High-resolution trace gas detection by sub-Doppler noise-immune cavity-enhanced optical heterodyne molecular spectrometry: application to detection of acetylene in human breath.

A sensitive high-resolution sub-Doppler detecting spectrometer, based on noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS), for trace gas detection of species whose transitions have severe spectral overlap with abundant concomitant species is presented. It is designed around a NICE-OHMS instrumentation utilizing balanced detection that provides shot-noise limited Doppler-broadened (Db) detection. By synchronous dithering the positions of the two cavity mirrors, the effect of residual etalons between the cavity and other surfaces in the system could be reduced. An Allan deviation of the absorption coefficient of 2.2 × 10-13 cm-1 at 60 s, which, for the targeted transition in C2H2, corresponds to a 3σ detection sensitivity of 130 ppt, is demonstrated. It is shown that despite significant spectral interference from CO2 at the targeted transition, which precludes Db detection of C2H2, acetylene could be detected in exhaled breath of healthy smokers.

Evaluating the metabolic perturbations in Mangifera indica (mango) ripened with various ripening agents/practices through gas chromatography - mass spectrometry based metabolomics.

Mangifera indica L. (mango) is said to be the king of fruits due to its rich nutritional properties and mainly originates from the Indian sub-continent. The consumption pattern of the mangoes has increased drastically, due to which, many ripening practices/agents were used to make it ready-to-eat fruit or juice for the consumers. The fruit quality and metabolic composition are said to be altered due to different ripening agents/practices. The present communication mainly deals to understand the metabolic perturbations in mango fruits due to different ripening practices/agents (room temperature ripening, ethylene, and calcium carbide) using gas chromatography - mass spectrometry based metabolomics. The partial least square-discriminant analysis has found 16 differential metabolites for different ripening agents/practices which are belong to the classes of amino acids, fatty acids, sugars, and polyols. Four metabolic pathways were found to alter in the fruit metabolome due to different ripening agents/practices. Fructose, glucose, and galactose were found to be significantly up-regulated due to calcium carbide ripening in comparison to other ripening agents/practices. Overall findings from the present study advocates that mass spectrometry based metabolomics can be valuable tool to understand the fruit quality and safety with respect to consumer health.

Effect of Varying Inert Gas and Acetylene Concentration on the Synthesis of Carbon Nanotubes.

The multiwalled carbon nanotubes (MWCNTs) with small diameter and high purity were achieved by chemical vapor deposition technique using silicon substrate. The introduction of specific concentration of inert gas with hydrocarbon played a key role in controlling morphology and diameter of MWCNTs. Nickel mixed ferrite nanoparticles were used as a catalyst for the growth of MWCNTs. Growth parameters like concentration of hydrocarbon source and inert gas flow, composition of catalyst particles and growth temperature were studied. In this work smaller diameter and twisted MWCNTs were formed by dilution of acetylene with argon gas. Electrical properties suggest a semimetallic behavior of synthesized MWCNTs.

Near infrared frequency comb vernier spectrometer for broadband trace gas detection.

We present a femtosecond frequency comb vernier spectrometer in the near infrared with a femtosecond Er doped fiber laser, a scanning high-finesse cavity and an InGaAs camera. By utilizing the properties of a frequency comb and a scanning high-finesse cavity such a spectrometer provides broad spectral bandwidth, high spectral resolution, and high detection sensitivity on a short time scale. We achieved an absorption sensitivity of ~8 × 10(-8) cm(-1)Hz(-1/2), corresponding to a detection limit of ~70 ppbv for acetylene, with a resolution of ~1.1 GHz in single images taken in 0.5 seconds and covering a frequency range of ~5 THz. Such measurements have broad applications for sensing greenhouse gases in this fingerprint near infrared region with a simple apparatus.

Hydrothermal synthesis and acetylene sensing properties of variety low dimensional zinc oxide nanostructures.

