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Fiber-optic photoacoustic (PA) sensing has important applications in trace gas detection. The fiber-optic Fabry-Perot acoustic sensor implemented applying a cantilever is a novel and highly sensitive PA detector. Demodulation technologies such as intensity demodulation, optical cross-correlation demodulation and spectral demodulation are the key to improving the performance and engineering applications of fiber-optic PA sensors. For the detection of weak PA signals, the white-light interferometry based lock-in detection method is highlighted. On this basis, the miniature fiber-optic PA sensor with the special characteristics of high sensitivity, intrinsic safety, long-distance measurement, and immunity to electromagnetic interference can be designed by combining the cantilever and PA probe. This review also outlines the application of cantilever-enhanced fiber-optic PA sensing technology in the fields of online analyzing of high-voltage electrical equipment, leakage gas monitoring, coal mine spontaneous combustion monitoring and environmental gas monitoring. Finally, the future trend of fiber-optic PA sensing is presented. [ABSTRACT FROM AUTHOR]

A highly sensitive sulfur dioxide (SO2) photoacoustic gas sensor was developed for the sulfur hexafluoride (SF6) decomposition detection in electric power systems by using a novel 266 nm low-cost high-power solid-state pulse laser and a high Q-factor differential photoacoustic cell. The ultraviolet (UV) pulse laser is based on a passive Q-switching technology with a high output power of 28 mW. The photoacoustic signal was normalized to the laser power to solve the fluctuation of the photoacoustic signal due to the power instability of the UV laser. A differential photoacoustic cell can obtain a high Q-factor and reduce the gas flow noise in SF6 buffer gas. The parameters of the SO2 sensor system were optimized in terms of laser power and operating pressure. A 1σ detection limit (SNR = 1) of 2.34 ppb was achieved with a 1 s integration time, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 7.62 × 10−10 cm−1WHz−1/2. [ABSTRACT FROM AUTHOR]

Nanoparticle (NPs) have attracted the attention of scientists and researchers in water remediation due to the improvement in its processability, and its cost effectiveness. The present work analyzed the synergistic effect of CuO (NPs) with different ratios (0, 0.5, 0.6, 0.7, 0.8, 0.9 and 1 wt %) on the structural, and optical properties of Fe 3 O 4 (NPs), that can be used in water desalination process. The general methodology for preparation and structural properties of CuO (NPs), Fe 3 O 4 (NPs) and CuO/Fe 3 O 4 (NCs) were analyzed by (XRD) and (TEM) measurements. The morphological combination of (SEM) with (EDX), were used for determining the elemental identification of CuO/Fe 3 O 4 (NCs). The characterization topography was found to be strongly affected by the change of the CuO concentration. Furthermore, the Urbach energy (E U ) , steepness parameter (σ) , electron-phonon interaction (E e-p ) , optical band gap (E g ) , refractive index (n) and optical conductivity (σ opt ) were calculated. The optical absorption studies in the UV–Visible region, revealed that the CuO/Fe 3 O 4 (NCs) was found to be direct allowed transition, and the energy bandgap value decreased from 2.52 eV to 2.15 eV based on the percentage change of CuO (NPs) in CuO/Fe 3 O 4 (NCs). Moreover, the value of thermal conductivity (k) , and thermal efficiency ( η ), showed an increase with the increase of the ratio of CuO (NPs), which may be an indication for opening an innovation way that can satisfy the need of seawater desalination technology. [ABSTRACT FROM AUTHOR]

This paper presents a miniature Rollar‐type resonant photoacoustic cell (RRPAC), consisting of two cylindrical resonant cavities and a buffer chamber. The finite element analysis of the acoustic field distributions for the RRPAC and T‐type resonant photoacoustic cell (TRPAC) is utilized, demonstrating that RRPAC can produce a greater photoacoustic signal than the conventional TRPAC. A high sensitivity trace C2H2 photoacoustic spectroscopy (PAS) system is successfully developed by combining a cantilever beam‐based acoustic sensor as the acoustic sensing unit and a high‐speed spectrometer as the demodulation unit with the RRPAC. The experimental results indicate that the 2f signal of the RRPAC at the first‐order resonance mode is approximately 1.5 times of the TRPAC with the same C2H2 concentration. The gas detection limit of the RRPAC PAS system for C2H2 is 40.7 ppb at an averaging time of 100 s. In comparison with the conventional TRPAC, the RRPAC exhibits higher sensitivity, thus providing a novel solution for the advancement of the PAS system. [ABSTRACT FROM AUTHOR]

In this study, we address the challenge of estimating the resonance frequency of a photoacoustic detector (PAD) gas cell under varying temperature conditions, which is crucial for improving the accuracy of gas concentration measurements. We introduce a novel approach that uses a long short-term memory network and a self-attention mechanism to model resonance frequency shifts based on temperature data. To investigate the impact of the gas mixture temperature on the resonance frequency, we modified the PAD to include an internal temperature sensor. Our experiments involved multiple heating and cooling cycles with varying methane concentrations, resulting in a comprehensive dataset of temperature and resonance frequency measurements. The proposed models were trained and validated on this dataset, and the results demonstrate real-time prediction capabilities with a mean absolute error of less than 1 Hz for frequency shifts exceeding 30 Hz over four-hour periods. This approach allows continuous, real-time tracking of the resonance frequency without interrupting the laser operation, significantly enhancing gas concentration measurements and contributing to the long-term stabilization of the sensor. The results suggest that the proposed approach is effective in managing temperature-induced frequency shifts, making it a valuable tool for improving the accuracy and stability of gas sensors in practical applications. [ABSTRACT FROM AUTHOR]

