Quantum Cascade Laser Spectroscopy
373
exhaled breath NO monitoring at 5.2 μm mid-IR spectral range [61]. The utilisation
of wavelength modulation technique along with high-sensitive OA-ICOS detection
strategy helped to reach noise-equivalent sensitivity of 2 ppbv of NO for a 15 s
data acquisition. Subsequently, the same group demonstrated the improvement of
the system by incorporating a continuous wave thermoelectric cooled DFB-QCL
at 5.45 μm (1835 cm
−1 ) to measure the NO in sub-ppb level and eventually, they
achieved noise equivalent minimum detection limit (MDL) of 0.7 ppbv with a 1 s
integration time due to coupling of QCL to the high-finesse optical cavity (pathlength
~700 m). Furthermore, a CRDS system based on a room temperature operated modehof free EC-QCL was demonstrated for mid-IR ultrasensitive NO detection in human
exhaled breath by Dutta Banik et al. [62]. The coupling of EC-QCL to high-sensitive
detection strategy and probing the fundamental band of NO near 5.2 μm enabled to
achieve the noise equivalent absorption coefficient of 1.01 × 10
−9 cm
−1 Hz
−1/2 .
In the view of having the particular interest of ammonia in exhaled breath related
to kidney malfunction and peptic ulcers, Manne and his research group developed a
mid-IR QCL based pulsed CRD spectrometer for quantification of NH 3 in exhaled
air [63]. They probed the almost interference-free transition line, originated from
fundamental vibrational band ν 2 with the intensity of 5.6 × 10
–19 cm
−1 molecule
cm
−2 , of ammonia (NH 3 ) near 967 cm
−1 and subsequently, achieved a sensitivity
of 50 ppb with a 20 s time resolution. Moreover, a quartz enhanced photoacoustic
spectroscopy (QEPAS) based gas analyser was developed near mid-IR spectral region
by Rafal et al. for real-time quantitative measurement of NH 3 in human exhaled breath
[64]. In their study, they utilized a widely tuneable (914–972 cm
−1 ) room-temperature
operated EC-QCL with emission power 42 mW to probe the ro-vibrational lines
of the ν 2 NH 3 fundamental absorption band. The detection sensitivity for exhaled
ammonia measurement was achieved <10 ppbv in 1 s time resolution. Later, Pradhan
and his research team from India developed a cw CRD spectrometer by exploiting a
widely tuneable EC-QCL near 6.2 μm for estimation of human exhaled breath NH 3
concentration with high sensitivity and molecular specificity [65]. To obtain the NH 3
concentration they scanned the pre-selected interference-free (from the ubiquitous
gas matrix in exhaled breath) transition line from fundamental ν 4 band centred at
1613.370 cm
−1 and they achieved the detection limit of 740 parts-per-trillion by
volume at a cavity pressure of 115 Torr for an integration time of ∼167 s.
After understanding the diagnostic potential of CO related to several diseases
like asthma, diabetes, Moeskops et al. developed a TE cooled DFB QCL based
CO breath sensor [66]. They probed the strong R(8)1 rovibrational transition of
CO at 2176.2835 cm
−1 for its quantitative estimation in human exhaled breath and
subsequently, they achieved a minimal detectable absorption of 1.2 × 10
−5 cm
−1 by
incorporating 20 m multi-pass gas cell. Recently, Maruin et al. has developed a quartz
enhanced photo-acoustic spectrometer near 4.7 μm spectral region for CO detection
in human breath in the clinical environment [67]. For this study, they utilized a room
temperature operated Fabry–Perot quantum cascade laser with high optical emission
power ~100 mW. The QCL based CO breath sensor achieved a minimum detection of 20 ppb in 1s data acquisition and they validated system performance with
conventional blood carboxy-hemoglobin (COHb %) measurement. In Jacek Wojtas
373
exhaled breath NO monitoring at 5.2 μm mid-IR spectral range [61]. The utilisation
of wavelength modulation technique along with high-sensitive OA-ICOS detection
strategy helped to reach noise-equivalent sensitivity of 2 ppbv of NO for a 15 s
data acquisition. Subsequently, the same group demonstrated the improvement of
the system by incorporating a continuous wave thermoelectric cooled DFB-QCL
at 5.45 μm (1835 cm
−1 ) to measure the NO in sub-ppb level and eventually, they
achieved noise equivalent minimum detection limit (MDL) of 0.7 ppbv with a 1 s
integration time due to coupling of QCL to the high-finesse optical cavity (pathlength
~700 m). Furthermore, a CRDS system based on a room temperature operated modehof free EC-QCL was demonstrated for mid-IR ultrasensitive NO detection in human
exhaled breath by Dutta Banik et al. [62]. The coupling of EC-QCL to high-sensitive
detection strategy and probing the fundamental band of NO near 5.2 μm enabled to
achieve the noise equivalent absorption coefficient of 1.01 × 10
−9 cm
−1 Hz
−1/2 .
In the view of having the particular interest of ammonia in exhaled breath related
to kidney malfunction and peptic ulcers, Manne and his research group developed a
mid-IR QCL based pulsed CRD spectrometer for quantification of NH 3 in exhaled
air [63]. They probed the almost interference-free transition line, originated from
fundamental vibrational band ν 2 with the intensity of 5.6 × 10
–19 cm
−1 molecule
cm
−2 , of ammonia (NH 3 ) near 967 cm
−1 and subsequently, achieved a sensitivity
of 50 ppb with a 20 s time resolution. Moreover, a quartz enhanced photoacoustic
spectroscopy (QEPAS) based gas analyser was developed near mid-IR spectral region
by Rafal et al. for real-time quantitative measurement of NH 3 in human exhaled breath
[64]. In their study, they utilized a widely tuneable (914–972 cm
−1 ) room-temperature
operated EC-QCL with emission power 42 mW to probe the ro-vibrational lines
of the ν 2 NH 3 fundamental absorption band. The detection sensitivity for exhaled
ammonia measurement was achieved <10 ppbv in 1 s time resolution. Later, Pradhan
and his research team from India developed a cw CRD spectrometer by exploiting a
widely tuneable EC-QCL near 6.2 μm for estimation of human exhaled breath NH 3
concentration with high sensitivity and molecular specificity [65]. To obtain the NH 3
concentration they scanned the pre-selected interference-free (from the ubiquitous
gas matrix in exhaled breath) transition line from fundamental ν 4 band centred at
1613.370 cm
−1 and they achieved the detection limit of 740 parts-per-trillion by
volume at a cavity pressure of 115 Torr for an integration time of ∼167 s.
After understanding the diagnostic potential of CO related to several diseases
like asthma, diabetes, Moeskops et al. developed a TE cooled DFB QCL based
CO breath sensor [66]. They probed the strong R(8)1 rovibrational transition of
CO at 2176.2835 cm
−1 for its quantitative estimation in human exhaled breath and
subsequently, they achieved a minimal detectable absorption of 1.2 × 10
−5 cm
−1 by
incorporating 20 m multi-pass gas cell. Recently, Maruin et al. has developed a quartz
enhanced photo-acoustic spectrometer near 4.7 μm spectral region for CO detection
in human breath in the clinical environment [67]. For this study, they utilized a room
temperature operated Fabry–Perot quantum cascade laser with high optical emission
power ~100 mW. The QCL based CO breath sensor achieved a minimum detection of 20 ppb in 1s data acquisition and they validated system performance with
conventional blood carboxy-hemoglobin (COHb %) measurement. In Jacek Wojtas