Various morphologies of low dimensional ZnO nanostructures, including spheres, rods, sheets, and wires, were successfully synthesized using a simple and facile hydrothermal method assisted with different surfactants. Zinc acetate dihydrate was chosen as the precursors of ZnO nanostructures. We found that polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), glycine, and ethylene glycol (EG) play critical roles in the morphologies and microstructures of the synthesized nanostructures, and a series of possible growth processes were discussed in detail. Gas sensors were fabricated using screen-printing technology, and their sensing properties towards acetylene gas (C2H2), one of the most important arc discharge characteristic gases dissolved in oil-filled power equipments, were systematically measured. The ZnO nanowires based sensor exhibits excellent C2H2 sensing behaviors than those of ZnO nanosheets, nanorods, and nanospheres, indicating a feasible way to develop high-performance C2H2 gas sensor for practical application.

Acetyl Bromide Method for Total Lignin Content Determination in Plant Biomass.

Lignin is a tough biopolymer that gives plants strength and protection. It is also a major obstacle for converting plant biomass into biofuels because it prevents enzymes from accessing the sugar-rich fibers. To optimize biofuel production, we need to measure the lignin content in plant tissues accurately and efficiently. In this protocol, we describe a simple and reliable method to measure the total lignin content in plant tissues. The method uses acetyl bromide, a chemical that dissolves lignin into soluble derivatives and makes it possible to detect them by their absorbance at 280 nm. The method consists of two steps: first, we obtained destarched cell wall material from the plant samples, and second, we treat the cell wall material with acetyl bromide and measure the absorbance of the lignin solution. This method can capture all types of lignin and works well with different plant tissues.

Dual-comb spectroscopy using frequency-doubled combs around 775 nm.

Two frequency-doubled combs are generated by nonlinear frequency conversion to realize spectroscopic measurements around 775 nm. Frequency-doubled interferograms are corrected in real-time by monitoring the relative instabilities between the combs at their fundamental frequency. Rubidium absorption lines are used to demonstrate the technique's accuracy and serve as absolute references to calibrate the frequency grid of computed spectra. The method allows frequency-doubled interferograms to be averaged without distortion during long periods of time. The calibrated frequency grid is validated by the measurement of the oxygen A-band. Moreover, the measurement analysis of the acetylene ν(1) + 3ν(3) overtone band has revealed some discrepancies with previous publications.

Fast response in-line gas sensor using C-type fiber and Ge-doped ring defect photonic crystal fiber.

An in-line chemical gas sensor was proposed and experimentally demonstrated using a new C-type fiber and a Ge-doped ring defect photonic crystal fiber (PCF). The C-type fiber segment served as a compact gas inlet/outlet directly spliced to PCF, which overcame previous limitations in packaging and dynamic responses. C-type fiber was prepared by optimizing drawing process for a silica tube with an open slot. Splicing conditions for SMF/C-type fiber and PCF/C-type fiber were experimentally established to provide an all-fiber sensor unit. To enhance the sensitivity and light coupling efficiency we used a special PCF with Ge-doped ring defect to further enhance the sensitivity and gas flow rate. Sensing capability of the proposed sensor was investigated experimentally by detecting acetylene absorption lines.

Field application of nitrogen and phenylacetylene to mitigate greenhouse gas emissions from landfill cover soils: effects on microbial community structure.

Landfills are large sources of CH(4), but a considerable amount of CH(4) can be removed in situ by methanotrophs if their activity can be stimulated through the addition of nitrogen. Nitrogen can, however, lead to increased N(2)O production. To examine the effects of nitrogen and a selective inhibitor on CH(4) oxidation and N(2)O production in situ, 0.5 M of NH(4)Cl and 0.25 M of KNO(3), with and without 0.01% (w/v) phenylacetylene, were applied to test plots at a landfill in Kalamazoo, MI from 2007 November to 2009 July. Nitrogen amendments stimulated N(2)O production but had no effect on CH(4) oxidation. The addition of phenylacetylene stimulated CH(4) oxidation while reducing N(2)O production. Methanotrophs possessing particulate methane monooxygenase and archaeal ammonia-oxidizers (AOAs) were abundant. The addition of nitrogen reduced methanotrophic diversity, particularly for type I methanotrophs. The simultaneous addition of phenylacetylene increased methanotrophic diversity and the presence of type I methanotrophs. Clone libraries of the archaeal amoA gene showed that the addition of nitrogen increased AOAs affiliated with Crenarchaeal group 1.1b, while they decreased with the simultaneous addition of phenylacetylene. These results suggest that the addition of phenylacetylene with nitrogen reduces N(2)O production by selectively inhibiting AOAs and/or type II methanotrophs.

