Photoacoustic Spectroscopy Technique Research Articles

Study of the Pigments in Colombian Powdered Coffee Using Photoacoustic Spectroscopy

Biological pigments are chemical compounds that absorb light in the wavelength range of the visible region. They are present in all living organisms, vegetables being among their main producers. In this work, the photoacoustic spectroscopy technique was used to investigate some qualitative features related to pigments of ground and roasted coffee. The samples were collected at several Colombian commercial markets from different regions. Colombian coffee is known worldwide for its quality and flavor, being the main agricultural export product of the country. Therefore, it is important to study the composition and color of ground and roasted coffee in order to show quality and special characteristics of local varieties. Studying the content of pigments after roasting and grinding the coffee can allow a better understanding of the coloring process, which can lead to the definition of new criteria for evaluating the quality and other characteristics of the final product by comparing the optical spectra. In this work, the optical absorption spectra obtained by photoacoustic spectroscopy show absorption bands that match those of the pigments capsanthin, lutein and chlorophyll. In addition, an absorption peak in the near-infrared region was revealed, which also provides information regarding the composition of roasted and ground coffee.

Open-path measurement of ozone and methane gases using quartz-enhanced photoacoustic spectroscopy

ABSTRACTWe demonstrate a standoff system based on quartz-enhanced photoacoustic spectroscopy technique for the concentration measurements of atmospheric ozone and methane. The technique is a modified version of Photoacoustic spectroscopy. Two primary features of this technique are the employment of a tunable quantum cascade laser and a resonant quartz-crystal tuning fork detector. Both of these features facilitate simultaneous sensing of multiple molecular species. External-cavity quantum cascade laser having a spectral range from 7 to 10 micron is used. Diurnal concentration variations of methane and ozone are estimated for open-path up to 25 m. The ambient methane and ozone concentration maxima were observed to have values of 3.5 parts per million by volume and 140 parts per billion by volume, respectively. Finite-element mesh-based software is used to simulate the Eigen frequency of the tuning fork sensor. High-resolution transmission molecular spectroscopic database of atmospheric gases and the real-time gas concentration data from the Delhi Pollution Control Committee have been used as references.

Technical Note: Characterisation of Loess Soils Using near Infrared Photoacoustic Spectroscopy

The photoacoustic spectroscopy (PAS) technique has emerged as a valuable tool for the study of soil materials. The present work developed the experimental set-up for near infrared (800–2400 nm) photoacoustic spectroscopy (NIR-PAS), which consists of photoacoustic (PA) accessory, tungsten bromine lamp, monochromator, chopper and lock-in-amplifier, and this spectrometer was first applied to record the spectra of soils ( n = 50) collected from the Loess Plateau of China; partial least-squares regression (PLSR) models and leave-one-out cross-validation were used to predict soil organic matter (SOM), clay, carbonate and available phosphorus content. The spectra varied among different soil samples; SOM played an important role in the spectral appearance, and the intensity and position of five typical absorption bands significantly shifted owing to the variances in the components and structure of SOM. The PLSR model demonstrated a good performance in the prediction of SOM with a root mean square error of 2.5 g kg−1 and a ratio of standard deviation to prediction error of 2.3. This pilot study demonstrates that NIR-PAS exhibits typical infrared absorptions and may be suitable for analysing soil samples.

Standoff Detection of Hazardous Molecules for Defense Applications

The paper is focused on the development of measurement technique and processing of signal for the detection of chemical, explosive, biological agents and its simulants using Engineered Quartz Enhanced Laser Photoacoustic Spectroscopy (QE-LPAS) technique. Hazardous materials like Sarin, TATP (Tri acetone tri-peroxide) and their simulants like DMMP (Dimethyl Methyl Phosphonate), Acetone, and atmospheric species were detected at 7 to 11 μm wavelength band. QE PAS technique is developed and demonstrated from a standoff distance of up to 30 meters in gaseous/vapourous and aerosols based on retro-reflector in ~2.0 ppm concentration. Hazardous biomolecules like Tryphatophan and DPA were detected on diffused aluminum adsorbed surface plate. Explosive and its simulants, TNT on adsorbed surface and DMMP, Nitrobenzene, Acetone were detected in vapour/aerosol form. A dedicated single screen, single user, user friendly Graphical User Interface (GUI) for controlling the entire system, acquisition and processing of the incoming signal and demonstration of results has been developed with the help of Laboratory Virtual Instrument Engineering Workbench (LABVIEW).

Aerosol absorption measurement at SWIR with water vapor interference using a differential photoacoustic spectrometer.

