Oxygen-18 and carbon-13 isotopes in eCO2and erythrocytes carbonic anhydrase activity of Finnish prediabetic population.

Complex human physiological processes create the stable isotopic composition of exhaled carbon dioxide (eCO2), measurable with noninvasive breath tests. Recently, isotope-selective breath tests utilizing natural fluctuation in18O/16O isotope ratio in eCO2have been proposed for screening prediabetic (PD) individuals. It has been suggested that18O/16O fractionation patterns reflect shifts in the activity of carbonic anhydrase (CA), an enzyme involved in the metabolic changes in the PD state. To evaluate the applicability of the breath sampling method in Finnish PD individuals, breath delta values (BDVs, ‰) of18O/16O (δ18O) were monitored for 120 min in real-time with a high-precision optical isotope ratio spectrometer, both in the fasting state and during a 2 h oral glucose tolerance test (2 h OGTT) with non-labeled glucose. In addition, the BDV of13C/12C (δ13C) was measured, and total erythrocyte CA activity was determined.δ18O and CA did not demonstrate any statistically significant differences between PD and non-diabetic control (NDC) participants. Instead,δ13C was significantly lower in PD patients in comparison to NDCs in the fasting state and at time points 90 and 120 min of the 2 h OGTT, thus indicating slightly better potential in identifying Finnish PD individuals. However, overlapping values were measured in PD participants and NDCs, and therefore,δ13C cannot be applied as a sole measure in screening prediabetes at an individual level. Thus, because the combination of environmental and lifestyle factors and anthropometric parameters has a greater effect on glucose metabolism and CA activity in comparison to the PD state,18O/16O and13C/12C fractionations or CA activity did not prove to be reliable biomarkers for impaired glucose tolerance in Finnish subjects.This study was conducted under the clinicaltrials.gov ID NCT03156478.

Active Hyperspectral Sensor Based on MEMS Fabry-Pérot Interferometer.

An active hyperspectral sensor (AHS) was developed for target detection and classification applications. AHS measures light scattered from a target, illuminated by a broadband near-infrared supercontinuum (SC) light source. Spectral discrimination is based on a voltage-tunable MEMS Fabry-Pérot Interferometer (FPI). The broadband light is filtered by the FPI prior to transmitting, allowing for a high spectral-power density within the eye-safety limits. The approach also allows for a cost-efficient correction of the SC instability, employing a non-dispersive reference detector. A precision of 0.1% and long-term stability better than 0.5% were demonstrated in laboratory tests. The prototype was mounted on a car for field measurements. Several road types and objects were distinguished based on the spectral response of the sensor targeted in front of the car.

Determining Biogenic Content of Biogas by Measuring Stable Isotopologues 12CH4, 13CH4, and CH3D with a Mid-Infrared Direct Absorption Laser Spectrometer.

A tunable laser absorption spectrometer (TLAS) was developed for the simultaneous measurement of δ13C and δD values of methane (CH4). A mid-infrared interband cascade laser (ICL) emitting around 3.27 µm was used to measure the absorption of the three most abundant isotopologues in CH4 with a single, mode-hop free current sweep. The instrument was validated against methane samples of fossil and biogenic origin with known isotopic composition. Three blended mixtures with varied biogenic content were prepared volumetrically, and their δ13C and δD values were determined. Analysis demonstrated that, provided the isotopic composition of the source materials was known, the δ13C and δD values alone were sufficient to determine the biogenic content of the blended samples to within 1.5%.

Long distance active hyperspectral sensing using high-power near-infrared supercontinuum light source.

A hyperspectral remote sensing instrument employing a novel near-infrared supercontinuum light source has been developed for active illumination and identification of targets. The supercontinuum is generated in a standard normal dispersion multi-mode fiber and has 16 W total optical output power covering 1000 nm to 2300 nm spectral range. A commercial 256-channel infrared spectrometer was used for broadband infrared detection. The feasibility of the presented hyperspectral measurement approach was investigated both indoors and in the field. Reflection spectra from several diffusive targets were successfully measured and a measurement range of 1.5 km was demonstrated.

Compact multipass optical cell for laser spectroscopy.

A multipass cell (MPC) design for laser absorption spectroscopy is presented. The development of this new type of optical cell was driven by stringent criteria for compactness, robustness, low volume, and ease of use in optical systems. A single piece of reflective toroidal surface forms a near-concentric cavity with a volume of merely 40 cm(3). Contrary to traditional MPCs, this design allows for flexible path-length adjustments by simply changing the aiming angle of the laser beam at the entrance window. Two effective optical path lengths of 2.2 and 4.1 m were chosen to demonstrate the cell's suitability for high-precision isotope ratio measurements of CO(2) at 1% and ambient mixing ratio levels.

Novel laser spectroscopic technique for continuous analysis of N2O isotopomers--application and intercomparison with isotope ratio mass spectrometry.

