Opto-ultrasound biosensor for wearable and mobile devices: realization with a transparent ultrasound transducer

Transparent ultrasonic transducers based on relaxor ferroelectric crystals for advanced photoacoustic imaging

Photoacoustic imaging is a promising non-invasive functional imaging modality for fundamental research and clinical diagnosis. However, achieving capillary-level resolution, wide field-of-view, and high frame rates remains challenging. To address this, we propose a transparent ultrasonic transducer design using our developed transparent Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals. Our fabrication technique incorporates quartz-glass-and-epoxy matching layers with low-resistance indium-tin-oxide electrodes through a brass-ring based structure, enabling a high frequency (28.5 MHz), wide bandwidth (78%), and enhanced pulse-echo sensitivity (2.5 V under 2-μJ pulse excitation). Our Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3-based transparent ultrasonic transducer demonstrates a four-fold enhancement in photoacoustic detection sensitivity when compared to the LiNbO3-based counterpart, leading to a 13 dB improvement of signal-to-noise ratio in microvascular photoacoustic imaging. This enables dynamic monitoring of mouse cerebral cortex microvasculature during seizures at 0.8 Hz frame rates over a 1.5 × 1.5 mm2 field-of-view. Our work paves the way for high-performance and compact photoacoustic imaging systems using advanced piezoelectric materials.

Quantitative volumetric photoacoustic assessment of vasoconstriction by topical corticosteroid application in mice skin

Topical corticosteroids manage inflammatory skin conditions via their action on the immune system. An effect of application of corticosteroids to the skin is skin blanching caused by peripheral vasoconstriction. This has been used to characterize, in some cases relative potency and also as a way to compare skin penetration. Chromameters have been used to assess skin blanching-the outcome of vasoconstriction caused by topical corticosteroids-but do not directly measure vasoconstriction. Here, we demonstrate quantitative volumetric photoacoustic microscopy (PAM) as a tool for directly assessing the vasoconstriction followed by topical corticosteroid application, noninvasively visualizing skin vasculature without any exogeneous contrast agent. We photoacoustically differentiated the vasoconstrictive ability of four topical corticosteroids in small animals through multiparametric analyses, offering detailed 3D insights into vasoconstrictive mechanisms across different skin depths. Our findings highlight the potential of PAM as a noninvasive tool for measurement of comparative vasoconstriction with potential for clinical, pharmaceutical, and bioequivalence applications.

Emerging Wearable Ultrasound Technology

This perspective article provides a brief overview on materials, fabrications, beamforming, and applications for wearable ultrasound devices, a rapidly growing field with versatile implications. Recent developments in miniaturization and soft electronics have significantly advanced wearable ultrasound devices. Such devices offer distinctive advantages over traditional ultrasound probes, including prolonged usability and operator independence, and have demonstrated their effectiveness in continuous monitoring, noninvasive therapies, and advanced human-machine interfaces. Wearable ultrasound devices can be classified into three main categories: rigid, flexible, and stretchable, each having distinctive properties and fabrication strategies. Key unique strategies in device design, packaging, and beamforming for each type of wearable ultrasound devices are reviewed. Furthermore, we highlight the latest applications enabled by wearable ultrasound technology in various areas. This article concludes by discussing the outstanding challenges within the field and outlines potential pathways for future advancements.

A Stable and Sensitive Engineering Bacterial Sensor via Physical Biocontainment and Two-Stage Signal Amplification

Although engineering bacterial sensors have outstanding advantages in reflecting the actual bioavailability and continuous monitoring of pollutants, the potential escape risk of engineering microorganisms and lower detection sensitivity have always been one of the biggest challenges limiting their wider application. In this study, a core-shell hydrogel bead with functionalized silica as the core and alginate-polyacrylamide as the shell have been developed not only to realize zero escape of engineered bacteria but also to maintain cell activity in harsh environments, such as extremely acidic/alkaline pH, high salt concentration, and strong pressure. Particularly, after combining the selective preconcentration toward pollutants by functionalized core and the positive feedback signal amplification of engineering bacteria, biosensors have realized two-stage signal amplification, significantly improving the detection sensitivity and reducing the detection limit. In addition, this strategy was actually applied to the detection of As(III) and As(V) coexisting in environmental samples, and the detection sensitivity was increased by 3.23 and 4.39 times compared to sensors without signal amplification strategy, respectively, and the detection limits were as low as 0.39 and 0.86 ppb, respectively.