Laser spectroscopy offers a significant tool for revealing specific molecular details with the desired accuracy and sensitivity. However, it poses challenges to maintain high sensitivity when targeting a micro‐region. Here, a dual‐enhanced photothermal approach is presented using a high‐finesse fiber Fabry–Pérot (F–P) cavity, tailored for highly sensitive chemical sensing with nanoliter‐scale light–matter interaction. A spheric surface (diameter: 50 µm, radius of curvature: 910 µm) is created on the fiber tip using focused ion beam milling. By adding a high‐reflectivity dielectric coating to the spheric surface, a fiber F–P cavity is obtained with a length of 473 µm and a finesse exceeding 4000. The intra‐cavity pump light within the gas‐filled fiber cavity generates a strong photothermal effect upon gas absorption. This effect induces phase modulation, which is amplified and detected by coupling a probe laser to the fiber cavity‐based interferometer. A minimum detection limit of 10 parts‐per‐billion (ppb) of C2H2 at 1530.37 nm is demonstrated using only 1 mW of pump power, corresponding to a normalized noise equivalent absorption coefficient of 9.1×10−11 cm−1∙W∙Hz−1/2. This platform breaks the bottleneck of ultrasensitive gas detection with a very short light–matter interaction length, promising significant advancements in microscale chemical analysis through optical investigations. [ABSTRACT FROM AUTHOR]

Photoacoustic imaging is an emerging biomedical imaging technique that enables non-invasive visualization of the optical absorption properties of biological tissues in vivo. Although numerous studies have used contrast agents to achieve high-contrast imaging in deep tissues, targeting specific areas remains a challenge when using agents that are continuously activated. Recent research has focused on developing triggered contrast agents that are selectively activated in target areas. This review delves into the use of pH-triggered contrast agents in photoacoustic imaging, which take advantage of the lower pH of the tumor microenvironment compared to normal tissues. The paper discusses the mechanisms of pH-triggered contrast agents that contribute to improving depth and contrast in photoacoustic tumor imaging. In addition, the integration of functionalities, such as photothermal therapy and drug delivery monitoring, into these agents demonstrates significant potential for biomedical applications. [ABSTRACT FROM AUTHOR]

Diffuse reflectance spectroscopy (DRS) and photoacoustic absorption spectroscopy (PAS) are investigated in model systems that mimic topological structures found in vegetal fibers, e.g., made of oriented hollow channels. Among this wide family, the shiny optical aspect of Golden grass stems has motivated detailed investigations of their chemical composition, microstructure, and electronic properties. In this work, diffuse reflectance and absorption of a photon flux within a collection of parallel hollow fibers are addressed using 2D optical models, neglecting interface scattering. Analytical results obtained for hollow square tube (HST) and plane parallel membrane (PPM) arrays are validated by full ray-tracing calculations. Optical paths with multiple reflection/refraction events at air-fiber interfaces selectively enhance DRS and PAS intensities and thus explain the shiny golden-like aspect of Golden grass, in contrast with specular reflectance calculated from the complex refractive index. A simple method is proposed to retrieve the complex dielectric function of fiber walls from the measured PAS and DRS intensities, using analytical equations obtained with hollow fiber topologies, in a low-energy region not easily accessible by photoelectron energy loss spectroscopy. [ABSTRACT FROM AUTHOR]

Based on photoacoustic spectroscopy and finite element simulation technology, a simulation model of sound field excitation in a cylindrical resonant photoacoustic cell was established. The finite element simulation method was used to analyze the acoustic mode and sound pressure distribution of the cavity structure of the photoacoustic cell. The effects of the geometric parameters of the resonator and the buffer cavity on the performance of the photoacoustic cell were compared. The frequency response characteristics of the photoacoustic cell and the effects of the air intake and the air outlet were studied. Based on the simulation results, a cylindrical resonant photoacoustic cell was designed, and a photoacoustic sensor for NO2 detection was built. NO2 with a volume fraction of 10−5 was taken as the sample gas through frequency scanning to obtain the frequency response curve of the system. The resonant frequency is 1730 Hz, and the cell constant is about 542.3 (Pa*cm)/W. The quality factor is 10.05. By linear fitting the calibration curve of the sensor, the fitting slope is 0.012 µV/ppb, and R2 is 0.998. Atmospheric NO2 detection was carried out for two consecutive weeks, whose findings are in good agreement with the data released by a Huainan environmental monitoring site. The experimental results show that the system can detect NO2 in the atmosphere with high sensitivity. [ABSTRACT FROM AUTHOR]

Dual-mode photoacoustic/ultrasound endoscopy (ePAUS) is a promising tool for preclinical and clinical interventions. To be clinically useful, ePAUS must deliver high-performance ultrasound imaging comparable to commercial systems and maintain high photoacoustic imaging performance at long working distances. This requires a transducer with an intact physical aperture and coaxial alignment of acoustic and optical beams within the probe, a challenging integration task. We present a high-performance ePAUS probe with a miniaturized, optically transparent ultrasonic transducer (TUT) called ePAUS-TUT. The 1.8-mm-diameter probe, fitting into standard endoscopic channels, aligns acoustic and optical beams efficiently, achieving commercial-level ultrasound and high-resolution photoacoustic imaging over long distances. These imaging capabilities were validated through in vivo imaging of a rat's rectum and a pig's esophagus. The ePAUS-TUT system substantially enhances feasibility and potential for clinical applications. [ABSTRACT FROM AUTHOR]