RATIONALE: Nitrous oxide (N(2)O), a highly climate-relevant trace gas, is mainly derived from microbial denitrification and nitrification processes in soils. Apportioning N(2)O to these source processes is a challenging task, but better understanding of the processes is required to improve mitigation strategies. The N(2)O site-specific (15)N signatures from denitrification and nitrification have been shown to be clearly different, making this signature a potential tool for N(2)O source identification. We have applied for the first time quantum cascade laser absorption spectroscopy (QCLAS) for the continuous analysis of the intramolecular (15)N distribution of soil-derived N(2)O and compared this with state-of-the-art isotope ratio mass spectrometry (IRMS). METHODS: Soil was amended with nitrate and sucrose and incubated in a laboratory setup. The N(2)O release was quantified by FTIR spectroscopy, while the N(2)O intramolecular (15)N distribution was continuously analyzed by online QCLAS at 1 Hz resolution. The QCLAS results on time-integrating flask samples were compared with those from the IRMS analysis. RESULTS: The analytical precision (2σ) of QCLAS was around 0.3‰ for the δ(15)N(bulk) and the (15)N site preference (SP) for 1-min average values. Comparing the two techniques on flask samples, excellent agreement (R(2)= 0.99; offset of 1.2‰) was observed for the δ(15)N(bulk) values while for the SP values the correlation was less good (R(2 )= 0.76; offset of 0.9‰), presumably due to the lower precision of the IRMS SP measurements. CONCLUSIONS: These findings validate QCLAS as a viable alternative technique with even higher precision than state-of-the-art IRMS. Thus, laser spectroscopy has the potential to contribute significantly to a better understanding of N turnover in soils, which is crucial for advancing strategies to mitigate emissions of this efficient greenhouse gas.

Transversely excited multipass photoacoustic cell using electromechanical film as microphone.

A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in an optical multipass configuration. A detection limit of 22 ppb (10(-9)) was achieved for flowing NO(2) in N(2) at normal pressure by using the maximum of 70 laser beams between the resonator plates. The corresponding minimum detectable absorption and the normalized noise-equivalent absorption coefficients were 2.2 × 10(-7) cm(-1) and 3.2 × 10(-9) cm(-1) WHz(-1/2), respectively.

Electromechanical film as a photoacoustic transducer.

An electromechanical film, EMFi, is utilized as a transducer in a photoacoustic (PA) gas sensor. The film is a sensitive acoustic transducer, it is easily formable, and it exhibits a wide frequency response regardless of its large surface area. As a demonstration of its capabilities, the EMFi-based PA detector is used to measure NO(2) with pulsed excitation at 436 and 473 nm. The minimum detectable absorption coefficient is extrapolated to be 5.10(-7) cm(-1). Improvements for EMFi-based PA detector are discussed.

Fluorescence cross sections of bioaerosols and suspended biological agents.

Laser-induced fluorescence is used to investigate fluorescence properties of unwashed Bacillus thuringiensis and Bacillus subtilis spores, ovalbumin, and washed bacteriophage MS2. A fluorescence detector is calibrated to obtain absolute fluorescence cross sections. Fluorescence maps of biological aerosols and suspensions are measured at a wide excitation range from 210 to 419 nm and a wide detection range from 315 to 650 nm. The dominant features of the measured spectra are the amino acid peaks, having excitation maxima at 220 and 280 nm. The peaks are similar for the bacterial spores, both for aerosols and suspensions, whereas the peaks are shifted toward the shorter emission wavelengths for the suspended ovalbumin and MS2. Moreover, the fluorescence emission, excited above 320 nm is more intensive for the aerosols than the suspensions.

Wavelength modulation waveforms in laser photoacoustic spectroscopy.

Different wavelength modulation waveforms were studied comprehensively in tunable diode laser photoacoustic spectroscopy. The generation of the photoacoustic signal was studied by way of simulations and experiments. A cantilever-enhanced photoacoustic detector and CO(2) sample gas were used in the experiments. The modulation waveforms compared in this study were sinusoidal, triangular, shaped, and quasi-square waves. All four waveforms allow background-free detection of trace gases. Compared to the conventionally used sinusoidal modulation, the triangular, shaped, and quasi-square waves enhanced the photoacoustic signal by factors of 1.12, 1.42, and 1.57, respectively.

Resonant photoacoustic cell for pulsed laser analysis of gases at high temperature.

A new approach to high temperature gas analysis by means of photoacoustic (PA) spectroscopy is presented. The transverse modes of the resonant PA cell were excited with a pulsed laser and detected with a microphone. Changes in the properties of the PA cell resulting from a varying temperature are discussed and considered when processing the PA signal. The feasibility of the proposed method was demonstrated by studying PA response from saturated vapor of potassium chloride (KCl) in the temperature range extending from 410 to 691 degrees C. The PA spectrum, the detection limit, and the signal saturation of KCl vapor are discussed. At 245 nm excitation wavelength and 300 microJ pulse energy, the achieved detection limit for KCl is 15 ppb.