Photoacoustic Measurements Research Articles

Synthesis, characterization, and sensitivity tests of a novel sensor based on barium antimonate powders

Barium antimonate (BaSb2O6) powders were prepared using a microwave-assisted wet chemistry process. The powders were calcined at 800 °C and their crystallinity was studied by X-ray diffraction, finding a hexagonal crystal structure with cell parameters a = 5.303 Å and c = 5.758 Å, and a P-31m (162) space group. Material’s morphology and particle size were analyzed by field-emission scanning and transmission electron microscopy, finding that nano-plates (~ 70 nm) and other apparently shapeless particles (~ 70 nm) were produced. By means of X-Ray Photoelectron Spectroscopy, it was found that the Ba 3d had a doublet (Ba 3d5/2 and Ba 3d3/2) with binding energies at 779.69 and 794.97 eV, respectively, which was associated with the Ba2+ oxidation state. The Sb 3d spectrum presented a doublet (Sb 3d5/2 and Sb 3d3/2) at 530.44 and 539.79 eV, while the O 1 s at 530.30 eV overlapped the Sb 3d5/2 peak. Photoacoustic Spectroscopy measurements of the oxide showed a band gap of 3.43 eV. Pellets manufactured with BaSb2O6’s powders calcined at 800 °C were tested in CO (1–300 ppm) and C3H8 (1–500 ppm) atmospheres at different operating temperatures (100, 200 and 300 °C). The pellets exhibited an excellent response, showing a high sensitivity as concentrations and temperature increased. Furthermore, the results indicated that the BaSb2O6 is highly selective to CO atmospheres. In particular, the good response of the pellets suggests that this oxide can be applied as a potential sensor for toxic gases.

High-Sensitivity Low-Frequency Fabry-Perot Ultrasonic Hydrophone With Chitosan Diaphragm

Herein we demonstrate a miniature flexible optical fiber Fabry-Perot (F-P) underwater ultrasonic sensor with chitosan diaphragm coated onto the tip of a capillary with an inner diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\mu $ </tex-math></inline-formula> m. Due to its low Young’s modulus and high surface finish, the chitosan film with a thickness of ~955 nm, formed by low-speed spin-coating of a 3% solution of biotech chitosan dissolved in 2% acetic acid, enables a high sensitivity to low-frequency ultrasonic sound pressure for the developed sensor. Because of the molecular permeability of chitosan, this type of sensor contributes to effectively reducing the working point shift of the F-P sensor caused by static pressure in underwater ultrasonic measurement. Then the ultrasonic test in a water tank offered a high sound pressure sensitivity of 52.6 mV/kPa in the tested ultrasonic range of 100 kHz to 800 kHz with a noise-limited minimum detectable pressure level of ~2.37 mPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . Also, the directivity measurement showed the maximum signal deviation of 2.47 dB in response to ultrasound pressure in the angle range of −90° – 90°. The proposed technique greatly simplifies the miniaturized integration of all-optical ultrasonic detectors, thus suggesting the great potential in ultra-high sensitivity hydrophone in biomedical photoacoustic measurement.

Estimation of linear expansion coefficient and thermal diffusivity by photoacoustic numerical self-consistent procedure

In this paper, a self-consistent inverse procedure is developed for the estimation of linear thermal expansion coefficient and thermal diffusivity of solids from transmission photoacoustic measurement. This procedure consists of two single-parameter fitting processes applied alternately: phase data are fitted by shifting thermal diffusion coefficient, while amplitude data are fitted by shifting thermal expansion coefficient. Each fitting process uses the resulting parameter of the other, previously finished one, thus converging to the best solution-pair achievable. In numerical experiments, the convergence proves to be very fast. The achieved parameter estimation error is as low as 1%, and it can be lowered further more by increasing the fitting resolution in parameter space. The application of the procedure on experimentally obtained aluminum photoacoustic response (measurements) on three thickness levels returns the estimates of its thermal diffusion and thermal expansion coefficients within expected literature boundaries.

Semantic segmentation of multispectral photoacoustic images using deep learning

Photoacoustic (PA) imaging has the potential to revolutionize functional medical imaging in healthcare due to the valuable information on tissue physiology contained in multispectral photoacoustic measurements. Clinical translation of the technology requires conversion of the high-dimensional acquired data into clinically relevant and interpretable information. In this work, we present a deep learning-based approach to semantic segmentation of multispectral photoacoustic images to facilitate image interpretability. Manually annotated photoacoustic and ultrasound imaging data are used as reference and enable the training of a deep learning-based segmentation algorithm in a supervised manner. Based on a validation study with experimentally acquired data from 16 healthy human volunteers, we show that automatic tissue segmentation can be used to create powerful analyses and visualizations of multispectral photoacoustic images. Due to the intuitive representation of high-dimensional information, such a preprocessing algorithm could be a valuable means to facilitate the clinical translation of photoacoustic imaging.