In this work, a miniaturized Y-sphere coupled photoacoustic (YSCPA) sensor is proposed for trace C2H2 gas detection. The cavity volume of the designed YSCPA sensor is about 0.7 mL. The finite element method (FEM) has been performed to analyze the comparative performance of the YSCPA sensor and T-type PA sensor, indicating that the first-order resonance frequency (FORF) of the newly proposed YSCPA sensor has been reduced by half while the PA signal has been improved by a factor of 3 compared to the T-type PA sensor. C2H2 is employed as a target gas to test the performance of the YSCPA sensor. The experimental test results show that the response time of the gas is 26 s. The minimum detection limit (MDL) reaches 189 ppb at a lock-in integration time of 1 s. By extending the lock-in integration time to 100 s, the MDL of the designed PA sensor is reduced to 18.1 ppb. The designed YSCPA sensor has the advantages of small size, low gas consumption, simple structure, and high sensitivity, which is expected to be an effective solution for rapid and real-time monitoring of dissolved C2H2 gas in transformer oil. [ABSTRACT FROM AUTHOR]

Diabetes mellitus is a prevalent disease with a rapidly increasing incidence projected worldwide, affecting both industrialized and developing regions. Effective diabetes management requires precise therapeutic strategies, primarily through self-monitoring of blood glucose levels to achieve tight glycemic control, thereby mitigating the risk of severe complications. In recent years, there have been significant advancements in non-invasive techniques for measuring blood glucose using photoacoustic spectroscopy (PAS), as it shows great promise for the detection of glucose using the infrared region (e.g., MIR and NIR) of light. A critical aspect of this method is the detection of the photoacoustic signal generated from blood glucose, which needs to be amplified through a photoacoustic resonator (PAR). In this work, an overview of various types of PARs used for non-invasive glucose sensing is reviewed, highlighting their operating principle, design requirements, limitations, and potential improvements needed to enhance the analysis of photoacoustic signals. The motivation behind this review is to identify and discuss main parameters crucial to the efficient design of PARs used in non-invasive glucose detection, which will be helpful for furthering the basic understanding of this technology and achieving the highly sensitive PAR required for non-invasive glucose monitoring. [ABSTRACT FROM AUTHOR]

The use of foods to color other foods (coloring food) should be considered in food production. In this study, freeze-dried canistel (Pouteria campechiana (Kunth) Baehni) pulp underwent a photostability test. A blue LED light with a maximum intensity of 420 nm was utilized to induce photodegradation of the pulp. After irradiation, the samples were analyzed using photoacoustic spectroscopy. Different concentrations (2%, 4%, and 6%) of the pulp were employed as coloring food in ice cream, and the ice cream was thoroughly characterized. Photoacoustic spectroscopy provided valuable insights into dehydrated canistel pulp, revealing two stages of photoreaction involving carotenoids (violaxanthin and ξ-carotene) and demonstrating photostability under visible LED irradiation. The ice cream made with natural food dye produce elevated levels of bioactive compounds and retained a stable color throughout storage. All ice creams exhibited thixotropy. Ice creams with higher pulp concentrations displayed greater resistance to shear stress and, in sensory tests, received the highest scores, attributed to their intense yellow color. Dehydrated canistel pulp holds significant potential for use as food coloring in the industry due to its photostability. [ABSTRACT FROM AUTHOR]

The rapid growth of industry and the global drive for modernization have led to an increase in gas emissions, which present significant environmental and health risks. As a result, there is a growing need for precise and sensitive gas-monitoring technologies. This review delves into the progress made regarding photoacoustic gas sensors, with a specific focus on the vital components of acoustic cells and acoustic detectors. This review highlights photoacoustic spectroscopy (PAS) as an optical detection technique, lauding its high sensitivity, selectivity, and capability to detect a wide range of gaseous species. The principles of photoacoustic gas sensors are outlined, emphasizing the use of modulated light absorption to generate heat and subsequently detect gas pressure as acoustic pressure. Additionally, this review provides an overview of recent advancements in photoacoustic gas sensor components while also discussing the applications, challenges, and limitations of these sensors. It also includes a comparative analysis of photoacoustic gas sensors and other types of gas sensors, along with potential future research directions and opportunities. The main aim of this review is to advance the understanding and development of photoacoustic gas detection technology. [ABSTRACT FROM AUTHOR]

Trace gas analysis is a key tool for the investigation of man-made environmental pollution as well as for early detection of respiratory diseases. To detect tiny concentrations, sensitive methods such as cavity ring down spectroscopy or plasmonic sensors have been used. Here, we demonstrate the combination of the photoacoustic effect in a classical cell with a novel, rapidly tunable, narrowband fiber-feedback optical parametric oscillator. The high sensitivity of photoacoustic cells and the extremely narrow linewidth as well as the wide and rapid tunability of the fiber-feedback optical parametric oscillator enable a high resolution of the rotational and vibrational bands of molecules in the near-infrared region. Photoacoustic spectra of methane, carbon dioxide, and water at ambient pressure are obtained in a broad spectral range and compared to high-resolution transmission molecular absorption database. In particular, scanning the entire carbon dioxide overtone around 4965 cm−1 at 2000 ppm takes 185 s with a signal-to-noise ratio of 31. This approach enables a wide tunability in the entire near- and mid-infrared spectral region suitable for many environmental and medical applications. [ABSTRACT FROM AUTHOR]