Oxygen and the light-dark cycle of nitrogenase activity in two unicellular cyanobacteria.

Cyanobacteria capable of fixing dinitrogen exhibit various strategies to protect nitrogenase from inactivation by oxygen. The marine Crocosphaera watsonii WH8501 and the terrestrial Gloeothece sp. PCC6909 are unicellular diazotrophic cyanobacteria that are capable of aerobic nitrogen fixation. These cyanobacteria separate the incompatible processes of oxygenic photosynthesis and nitrogen fixation temporally, confining the latter to the dark. Although these cyanobacteria thrive in fully aerobic environments and can be cultivated diazotrophically under aerobic conditions, the effect of oxygen is not precisely known due to methodological limitations. Here we report the characteristics of nitrogenase activity with respect to well-defined levels of oxygen to which the organisms are exposed, using an online and near real-time acetylene reduction assay combined with sensitive laser-based photoacoustic ethylene detection. The cultures were grown under an alternating 12-12 h light-dark cycle and acetylene reduction was recorded continuously. Acetylene reduction was assayed at 20%, 15%, 10%, 7.5%, 5% and 0% oxygen and at photon flux densities of 30 and 76 mumol m(-2) s(-1) provided at the same light-dark cycle as during cultivation. Nitrogenase activity was predominantly but not exclusively confined to the dark. At 0% oxygen nitrogenase activity in Gloeothece sp. was not detected during the dark and was shifted completely to the light period, while C. watsonii did not exhibit nitrogenase activity at all. Oxygen concentrations of 15% and higher did not support nitrogenase activity in either of the two cyanobacteria. The highest nitrogenase activities were at 5-7.5% oxygen. The highest nitrogenase activities in C. watsonii and Gloeothece sp. were observed at 29 degrees C. At 31 degrees C and above, nitrogenase activity was not detected in C. watsonii while the same was the case at 41 degrees C and above in Gloeothece sp. The differences in the behaviour of nitrogenase activity in these cyanobacteria are discussed with respect to their presumed physiological strategies to protect nitrogenase from oxygen inactivation and to the environment in which they thrive.

Identification of calcium carbide-ripened sapota (Achras sapota) fruit by headspace SPME-GC-MS.

The effect of post-harvest ripening by ethylene and calcium carbide was studied by headspace solid-phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS) method. Sapota (sapodilla) fruits were ripened with ethylene gas, technical grade calcium carbide and pure calcium carbide ripeners and the samples were homogenised after complete ripening. The samples were subjected to HS-SPME-GC-MS and the obtained results showed the presence of various alcohols, aldehydes, acids, ketones and esters which were commonly present in the samples. The fruit samples ripened with technical grade calcium carbide showed the presence of 3,5-dimethyl-1,2,4-trithiolane isomers, which can be used as markers to identify sapota fruits ripened with technical grade calcium carbide. The technical grade calcium carbide contains divinyl sulphide which might have been transformed into the trithiolane isomers. These isomers were not observed in the fruits ripened with pure calcium carbide and also with ethylene gas. Hence the formation of trithiolane residues may be attributed to the presence of divinyl sulphide impurity present in calcium carbide and its conversion due to the action of ethylene releasing enzymes present in the fruits.

Noninvasive Assessment of Cardiac Output: Accuracy and Precision of the Closed-Circuit Acetylene Rebreathing Technique for Cardiac Output Measurement.

