longer averaging

Part per trillion nitric oxide measurement by optical feedback cavity-enhanced absorption spectroscopy in the mid-infrared

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Il significato delle cose di ogni giorno

International audienceCarbon monoxide (CO) monitoring in human breath is the focus of many investigations as CO could possibly be used as a marker of various diseases. Detecting CO in human breath remains a challenge because low concentrations (<ppm) must be selectively detected and short response time resolution is needed to detect the end expiratory values reflecting actual alveolar concentrations. A laser spectroscopy based instrument was developed (ProCeas) that fulfils these requirements. The aim of this study was to validate the use of a ProCeas for human breath analysis in order to measure the changes of endogenous exhaled CO (eCO) induced by different inspired fractions of oxygen (FiO2) ranging between 21% and 100%. This study was performed on healthy volunteers. 30 healthy awaked volunteers (including asymptomatic smokers) breathed spontaneously through a facial mask connected to the respiratory circuit of an anesthesiology station. FiO2 was fixed to 21%, 50% and 100% for periods of 5 minutes. CO concentrations were continuously monitored throughout the experiment with a ProCeas connected to the airway circuit. The respiratory cycles being resolved, eCO concentration is defined by the difference between the value at the end of the exhalation phase and the level during inhalation phase. Inhalation of 100% FiO2 increased eCO levels by a factor of four in every subjects (smokers and non smokers). eCO returned in a few minutes to the initial value when FiO2 was switched back to 21%. This magnification of eCO at 21% and 100% FiO2 is greater than those described in previous publications. We hypothesize that these results can be explained by the healthy status of our subjects (with low basal levels of eCO) and also by the better measurement precision of ProCeas

A transportable spectrometer for in situ and local measurements of iodine monoxide at mixing ratios in the 10-14 range

International audienceWe present a robust, compact, and transportable instrument that measures the iodine monoxide atmospheric radical at extremely low concentration, down to 40 ppqv (parts per quadrillion by volume, 1:1015). As nitrogen dioxide is strongly absorbed in the same spectral region it could be simultaneously measured down to 4 pptv (parts per trillion by volume, 1:1012). Relying on ''mode locked cavity-enhanced absorption spectroscopy,'' the instrument makes use of a free-running commercial femtosecond Titane Saphir laser. We demonstrate that this multiplex detection scheme provides shot noise limited spectra for acquisition times as long as 5 min. Moreover, this instrument is very versatile as it can be potentially tuned from the infrared to the ultraviolet (1080-340 nm) to reach various molecular absorptions. It has been recently deployed at the Station Biologique de Roscoff on the North West Atlantic coast of France

SPECIES: a balloon-borne and airborne instrument coupling infrared lasers with Optical Feedback Cavity Enhanced Absorption Spectroscopy technique for atmospheric in-situ trace-gas measurements

International audienceThe balloon-borne and airborne instrument SPECIES (SPECtromètre Infrarouge à lasErs in Situ) recently built in our laboratory will be described. This is a mid-infrared absorption spectrometer, including four channels by coupling Interband or Quantum Cascade Lasers (ICLs or QCLs) to Optical-Feedback Cavity-Enhanced Absorption Spectroscopy (OF-CEAS). Using cavities of 50 cm length, this leads to very high resolution ( 5 km) and thus, low detection limits for the trace gases to be measured. It can contribute to the detailed description and understanding of the functioning of the free troposphere and stratosphere in terms of composition, chemical reactivity and circulation of air masses by carrying out fast ( 4 days). High accuracies are obtained when calibration in flight, or at ground before and after the flight, is performed against standards. In addition to providing reference measurements for calibration/validation of space missions, these performances can lead to in-depth characterization of particular atmospheric processes

Comparison of optical-feedback cavity-enhanced absorption spectroscopy and gas chromatography for ground-based and airborne measurements of atmospheric CO concentration

International audienceWe present the first comparison of carbon monoxide (CO) measurements performed with a portable laser spectrometer that exploits the optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) technique, against a high-performance automated gas chromatograph (GC) with a mercuric oxide reduction gas detector (RGD). First, measurements of atmospheric CO mole fraction were continuously collected in a Paris (France) suburb over 1 week. Both instruments showed an excellent agreement within typically 2 ppb (part per billion in volume), fulfilling the World Meteorological Organization (WMO) recommendation for CO inter-laboratory comparison. The compact size and ro-bustness of the OF-CEAS instrument allowed its operation aboard a small aircraft employed for routine tropospheric air analysis over the French Orléans forest area. Direct OF-CEAS real-time CO measurements in tropospheric air were then compared with later analysis of flask samples by the gas chromatograph. Again, a very good agreement was observed. This work establishes that the OF-CEAS laser spectrometer can run unattended at a very high level of sensitivity (< 1 ppb) and stability without any periodic calibration

Frequency Comb Based Spectrometer forin Situand Real Time Measurements of IO, BrO, NO2, and H2CO at pptv and ppqv Levels

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Monitoring of endogenous nitric oxide exhaled by pig lungs during ex-vivo lung perfusion

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