The aim of this work was the development and morphological/chemical, spectroscopic, and structural characterization of titanium dioxide, niobium pentoxide, and titanium:niobium (Ti:Nb) oxides, as well as materials modified with ruthenium (Ru) with the purpose of providing improvement in photoactivation capacity with visible sunlight radiation. The new materials synthesized using the sol-gel methodology were characterized using the following techniques: scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), photoacoustic spectroscopy (PAS), and X-ray diffraction (XRD). The SEM–EDS analyses showed the high purity of the bases, and the modified samples showed the adsorption of ruthenium on the surface with the crystals' formation and visible agglomerates for higher calcination temperature. The nondestructive characterization of PAS in the ultraviolet visible region suggested that increasing calcination temperature promoted changes in chemical structures and an apparent decrease in gap energy. The separation of superimposed absorption bands referring to charge transfers from the ligand to the metal and the nanodomains of the transition metals suggested the possible absorption centers present at the absorption threshold of the analyzed oxides. Through the XRD analysis, the formation of stable phases such as T-Nb16.8O42, o -Nb12O29, and rutile was observed at a lower temperature level, suggesting pore induction and an increase in surface area for the oxides studied, at a calcination temperature below that expected by the related literature. In addition, the synthesis with a higher temperature level altered the previously existing morphologies of the Ti:Nb, base and modified with Ru, forming the new mixed crystallographic phases Ti2Nb10O29 and TiNb2O7, respectively. As several semiconductor oxide applications aim to reduce costs with photoexcitation under visible light, the modified Ti:Ru oxide calcined at a temperature of 800 °C and synthesized according to the sol-gel methodology used in this work is suggested as the optimum preparation point. This study presented the formation of a stable crystallographic phase (rutile), a significant decrease in gap energy (2.01 eV), and a visible absorption threshold (620 nm). [ABSTRACT FROM AUTHOR]

AbstractAn all-optical double-pass quartz enhanced photoacoustic spectroscopy (QEPAS) sensor for the detection of acetylene (C2H2) at part-per-billion (ppb) levels was developed and experimentally validated. By employing an erbium-doped fiber amplifier (EDFA) capable of emitting up to 1 W of optical power, a commercial quartz tuning fork (QTF) resonating at 30.7 kHz, and double-pass acoustic microresonators, the amplitude of the QEPAS signal was significantly enhanced, thereby improving the sensitivity of the C2H2-QEPAS sensor. Instead of using piezoelectric detection in conventional QEPAS, a highly sensitive fiber-optic Fabry–Perot interferometer (FPI) was employed to measure the vibration of the QTF prong. A working point self-stabilizing technique was exploited to improve the demodulation sensitivity and stability. The linear response of the sensor to laser power and C2H2 concentration confirmed that no saturation occurred. With an excitation laser power of 1 W and a C2H2 absorption line of 1532.83 nm, a C2H2 minimum detection limit (MDL) of 19.1 ppb was achieved, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 1.58 × 10−8 cm−1∙W∙Hz−1/2. Owing to its high sensitivity, long-term stability, and immunity to electromagnetic interferences, the QEPAS sensor provides considerable potential for remote gas sensing in environmental monitoring and other applications. [ABSTRACT FROM AUTHOR]

Lanthanum doped MgTiO 3 (La–MgTiO 3 ; n (La): n (Mg) = 0.05:0.95) was synthesized using a sol–gel method, and a layer of this material was supported on quartz microspheres to produce La–MgTiO 3 (x%)/SiO 2 microspheres (LMTO(x%)/SiO 2 ; where x% represents the weight fraction of La–MgTiO 3 in the microspheres). The crystal size of MgTiO 3 decreased from 43.4 nm in La–MgTiO 3 to 29.2 nm in LMTO(20 %)/SiO 2 , and the bandgap energies increased from 3.34 eV (La–MgTiO 3) to 3.91 eV (LMTO(20 %)/SiO 2). The supported La–MgTiO 3 contributed the most to the total surface area of the LMTO(x%)/SiO 2 microspheres; further, the specific surface area of the microspheres decreased with decreasing La–MgTiO 3 content. The photoluminescence intensity of the microspheres was significantly lower than that of La–MgTiO 3. The activity of La–MgTiO 3 was enhanced after loading onto the quartz microspheres. The maximum photocatalytic activity was obtained using LMTO(40 %)/SiO 2 , while the azophloxine degradation efficiency slightly decreased after five reaction cycles. [ABSTRACT FROM AUTHOR]

The current work proposes developing the wavefront-enhanced laser-induced-breakdown spectroscopy (WELIBS) approach using a crystalline quartz slide instead of the crystalline silicon wafer. Such substitution widens the application of WELIBS in the UV, visible, and IR laser wavelength ranges, not only the IR, as in the case of the silicon wafer. A Shack--Hartmann wavefront sensor (SHWFS) has been used to prove the capability of the crystalline quartz slide to convert the wavefront shape from quasi-Gaussian to a flat-top one in different ranges of wavelengths. The analytical performance of the novel WELIBS arrangement with the crystalline quartz slide has been studied using a pure zinc target, which showed a pronounced enhancement in the intensity of the spectral lines (two to sixfold) compared to the conventional LIBS technique for the three laser wavelengths the IR (1064 nm), the green (532 nm), and the UV (355 nm). Furthermore, seven certified bronze alloy samples have been used to study the achieved analytical improvement of the novel WELIBS analytical performance by testing its capability of estimating the limit of detection (LOD) of different minor elements. From the WELIBS and LIBS spectra of the bronze alloys, calibration lines of Zn, Sn, and Pb have been plotted to estimate the limit of detection for each element. The LOD for WELIBS was half that of LIBS. WELIBS with the quartz slide for beam shaping is superior to WELIBS with the Si wafer since it can be used with different laser wavelengths and not only the IR and provides similar, or better, analytical enhancement than the conventional LIBS. [ABSTRACT FROM AUTHOR]

