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Senescence is an intricate physiological progression that can be instigated by a multiplicity of factors. Aberrant cellular senescence is capable of precipitating a substantial array of diseases. During chemotherapy, drugs typically tend to gradually accumulate in the liver, thereby inducing liver senescence and leading to a successive deterioration in its physiological function. β-galactosidase (β-gal), serving as a significant index in the exploration of senescence, has attracted considerable attention. In this study, a fluorescence/photoacoustic (FL/PA) biomodal probe (Gal-QCS) was developed based on a hemicyanine fluorophore for the imaging of β-gal in the process of drug-induced liver senescence. Gal-QCS demonstrates rapid responsiveness, high sensitivity, and remarkable selectivity in detecting β-gal in aqueous solutions. After incubation with β-gal, the fluorescence signal at 810 nm significantly increases, and concurrently, the photoacoustic signal at 775 nm also exhibits a substantial increment. Upon the induction of cell senescence with camptothecin, Gal-QCS can expeditiously and selectively image senescent cells. Moreover, after administering this probe to mice with liver senescence, the FL/PA signals in the livers of senescent mice were enhanced by 10.53-fold and 1.43-fold, respectively. This work robustly substantiates the potential and application prospects of Gal-QCS in detecting drug-induced liver senescence, with β-gal serving as a biomarker. [ABSTRACT FROM AUTHOR]

Transcranial ultrasound imaging is a popular method to study cerebral functionality and diagnose brain injuries. However, the detected ultrasound signal is greatly distorted due to the aberration caused by the skull bone. The aberration mechanism mainly depends on thickness and porosity, two important skull physical characteristics. Although skull bone thickness and porosity can be estimated from CT or MRI scans, there is significant value in developing methods for obtaining thickness and porosity information from ultrasound itself. Here, we extracted various features from ultrasound signals using physical skull‐mimicking phantoms of a range of thicknesses with embedded porosity‐mimicking acoustic mismatches and analyzed them using machine learning (ML) and deep learning (DL) models. The performance evaluation demonstrated that both ML‐ and DL‐trained models could predict the physical characteristics of a variety of skull phantoms with reasonable accuracy. The proposed approach could be expanded upon and utilized for the development of effective skull aberration correction methods. [ABSTRACT FROM AUTHOR]

Abstract In vivo, molecular imaging is prevalent for biology research and therapeutic practice. Among advanced imaging technologies, photoacoustic (PA) imaging and sensing is gaining interest around the globe due its exciting features like high resolution and good (~ few cm) penetration depth. PA imaging is a recent development in ultrasonic technology that generates acoustic waves by absorbing optical energy. However, poor light penetration through tissue continues to be the key obstacle in the field. The NPs as contrast agents can assist in overcoming tissue penetration depth as NPs can produce high signal to noise (SNR) PA signal which aids reconstruction of high resolution of the PA images in deep tissue sights. Subsequently, NPs are very effective in PA based targeted and precise theranostic applications. This article detail about various NPs (organic, inorganic and hybrid) used in PA imaging and spectroscopy applications including various disease diagnosis, therapy and theranostic. It also features optical property, advantages and limitations of various NPs utilised in PA techniques which would comprehend readers about the potential of NPs in evolving PA technique from laboratory to clinical modality in future. Graphical abstract

Abstract Cellular senescence is considered an important tumour suppression mechanism in response to damage and oncogenic stress in early lesions. However, when senescent cells are not immune-cleared and persist in the tumour microenvironment, they can drive a variety of tumour-promoting activities, including cancer initiation, progression, and metastasis. Additionally, there is compelling evidence demonstrating a direct connection between chemo(radio)therapy-induced senescence and the development of drug resistance and cancer recurrence. Therefore, detection of senescent cells in tissues holds great promise for predicting cancer occurrence earlier, assessing tumour progression, aiding patient stratification and prognosis, and informing about the efficacy of potential senotherapies. However, effective detection of senescent cells is limited by lack of biomarkers and readout strategies suitable for in vivo clinical imaging. To this end, a nanoprobe composed of biocompatible polydopamine (PDA) nanoparticle doped with FDA-approved indocyanine green (ICG) dye, namely PDA-ICG, was designed as a contrast agent for senescence detection using photoacoustic imaging (PAI). In an in vitro model of chemotherapy-induced senescence, PDA-ICG nanoprobe showed an elevated uptake in senescent cells relative to cancer cells. In addition to its improved photostability, 2.5-fold enhancement in photoacoustic signal relative to ICG was observed. Collectively, the results indicate that the PDA-ICG nanoprobe has the potential to be used as a contrast agent for senescence detection of chemotherapy-induced senescence using PAI.