Atmospheric aerosol plays an important role in atmospheric radiation balance through absorbing and scattering the solar radiation, which changes local weather and global climate. Accurate measurement is highly requested to estimate the radiative effects and climate effects of atmospheric aerosol. Photoacoustic spectroscopy (PAS) technique, which observes the aerosols on their natural suspended state and is insensitive to light scattering, is commonly recognized as one of the best candidates to measure the optical absorption coefficient (OAC) of aerosols. In the present work, a method of measuring aerosol OAC at the wavelength where could also be absorbed by water vapor was proposed and corresponding measurements of the absorption properties of the atmospheric aerosol at the short wave infrared (SWIR, 1342 nm) wavelength were carried out. The spectrometer was made up of two high performance homemade photoacoustic cells. To improve the sensitivity, several methods were presented to control the noise derived from gas flow and vibration from the sampling pump. Calibration of the OAC and properties of the system were also studied in detail. Using the established PAS instrument, measurement of the optical absorption properties of the atmospheric aerosol were carried out in laboratory and field environment.

Stryphnodendron adstringens: Clarifying Wound Healing in Streptozotocin-Induced Diabetic Rats.

Diabetes mellitus is a serious public health problem in which a major complication is impaired wound healing. Among the strategies developed to foster tissue repair is the use of medicinal plants. The bark of Stryphnodendron adstringens, which is popularly used as an aid in wound healing, has a documented effect on wound repair in normal rats. This study evaluated the healing action of the crude extract of S. adstringens in diabetic rats, and its chemical content. Compounds present in the crude extract were characterized by mass spectrometry. In diabetic rats (streptozotocin 35 mg/kg), two wounds made in the skin were treated daily for 4, 7, 10, and 14 days with gel containing 1 % crude extract or with base gel. Histological analyses involved the measurement of the length and thickness of the re-epithelialized surface, quantification of the number of cells in mitosis, and types I and III collagen fibers. Also, cutaneous permeation by photoacoustic spectroscopy, and the expression of cyclooxygenase-2 and vascular endothelial growth factor by Western blot were assessed. The crude extract fingerprint showed masses indicating proanthocyanidins. The crude extract mainly stimulated cell migration and proliferation of keratinocytes at the beginning of the treatment in addition to stimulating the replacement of type III collagen fibers by type I collagen fibers at 10 and 14 days. The photoacoustic spectroscopy technique showed that the gel containing 1 % of crude extract permeated through the skin to the dermis, where the crude extract was found. Vascular endothelial growth factor was stimulated after 7 days of treatment with the crude extract and cyclooxygenase-2 at 4, 7, and 10 days. The crude extract of S. adstringens acted in tissue repair in wounds in diabetic rats by stimulating the production of collagen fibers at the wound site. The crude extract favored the formation of a more organized extracellular matrix and filled the entire extent of the wound, and also fostered the upregulation of cyclooxygenase-2 and vascular endothelial growth factor, which are essential to this process. These crude extract actions in diabetic wounds are probably due to the presence of proanthocyanidins.

All-Optical Cantilever-Enhanced Photoacoustic Spectroscopy in the Open Environment

A novel all-optical cantilever-enhanced photoacoustic spectroscopy technique for trace gas detection in the open environment is proposed. A cantilever is set off-beam to “listen to” the photoacoustic signal, and an improved quadrature-point stabilization Fabry–Perot demodulation unit is used to pick up the vibration signal of the acoustic transducer instead of a complicated Michelson interferometer. The structure parameters of the cantilever are optimized to make the sensing system work more stably and reliably using a finite element method, which is then fabricated by surface micro-machining technology. Finally, related experiments are carried out to detect the absorption of water vapor at one atmosphere in the open environment. It was found that the normalized noise-equivalent absorption coefficient obtained by a traditional Fabry–Perot demodulation unit is \(3.38 \times 10^{-7}\,\hbox {cm}^{-1}\cdot \hbox {W}\cdot \hbox {Hz}^{-1/2}\), while that by a quadrature- point stabilization Fabry–Perot demodulation unit is \(1.08 \times 10^{-7}\,\hbox {cm}^{-1}\cdot \hbox {W}\cdot \hbox {Hz}^{-1/2}\), which indicates that the sensitivity is increased by a factor of 3.1 using improved cantilever-enhanced photoacoustic spectroscopy.