Assessment of ammonia sensors and photoacoustic measurement systems using a gas calibration unit

• Study shows measurement techniques for extensive tests of gas measuring devices. • We focused on suitability of devices for measuring ammonia at different humidities. • Photoacoustic gas analysers and electrochemical gas sensors were testet. • With a gas calibration unit, accuracy, response time and drift behavior can be tested. • Pre-testing at laboratory level is crucial to assess the suitability for field trials. The accurate measurement of environmentally-relevant gases such as ammonia (NH 3 ) is increasingly important, especially in agricultural science. Accurate and continuous measurement of gases is essential for evaluating NH 3 and other gases as resource-based indicators of air quality in forced ventilation barns and for determining emission rates. To better assess measuring devices under different barn conditions (e.g. relative humidity or concentration range) self-conducted tests should be implemented at the laboratory scale before, during and after (experimental) measurements in the barn, independent of the manufacturer's specifications. Therefore, in this study, a gas calibration unit was set up for measurements at the laboratory scale. Moreover, measurement protocols were developed to investigate the accuracy at different gas concentrations and relative humidity levels and the responsiveness to rapid gas concentration changes. Measurements were performed with photoacoustic gas analysers (INNOVA 1412) and transmitters with electrochemical gas sensors (Polytron 8100 and C300). In addition to the presentation of results of the devices used in this case, this study should above all offer suggestions for quality monitoring to test sensors more intensively at the laboratory scale in order to be able to use them in a more targeted manner according to their optimal suitability.

A novel needle probe for deeper photoacoustic viscoelasticity measurement

We present for the first time, to the best of our knowledge, a needle probe for photoacoustic viscoelasticity (PAVE) measurements at a depth of 1 cm below the sample surface. The probe uses a gradient index rod lens, encased within a side-facing needle (0.7 mm outer diameter), to direct excitation light (532 nm) and detection light (1325 nm) focused on the sample, collecting and directing the returned detection light in a spectral domain low coherence interferometry system, which allows for obtaining optical phase differences due to photoacoustic oscillations. The feasibility of needle probe for PAVE depth characterization was investigated on gelatin phantoms and in vitro biological tissues. The experimental results in an in vivo animal model predict the great potential of this technique for in vivo tumor boundary detection.

Characterization of Cuban and Brazilian natural zeolites by photoacoustic spectroscopy and electron paramagnetic resonance.

This report describes the photoacoustic and electron paramagnetic resonance investigations of Brazilian and Cuban zeolites. Photoacoustic optical absorption measurements indicate the presence of iron (Fe3+) ions with their respective transition bands for both zeolites. Two species of manganese (Mn2+ and Mn3+) were identified in the Cuban sample and the electronic transitions assigned. Iron and manganese ions were confirmed through nonradiative relaxation (τ) and characteristic diffusion (τβ) times evaluation, whose values were found to be τBRA = 5.40 ms, τCUB = 4.60 ms, τβBRA = 387 μs and τβCUB = 305 μs. Crystal field (Dq-BRA/Dq-CUB = 1048 cm-1/945 cm-1) plus Racah (B-BRA/B-CUB = 457 cm-1/813 cm-1 and C-BRA/C-CUB = 3655 cm-1/2496 cm-1) parameters were assessed as well. Paramagnetic resonance corroborated Fe3+ ions present in the Brazilian zeolite occupying sites showing axial and/or rhombic symmetry distortions. For the Cuban sample, results reveal the characteristic hyperfine sextet lines of Mn2+ overlapping the Fe3+ line. Values of Landé factor and isotropic hyperfine splitting constant were found to be 2.0 and 9.7 mT, respectively. This tells us that the Mn2+ lies in octahedral symmetry probably replacing calcium ions and point towards an ionic bonding character of the Mn2+ and its surroundings.

Photoacoustic measurement of localized optical dichroism in chiral crystals.

In this communication, we present a novel method to measure local optical dichroism (OD) in opaque crystal powder suspensions using photoacoustic (PA) effect. Our method is based upon the novel laser speckle contrast technique, in combination with a simple statistical approach, we were able to measure the OD of chiral crystals suspensions under completely random orientation.

Photocatalytic Activity of Radial Rutile Titanium(IV) Oxide Microspheres for Aerobic Oxidation of Organics.

