Laser Photoacoustic Detection Research Articles

Spectral analysis for photoacoustic pressure sensor designs: Theoretical model improvement and experimental validation

In the pulsed laser photoacoustic (PA) detection and spectroscopy applications, the fundamental frequency of the PA signal produced, and the sensor resonance frequency should be as close as possible to each other so that analyzes from the obtained signals can be performed effectively. In order to determine the fundamental frequency of the PA wave, a theoretical model approach based on the development of the frequency domain solution of the PA wave equation is presented for use in the PA pressure sensor designs. For the validation of the theoretical model approach, a PA experimental setup was established, and measurements were made in distilled water. The theoretical and the experimental PA frequency spectra were determined to be very compatible with each other. Thus, the theoretical model approach was experimentally validated. According to the theoretical model approach, fundamental frequency values obtained from the experimental measurement results were determined with an average accuracy of ∓ 4.212%. Furthermore, it has been determined that this value has fallen to ∓0.267% in the measurements. With the obtained results from the theoretical model approach, we propose that the PA pressure sensors with the more selective and narrower band can be designed for the more sensitive detection. Moreover, in this study the effects of different laser parameters such that pulse duration, and laser beam width, on the spectral content of the obtained PA signal are analyzed. These analyses will shed light on the vision of acoustic pressure sensor design by helping to select the most optimum parameters for the PA detection.

Laser Photoacoustic Detection of Residual Stresses in Metal Plates with a Hole

The nature of the change in the photoacoustic signal around the hole in samples of duralumin is studied. A com- parison of the experimental results with the solution of the classical problem for stress distribution around a circular hole in a prestressed plate is made. A good correspondence between the behavior of the photoacoustic signal with piezoelectric recording and the distribution of stresses around the hole is demonstrated. The possibility of estimating the internal stresses by the photoacoustic method in combination with the hole drilling method is shown.

First application of multilayer graphene cantilever for laser photoacoustic detection

Abstract The mechanical behaviours of multilayer graphene (MLG) membranes and cantilevers were investigated for the sensitive detection of acoustic waves in gases. The aim of this work was to find sensors for laser photoacoustic spectroscopy with high sensitivity. The application of the MLG cantilever for photoacoustic detection was reported for the first time. MLG membranes and cantilevers were prepared from highly ordered pyrolytic graphite (HOPG) by multiple mechanical cleavages allowing simple adjustment of the membrane/cantilever thickness and relevant mechanical parameters. The MLG cantilever/membrane movements induced by pressure waves triggered by the absorption of the CO 2 laser pulse in the gas-filled photoacoustic cell were detected by a He-Ne laser beam reflected from the cantilever/membrane to a position sensitive detector (optical microphone). The sensitivity of the MLG cantilevers for the photoacoustic detection of methanol vapours (testing gas) was more than one order of magnitude higher in comparison with a top class microphone (Bruel & Kjaer). The signal-to-noise ratio of 19, 61, and 70 together with the limits of detection of 0.75 ppm, 0.42 and 0.33 ppm were calculated for the condenser microphone, the MLG membrane, and the MLG cantilever, respectively. Additionally, the high sensitivity of both MLG elements for the photoacoustic detection is also promising thanks to the single layer graphene with very a small thickness on the nanometer scale.

Silicon micro-levers and a multilayer graphene membrane studied via laser photoacoustic detection