David Mauzerall was born on July 22, 1929 to a working-class family in the small, inland textile town of Sanford, Maine. Those humble origins instilled a lifelong frugality and an innovative spirit. After earning his PhD degree in 1954 in physical organic chemistry with Frank Westheimer at the University of Chicago, he joined The Rockefeller Institute for Medical Research (now University) as a postdoctoral fellow that summer, rose to the rank of professor, and remained there for the rest of his career. His work over more than 60 years encompassed porphyrin biosynthesis, photoinduced electron-transfer reactions in diverse architectures (solutions, bilayer lipid membranes, reaction centers, chromatophores, and intact leaves), the light-saturation curve of photosynthesis, statistical treatments of photoreactions, and "all-things porphyrins." His research culminated in studies he poetically referred to as "listening to leaves" through the use of pulsed photoacoustic spectroscopy to probe the course and thermodynamics of photosynthesis in its native state. His research group was always small; indeed, of 185 total publications, 39 were singly authored. In brief, David Mauzerall has blended a deep knowledge of distinct disciplines of physical organic chemistry, photochemistry, spectroscopy and biophysics with ingenious experimental methods, incisive mathematical analysis, pristine personal integrity, and unyielding love of science to deepen our understanding of photosynthesis in its broadest context. He thought creatively – and always independently. His work helped systematize the fields of photosynthesis and the origin of life and made them more quantitative. The present article highlights a number of salient scientific discoveries and includes comments from members of his family, friends, and collaborators (Gary Brudvig, Greg Edens, Paul Falkowski, Alzatta Fogg, G. Govindjee, Nancy Greenbaum, Marilyn Gunner, Harvey Hou, Denise and Michele Mauzerall, Thomas Moore, and William Parson) as part of a celebration of his 95th birthday. [ABSTRACT FROM AUTHOR]

Recent advancements in photoacoustic (PA) imaging have leveraged reversibly photoswitchable chromophores, known for their dual absorbance states, to enhance imaging sensitivity through differential techniques. Yet, their deployment in tumor imaging has faced obstacles in achieving targeted delivery with high efficiency and specificity. Addressing this challenge, we introduce innovative protein assemblies, DrBphP-CBD, by genetically fusing a photosensory module from Deinococcus radiodurans bacterial phytochrome (DrBphP) with a collagen-binding domain (CBD). These protein assemblies form sub-100-nanometer structures composed of 24 DrBphP dimers and 12 CBD trimers, presenting 24 protein subunits. Their affinity for collagens, combined with impressive photoswitching contrast, markedly improves PA imaging precision. In various tumor models, intravenous administration of DrBphP-CBD has demonstrated enhanced tumor targeting and retention, augmenting contrast in PA imaging by minimizing background noise. This strategy underscores the clinical potential of DrBphP-CBD as PA contrast agents, propelling photoswitchable chromoproteins to the forefront of precise cancer diagnosis. [ABSTRACT FROM AUTHOR]

Activatable type I photosensitizers are an effective way to overcome the insufficiency and imprecision of photodynamic therapy in the treatment of hypoxic tumors, however, the incompletely inhibited photoactivity of pro‐photosensitizer and the limited oxidative phototoxicity of post‐photosensitizer are major limitations. It is still a great challenge to address these issues using a single and facile design. Herein, a series of totally caged type I pro‐photosensitizers (Pro‐I‐PSs) are rationally developed that are only activated in tumor hypoxic environment and combine two oxygen‐independent therapeutic mechanisms under single‐pulse laser irradiation to enhance the phototherapeutic efficacy. Specifically, five benzophenothiazine‐based dyes modified with different nitroaromatic groups, BPN 1−5, are designed and explored as latent hypoxia‐activatable Pro‐I‐PSs. By comparing their optical responses to nitroreductase (NTR), it is identified that the 2‐methoxy‐4‐nitrophenyl decorated dye (BPN 2) is the optimal Pro‐I‐PSs, which can achieve NTR‐activated background‐free fluorescence/photoacoustic dual‐modality tumor imaging. Furthermore, upon activation, BPN 2 can simultaneously produce an oxygen‐independent photoacoustic cavitation effect and a photodynamic type I process at single‐pulse laser irradiation. Detailed studies in vitro and in vivo indicated that BPN 2 can effectively induce cancer cell apoptosis through synergistic effects. This study provides promising potential for overcoming the pitfalls of hypoxic‐tumor photodynamic therapy. [ABSTRACT FROM AUTHOR]

This study is devoted to an optoacoustic study of the features of laser radiation absorption in an aqueous solution of the styryl-dye inclusion complex in cucurbituril. The research was performed on an experimental setup where a femtosecond regenerative amplifier based on chromium forsterite (Cr:F) was used as a pumping laser. The third harmonic of radiation with a wavelength of 420 nm and a pulse duration of 130 fs was used. Optoacoustic generation was produced in a quartz cuvette with the investigated solution, and the receiver of acoustic signals was a flat piezoceramic plate with a resonant frequency of 1 MHz. Optoacoustic signals were compared in a solution of pure Kr.1 styryl dye and the same dye in the presence of complexes with cucurbituril. With the same optical density of solutions, complexation leads to a more than twofold decrease in the optoacoustic response. [ABSTRACT FROM AUTHOR]