Radial rutile TiO2 nanorod homomesocrystals (TiO2 -NR HOMCs) or the so-called "sea urchin-like TiO2 microspheres" were synthesized by using a hydrothermal method. TiO2 -NR HOMCs show photocatalytic activity for aerobic oxidative degradation of 2-naphthol under irradiation of UV- and visible light. Furthermore, extremely small iron oxide clusters were formed on the surface of TiO2 -NR HOMCs (FeOx /TiO2 -NR HOMCs) by the chemisorption-calcination technique to reduce the band gap. The FeOx -surface modification gives rise to drastic enhancement of the UV- and visible-light activity. Reversed double-beam photoacoustic spectroscopy measurements were performed for TiO2 -NR HOMCs and FeOx /TiO2 -NR HOMCs to obtain the ERDT (energy-resolved distribution of electron traps)/CBB (conduction-band bottom) patterns. The ERDT/CBB pattern of TiO2 -NR HOMCs consists of two components derived from rutile (C1) and amorphous TiO2 (C2). In the pattern, the surface electron traps in C2 exist near the CBB to be removed by the FeOx -surface modification. By taking this finding into consideration, the striking surface modification effect is ascribable to the electrocatalytic activity (or the action as an electron reservoir) of the FeOx clusters for multiple ORR, the suppression of recombination, and the increase in the visible-light harvesting efficiency.

Characterization of multi-biomarkers for bone health assessment based on photoacoustic physicochemical analysis method

Photoacoustic (PA) techniques are potential alternatives to histopathology. The physicochemical spectrogram (PCS) generated by the PA measurement at multiple wavelengths can presents the morphology and chemical composition target at multi-biomarkers simultaneously. In this work, via multi-wavelength PA measurements performed on rabbit bone models, we investigated the feasibility of using PCSs for bone health assessment. A comprehensive analysis of the PCSs, termed PA physicochemical analysis (PAPCA), was conducted. The “slope” and “relative content” were used as the PAPCA-quantified parameters to characterize the changes in the physical and chemical properties of bone tissue, respectively. The findings are consistent well with the gold-standard imaging results. It demonstrated that the PAPCA can be used to characterize both the microstructure and content of multi-biomarkers which highly related with bone health. Considering the PA technique is noninvasive and radiation-free, it has great potential in the implementation and monitoring of bone diseases progression.

Fluorescence and Photoacoustic Spectroscopy-Based Assessment of Mitochondrial Dysfunction in Oral Cancer Together with Machine Learning: A Pilot Study.

The current study reports an integrated approach of machine learning and tryptophan fluorescence and photoacoustic spectral properties to assess the mitochondrial status under oral pathological conditions. The mitochondria in the study were isolated from oral cancer tissues and adjacent normal counterparts, and the corresponding fluorescence and photoacoustic spectra of tryptophan were recorded at 281 nm pulsed laser excitations. A set of features were selected from the pre-processed spectra and were used to classify the data using support vector machine (SVM) learning in the MATLAB platform. SVM analysis demonstrated clear differentiation between mitochondria isolated from normal and cancer tissues for fluorescence (sensitivity, 86.6%; specificity, 90%) and photoacoustic (sensitivity, 86.6%; specificity, 96.6%) measurements. Further investigation into the influence of change in protein conformation on the nature of tryptophan spectral properties was evaluated by 8-anilino-1-naphthalene sulfonic acid (ANS) fluorescence assay. The impact of protein structural changes on the mitochondrial functions was also estimated by mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and cytochrome c oxidase (COX) assays, suggesting an altered mitochondrial function. The findings indicate that tryptophan fluorescence and photoacoustic spectral properties together with machine learning algorithms may delineate the mitochondrial functional status in vitro, indicating its translational potential.

Towards temperature controlled retinal laser treatment with a single laser at 10 kHz repetition rate

Abstract Laser photocoagulation is one of the most frequently used treatment approaches in ophthalmology for a variety of retinal diseases. Depending on indication, treatment intensity varies from application of specific micro injuries down to gentle temperature increases without inducing cell damage. Especially for the latter, proper energy dosing is still a challenging issue, which mostly relies on the physician’s experience. Pulsed laser photoacoustic temperature measurement has already proven its ability for automated irradiation control during laser treatment but suffers from a comparatively high instrumental effort due to combination with a conventional continuous wave treatment laser. In this paper, a simplified setup with a single pulsed laser at 10 kHz repetition rate is presented. The setup combines the instrumentation for treatment as well as temperature measurement and control in a single device. In order to compare the solely pulsed heating with continuous wave (cw) tissue heating, pulse energies of 4 µJ were applied with a repetition rate of 1 kHz to probe the temperature rise, respectively. With the same average laser power of 60 mW an almost identical temporal temperature course was retrieved in both irradiation modes as expected. The ability to reach and maintain a chosen aim temperature of 41 °C is demonstrated by means of model predictive control (MPC) and extended Kalman filtering at a the measurement rate of 250 Hz with an accuracy of less than ±0.1 °C. A major advantage of optimization-based control techniques like MPC is their capability of rigorously ensuring constraints, e.g., temperature limits, and thus, realizing a more reliable and secure temperature control during retinal laser irradiation.