Introduction to the feature issue: Advances in Optical Biosensors for Biomedical Applications

The feature issue of Biomedical Optics Express titled "Advances in Optical Biosensors for Biomedical Applications" presents a comprehensive collection of cutting-edge optical biosensor research. With the growing demand for sensitive, label-free, and real-time detection of biological analytes, optical biosensors have emerged as important devices in a wide range of biomedical applications, including medical diagnostics, bioanalysis, and personalised healthcare. This collection of 26 papers highlights recent advances and innovations in the development, design, and implementation of optical biosensors. The feature issue serves as an opportunity for disseminating ground-breaking findings, promoting new ideas, and inspiring further developments in optical biosensors for medical applications. The authors provide breakthrough technology, innovative approaches, and practical clinical applications that have the potential to revolutionize healthcare and biomedical research.

Highly sensitive self-focused ultrasound transducer with a bionic back-reflector for multiscale-resolution photoacoustic microscopy

In this study, we designed a self-focused ultrasonic transducer made of polyvinylidene fluoride (PVDF). This transducer involves a back-reflector, which is modeled after tapetum lucidum in the eyes of some nocturnal animals. The bionic structure reflects the ultrasound, which passes through the PVDF membrane, back to PVDF and provides a second chance for the PVDF to convert the ultrasound to electric signals. This design increases the amount of ultrasound absorbed by the PVDF, thereby improving the detection sensitivity. Both ultrasonic and photoacoustic (PA) experiments were conduct to characterize the performance of the transducer. The results show that the fabricated transducer has a center frequency of 13.07 MHz, and a bandwidth of 96% at -6 dB. With an acoustic numerical aperture (NA) of 0.64, the transducer provides a lateral resolution of 140µm. Importantly, the bionic design improves the detection sensitivity of the transducer about 30%. Finally, we apply the fabricated transducer to optical-resolution (OR) and acoustic-resolution photoacoustic microscopy (AR-PAM) to achieve multiscale-resolution PA imaging. Imaging of the bamboo leaf and the leaf skeleton demonstrates that the proposed transducer can provide high spatial resolution, better imaging intensity and contrast. Therefore, the proposed transducer design will be useful to enhance the performance of multiscale-resolution PAM.

Broadband transparent ultrasound transducer with polymethyl methacrylate as matching layer for in vivo photoacoustic microscopy

Photoacoustic imaging (PAI) uniquely combines optics and ultrasound, presenting a promising role in biomedical imaging as a non-invasive and label-free imaging technology. As the traditional opaque ultrasound (US) transducers could hinder the transportation of the excitation light and limit the performance of PAI system, piezoelectric transparent ultrasonic transducers (TUTs) with indium tin oxide (ITO) electrodes have been developed to allow light transmission through the transducer and illuminate the sample directly. Nevertheless, without having transparent matching materials with appropriate properties, the bandwidth of those TUTs was generally narrow. In this work, we propose to employ polymethyl methacrylate (PMMA) as the matching layer material to improve the bandwidth of lithium niobate (LN)-based TUTs. The effects of PMMA matching layer on the performance of TUTs have been systematically studied. With the optimized PMMA matching layer, the very wide bandwidth of > 50 % could be achieved for the TUTs even with different transducer frequencies, leading to the great enhancement of axial resolution when compared to the similar reported work. In addition, the imaging performance of the developed TUT prototype has been evaluated in a PAI system and demonstrated by both phantom and in vivo small animal imaging.

Non-contact measurement of neck pulses achieved by imaging micro-motions in the neck skin

We report a method and system of micro-motion imaging (µMI) to realize non-contact measurement of neck pulses. The system employs a 16-bit camera to acquire videos of the neck skin, containing reflectance variation caused by the neck pulses. Regional amplitudes and phases of pulse-induced reflection variation are then obtained by applying a lock-in amplification algorithm to the acquired videos. Composite masks are then generated using the raw frame, amplitude and phase maps, which are then used to guide the extraction of carotid pulse (CP) and jugular vein pulse (JVP) waveforms. Experimental results sufficiently demonstrate the feasibility of our method to extract CP and JVP waves. Compared with conventional methods, the proposed strategy works in a non-contact, non-invasive and self-guidance manner without a need for manual identification to operate, which is important for patient compliance and measurement objectivity. Considering the close relationship between neck pulses and cardiovascular diseases, for example, CA stenosis, the proposed µMI system and method may be useful in the development of early screening tools for potential cardiovascular diseases.

Introduction to the Biophotonics Congress 2022 feature issue

A feature issue is being presented by a team of guest editors containing papers based on studies presented at the Optica Biophotonics Congress: Biomedical Optics held on April 24-27, 2022 in Fort Lauderdale, Florida, USA.