Background Accurate assessment of cardiac output is critical to the diagnosis and management of various cardiac disease states; however, clinical standards of direct Fick and thermodilution are invasive. Noninvasive alternatives, such as closed-circuit acetylene (C2H2) rebreathing, warrant validation. Methods and Results We analyzed 10 clinical studies and all available cardiopulmonary stress tests performed in our laboratory that included a rebreathing method and direct Fick or thermodilution. Studies included healthy individuals and patients with clinical disease. Simultaneous cardiac output measurements were obtained under normovolemic, hypovolemic, and hypervolemic conditions, along with submaximal and maximal exercise. A total of 3198 measurements in 519 patients were analyzed (mean age, 59 years; 48% women). The C2H2 method was more precise than thermodilution in healthy individuals with half the typical error (TE; 0.34 L/min [r=0.92] and coefficient of variation, 7.2%) versus thermodilution (TE=0.67 [r=0.70] and coefficient of variation, 13.2%). In healthy individuals during supine rest and upright exercise, C2H2 correlated well with thermodilution (supine: r=0.84, TE=1.02; exercise: r=0.82, TE=2.36). In patients with clinical disease during supine rest, C2H2 correlated with thermodilution (r=0.85, TE=1.43). C2H2 was similar to thermodilution and nitrous oxide (N2O) rebreathing technique compared with Fick in healthy adults (C2H2 rest: r=0.85, TE=0.84; C2H2 exercise: r=0.87, TE=2.39; thermodilution rest: r=0.72, TE=1.11; thermodilution exercise: r=0.73, TE=2.87; N2O rest: r=0.82, TE=0.94; N2O exercise: r=0.84, TE=2.18). The accuracy of the C2H2 and N2O methods was excellent (r=0.99, TE=0.58). Conclusions The C2H2 rebreathing method is more precise than, and as accurate as, the thermodilution method in a variety of patients, with accuracy similar to an N2O rebreathing method approved by the US Food and Drug Administration.

Surface composition of Kuiper belt object 1993SC.

The 1.42- to 2.40-micrometer spectrum of Kuiper belt object 1993SC was measured at the Keck Observatory in October 1996. It shows a strongly red continuum reflectance and several prominent infrared absorption features. The strongest absorptions in 1993SC's spectrum occur near 1.62, 1.79, 1.95, 2.20, and 2.32 micrometers in wavelength. Features near the same wavelengths in the spectra of Pluto and Neptune's satellite Triton are due to CH4 on their surfaces, suggesting the presence of a simple hydrocarbon ice such as CH4, C2H6, C2H4, or C2H2 on 1993SC. In addition, the red continuum reflectance of 1993SC suggests the presence of more complex hydrocarbons.

Simulation of inelastic electronic tunneling spectra of adsorbates from first principles.

We present first-principles simulations for inelastic electron tunneling spectra of molecules adsorbed on metal surface as measured in scanning tunneling microscopy experiments. Both elastic and inelastic tunneling processes are modeled in terms of Tersoff-Hamann approximation with a full vibration analysis at density functional theory levels. The calculated spectra of carbon oxide and acetylene molecules adsorbed on Cu(100) surface have well reproduced their experimental counterparts. The inelastic electron tunneling images of the observable vibration modes have been provided. The performance of gradient-corrected density functional is compared with that of local density functional.

Tropospheric trace gases at Bremen measured with FTIR spectrometry.

The total column densities of acetylene (C(2)H(2)), carbon monoxide (CO), hydrogen cyanide (HCN) and ethane (C(2)H(6)) measured in Bremen (Germany, 53.107 degrees N, 8.854 degrees E) were compared with data from Mace Head/Ireland (MHD) and GEOS-Chem model simulations. The data were obtained between August 2002 and October 2006 with the ground based high resolution Fourier Transform Infra-Red (FTIR) Spectrometry, using the sun as the light source. The analysis showed good agreements between all the three data sets for the seasonal cycle of CO. Enhancements in summer 2003 and summer 2004 due to influence of biomass burning were identified in all three data sets. The high correlations between C(2)H(6) and C(2)H(2), C(2)H(2) and CO, and for C(2)H(6) and CO support the similarities in their sources and sinks. The results suggest that the background air in Bremen is mainly influenced by long-ranged transport of biomass burning products. Local pollution plays a minor role for the measurements performed in Bremen.

NIR spectroscopic method for the detection of calcium carbide in artificial ripening of mangoes (Magnifera indica).