Cantilever-enhanced photoacoustic measurement of light-absorbing aerosols

Photoacoustic detection is a sensitive method for measurement of light-absorbing particles directly in the aerosol phase. In this article, we demonstrate a new sensitive technique for photoacoustic...

A silicon micromechanical resonator with capacitive transduction for enhanced photoacoustic spectroscopy

This paper presents the design of a silicon micromechanical resonator with capacitive transduction for a gas sensor based on photoacoustic spectroscopy. It overcomes problems imposed by opposite physical trends originating from the sensor’s working principles. The capacitive transduction mechanism is considered incompatible with the photoacoustic gas detection as it reduces the mechanical displacement by a damping effect, thus decreasing the sensitivity. This occurs because the same part serves two functions: photoacoustic excitation and capacitive transduction. The suggested approach in this study focuses on the spatial separation of these two functions. We propose the first reported mechanical microresonator for photoacoustic gas sensing, which decouples photoacoustic excitation and capacitive transduction. The design has been modeled, fabricated, characterized, and compared with the on-beam Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) technique, a reference for compact and selective gas sensors. The performed photoacoustic measurement has been realized on calibrated concentrations of methane. For a 1 s integration time in first harmonic detection, we obtained a limit of detection (LOD) of 667 ppmv for silicon microresonator. In comparison to on-beam QEPAS technique, we obtained LOD of 163 ppmv, which constitutes a factor 4 between QEPAS and MEMS. The conditions for both experiments were the same.

Laser-induced ultrasound transmitters for large-volume ultrasound tomography

We present a protocol for the design, fabrication and characterisation of laser-induced ultrasound transmitters with a specific, user-defined frequency response for the purpose of ultrasound tomography of large-volume biomedical samples. Using an analytic solution to the photoacoustic equation and measurements of the optical and acoustic properties of the materials used in the transmitters, we arrive at a required mixture of carbon black and polydimethylsiloxane to achieve the desired frequency response. After an in-depth explanation of the fabrication and characterisation approaches we show the performance of the fabricated transmitter, which has a centre frequency of 0.9 MHz, 200% bandwidth and 45.8∘ opening angle, multi-kPa pressures over a large depth range in water.

Direct photoacoustic measurement of silicon nanoparticle degradation promoted by a polymer coating

Nanomaterials with controllable biodegradation properties respond to the main challenge of cancer nanomedicine to minimise side effects and maximise the delivery efficacy to tumours. These biodegradation properties vary from clear aqueous solutions to protein-abundant biological fluids. A photoacoustic method suitable for in vitro quantification of highly scattering colloids with optical absorption properties is introduced and demonstrated by determination of the degradation rate of laser-synthesized silicon nanoparticles (Si NPs) in turbid serum solutions. In vitro screening of a variety of polymer surface-coatings of Si NPs revealed a stand-alone property of polyallylamine (PAA) to accelerate the Si NP dissolution. PAA-coated Si NP half-life was measured ∼ 100-min in aqueous solutions and slowed down to ∼ 24 h in serum. As-produced PAA-coated Si NPs appeared suitable for blockade of the mononuclear phagocyte system. Pre-treatment with PAA-Si NPs caused 1.4-times reduced uptake of magnetic particles by human THP-1 cells in vitro and a 13-fold increase of the magnetic particle delivery to the B16-F1 xenograft tumours in vivo. The demonstrated photoacoustic method is believed to facilitate design and screening of biodegradable materials suitable for in vivo applications such as controlled drug release.

Bi-modal photothermal/optical microscopy for complementary bio-imaging with high resolution and contrast

In the paper, combined bi-modal microscopic visualization of biological objects based on reflection-mode optical and photoacoustic measurements was presented. Gas-microphone configuration was chosen for the registration of photothermal response. Precise positioning of the scanning laser beam with modulated intensity was performed employing acousto-optic deflectors. Photoacoustic images are shown to give complementary details to the optical images obtained in the reflected light. Specifically, the photoacoustic imaging mode allows much better visualization of the features with enhanced heat localization due to the reduced heat outflow. For example, the application of the photoacoustic imaging mode was especially successful to visualize Drosophila fly's micro-hairs. Furthermore, the photoacoustic image quality was shown to be adjusted through modulation frequency.