In vivo, molecular imaging is prevalent for biology research and therapeutic practice. Among advanced imaging technologies, photoacoustic (PA) imaging and sensing is gaining interest around the globe due its exciting features like high resolution and good (~ few cm) penetration depth. PA imaging is a recent development in ultrasonic technology that generates acoustic waves by absorbing optical energy. However, poor light penetration through tissue continues to be the key obstacle in the field. The NPs as contrast agents can assist in overcoming tissue penetration depth as NPs can produce high signal to noise (SNR) PA signal which aids reconstruction of high resolution of the PA images in deep tissue sights. Subsequently, NPs are very effective in PA based targeted and precise theranostic applications. This article detail about various NPs (organic, inorganic and hybrid) used in PA imaging and spectroscopy applications including various disease diagnosis, therapy and theranostic. It also features optical property, advantages and limitations of various NPs utilised in PA techniques which would comprehend readers about the potential of NPs in evolving PA technique from laboratory to clinical modality in future. [ABSTRACT FROM AUTHOR]

Stable neutral metal radicaloid complexes have been synthesized from a modified tetrapyrrolic pigment, bilatriene, with iridium(I) and rhodium(I) cyclooctadiene (COD) synthons. The bilatriene skeleton contains α‐linked conjugated pyrrole units, whereas an N‐confused analogue used in this work possesses β‐linked pyrrole moieties at the terminal, demonstrating a unique metal binding capability. Unprecedentedly, the metal‐COD cations are accommodated at the outer nitrogen sites, which induced the formation of open‐shell metal‐radicaloid species. The resulting compounds are highly stable under ambient conditions and demonstrated facile redox conversion to afford the corresponding cation and anion species. Furthermore, the radicaloid complexes showed a distinct second near‐infrared absorption (NIR‐II) capability extending up to 1500 nm along with high photostability. These features emphasized that the complexes can be potential NIR‐II light‐responsible photothermal and photoacoustic imaging contrast agents based on the metal‐radicaloid dye platform. [ABSTRACT FROM AUTHOR]

This short review discusses the recent developments in low‐cost, high‐resolution optoacoustic microscopy systems, integrating laser diodes for signal excitation, which are 20–40 times cheaper than the typically employed Q‐switched nanosecond laser sources. The development of laser diode‐based microscopes can substantially improve not only cost efficiency, but also multispectral capabilities, robustness, portability and overall imaging performance of the optoacoustic technique. To this end, we demonstrate relevant implementations in both time and frequency domain, highlighting their representative applications in biomedical research such as microvasculature imaging, oxygen saturation assessments, hybrid and multiview microscopy of model organisms and tissues and Doppler flow speed measurements. Finally, we analyse the benefits and limitations of each approach, identifying the respective application contexts where they achieve optimum performance. [ABSTRACT FROM AUTHOR]

Within the photo-thermoelastic theory, a stochastic photoacoustic half-space problem with a white noise effect is considered. A novel model under the effect of acoustic pressure during thermo-plasma-mechanical processes is studied. The normal mode analysis method for the two-dimensional (2D) problem is employed to get the solution in the spacetime domain with analytical expressions of the main quantities under deliberation. Two types of solutions were considered "stochastic and deterministic" for all physical quantities under investigation. Due to the optical, acoustic, and heat transfer properties, the stochastic processes are obtained by introducing the random functions of the basic fields. The mean and variance were derived analytically and discussed for all distributions. Numerical computations for copper semiconductor material are done, and the results are displayed graphically. [ABSTRACT FROM AUTHOR]

Aim: As non‐operative management of rectal cancer proliferates, re‐staging and surveillance methods are critical in selecting appropriate patients for organ preservation versus proctectomy. In previous work, the authors have shown that transrectal acoustic resolution photoacoustic microscopy (ARPAM) co‐registered with ultrasound can differentiate residual cancer from complete tumoural response to neoadjuvant therapy. We hypothesize that these findings are due to changes in microvascular density (MVD). Methods: Patients with rectal adenocarcinoma who underwent neoadjuvant therapy, transrectal photoacoustic imaging and resection were included. We first compared immunohistochemical staining with erythroblast transformation‐specific‐related gene (ERG) immunostain to standard CD31 to confirm adequate identification of endothelium. Tissue sections from identical blocks were stained with CD31 and ERG, and then a correlation was calculated between manually labelled CD31‐stained vessels and ERG nuclei density. Second, representative tissue blocks from responders, partial responders and non‐responders were stained with ERG. ERG nuclei density was quantified as a proxy for MVD. Results: CD31 MVD and ERG nuclei density were strongly correlated (R2 = 0.87; P < 0.01). In the tumour bed of patients after neoadjuvant therapy, MVD of complete responders (599 nuclei/mm2; 95% CI 434–764) is significantly higher (P < 0.01) than that of partial responders (185 nuclei/mm2; 95% CI 64–306) and non‐responders (117 nuclei/mm2; 95% CI 42–192). No significant difference was found between the partial responders and non‐responders (P = 0.60). Conclusion: Microvascular density appears highest in cases of complete tumour response to neoadjuvant therapy, similar to normal rectal tissue. The histological microvascular patterns seen in treated tissue may explain the imaging patterns seen in photoacoustic microscopy. [ABSTRACT FROM AUTHOR]

In the realm of healthcare and the advancing field of medical sciences, the development of efficient drug delivery systems become an immense promise to cure several diseases. Despite considerable advancements in drug delivery systems, numerous challenges persist, necessitating further enhancements to optimize patient outcomes. Smart nano-carriers, for instance, 2D sheets nano-carriers are the recently emerging nanosheets that may garner attention for targeted delivery of bioactive compounds, drugs, and genes to kill cancer cells. Within these advancements, Ti3C2TX-MXene, characterized as a two-dimensional transition metal carbide, has surfaced as a prominent intelligent nanocarrier within nanomedicine. Its noteworthy characteristics facilitated it as an ideal nanocarrier for cancer therapy. In recent advancements in drug delivery research, Ti3C2TX-MXene 2D nanocarriers have been designed to release drugs in response to specific stimuli, guided by distinct physicochemical parameters. This review emphasized the multifaceted role of Ti3C2TX-MXene as a potential carrier for delivering poorly hydrophilic drugs to cancer cells, facilitated by various polymer coatings. Furthermore, beyond drug delivery, this smart nanocarrier demonstrates utility in photoacoustic imaging and photothermal therapy, further highlighting its significant role in cellular mechanisms. [ABSTRACT FROM AUTHOR]