Abstract. Laser photoacoustic spectroscopy (PAS) is a method that utilizes the sensing of the pressure waves that emerge upon the absorption of radiation by absorbing species. The use of the conventional electret microphone as a pressure sensor has already reached its limit, and a new type of microphone – an optical microphone – has been suggested to increase the sensitivity of this method. The movement of a micro-lever or a membrane is sensed via a reflected beam of light, which falls onto a position-sensing detector. The use of one micro-lever as a pressure sensor in the form of a silicon cantilever has already enhanced the sensitivity of laser PAS. Herein, we test two types of home-made sensing elements – four coupled silicon micro-levers and a multilayer graphene membrane – which have the potential to enhance this sensitivity further. Graphene sheets possess outstanding electromechanical properties and demonstrate impressive sensitivity as mass detectors. Their mechanical properties make them suitable for use as micro-/nano-levers or membranes, which could function as extremely sensitive pressure sensors. Graphene sheets were prepared from multilayer graphene through the micromechanical cleavage of basal plane highly ordered pyrolytic graphite. Multilayer graphene sheets (thickness ∼102 nm) were then mounted on an additional glass window in a cuvette for PAS. The movements of the sheets induced by acoustic waves were measured using an He–Ne laser beam reflected from the sheets onto a quadrant detector. A discretely tunable CO2 laser was used as the source of radiation energy for the laser PAS experiments. Sensitivity testing of the investigated sensing elements was performed with the aid of concentration standards and a mixing arrangement in a flow regime. The combination of sensitive microphones and micromechanical/nanomechanical elements with laser techniques offers a method for the study and development of new, reliable and highly sensitive chemical sensing systems. To our knowledge, we have produced the first demonstration of the feasibility of using four coupled silicon micro-levers and graphene membranes in an optical microphone for PAS. Although the sensitivity thus far remains inferior to that of the commercial electret microphone (with an S / N ratio that is 5 times lower), further improvement is expected to be achieved by adjusting the micro-levers and membrane elements, the photoacoustic system and the position detector.

Quantum cascade laser photoacoustic detection of nitrous oxide released from soils for biofuel production

In order to investigate the generation of greenhouse gases in sugarcane ethanol production chain, a comparative study of N2O emission in artificially fertilized soils and soils free from fertilizers was carried out. Photoacoustic spectroscopy using quantum cascade laser with an emission ranging from 7.71 to 7.88 µm and differential photoacoustic cell were applied to detect nitrous oxide (N2O), an important greenhouse gas emitted from soils cultivated with sugar cane. Owing to calibrate the experimental setup, an initial N2O concentration was diluted with pure nitrogen and detection limit of 50 ppbv was achieved. The proposed methodology was selective and sensitive enough to detect N2O from no fertilized and artificially fertilized soils. The measured N2O concentration ranged from ppmv to ppbv.

The level of ethylene biomarker in the renal failure of elderly patients analyzed by photoacoustic spectroscopy

In recent years there has been a large increase in the areas related to developments in the prevention of diseases, especially in explaining the role of oxidative stress. Lipid peroxidation and oxidative stress contributes to morbidity in hemodialysis (HD) patients. It is therefore relevant to analyze the impact of oxidative stress and its related species (ethylene) immediately after dialysis treatment in order to prevent trauma in the renal failure of elderly patients. In this paper we describe recent progress in laser photoacoustic spectroscopy detection of ethylene in renal failure patients. We have found that HD treatment increases ethylene concentration in the exhaled breath of elderly patients and may intensify oxidative stress.

Integrative System of Fast Photoacoustic Imaging

Abstract An integrative fast (Photoacoustic) PA imaging system based on multi-element linear ultrasonic transducer array was developed, which integrates laser delivery, photoacoustic excitation and photoacoustic detection into a portable system. It collects PA signals by a multi-element linear transducer array in a reflection mode. The PA images with high spatial resolution and high contrast were obtained. Compared to other existing PA imaging methods, the integrative PA imaging system is characterized by rapidness, convenience and high practicality. The integrative system is mobile and portable, and it is suitable for imaging samples in natural condition with various different shapes. It will provide a novel and effective PA imaging approach for clinic diagnosis of neoplasm and tissue functional imaging in vivo, and has potential to be developed into a practical apparatus used in the early non-invasive detection of breast-cancer.

Emission of volatile compounds by Erwinia amylovora: biological activity in vitro and possible exploitation for bacterial identification

Several analytical techniques such as gas chromatography–mass spectrometry, proton transfer reaction–mass spectrometry and laser photoacoustic detection, were used to characterize the volatiles emitted by Erwinia amylovora and other plant-pathogenic bacteria. Diverse volatiles were found to be emitted by the different bacterial species examined. The distinct blend of volatiles produced by bacteria allowed their identification using an electronic nose (e-nose). The present study reports the discrimination of E. amylovora, the fire blight pathogen, from other plant-associated bacteria using an e-nose based on metal oxide semiconductor sensors. Two different approaches were used for bacterial identification. The first one was the direct comparison of the odorous profiles of unknown bacterial isolates with four selected reference species. The second approach was the use of previously developed databases representing the odorous variability among several bacterial species. Using these two strategies, the e-nose successfully identified the isolates in 87.5 and 62.5% of the cases, respectively. Finally, the profiling of the volatiles emitted by E. amylovora lead to identify some metabolic markers with a potential biological activity in vitro.