The present study presents a novel method employing Near Infrared Spectroscopy (NIR) for detection of the use of calcium carbide in artificial ripening of mangoes. Use of calcium carbide has been banned in artificial ripening of fruits as it contains traces of arsenic. Mango samples were ripened artificially using calcium carbide and compared with naturally ripened mangoes using NIR spectroscopic wavelength ranging from 600 to 1100 nm. The captured NIR spectra from mango samples were analysed using multivariate methods including principal component analysis, particle least square and successive projection algorithm. The obtained results showed distinguishing zones for naturally and artificially ripened mangoes. Furthermore, the arsenic content was obtained through ICP-MS analysis, and it was found that mangoes ripened artificially using calcium carbide have a higher content of arsenic. Hence, arsenic was used as a principal component in the analysis. The developed method is not unique to samples that were grown in any particular region or year as it and can be used universally as NIR will give the distinguishing comparison between naturally- and artificially ripened mangoes. This method is simple, non-invasive, non-destructive and rapid for detection of use of calcium carbide in the artificial ripening of mangoes.

Near-Infrared Broadband Cavity-Enhanced Spectroscopic Multigas Sensor Using a 1650 nm Light Emitting Diode.

A near-infrared broadband cavity-enhanced sensor system was demonstrated for the first time using an energy-efficient light emitting diode (LED) with a central emission wavelength at 1650 nm and a light power of ∼16 mW. A portable absorption gas cell was designed for realizing a compact and stable optical system for easy alignment. An ultrashort 8-cm-long cavity was fabricated consisting of two mirrors with a ∼99.35% reflectivity. Methane (CH4) measurement was performed employing two detection schemes, i.e., NIRQuest InGaAs spectrometer and scanning monochromator combined with phase-sensitive detection. Retrieval of CH4 concentration was performed using a least-squares fitting algorithm. Sensitivities (i.e., minimum detectable absorption coefficient) were achieved of 1.25 × 10-6 cm-1 for an averaging time of 45 s using the NIRQuest InGaAs spectrometer and 1.85 × 10-6 cm-1 for an averaging time of 8 min using the scanning spectrometer in combination with lock-in detection. Field monitoring of CH4 gas leakage was performed using the NIRQuest spectrometer. Multigas sensing of CH4 and acetylene (C2H2) was carried out simultaneously using the high-resolution scanning spectrometer. A linear response of the retrieved concentration level versus nominal value was observed with a large dynamic range, demonstrating the reliability of the compact LED-based near-infrared broadband cavity-enhanced absorption spectroscopy (NIR-IBBCEAS) for multigas sensing applications.

On-chip gas detection in silicon optical microcavities.

We demonstrate a chip-scale photonic system for the room-temperature detection of gas composition and pressure using a slotted silicon microring resonator. We measure shifts in the resonance wavelength due to the presence and pressure of acetylene gas and resolve differences in the refractive index as small as 10(-4) in the near-IR. The observed sensitivity of this device (enhanced due to the slot-waveguide geometry) agrees with the expected value of 490 nm/refractive index unit.

Infra-red multi-mode absorption spectroscopy of acetylene using an Er/Yb:glass micro-laser.

Multi-mode absorption spectroscopy, MUMAS, in the near-infra-red is reported for the first time. A diode laser pumped Er/Yb:glass micro-cavity laser emitting multiple longitudinal modes at 1.53 microm was used to detect several transitions in the nu(1)+nu(3) overtone band of C2H2.

Gold nanoparticle-based method for detection of calcium carbide in artificially ripened mangoes (Magnifera indica).

A new approach was developed for a simple and easy colorimetric detection assay to detect the use of calcium carbide in artificial ripening of fruits. Residues of arsenic on the fruit surface were used as an indicator for this. Use of calcium carbide in artificial ripening has been banned in many countries including India. In the present study, we have used a gold nanoparticle (AuNP)-based colorimetric detection method for determination of artificial ripening of fruits. ICP-MS analysis showed the presence of higher amounts of arsenic on fruits ripened using calcium carbide. Lauryl sulphate (LS)-capped AuNP aggregates in the presence of arsenic, replacing the LS, resulting in a colour change from red to purple. Hence, the developed method can be used for easy and rapid detection of use of calcium carbide in artificial ripening of fruits.