The complex composition of cultural heritage (CH) items presents significant challenges in assessing their condition and predicting potential risks of material degradation. Typically employed diagnostic optical methods are inevitably limited by light scattering, thus restricting in-depth investigations of objects with complex structural and optical properties. To address this issue, we introduce a novel reflection-mode optoacoustic (OA) diagnostic system for non-contact and non-invasive measurements of CH, placing emphasis on the detection of ageing-related modifications in artistic media such as paints. In this direction, the sensitivity of OA measurements was proven to be up to two orders of magnitude higher than conventional absorption spectroscopy assessments. Furthermore, we have evaluated the in-depth imaging capabilities of the developed OA system, demonstrating that it can offer superior contrast levels of sketches beneath opaque paint layers compared to standard near-infrared diagnostic techniques. The current OA imaging technology may advance state-of-the-art diagnostic capabilities in CH preservation by delivering unprecedented depth-to-resolution ratios combined with exceptional optical absorption sensitivity in a non-invasive manner. These features are crucial for the early detection of material degradation and the comprehensive analysis of CH objects, facilitating the development of optimal conservation strategies to prolong their lifespan and preserve their aesthetic value. [ABSTRACT FROM AUTHOR]

Caigui Yu,1– 3,&ast; Lu Zhong,1– 3,&ast; Yanxiang Zhou,1– 3,&ast; Nan Jiang,1– 3 Jinling Chen,1– 3 Sheng Cao1– 3 1Department of Ultrasound Imaging, Renmin Hospital of Wuhan University, Wuhan, 430060, People’s Republic of China; 2Hubei Key Laboratory of Cardiology, Wuhan, 430060, People’s Republic of China; 3Cardiovascular Research Institute, Wuhan University, Wuhan, 430060, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Jinling Chen; Sheng Cao, Department of Ultrasound Imaging, Renmin Hospital of Wuhan University, 238&num; Jiefang Road, Wuhan, 430060, People’s Republic of China, Email jenny2774@163.com; caosheng209@126.comObjective: To explore the feasibility of using cRGD-GNR-PFP-NPs to assess plaque vulnerability in an atherosclerotic plaque mouse model by dual-modal photoacoustic/ultrasonic imaging.Methods: A nanomolecular probe containing gold nanorods (GNRs) and perfluoropentane (PFP) coated with the cyclic Arg-Gly-Asp (cRGD) peptide were prepared by double emulsion solvent evaporation and carbodiimide methods. The morphology, particle size, potential, cRGD conjugation and absorption features of the nanomolecular probe were characterized, along with its in vitro phase transformation and photoacoustic/ultrasonic dual-modal imaging properties. In vivo fluorescence imaging was used to determine the distribution of cRGD-GNR-PFP-NPs in vivo in apolipoprotein E-deficient (ApoE−/−) atherosclerotic plaque model mice, the optimal imaging time was determined, and photoacoustic/ultrasonic dual-modal molecular imaging of integrin αvβ 3 expressed in atherosclerotic plaques was performed. Pathological assessments verified the imaging results in terms of integrin αvβ 3 expression and plaque vulnerability.Results: cRGD-GNR-PFP-NPs were spherical with an appropriate particle size (average of approximately 258.03± 6.75 nm), a uniform dispersion, and a potential of approximately − 9.36± 0.53 mV. The probe had a characteristic absorption peak at 780~790 nm, and the surface conjugation of the cRGD peptide reached 92.79%. cRGD-GNR-PFP-NPs were very stable in the non-excited state but very easily underwent phase transformation under low-intensity focused ultrasound (LIFU) and had excellent photoacoustic/ultrasonic dual-modal imaging capability. Mice fed a high-fat diet for 20 weeks had obvious hyperlipidemia with larger, more vulnerable plaques. These plaques could be specifically targeted by cRGD-GNR-PFP-NPs as determined by in vivo fluorescence imaging, and the enrichment of nanomolecular probe increased with the increasing of plaque vulnerability; the photoacoustic/ultrasound signals of the plaques in the high-fat group were stronger. The pathological assessments were in good agreement with the cRGD-GNR-PFP-NPs plaque accumulation, integrin αvβ 3 expression and plaque vulnerability results.Conclusion: A phase variant photoacoustic/ultrasonic dual-modal cRGD nanomolecular probe was successfully prepared and can be used to identify plaque vulnerability safely and effectively.Keywords: atherosclerosis, vulnerability, photoacoustic, ultrasound, low-intensity focused ultrasound

The emergence of drug-resistant bacteria poses a serious threat to human health and safety, thus requiring the exploration of effective antibacterial strategies. Herein, BiOCl nanosheets were synthesized using a polyol solvothermal method, and then Bi2S3 nanorods were in situ grown on the surface of BiOCl by doping S element with thioacetamide, forming BiOCl@Bi2S3 composites. The experimental results show that in comparison to BiOCl nanosheets, the BiOCl@Bi2S3 composite enhances the photodynamic, sonodynamic, and thermal effects under the combined action of ultrasound (US) and 808 nm near-infrared (NIR) light to generate more radical oxygen species (ROS) and induces local hyperthermia. Therefore, under the conditions of photoacoustic combination for 20 min, the composite material has excellent rapid antibacterial effect of 99.7% against Staphylococcus aureus and 100.0% against Escherichia coli. Additionally, the BiOCl@Bi2S3 composite has a good biocompatibility with NIH-3T3 cells. This study will provide insights into the design of efficient and safe antibacterial materials. [ABSTRACT FROM AUTHOR]