Illicit drug production in clandestine laboratories involves the use of large quantities of different chemicals that can be obtained for legitimate purposes. The identification of these chemicals, including reagents, catalyzers and solvents, is crucial for forensic investigations. From a legal point of view, a drug precursor is a material that is specific and critical to the production of a finished chemical and that constitutes a significant portion of the final molecular structure of the drug. In this study, a gas chromatography quartz-enhanced photoacoustic spectroscopy (GC-QEPAS) sensor—in conjunction with a deep learning model—was evaluated for its effectiveness in the detection and identification of interesting compounds for the production of amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), phenylcyclohexyl piperidine (PCP), and cocaine. The GC-QEPAS sensor includes a gas sampler, a fast GC for separation, and a QEPAS detector, which excites molecules exiting the GC column using a quantum cascade laser to provide the infra-red (IR) spectrum. The on-site capability of the GC-QEPAS system offers significant advantages over the current instruments employed in this field, including rapid analysis, which is crucial in field operations. This allows law enforcement to quickly identify specimens of interest on site. The system's performance was validated by taking into account the limit of detection, repeatability, and within-laboratory reproducibility. The results showed excellent repeatability and reproducibility for both the GC and QEPAS modules. The deep learning model, a multilayer perceptron neural network, was trained using IR spectra and retention times, achieving very high classification accuracy in the testing conditions. This study demonstrated the efficacy of the GC-QEPAS sensor combined with a deep learning model for the reliable identification of drug precursors, providing a robust tool for law enforcement during criminal investigations in clandestine laboratories. [ABSTRACT FROM AUTHOR]

Over the past few decades, the number of patients with neurological diseases has increased significantly, posing huge challenges and opportunities for the development of brain imaging technology. As a hybrid imaging method combining optical excitation and acoustic detection techniques, photoacoustic tomography (PAT), has experienced rapid development, due to high optical contrast and spatial resolution at depth inside tissues. With the development of lasers, ultrasonic detectors, and data computations, PAT has been widely applied for the diagnosis of oncology, dermatosis, etc. However, the energy of light and ultrasound would be greatly attenuated while penetrating the skull, due to the reflection, absorption, and scattering effects, resulting in limited application of PAT in brain imaging. In this review, we summarized the achievements of PAT and its application in the detection of brain diseases including glioma, stroke, traumatic brain injury, Alzheimer's disease, epilepsy, and Parkinson's disease. Moreover, various PAT systems and multi‐modality photoacoustic imaging are introduced for potential clinical applications. Finally, the challenges and current limitations of PAT for further brain imaging are also discussed. [ABSTRACT FROM AUTHOR]

Integrated multimodal imaging in theranostics nanomaterials offers extensive prospects for precise and noninvasive cancer treatment. Precisely controlling the structural evolution of plasmonic nanoparticles is crucial in the development of photothermal agents. However, previous successes have been limited to static assemblies and single‐component structures. Here, an activatable plasmonic theranostics system utilizing self‐assembled 1D silver‐coated gold nanochains (1D nanochains) is presented for precise tumor diagnosis and effective treatment. The absorbance of the adaptable core–shell chain structure can shift from visible to near‐infrared (NIR) regions due to the fusion between nearby Au@Ag nanoparticles induced by elevated H2O2 levels in the tumor microenvironment (TME), resulting in the creation of a novel 3D aggregates with strong NIR absorption. With a high photothermal conversion efficiency of 60.2% at 808 nm, nanochains utilizing the TME‐activated characteristics show remarkable qualities for photoacoustic imaging and significantly limit tumor growth in vivo. This study may pave the way for precise tumor diagnosis and treatment through customizable, optically tunable adaptive plasmonic nanostructures. [ABSTRACT FROM AUTHOR]

High-precision displacement sensing has been widely used across both scientific research and industrial applications. The recent interests in developing micro-opto-electro-mechanical systems (MOEMS) have given rise to an excellent platform for miniaturized displacement sensors. Advancement in this field during past years is now yielding integrated high-precision sensors which show great potential in applications ranging from photoacoustic spectroscopy to high-precision positioning and automation. In this review, we briefly summarize different techniques for high-precision displacement sensing based on MOEMS and discuss the challenges for future improvement. [ABSTRACT FROM AUTHOR]

This paper proposes a novel microcone-curved resonant photoacoustic cell (MCR-PAC) for highly sensitive trace gas detection. The MCR-PAC features with microcone-curved resonant region and cylindrical buffer chamber, which dominates the photoacoustic signal amplification. By introducing the hyperbolic eccentricity as a new optimization dimension, the quality factor of the MCR-PAC is remarkably strengthened to enhance the acoustic pressure amplitude. At an eccentricity value of 5, the volume of the photoacoustic resonant cavity is approximately 0.23 cm3. Targeting trace acetylene, the system achieves a minimum detection limit of 1.41 ppb with an integration time of 290 s, corresponding normalized noise equivalent absorption coefficient is 1.88×10−9 W·cm−1·Hz−1/2. Compared to the traditional T-type PAC, the overall performance of MCR-PAC has been enhanced nearly fourfold. With its compact millimeter-scale dimensions and high sensitivity, the MCR-PAC demonstrates extensive potential for application in environmental monitoring and breath diagnostics.