Quantum-cascade laser photoacoustic detection of methane emitted from natural gas powered engines

In this work we present a laser photoacoustic arrangement for the detection of the important greenhouse gas methane. A quantum-cascade laser and a differential photoacoustic cell were employed. A detection limit of 45 ppbv in nitrogen was achieved as well as a great selectivity. The same methodology was also tested in the detection of methane issued from natural gas powered vehicles (VNG) in Brazil, which demonstrates the excellent potential of this arrangement for greenhouse gas detection emitted from real sources.

CO 2 laser photoacoustic detection of ammonia emitted by ceramic industries

A homemade photoacoustic spectrometer has been constructed for monitoring gas emission from several sources. Numerous air pollutant gases are emitted exhaust of industries, vehicles and power plants. The photoacoustic technique is extremely sensitive and selective in detecting various gases. This work focuses on the gas emitted by the ceramic industry in northern Rio de Janeiro State in Brazil, the ceramic industry plays a remarkable role in the economy activity of this region, in recent years, this region developed into a significant red ceramic complex. The potential impact on the atmospheric environment of the region due to gaseous pollutant emissions from these anthropogenic sources needs to be evaluated. In this work we identified NH 3 present in the samples collected in the kiln of a ceramic plant, in the concentration range of 33–52 ppmV. The ammonia gas present in our collected samples might come from the excess nitrogen in the manure soil from where the ceramic material was extracted. This soil was used for the sugarcane culture which is another important economic activity of this region.

EFFECT OF TEMPERATURE ON THE SENSITIVITY OF NITROGENASE TO OXYGEN IN TWO HETEROCYSTOUS CYANOBACTERIA1

The effect of temperature and oxygen on nitrogenase activity in two heterocystous cyanobacteria, Anabaena variabilis Kütz. ATCC29413 and Nostoc sp. PCC7120, was investigated. The cyanobacteria were grown under a 12:12 light:dark (L:D) cycle at 27°C and were subsequently exposed to different temperatures (27, 36, 39, and 42°C) at different steady‐state O2 concentrations (20, 10, 5, 0%). Light response curves of nitrogenase activity were recorded under each of these conditions using an online acetylene reduction assay combined with a sensitive laser photoacoustic ethylene detection method. The light response curves were fitted with the rectangular hyperbola model from which the model parameters Nm, Nd, and α were derived. In both strains, nitrogenase activity (Ntot = Nm + Nd) was the highest at 39°C–42°C and at 0% O2. The ratio Ntot/Nd was 4.1 and 3.1 for Anabaena and Nostoc, respectively, indicating that respectively 25% and 33% of nitrogenase activity was supported by respiration (Nd). Ntot/Nd increased with decreasing O2 concentration and with increasing temperature. Hence, each of these factors caused a relative increase in the light‐driven nitrogenase activity (Nm). These results demonstrate that photosynthesis and respiration both contribute to nitrogenase activity in Anabaena and Nostoc and that their individual contributions depend on both O2 concentration and temperature as the latter may dynamically alter the flux of O2 into the heterocyst.

Laser Photoacoustic Detection of CO2 in Old Disc Tree-Rings

A homemade CO2–laser photoacoustic spectrometer has been used for monitoring CO2 in gas samples extracted under vacuum from the wood of old spruce disc tree-rings for a ∼60 year series. The experimental results show that (1) the CO2 concentration exhibits annual trends correlated with an increase in atmospheric CO2 in a number of cases; (2) at the time when the annual CO2 trend changes from positive to negative, the annual tree-ring stable carbon isotope ratios (δ13C) of CO2 change as well; (3) the disc tree-ring widths are observed to decrease in most cases where the annual CO2 increased; (4) simultaneously with the annual CO2 variation, annual H2O distribution was detected in gas samples of the wood tree-rings of one spruce disc. The observed patterns of the annual CO2 distribution in the disc tree-rings are assumed to be the evidence of the impact of the atmospheric CO2 increase. In other words, a change in the concentration gradient between the stem and the atmospheric CO2 may lead to a gradual CO2 accumulation in the stem because of a decrease in the diffusion rate and to a change in the tree parameters.