Photoacoustic (PA) emitters are emerging ultrasound sources offering high spatial resolution and ease of miniaturization. Thus far, PA emitters rely on electronic transitions of absorbers embedded in an expansion matrix such as polydimethylsiloxane (PDMS). Here, it is shown that mid‐infrared vibrational excitation of C─H bonds in a transparent PDMS film can lead to efficient mid‐infrared photoacoustic conversion (MIPA). MIPA shows 37.5 times more efficient than the commonly used PA emitters based on carbon nanotubes embedded in PDMS. Successful neural stimulation through MIPA both in a wide field with a size up to a 100 µm radius and in single‐cell precision is achieved. Owing to the low heat conductivity of PDMS, less than a 0.5 °C temperature increase is found on the surface of a PDMS film during successful neural stimulation, suggesting a non‐thermal mechanism. MIPA emitters allow repetitive wide‐field neural stimulation, opening up opportunities for high‐throughput screening of mechano‐sensitive ion channels and regulators. [ABSTRACT FROM AUTHOR]

Neuromodulation is a powerful tool for fundamental studies in neuroscience and potential treatments of neurological disorders. Both photoacoustic (PA) and photothermal (PT) effects are harnessed for non‐genetic high‐precision neural stimulation. Using a fiber‐based device excitable by a nanosecond pulsed laser and a continuous wave laser for PA and PT stimulation, respectively, PA and PT neuromodulation is systematically investigated at the single neuron level. These results show that to achieve the same level of neuron activation recorded by Ca2+ imaging, the laser energy needed for PA stimulation is 1/40 of that needed for PT stimulation. The threshold energy for PA stimulation is found to be further reduced in neurons overexpressing mechano‐sensitive channels, indicating direct involvement of mechano‐sensitive channels in PA stimulation. Electrophysiology study of single neurons upon PA and PT stimulation is performed by patch clamp recordings. Electrophysiological features induced by PA are distinct from those by PT, confirming that PA and PT stimulation operate through different mechanisms. These insights offer a foundation for the rational design of more efficient and safer non‐genetic neural modulation approaches. [ABSTRACT FROM AUTHOR]

Copper sulphide nanoparticles are synthesized by laser ablation of a copper target in DMSO by a 527 nm nanosecond pulsed laser. These nanoparticles have double stoichiometry (CuS and Cu1.8S) and crystalline structures, sizes under 30 nm, and they present substantial absorbance in the second near‐infrared window and photoluminescence in the visible region. The nanoparticles are used as photothermal and photoacoustic agents at 1080 nm and 1064 nm, respectively. Utilizing as a photothermal agent, these nanoparticles rapidly exhibit local heating, photothermal stability, and a temperature change of 52.2 °C within 300 s at 1 mg mL−1 concentration and 3.23 W cm−2 laser intensity. On the other hand, while employed as a photoacoustic agent, they enhanced the contrast significantly and increased the brightness proportional to their concentrations when compared to ultrasound imaging. Additionally, the biocompatibility properties of these nanoparticles were tested with cancer cells, and they were subjected to laser ablation to assess their photothermal effects. In this article, we demonstrate that copper sulphide nanoparticles synthesized by pulsed laser ablation hold great promise for photothermal and photoacoustic applications, especially in biomedical applications. [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]

Skin architecture and its underlying vascular structure could be used to assess the health status of skin. A non‐invasive, high resolution and deep imaging modality able to visualize skin subcutaneous layers and vasculature structures could be useful for determining and characterizing skin disease and trauma. In this study, a multispectral high‐frequency, linear array‐based photoacoustic/ultrasound (PAUS) probe is developed and implemented for the imaging of rat skin in vivo. The study seeks to demonstrate the probe capabilities for visualizing the skin and its underlying structures, and for monitoring changes in skin structure and composition during a 5‐day course of a chemical burn. We analayze composition of lipids, water, oxy‐hemoglobin, and deoxy‐hemoglobin (for determination of oxygen saturation) in the skin tissue. The study successfully demonstrated the high‐frequency PAUS imaging probe was able to provide 3D images of the rat skin architecture, underlying vasculature structures, and oxygen saturation, water, lipids and total hemoglobin. [ABSTRACT FROM AUTHOR]

Nondestructive testing (NDT) is of paramount importance in ensuring the safe operation of equipment. Among various NDT techniques, ultrasonic NDT has garnered widespread attention due to its high sensitivity, fast speed, and accurate defect location. Photoacoustic NDT, a burgeoning field in ultrasonic NDT, is particularly attractive due to its immunity to electromagnetic interference. However, existing photoacoustic NDT systems suffer from inadequate excitation intensity and complex ultrasonic signal characteristics, impeding large-area NDT and accurate crack visualization. In this study, we present an all-fiber photoacoustic system for large-area NDT. To address the issues, we have developed a photoacoustic generator unit that can be optimized and controlled to generate stronger ultrasonic signals. Furthermore, we have employed mode decomposition to simplify the detected ultrasonic signals by mitigating the acoustic impedance mismatch-induced mode mixing problem in the system. As a result, the technology allows for large-area crack monitoring of up to 50*50 cm2 with an improved resolution of 1 mm. The present technology paves the way for high-resolution equipment crack monitoring with substantially enhanced accuracy in various environments. [ABSTRACT FROM AUTHOR]