Compact sensor for methane detection in the mid infrared region based on Quartz Enhanced Photoacoustic Spectroscopy

A compact system for methane sensing based on the Quartz-Enhanced Photoacoustic Spectroscopy technique has been developed. This development has been taken through two versions which were based respectively on a Fabry Perot quantum wells diode laser emitting at 2.3μm, and on a quantum wells distributed feedback diode laser emitting at 3.26μm. These lasers emit near room temperature in the continuous wave regime. A spectrophone consisting of a quartz tuning fork and one steel microresonator was used. Second derivative wavelength modulation detection was used to perform low methane concentration measurements. The sensitivity and the linearity of the QEPAS sensor were studied. A normalized noise equivalent absorption coefficient of 7.26×10−6cm−1W/Hz1/2 was achieved. This corresponds to a detection limit of 15ppmv for 12s acquisition time.

Oxidation state determination of uranium in various uranium oxides: Photoacoustic spectroscopy complimented by photoluminescence studies

Photoacoustic spectroscopy (PAS) has been utilized for the determination of U(IV). Initial experiments were carried out for determination of U(IV) in uranium tetra fluoride, and were further extended to the determination of U(IV) in uranium oxide samples having various O/M ratios like UO2.00, UO2.17, U3O8, and U3O7. All these oxides, since dark gray/black in color, were having featureless spectra in the visible region, hence solid state reaction of uranium oxide with ammonium bi-fluoride was utilized for the formation of U(IV) and U(VI) oxyfluorides, having narrow well resolved spectra, prior to estimation by Photoacoustic spectroscopy technique. The strong absorption for U(IV) complex at 630nm was monitored using a He–Ne laser resulting in good sensitivity for determination of U(IV). It was observed that fluorinated uranium dioxide (UO2) is having spectra similar to U(IV); fluorinated uranium trioxide (UO3) is having spectra of uranyl only whereas Triuranium octoxide (U3O8) spectra consist of both U(IV) and uranyl component. This was further supported by photoluminescence studies.

Photoacoustic Characterization of Randomly Oriented Silver Nanowire Films

In this work, the photoacoustic characterization in the UV/Vis range of randomly oriented silver nanowire films deposited onto either a quartz or polymeric substrate is presented. This study was performed for a set of films differing in both metallic nanowire dimensions, as well as metal content. Samples were prepared starting from suspensions of Ag nanowires in isopropanol (IPA) $$(25~\mathrm{mg}{\cdot }\mathrm{ml}^{-1})$$ , differing in both the length and diameter of the nanowires. The obtained films were characterized by scanning electron micrography (SEM) images; thus, the metal filling factor was retrieved with MATLAB software based on a visual method. Following the morphological characterization, both spectrophotometry and the photoacoustic spectroscopy (PAS) technique were employed to investigate in detail the absorbance spectra of silver nanowire films, in order to evidence their peculiar properties in the UV/Vis spectral range. Specifically, this photothermal technique is particularly useful to investigate a film that may exhibit relevant scattering phenomena, as for metallic nanowire films. The obtained experimental results show that the choice of the metal filling factor may affect the absorbance spectra of the resulting mesh.

Evaluation of Nitrous Oxide Emitted from Diesel/Biodiesel Blends during Combustion in a Diesel Engine at Laboratory Scale by a Photoacoustic Spectroscopy Technique

The aim of this work was to evaluate the emission of nitrous oxide (N2O) using a diesel engine at laboratory scale without a catalytic converter with diesel/biodiesel blends (%) of 95:5 (B5), 90:10 (B10), 85:15 (B15), 80:20 (B20), 75:25 (B25), and 50:50 (B50). Measurements of N2O in the exhaust gas were made using an experimental setup based on photoacoustic spectroscopy using a quantum cascade laser that was validated to be selective and sensitive in the range from 1.7 to 2.72 ppmv. According to the experimental results, the lowest N2O concentration was found to be in the B5 diesel/biodiesel blend. Also, formaldehyde and methane compounds were detected qualitatively, indicating the possible presence of these chemicals in the combustion of diesel/biodiesel blends.

Characterization of optical, thermal and electrical properties of SWCNTs/PMMA nanocomposite films