CO 2 laser photoacoustic detection of ethylene emitted by diesel engines used in urban public transports

In this work, CO 2 laser photoacoustic spectroscopy was used to detect and monitor ethylene concentrations from about 0.6 ppmV up to 47 ppmV emitted by urban public transports in Campos dos Goytacazes city in Rio de Janeiro state, Brazil. The photoacoustic method proved to be a very sensitive and selective gas detection technique. As ethylene is a rather reactive compound due to its double bond between the two carbon atoms, it acts as one of the precursors for the tropospheric ozone generation, a gas species that is present in the photochemical smog, is an important greenhouse gas and whose formation is strongly associated with the presence of sun light and nitrogen oxide compounds. For this reason, ethylene renders itself an important pollutant in the atmosphere. In addition, the valid Brazilian legislation is only concerned with the total emission of hydrocarbons from the vehicle exhausts. It means that it does not discriminate the emission of some pollutant gas compounds, such as ethylene. This situation is greatly aggravated by the fact that most of the mass and cargo transport in Brazil is made by roads and powered by diesel oil.

Biphasic ethylene production during the hypersensitive response in Arabidopsis

The hypersensitive response (HR) is a cell death phenomenon associated with localised resistance to pathogens. Biphasic patterns in the generation of H2O2, salicylic acid and ethylene have been observed in tobacco during the early stages of the HR. These biphasic models reflect an initial elicitation by pathogen-associated molecular patterns followed by a second phase, induced by pathogen-encoded avirulence gene products. The first phase has been proposed to potentiate the second, to increase the efficacy of plant resistance to disease. This potentiation is comparable to the “priming” of plant defences which is seen when plants display systemic resistance to disease. The events regulating the generation of the biphasic wave, or priming, remains obscure, however recently we demonstrated a key role for nitric oxide in this process in a HR occurring in tobacco. Here we use laser photoacoustic detection to demonstrate that biphasic ethylene production also occurs during a HR occurring in Arabidopsis. We suggest that ethylene emanation during the HR represents a ready means of visualising biphasic events during the HR and that exploiting the genomic resources offered by this model species will facilitate the development of a mechanistic understanding of potentiating / priming processes.

Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation

A photoacoustic sensor has been developed for trace-gas monitoring using a near-infrared semiconductor laser emitting in the 2ν3 band of methane at 1.65 μm. The apparatus was designed for on-line process control in the manufacturing of the novel low-water-peak fibres developed for optical telecommunications. The importance of collisional relaxation processes in the generation of the photoacoustic signal is reported in the particular case of CH4 detection in dry O2 and O2–N2 mixtures. The negative influence of these effects results in a strongly reduced and phase-shifted photoacoustic signal, induced by a fast resonant coupling between the vibrational states of methane and oxygen, associated with the slow relaxation of the excited oxygen molecules. An unusual parabolic response of the sensor with respect to the methane concentration has been observed and is discussed. Finally, the beneficial effect of several species, including water vapour and helium, acting as a catalyst to hasten the relaxation of the CH4–O2 system, is demonstrated.

Laser photoacoustic detection allows in planta detection of nitric oxide in tobacco following challenge with avirulent and virulent Pseudomonas syringae Pathovars.

We demonstrate the use of laser photoacoustic detection (LPAD) as a highly sensitive method to detect in planta nitric oxide ((*)NO) production from tobacco (Nicotiana tabacum). LPAD calibration against (*)NO gas demonstrated a linear relationship over 2 orders of magnitude with a detection threshold of <20 pmol h(-1) (1 part per billion volume [ppbv]). The specificity of the photoacoustic signal for (*)NO when adding gas or the (*)NO donor, sodium nitroprusside, on injection into plant leaves, was demonstrated by its abolition with O(3) ((*)NO + O(3) --> NO(2) + O(2)). The utility of the LPAD method was shown by examination of a nonhost hypersensitive response and a disease induced by Pseudomonas syringae (P. s.) pv phaseolicola and P. s. pv tabaci in tobacco. (*)NO was detected within 40 min of challenge with P. s. pv phaseolicola, some 5 h before the initiation of visible tissue collapse. The wildfire tobacco pathogen P. s. pv tabaci initiated (*)NO generation at 2 h postinfection. The use of (*)NO donors, the scavenger CPTIO ([4-carboxyphenyl]-4,5-dihydro-4,4,5,5-tetramethyl-3-oxide), and the mammalian nitric oxide synthase inhibitor l-NMMA (N(G)-monomethyl-l-arginine) indicated that (*)NO influenced the kinetics of cell death and resistance to both avirulent and virulent bacteria in tobacco. These observations suggest that (*)NO is integral to the elicitation of cell death associated with these two bacterial pathogens in tobacco.