Bioanalysis based on optical imaging has gained significant progress in the last few decades. Luminescence probes are capable of detecting, monitoring, and tracing particular biomolecules in complex biological systems to figure out the roles of these molecules in organisms. Considering the rapid development of luminescence probes for bio-applications and their promising future, we have attempted to explore the working principles and recent advances in bio-applications of luminescence probes, in the hope of helping readers gain a detailed understanding of luminescence probes developed in recent years. In this review, we first focus on the current widely used luminescence probes, including fluorescence probes, bioluminescence probes, chemiluminescence probes, afterglow probes, photoacoustic probes, and Cerenkov luminescence probes. The working principles for each type of luminescence probe are concisely described and the bio-application of the luminescence probes is summarized by category, including metal ions detection, secretion detection, imaging, and therapy. [ABSTRACT FROM AUTHOR]

Semiconductor materials play a crucial role in the fields of science, engineering, and technology due to their high importance. In this work, photoelastic (PE) deformations due to the photonically excited processes are studied according to the photogenerated carriers (plasma waves) during the recombination processes. A photoacoustic theoretical model for the optically excited Silicon (Si) polymer material under the effect of magnetic field is introduced. The coupled between the acoustic and plasm-thermomechanical waves is considered. The governing equation according to the photo-thermoelasticity theory with acoustic pressure is derived. The optoelectronic and thermoelastic properties of semiconductor material are taken into account. The analytical expression of the main physical fields (temperature, mechanical stress, displacement, carrier density, and acoustic pressure) is obtained mathematically using the harmonic wave technique. The theoretical results are represented graphically due to the strength of the magnetic field in two and three dimensions (2D and 3D) and some comparisons are investigated.

Compositional changes in relation to musculoskeletal injuries are difficult to measure non-invasively. This study aims to use non-invasive label-free imaging with Multispectral Optoacoustic Tomography (MSOT) to evaluate compositional changes with injury. Five different patient groups were examined, covering diagnoses of Achilles or patellar tendinopathy, Achilles tendon rupture and gastrocnemius muscle strain injury. Injured and contralateral limbs were imaged using a commercial MSOT device. Hemoglobin, collagen, and lipid contents were estimated. Some patients were examined before and after exercise. Hemoglobin measures had high reproducibility and displayed systematic changes in response to exercise. The content and exercise response of hemoglobin was equal on both limbs. In contrast, collagen and lipid measures were inconsistent and did not display the expected distribution. In conclusion, MSOT is applicable to imaging of hemoglobin in musculoskeletal injuries, providing complimentary information to conventional ultrasound, but applicability to other components like collagen and lipids could not be shown.

Separated evaluation of factors in the external quantum efficiency (EQE) is important in order to improve the characteristics of semiconductors optical devices. Especially, the internal quantum efficiency (IQE) is an important value which indicates crystal quality of the active layers, and an accurate method for estimating the IQE values is required. The IQE is usually estimated from temperature dependence of photoluminescence (PL) intensity by assuming that the IQE at cryogenic temperature is 100%. However, III-nitride semiconductor materials, used in many optical devices, usually have large defect density, and the assumption is not necessarily valid. In our previous report, we demonstrated the simultaneous photoacoustic (PA) and PL measurements to accurately estimate the IQE values in GaN films with various qualities and obtained reasonable results. In this work, we have successfully realized reproducible measurements with high accuracy for an InGaN-QW sample by suppressing the background noise significantly. Furthermore, we have also measured the values of EQE by using an integrating-sphere. Since the light extraction efficiency (LEE) can be obtained by the values of IQE and EQE, it has been shown that the overall picture of emission efficiency can be provided by our method.

We evaluate different methods to detect benzene at a parts-per-billion level regarding their potential to be used in a wearable sensor. Benzene is a carcinogenic molecule, regarded as a major health threat by the World Health Organization. A wearable sensor is necessary to detect leaks immediately, but it is challenging to achieve such low limits of detection and quantification, even with laboratory equipment. A wearable sensor must, in addition to good selectivity and sensitivity, meet stricter requirements of size, weight, temperature, repeatability, and power consumption. We conclude that the most promising techniques for a wearable sensor are either infrared photoacoustic spectroscopy near 14.8 μm, or a photoionization detector combined with one of three selective devices: micro-gas chromatography, cavitands, or catalytic filters (WO3, for example). Ultraviolet photoacoustic spectroscopy may also be a suitable future technique for a wearable benzene sensor when efficient LEDs and lasers become available at many UV-C wavelengths.