The optical, thermal and electrical behavior of single-wall carbon nanotubes (SWCNTs)/poly(methyl methacrylate) (PMMA) composite are studied as a function of SWCNTs concentration. The nanocomposites were prepared in the form of films by solution casting technique. The concentrations of SWCNTs in SWCNTs/PMMA films were 0, 0.5, 1, 1.5, 2, 3.5, 5, 7.5, and 10 wt%. High-resolution transmission electron microscopy showed that SWCNTs doped in PMMA is less fragmented as compared to the powder SWCNTs. This is due to the interactions with polymers as well as the fabrication method. X-ray diffraction patterns of SWCNTs/PMMA composite films indicated that there is no covalent interaction between SWCNTs and PMMA. In addition, it demonstrates a homogeneous dispersion of SWCNTs in PMMA matrix. The optical properties of SWCNTs/PMMA films of SWCNTs concentration from 0 to 2.0 wt% have shown that the absorption intensity of the composite was enhanced ≈8.5 times as compared to the plain PMMA. Photoacoustic spectroscopy technique was used as a powerful and non-destructive tool to determine the thermal diffusivity (α), thermal effusivity (e) and thermal conductivity (k). The composites exhibited ≈160 % improvement in k at 2.0 wt%. Furthermore, the DC electrical conductivity measurements of SWCNTs/PMMA showed that the percolation threshold value was about 2.0 wt% of SWCNTs loading.

Ultraviolet (UVB and UVA) Photoprotector Activity and Percutaneous Penetration of Extracts Obtained from Arrabidaea chica

The aim of this work is to investigate the photoprotection activity and toxicity level of formulations containing the extract and its fractions obtained from leaves of Arrabidaea chica. The ex vivo percutaneous penetration of the extract was evaluated using the photoacoustic spectroscopy technique. The formulation presented optical absorption in the ultraviolet region, including UVA and UVB. This formulation was obtained without adding inorganic UV filters, as is frequently used in commercial sunscreens. The results showed a penetration rate similar to those of commercial sunscreens with its presence on the skin surface at least 180 min after the application. This formulation presented no toxic effects evaluated using hematological, biochemical, and histological assays. The results suggest that the formulation from the leaves of A. chica provides substantial protection against UVA + UVB radiation with a possible advantage of being natural and free of inorganic compounds compared with the majority of available commercial sunscreens.

Portable detection system for standoff sensing of explosives and hazardous materials

Standoff Quartz Enhanced Laser Photoacoustic Spectroscopy (QE-LPAS) technique is emerging as a powerful technique for detection of hazardous chemicals, biological and explosive agents. Experimentally, we have recorded standoff photoacoustic spectrum of hazardous molecules adsorbed at diffused surfaces from a distance of up to 25m. Tunable mid infrared quantum cascade lasers (MIR-QCL) in the wavelength range 7.0–12.0μm are being used as optical source. Samples of Dinitrotoluene (DNT), Pentaerythritoltetranitrate (PETN) having adsorbed concentration of approximately 5.0μg/cm2 were detected. Acetone and nitrobenzene samples in liquid having concentration 200nl approximately sealed in polythene sachet were detected from a standoff distance of up to 25m. All the above measurements are reported for a Signal to Noise Ratio (SNR) of 10, optimized for maintaining very less false alarm rates for field measurements. A portable trolley mounted system has been developed for field applications.

Photosensitizer and light diffusion through dentin in photodynamic therapy

Photodynamic therapy has been considered a potential antimicrobial modality against oral infections, including dental caries. A model to estimate the penetration of both photosensitizers and light through human dentin, a factor of interest in photodynamic therapy, is proposed. The photoacoustic spectroscopy technique was used to evaluate in vitro dentin permeability of three different photosensitizers. Using the dentin optical absorption and scattering coefficients, it was possible to propose a semi-quantitative model predicting both photosensitizer and light doses within dentin. The graphic illustrations obtained provided guidelines that may be useful in photodynamic therapy protocols used as antimicrobial tools in caries lesions.

Alternative Method to Characterize Corn Grain by Means of Photoacoustic Spectroscopy

The application of photothermal (PT) techniques to obtain the optical and thermal properties of different materials has been widely reported in the literature. Among the PT techniques, photoacoustic spectroscopy stands out because this technique has been used to characterize different types of materials in solid, liquid, and gaseous phases, as well as homogeneous and inhomogeneous samples as biological materials which present great complexity in their structure. In particular, the seeds and corn kernels comprise different structural components such as endosperm, pericarp, embryo, and pedicel. The color attribute is very important in the grains because it gives information about the chemical composition and nutritional quality attributes which are important in consumer acceptance. In this investigation optical absorption spectra of corn grains were obtained by using photoacoustic spectroscopy in a wavelength range from 325 nm to 800 nm. Two varieties of corn grains were studied, establishing a complete block design at random for the measurements. From the obtained optical absorption spectra, the optical absorption coefficient (\(\beta \)) was calculated as a function of the wavelength for each sample. A complementary study of the percentage of reflectance for these samples was carried out by using ultraviolet/visible spectrometry with an integrating sphere. The data were subjected to an analysis of the variance using software of the statistical analysis system. The results revealed significant differences (\(P\le 0.05\)) between corn varieties in the range of 325 nm to 670 nm. The application of the photoacoustic spectroscopy technique as an alternative to conventional methods for the characterization of maize grain through an analysis of \(\beta \) could be important for characterizing non-homogeneous materials like grains of corn, whose characterization is relevant in the food industry.