This study presents a detailed quantitative analysis of kinetic cooling in methane photoacoustic spectroscopy, leveraging the capabilities of a digital twin model. Using a quantum cascade laser tuned to 1210.01 cm⁻¹, we investigated the effects of varying nitrogen-oxygen matrix compositions on the photoacoustic signals of 15 ppmV methane. Notably, the photoacoustic signal amplitude decreased with increasing oxygen concentration, even falling below the background signal at oxygen levels higher than approximately 6 %V. This phenomenon was attributed to kinetic cooling, where thermal energy is extracted from the surrounding gas molecules rather than added, as validated by complex vector analysis using a previously published digital twin model. The model accurately reproduced complex signal patterns through simulations, providing insights into the underlying molecular mechanisms by quantifying individual collision contributions. These findings underscore the importance of digital twins in understanding the fundamentals of photoacoustic signal generation at the molecular level.

A miniaturized, broadband (800–5000 Hz) absorber with >95% absorption is proposed and realized. The absorber is designed using quarter-wavelength resonator tubes coiled as a rectangular "meta-atom." The study describes the basic theoretical aspects of the absorber and compares it with the numerical simulations, fabrication, and experimental validation. The meta-atom, simple in design and made with fabrication-friendly materials, can provide greater spatial coverage through tiling over large surfaces. [ABSTRACT FROM AUTHOR]

Freeze- and spray-dried inclusion complexes (ICs) of chlorhexidine (CHX) in β-cyclodextrin were characterized by Fourier transform (FT)-Raman, 1H nuclear magnetic resonance (NMR), and photoacoustic spectroscopy. The active Raman modes of CHX were simulated using the density functional theory. By considering semiempirical calculations, it was observed that the guest penetrates on the wider rim of the host in a proportion of 1:2. We observe from the FT-Raman analysis that the drying method influences the CHX:β-cyclodextrin conformational adjustment by the rearrangement of hydrophilic biguanides of the guest. The photoacoustic spectroscopy results inferred that the freeze-drying method provided a better inclusion due to a lower interaction between phenyl groups and hexamethylene of CHX. The freeze-dried IC achieved a faster dissolution pattern. These ICs provided immediate drug dissolution profiles in an aqueous medium better than a pure drug. The release profiles of freeze- and spray-dried ICs were explained by Fickian diffusion. These data support further planning and development projects of novel immediate release systems based on CHX. [ABSTRACT FROM AUTHOR]

Liver fibrosis, a major global health issue, is marked by excessive collagen deposition that impairs liver function. Noninvasive methods for the direct visualization of collagen content are crucial for the early detection and monitoring of fibrosis progression. This study investigates the potential of spectral photoacoustic imaging (sPAI) to monitor collagen development in liver fibrosis. Utilizing a novel data-driven superpixel photoacoustic unmixing (SPAX) framework, we aimed to distinguish collagen presence and evaluate its correlation with fibrosis progression. We employed an established diethylnitrosamine (DEN) model in rats to study liver fibrosis over various time points. Our results revealed a significant correlation between increased collagen photoacoustic signal intensity and advanced fibrosis stages. Collagen abundance maps displayed dynamic changes throughout fibrosis progression. These findings underscore the potential of sPAI for the noninvasive monitoring of collagen dynamics and fibrosis severity assessment. This research advances the development of noninvasive diagnostic tools and personalized management strategies for liver fibrosis. [ABSTRACT FROM AUTHOR]

Endoscopy, enabling high-resolution imaging of deep tissues and internal organs, plays an important role in basic research and clinical practice. Recent advances in photoacoustic microscopy (PAM), demonstrating excellent capabilities in high-resolution functional imaging, have sparked significant interest in its integration into the field of endoscopy. However, there are challenges in achieving functional PAM in the endoscopic setting. This Perspective article discusses current progress in the development of endoscopic PAM and the challenges related to functional measurements. Then, it points out potential directions to advance endoscopic PAM for functional imaging by leveraging fiber optics, microfabrication, optical engineering, and computational approaches. Finally, it highlights emerging opportunities for functional endoscopic PAM in basic and translational biomedicine. [ABSTRACT FROM AUTHOR]

A compact photoacoustic spectroscopy system integrated with a non-coaxial multi-pass cell was developed for improving the instrument performance in the measurement of methane. The multi-pass cell with compact light spot mode was proposed for concentrating the light radiation within a limited space, which effectively reduces the instrument dimension. A distributed feedback (DFB) laser with a central wavelength of 1653 nm was employed to excite the photoacoustic signal of methane. A total of 21 round trips of reflection were achieved in an acoustic resonant cavity with a radius of 4 mm and a length of 36 mm. Four microphones were installed around the cavity to collect the signal. An 11-fold enhancement of the photoacoustic signal was achieved through the multi-pass cell, compared to a single-pass cell with dimension of 10 cm. The system was used to measure different concentrations of methane, which showed good linearity. The continuous detection of 10 ppm methane gas was carried out for 6000 s. The Allan standard deviation analysis indicates that the limit of detection of the system was 5.7 ppb with an optimum integration time of 300 s. [ABSTRACT FROM AUTHOR]

Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) is a technique in which the sound wave is detected by a quartz tuning fork (QTF). It enables particularly high specificity with respect to the excitation frequency and is well known for an extraordinarily sensitive analysis of gaseous samples. We have developed the first photoacoustic (PA) cell for QEPAS on solid samples. Periodic heating of the sample is excited by modulated light from an interband cascade laser (ICL) in the infrared region. The cell represents a half-open cylinder that exhibits an acoustical resonance frequency equal to that of the QTF and, therefore, additionally amplifies the PA signal. The antinode of the sound pressure of the first longitudinal overtone can be accessed by the sound detector. A 3D finite element (FE) simulation confirms the optimal dimensions of the new cylindrical cell with the given QTF resonance frequency. An experimental verification is performed with an ultrasound micro-electromechanical system (MEMS) microphone. The presented frequency-dependent QEPAS measurement exhibits a low noise signal with a high-quality factor. The QEPAS-based investigation of three different solid synthetics resulted in a linearly dependent signal with respect to the absorption. [ABSTRACT FROM AUTHOR]