Senescence is an intricate physiological progression that can be instigated by a multiplicity of factors. Aberrant cellular senescence is capable of precipitating a substantial array of diseases. During chemotherapy, drugs typically tend to gradually accumulate in the liver, thereby inducing liver senescence and leading to a successive deterioration in its physiological function. β-galactosidase (β-gal), serving as a significant index in the exploration of senescence, has attracted considerable attention. In this study, a fluorescence/photoacoustic (FL/PA) biomodal probe (Gal-QCS) was developed based on a hemicyanine fluorophore for the imaging of β-gal in the process of drug-induced liver senescence. Gal-QCS demonstrates rapid responsiveness, high sensitivity, and remarkable selectivity in detecting β-gal in aqueous solutions. After incubation with β-gal, the fluorescence signal at 810 nm significantly increases, and concurrently, the photoacoustic signal at 775 nm also exhibits a substantial increment. Upon the induction of cell senescence with camptothecin, Gal-QCS can expeditiously and selectively image senescent cells. Moreover, after administering this probe to mice with liver senescence, the FL/PA signals in the livers of senescent mice were enhanced by 10.53-fold and 1.43-fold, respectively. This work robustly substantiates the potential and application prospects of Gal-QCS in detecting drug-induced liver senescence, with β-gal serving as a biomarker.

In this study, we propose a robust photoacoustic (PA) signal processing framework for a material independent defect detection using empirical mode decomposition (EMD) and machine learning algorithms. First, a database of the PA signals with 960 samples has been obtained from aluminium, iron, plastic and wood materials using a laser, microphone and data acquisition board-based PA apparatus. Second, the EMD based time and time-frequency domain techniques are proposed to extract robust cross-material feature space focusing on laser induced acoustic signal, and the decomposed intrinsic mode (IMF) with 14 extracted features are performed on totally 960 samples PA signals to evaluate k-nearest neighbour (k-NN), decision tree (DT) and support vector machine (SVM) classifiers. Inter- material and cross-material evaluations are performed, and the accuracy rates up to 100% for SVM and 97.77% for k-NN are yielded. [ABSTRACT FROM AUTHOR]

The accuracy and efficacy of laser ablation procedures depend on the accurate placement of the laser applicator within the diseased tissue, monitoring the real-time temperature during the ablation procedure, and mapping the extent of the ablated region. Ultrasound (US) imaging has been widely used to guide ablation procedures. While US imaging offers significant advantages for guiding ablation procedures, its limitations include low imaging contrast, angular dependency, and limited ability to monitor the temperature. Photoacoustic (PA) imaging is a relatively new imaging modality that inherits the advantages of US imaging and offers enhanced capabilities for laser-guided ablations, such as accurate, angle-independent tracking of ablation catheters, the potential for quantitative thermometry, and monitoring thermal lesion formation. This work provides an overview of ultrasound-guided procedures and how different US-related artifacts limit their utility, followed by introducing PA as complementary to US as a solution to address the existing limitations and improve ablation outcomes. Furthermore, we highlight the integration of PA-driven features into existing US-guided laser ablation systems, along with their limitations and future outlooks. Integrated US/PA-guided laser ablation procedures can lead to safer and more precise treatment outcomes. [ABSTRACT FROM AUTHOR]

Elastography can be used as a diagnostic method for quantitative characterization of tissue hardness information and thus, differential changes in pathophysiological states of tissues. In this study, we propose a new method for shear wave elastography (SWE) based on laser-excited shear wave, called photoacoustic shear wave elastography (PASWE), which combines photoacoustic (PA) technology with ultrafast ultrasound imaging. By using a focused laser to excite shear waves and ultrafast ultrasonic imaging for detection, high-frequency excitation of shear waves and noncontact elastic imaging can be realized. The laser can stimulate the tissue with the light absorption characteristic to produce the thermal expansion, thus producing the shear wave. The frequency of shear wave induced by laser is higher and the frequency band is wider. By tracking the propagation of shear wave, Young's modulus of tissue is reconstructed in the whole shear wave propagation region to further evaluate the elastic information of tissue. The feasibility of the method is verified by experiments. Compared with the experimental results of supersonic shear imaging (SSI), it is proved that the method can be used for quantitative elastic imaging of the phantoms. In addition, compared with the SSI method, this method can realize the noncontact excitation of the shear wave, and the frequency of the shear wave excited by the laser is higher than that of the acoustic radiation force (ARF), so the spatial resolution is higher. Compared to the traditional PA elastic imaging method, this method can obtain a larger imaging depth under the premise of ensuring the imaging resolution, and it has potential application value in the clinical diagnosis of diseases requiring noncontact quantitative elasticity. [ABSTRACT FROM AUTHOR]

This work explores the complex interactions of magnetic fields, photothermal effects, thermoelasticity theory, and acoustic pressure in a nonlocal semiconductor medium. These numerous physical phenomena are integrated into a complete theoretical mathematical framework used to understand the dynamic behavior of wave propagation within semiconductors. Considering the spatial distribution of carriers and their interactions, the non-local character of the semiconductor material is taken into account. The physical fields as temperature, mechanical stress, displacement, carrier density, and acoustic pressure can be analytically represented mathematically using the harmonic wave approach. Numerical simulations and theoretical discussions are performed to understand the complex interactions between these fundamental physical processes. The stability analysis of the interaction between the mechanical thermal and acoustic properties of the nonlocality medium under the impact of magnetic field by add it to the physical quantities is investigation. The theoretical results are examined and graphically shown according to the nonlocal semiconductor with magnetic field.

In this study, we discussed the photothermal effect on a microelongated thermoelastic plate under the influence of acoustic pressure. This study is very important in many fields and has a wide application in industries. The problem is studied in the two-dimensional plane to obtain the thermoacoustic and mechanical waves behavior. Normal mode analysis is used to get the exact solution of the problem. Many comparisons between the physical quantities are made according to the different values of physical constants of many semiconductor materials. Graphical illustrations depict the numerical outcomes for the examined fields both with and without microelongation parameters.