An optical coherence photoacoustic microscopy system using a fiber optic sensor

In this work, a novel fiber optic sensor based on Fabry–Pérot interferometry is adopted in an optical coherence photoacoustic microscopy (OC-PAM) system to enable high-resolution in vivo imaging. The complete OC-PAM system is characterized using the fiber optic sensor for photoacoustic measurement. After characterization, the performance of the system is evaluated by imaging zebrafish larvae in vivo. With a lateral resolution of 3.4 μm and an axial resolution of 3.7 μm in air, the optical coherence microscopy subsystem visualizes the anatomy of the zebrafish larvae. The photoacoustic microscopy subsystem reveals the vasculature of the zebrafish larvae with a lateral resolution of 1.9 μm and an axial resolution of 37.3 μm. As the two modalities share the same sample arm, we obtain inherently co-registered morphological and vascular images. This OC-PAM system provides comprehensive information on the anatomy and vasculature of the zebrafish larvae. Featuring compactness, broad detection bandwidth, and wide detection angle, the fiber optic sensor enables a large field of view with a static sensor position. We verified the feasibility of the fiber optic sensor for dual-modality in vivo imaging. The OC-PAM system, as a non-invasive imaging method, demonstrates its superiority in the investigation of zebrafish larvae, an animal model with increasing significance in developmental biology and disease research. This technique can also be applied for functional as well as longitudinal studies in the future.

Detection of collagen by multi-wavelength photoacoustic analysis as a biomarker for bone health assessment

Collagen is an important biomarker of osteoporosis progression. Noninvasive, multispectral, photoacoustic (PA) techniques use pulsed laser light to induce PA signals to facilitate the visualization of chemical components that are strongly related to tissue health. In this study, the feasibility of multi-wavelength PA (MWPA) measurement of the collagen in bone, using the wavelength range of 1300–1800 nm, was investigated. First, the feasibility of this approach for detecting the collagen content of bone was demonstrated by means of numerical simulation. Then, ex vivo experiments were conducted on both animal and human bone specimens with different bone densities using the MWPA method. The relative collagen content was extracted and compared with the results of micro-computed tomography (micro-CT) and histology. The results showed that the “relative collagen content” parameter obtained using the MWPA approach correlated well with the bone volume ratio obtained from micro-CT images and histological analysis results. This study highlights the potential of the proposed PA technique for determining the collagen content of bones as a biomarker for bone health assessment.

Ultrasound irradiation effect on photosynthesis and transpiration of aquatic lirium plants

Purpose To find possible causes of the photobaric response decrease in photoacoustic measurements on Aquatic Lirium plants after ultrasonic irradiations reported elsewhere contributing to understanding the effect of ultrasonic irradiation on them and searching for environmentally friendly methodologies to control this weed. Materials and Methods The plants were extracted from their natural habitat in Xochimilco water canals, Mexico City. The irradiations on the plants were carried out to 2 hours exposure time, 17 kHz frequency, and 30 W x 4 output power. We used the photoacoustic spectroscopy technique at room temperature in the range of 400–750 nm to analyze the optical absorption response of photosynthetic pigments before and after ultrasonic irradiations. To monitor the leave transpiration rate, we used an LI-COR 6400XT portable system, expressed in units of mols H2O per second per unit area of the leaf surface. Results We obtained a significant decrease of the chlorophylls bands amplitude in the photoacoustic spectroscopy spectra and a drastic reduction in the leaves transpiration rate of irradiated plants that depends on the time elapsed after irradiation. Remarkable physical changes in the leaves and petioles of the irradiated plants were observed with the naked eye. Conclusions A significantly decreasing photosynthesis and transpiration in the leaves of the irradiated lirium plants were obtained. Together with the observed physical changes in the leaves and petioles, these results suggest an alteration in the water transport and the overall gas exchange mechanisms affecting the irradiated leaves' transpiration and photosynthesis processes that agree with the photobaric response decrease reported elsewhere. Due to the fundamental role of stomata in these mechanisms, it is suggested, as a possible cause, that the ultrasonic-induced disruption of stomata's mechanical operation by guard cells prevents them from performing their function normally. A hypothesis to be confirmed in future studies, for which a line of action is proposed.