Pharmacokinetics of ethylene in man by on-line laser photoacoustic detection

The pharmacokinetics of ethylene are determined using laser-based photoacoustic detection and a closed chamber setup. Concentration–time data are analyzed using a two-compartment and a physiologically based pharmacokinetic (PBPK) model. Endogenous production was 92 ± 13 pmol/h/kg for the two-compartment model and 75 ± 10 pmol/h/kg for the PBPK model. These values agree with previous work at our department but are significantly lower than published values based on gas chromatography. The blood:air partition coefficient in the PBPK model was determined by curve fitting, because simulations based on published values did not agree well with data. Curve fitting gave a value of 0.092 ± 0.029. The real-time nature and high sensitivity of photoacoustic detection make it a useful addition to gas chromatography in closed chamber studies.

Application of InAsSb/InAsSbP and lead chalcogenide infrared diode lasers for photoacoustic detection in the 3.2 and 5 μm region

An investigation of photoacoustic detection using 3.2–3.6 and 5 μm diode lasers is described. An inexpensive resonant photoacoustic system was developed based, on a simple glass cell and condenser and electret microphone (Brüel & Kjaer type 4144/Sennheiser type K6P). The system was tested on the single rotation–vibration lines of C 2H 2, CO, COS, and NH 3 gases. The best detection limits obtained are 300 ppm V for C 2H 2 and 20 ppm V for COS. Potential applications of infrared diode laser photoacoustic detection lie in the areas of analytical chemistry, atmospheric research, and investigation of the kinetics of reactive species.

Effects of O2 on N2 fixation in heterocystous cyanobacteria from the Baltic Sea

The effect of O2 on nitrogenase activity in natural samples of heterocystous cyanobacte- ria from the Baltic Sea was studied using on-line laser photo-acoustic trace-gas detection. This technique records nitrogenase activity in near real-time and allows measurements in continuously changing O2 concentrations. Our results showed that under non-steady state conditions the optimum concentration of O2 for N2 fixation differed from that at steady-state O2 levels. The optimum O2 concentration depended upon whether the O2 concentration was increasing or decreasing, with decreasing concentrations yielding higher O2 optima for dark nitrogenase activity than increasing O2 concentrations. The cyanobacteria rapidly adapt to changes in O2, and therefore measurements also reflect the history of O2 concentrations to which organisms have been exposed. Steady-state and non- steady-state O2 concentrations both decreased their optimum O2 concentration for nitrogenase activity rates with increasing irradiance. However, the optimum O2 concentration was always higher than zero, even at saturating irradiances. Hence, it appears that low levels of O2 are an obligatory requirement for maximum nitrogenase activity in the field. Low levels of respiration served as a source of additional energy, suggesting that even at light saturation, photosynthetic energy genera- tion in the heterocyst can not saturate the demand of nitrogenase for ATP. The large changes in nitro- genase activity due to the combined effect of variations in O2 concentration and light emphasize the necessity of including these effects in models that calculate the daily integral of N2 fixation.

Pulsed laser photoacoustic detection of SO_2 near 2257 nm

A trace concentration of SO(2) near 225.7 nm has been detected with a master-oscillator power-oscillator laser system for the first time, to our knowledge. A photoacoustic absorption spectrum of SO(2) has been recorded on the (1)A(2)-(1)B(2) (pi-pi*) transition. Parametric dependence of the photoacoustic signal has been investigated. A detection limit (signal-to-noise ratio of 1) of 1.3 parts in 10(9) [1.3 ppbv (parts per billion by volume)] for SO(2) have been determined at 1 atmospheric pressure inside a photoacoustic cell.