Microscopic defects in flip chips, originating from manufacturing, significantly affect performance and longevity. Post-fabrication sampling methods ensure product functionality but lack in-line defect monitoring to enhance chip yield and lifespan in real-time. This study introduces a photoacoustic remote sensing (PARS) system for in-line imaging and defect recognition during flip-chip fabrication. We first propose a real-time PARS imaging method based on continuous acquisition combined with parallel processing image reconstruction to achieve real-time imaging during the scanning of flip-chip samples, reducing reconstruction time from an average of approximately 1134 ms to 38 ms. Subsequently, we propose improved YOLOv7 with space-to-depth block (IYOLOv7-SPD), an enhanced deep learning defect recognition method, for accurate in-line recognition and localization of microscopic defects during the PARS real-time imaging process. The experimental results validate the viability of the proposed system for enhancing the lifespan and yield of flip-chip products in chip manufacturing facilities.

Mechanical properties of brain tissues are from principal features from different points of view; diagnosis, the performance of the brain and neurological disorders. Particularly viscoelastic properties of the brain tissues are determinative. In this study based on a proposed accurate and non-invasive method, we have measured the viscoelastic properties of prefrontal cortex and cerebellum, two important brain regions involved in motor learning and pathophysiology of autism spectrum disorder (ASD). In this regard, using photoacoustic systems, viscoelastic properties of tissues from the cerebellum and prefrontal cortex of normal and prenatal VPA (Valproic acid)-exposed (i.e. autistic-like) offspring rats are measured. Results of our study show that the cerebellums of normal tissues are stiffer than the tissue obtained from autistic-like rats, while the viscoelasticity of the prefrontal cortex of normal tissues is higher than that of autistic ones. The proposed method for the measurement of viscoelastic properties of the brain tissue has the potential not only for the fundamental studies but as a diagnosis technique.

Osteoporosis is a major public health threat with significant physical, psychosocial, and financial consequences. The calcaneus bone has been used as a measurement site for risk prediction of osteoporosis by noninvasive quantitative ultrasound (QUS). By adding optical contrast to QUS, our previous studies indicate that a combination of photoacoustic (PA) and QUS, that is, PAQUS, provides a novel opportunity to assess the health of human calcaneus. Calibration of the PAQUS system is crucial to realize quantitative and repeatable measurements of the calcaneus. Therefore, a phantom which simulates the optical, ultrasound, and architectural properties of the human calcaneus, for PAQUS system calibration, is required. Additionally, a controllable phantom offers researchers a versatile framework for developing versatile structures, allowing more controlled assessment of how varying bone structures cause defined alterations in PA and QUS signals. In this work, we present the first semi‐anthropomorphic calcaneus phantom for PAQUS. The phantom was developed based on nano computed‐tomography (nano‐CT) and stereolithography 3D printing, aiming to maximize accuracy in the approximation of both trabecular and cortical bone microstructures. Compared with the original digital input calcaneus model from a human cadaveric donor, the printed model achieved accuracies of 71.15% in total structure and 87.21% in bone volume fraction. Inorganic materials including synthetic blood, mineral oil, intralipid, and agar gel were used to model the substitutes of bone marrow and soft tissue, filling and covering the calcaneus phantom. The ultrasound and optical properties of this phantom were measured, and the results were consistent with those measured by a commercialized device and from previous in vivo studies. In addition, a short‐term stability test was conducted for this phantom, demonstrating that the optical and ultrasound properties of the phantom were stable without significant variation over 1 month. This semi‐anthropomorphic calcaneus phantom shows structural, ultrasound, and optical properties similar to those from a human calcaneus in vivo and, thereby, can serve as an effective source for equipment calibration and the comprehensive study of human patients. [ABSTRACT FROM AUTHOR]

Significance: We developed a high-speed optical-resolution photoacoustic microscopy (OR-PAM) system using a high-repetition-rate supercontinuum (SC) light source and a two-axes Galvano scanner. The OR-PAM system enabled real-time imaging of optical absorbers inside biological tissues with excellent excitation wavelength tunability. Aim: In the near-infrared (NIR) wavelength range, high-speed OR-PAM faces limitations due to the lack of wavelength-tunable light sources. Our study aimed to enable high-speed OR-PAM imaging of various optical absorbers, including NIR contrast agents, and validate the performance of high-speed OR-PAM in the detection of circulating tumor cells (CTCs). Approach: A high-repetition nanosecond pulsed SC light source was used for OR-PAM. The excitation wavelength was adjusted by bandpass filtering of broadband light pulses produced by an SC light source. Phantom and in vivo experiments were performed to detect tumor cells stained with an NIR contrast agent within flowing blood samples. Results: The newly developed high-speed OR-PAM successfully detected stained cells both in the phantom and in vivo. The phantom experiment confirmed the correlation between the tumor cell detection rate and tumor cell concentration in the blood sample. Conclusions: The high-speed OR-PAM effectively detected stained tumor cells. Combining high-speed OR-PAM with molecular probes that stain tumor cells in vivo enables in vivo CTC detection. [ABSTRACT FROM AUTHOR]