Purpose: Fluorescence-guided surgery (FGS) can play a key role in improving radical resection rates by assisting surgeons to gain adequate visualization of malignant tissue intraoperatively. Designed ankyrin repeat proteins (DARPins) possess optimal pharmacokinetic and other properties for in vivo imaging. This study aims to evaluate the preclinical potential of epithelial cell adhesion molecule (EpCAM)-binding DARPins as targeting moieties for near-infrared fluorescence (NIRF) and photoacoustic (PA) imaging of cancer. Methods: EpCAM-binding DARPins Ac2, Ec4.1, and non-binding control DARPin Off7 were conjugated to IRDye 800CW and their binding efficacy was evaluated on EpCAM-positive HT-29 and EpCAM-negative COLO-320 human colon cancer cell lines. Thereafter, NIRF and PA imaging of all three conjugates were performed in HT-29_luc2 tumor-bearing mice. At 24 h post-injection, tumors and organs were resected and tracer biodistributions were analyzed. Results: Ac2-800CW and Ec4.1-800CW specifically bound to HT-29 cells, but not to COLO-320 cells. Next, 6 nmol and 24 h were established as the optimal in vivo dose and imaging time point for both DARPin tracers. At 24 h post-injection, mean tumor-to-background ratios of 2.60 ± 0.3 and 3.1 ± 0.3 were observed for Ac2-800CW and Ec4.1-800CW, respectively, allowing clear tumor delineation using the clinical Artemis NIRF imager. Biodistribution analyses in non-neoplastic tissue solely showed high fluorescence signal in the liver and kidney, which reflects the clearance of the DARPin tracers. Conclusion: Our encouraging results show that EpCAM-binding DARPins are a promising class of targeting moieties for pan-carcinoma targeting, providing clear tumor delineation at 24 h post-injection. The work described provides the preclinical foundation for DARPin-based bimodal NIRF/PA imaging of cancer. [ABSTRACT FROM AUTHOR]

In this paper, a photoacoustic trace gas sensor based on a multi-pass enhanced open spherical photoacoustic cell (M-OPAC) was developed. A high-performance spherical photoacoustic (PA) cell was specially designed with high resonant frequency for suppressing various environmental noises, and integrated with a Herriot-type multi-pass optical system for enhancing PA signal. For evaluating the developed PA sensor system, details of theoretical simulation and experimental test were investigated for ambient water vapor (H2O) detection by utilizing a DFB diode laser with a central wavelength of 1391 nm, and wavelength modulation spectroscopy with second harmonic (WMS-2f) detection technique was employed. Compared to the conventional single-pass PA detection strategy, the developed multi-pass PA sensor shows a sensitivity enhancement of 4.3 times and demonstrates a good immunity to ambient noises. Moreover, the developed spherical open photoacoustic cell can be used for open monitoring of atmospheric adsorbent gases, which indicates a great potential for in-site and real-time gas monitoring without complex gas sampling procedures. [ABSTRACT FROM AUTHOR]

The water vapor in the ambient air affects the accuracy of the photoacoustic (PA) dissolved gas analysis system for transformer health monitoring. A laser PA system was evaluated by dry and humidified standard gases to study the influence of water vapor concentration on PA gas detection. Theoretical analysis was conducted on the effect of gas molecule relaxation on PA signal detection. A high‐frequency resonant PA cell and a low‐frequency nonresonant PA cell were used to detect acetylene (C2H2) and carbon monoxide (CO), respectively. The experimental results show that the PA signal of humidified CO is about 12 times higher than PA signal of dry gas for the resonant PA detection system, respectively. In addition, as the frequency is increased from 30 to 980 Hz, the PA signals of humidified and dry CO attenuate by 1.5 and 6.9 times, respectively. [ABSTRACT FROM AUTHOR]

The present manuscript deals with the identification of the spectral lines of the rare earth elements (REEs) in the LIBS spectra of the black sands collected from the Thiruvananthapuram (Kerala) beach using laser-induced breakdown spectroscopy (LIBS). LIBS spectra of the sand sample show the presence of spectral lines of Na, Mg, Mn, Al, and Cr. Along with these elements, the spectral lines of REEs such as Ce, Nd, Sm, Dy, Ho, Tm, etc., and the radioactive element Thorium (Th) are also present in the LIBS spectra of the black sand sample. The presence of REEs and radioactive elements makes the sand suitable for profitable extraction using various methods for different applications. The results of LIBS (presence of all REEs in sand) are also verified by photoacoustic spectroscopy (PAS). The Plasma temperature has been calculated using the Boltzmann plot to explain the distribution of the atoms in various higher energy states/levels. An attempt is made to explain the various transitions involved in the spectral lines of the rare earth ions in the LIBS spectra of the black sand sample using a possible energy level diagram. The concentration of some REEs (Dy, Sm, and Nd) and LOD has been calculated by using the calibration curve method. To the best of our knowledge, the investigation of rare earth and radioactive elements in the black sand of the Kerala beach using LIBS is reported for the first time. [ABSTRACT FROM AUTHOR]