Microencapsulation by Freeze-Drying of Potassium Norbixinate and Curcumin with Maltodextrin: Stability, Solubility, and Food Application

Stability of potassium norbixinate and curcumin by microencapsulation with maltodextrin DE20 and freeze-drying was evaluated as a function of exposition to light, air, different pH, water solubility, and in food applications. The best results were obtained with microencapsulated potassium norbixinate 1:20, which, when vacuum-packed and in the presence of natural light, showed color retention of 78%, while microencapsulated curcumin 1:20 showed color retention of 71%. Differential scanning calorimetry and thermogravimetry provided an indication of interaction between colorants and maltodextrin. Photoacoustic spectroscopy (PAS) showed that free and microencapsulated colorants exhibited high rates of absorption throughout the measured spectral region. This work evidenced that the freeze-drying process is favorable for microencapsulation of curcumin by maltodextrin, providing improved solubility to the microencapsulated colorant. Both microencapsulated colorants showed relevant results for use in a wide range of pH and food applications. The PAS technique was useful for the evaluation of the stability of free and microencapsulated colorants.

English

  The color of the tortilla is one of the properties that determine the purchasing decision and acceptance for the consumer. This sensory attribute is altered, when making tortillas with elements to improve digestion and nutrition. Therefore, the objective of this investigation was to determine some information about the color in different types of tortilla found in the commercial market in “Ecatepec, Edo de Mexico”. Optical absorption coefficients (β) were obtained from them by photoacoustic spectroscopy technique of closed cell, one of the photothermal techniques. Optical absorption spectra of each tortilla were recorded by means of photoacoustic spectroscopy (PAS) in the 350 to 700 nm range. Thirteen types of tortillas were evaluated, the experimental unit comprised three tortillas, among which one tortilla was selected at random for each repetition. The β values were determined from the photoacoustic (PA) signals amplitude and using the Rosencwaig and Gersho model. Data was subjected to variance analysis (ANOVA) using the SAS GLM procedures. The ANOVA revealed significant (p ≤ 0.05) differences among tortillas. The results were analyzed statistically and correlated with preferences of a group of people in the same area, when a sensory test was applied; the test evaluated the color attribute by using the hedonic scale.   Key words: Tortilla, color, optical absorption coefficient, photoacoustic spectroscopy, sensory evaluation

Part-per-trillion level SF_6 detection using a quartz enhanced photoacoustic spectroscopy-based sensor with single-mode fiber-coupled quantum cascade laser excitation

A sensitive spectroscopic sensor based on a hollow-core fiber-coupled quantum cascade laser (QCL) emitting at 10.54 μm and quartz enhanced photoacoustic spectroscopy (QEPAS) technique is reported. The design and realization of mid-IR fiber and coupler optics has ensured single-mode QCL beam delivery to the QEPAS sensor. The collimation optics was designed to produce a laser beam of significantly reduced beam size and waist so as to prevent illumination of the quartz tuning fork and microresonator tubes. SF(6) was selected as the target gas. A minimum detection sensitivity of 50 parts per trillion in 1 s was achieved with a QCL power of 18 mW, corresponding to a normalized noise-equivalent absorption of 2.7×10(-10) W·cm(-1)/Hz(1/2).

Thermal decomposition study of nitropyrazoles based on time-resolved pulsed photoacoustic spectroscopy

The paper reports the study of thermal decomposition of 3(5)-nitropyrozole, 4-nitropyrazole and 1-nitropyrazole using time-resolved pulsed photoacoustic spectroscopy technique for the first time. The second harmonic, i.e., λ = 532 nm, 7 ns pulse width at 10 Hz repetition rate, obtained from Q-switched Nd: YAG laser has been employed. In addition, we have studied the effect of pressure, temperature and incident laser energy on the thermal decomposition mechanism of nitropyrazoles. The strength of photoacoustic signal provides significant information about the multistep thermal decomposition mechanism of 3(5)-nitropyrazole and 4-nitropyrazole, while 1-nitropyrazole follows the path of direct decomposition based on single reaction, which is also verified by the thermal gravimetric–differential thermal analysis (TG–DTA) technique. We have also experimentally demonstrated the presence of free NO2 before the melting point, which is due to the thermal dissociation of solid nitropyrazole compounds.