Significance: Endocavity ultrasound (US) imaging is a frequently employed diagnostic technique in gynecology and urology for the assessment of male and female genital diseases that present challenges for conventional transabdominal imaging. The integration of photoacoustic (PA) imaging with clinical US imaging has displayed promising outcomes in clinical research. Nonetheless, its application has been constrained due to size limitations, restricting it to spatially confined locations such as vaginal or rectal canals. Aim: This study presents the development of a video-rate (20 Hz) endocavity PA/harmonic US imaging (EPAUSI) system. Approach: The approach incorporates a commercially available endocavity US probe with a miniaturized laser delivery unit, comprised of a single large-core fiber and a line beamshaping engineered diffuser. The system facilitates real-time image display and subsequent processing, including angular energy density correction and spectral unmixing, in offline mode. Results: The spatial resolutions of the concurrently acquired PA and harmonic US images were measured at 318 µm and 291 µm in the radial direction, respectively, and 1.22 deg and 1.50 deg in the angular direction, respectively. Furthermore, the system demonstrated its capability in multispectral PA imaging by successfully distinguishing two clinical dyes in a tissue-mimicking phantom. Its rapid temporal resolution enabled the capture of kinetic dye perfusion into an ex vivo porcine ovary through the depth of porcine uterine tissue. EPAUSI proved its clinical viability by detecting pulsating hemodynamics in the male rat's prostate in vivo and accurately classifying human blood vessels into arteries and veins based on sO2 measurements. Conclusions: Our proposed EPAUSI system holds the potential to unveil previously overlooked indicators of vascular alterations in genital cancers or endometriosis, addressing pressing requirements in the fields of gynecology and urology. [ABSTRACT FROM AUTHOR]

Significance: Neural regulation at high precision vitally contributes to propelling fundamental understanding in the field of neuroscience and providing innovative clinical treatment options. Recently, photoacoustic brain stimulation has emerged as a cutting-edge method for precise neuromodulation and shows great potential for clinical application. Aim: The goal of this perspective is to outline the advancements in photoacoustic brain stimulation in recent years. And, we also provide an outlook delineating several prospective paths through which this burgeoning approach may be substantively refined for augmented capability and wider implementations. Approach: First, the mechanisms of photoacoustic generation as well as the potential mechanisms of photoacoustic brain stimulation are provided and discussed. Then, the state-of-the-art achievements corresponding to this technology are reviewed. Finally, future directions for photoacoustic technology in neuromodulation are provided. Results: Intensive research endeavors have prompted substantial advancements in photoacoustic brain stimulation, illuminating the unique advantages of this modality for noninvasive and high-precision neuromodulation via a nongenetic way. It is envisaged that further technology optimization and randomized prospective clinical trials will enable a wide acceptance of photoacoustic brain stimulation in clinical practice. Conclusions: The innovative practice of photoacoustic technology serves as a multifaceted neuromodulation approach, possessing noninvasive, high-accuracy, and nongenetic characteristics. It has a great potential that could considerably enhance not only the fundamental underpinnings of neuroscience research but also its practical implementations in a clinical setting. [ABSTRACT FROM AUTHOR]

Significance: A Fabry-Perot (FP) polymer film sensor can be used to detect acoustic waves in a photoacoustic endoscope (PAE) if the dimensions can be adequately scaled down in size. Current FP sensors have limitations in size, sensitivity, and array configurability. Aim: We aim to characterize and demonstrate the imaging performance of a miniature FP sensor to evaluate the effects of reduced size and finite dimensions. Approach: A transfer matrix model was developed to characterize the frequency response of a multilayer miniature FP sensor. An analytical model was derived to describe the effects of a substrate with finite thickness. Finite-element analysis was performed to characterize the temporal response of a sensor with finite dimensions. Miniature 2 × 2 mm2 FP sensors were designed and fabricated using gold films as reflective mirrors on either side of a parylene C film deposited on a glass wafer. A single-wavelength laser was used to interrogate the sensor using illumination delivered by fiber subprobes. Imaging phantoms were used to verify FP sensor performance, and in vivo images of blood vessels were collected from a live mouse. Results: The finite thickness substrate of the FP sensor resulted in echoes in the time domain signal that could be removed by back filtering. The substrate acted as a filter in the frequency domain. The finite lateral sensor dimensions produced side waves that could be eliminated by surface averaging using an interrogation beam with adequate diameter. The fabricated FP sensor produced a noise-equivalent pressure = 0.76 kPa, bandwidth of 16.6 MHz, a spectral full-width at-half-maximum = 0.2886 nm, and quality factor Q = 2694. Photoacoustic images were collected from phantoms and blood vessels in a live mouse. Conclusions: A miniature wafer-based FP sensor design has been demonstrated with scaled down form factor for future use in PAE. [ABSTRACT FROM AUTHOR]

Cellular biomechanical properties provide essential insights into biological functions regarding health and disease. Current measurements of the biomechanical properties of cells require physical contact with cells or pre‐loading on the cells. Here, we have developed photoacoustic micro‐viscoelastography (PAMVE), which utilizes the phase characteristics of photoacoustic (PA) response, for mapping mechanocellular properties in a load‐free manner. PAMVE realizes the local viscoelasticity measurement on the macrophages and red blood cells with micrometer scale. Furthermore, PAMVE can successfully identify the adipose cell and skeletal muscle cell due to the difference in their composition‐related biomechanical properties. PAMVE represents an irreplaceable option for interrogating characteristic mechanocellular properties, opening the possibility of studying cellular mechanobiology and pathophysiology. [ABSTRACT FROM AUTHOR]