Design and tribological performance of graphene nanofluids dispersed by dragging effect of bicomponent gelator.

Nanofluids have excellent lubrication and high thermal conductivity. However, the agglomeration and sedimentation produced by the large surface energy of nanoparticles in base liquid threaten the long-term dispersion stability and impact the wide application of nanofluid. In this work, based on the self-assemble behavior and continuous network structure formed by low molecular weight organic gelator, the uniform clusters were formed through regulating the kinetics behavior in the gelling process. The dragging effect was demonstrated by oleic acid - sodium dodecyl sulfate (OA-SDS) bicomponent gelator and graphene oxide (GO) nanosheets. The results showed that GO nanofluids dispersed by OA-SDS were stable for more than 12 months. The well-dispersed GO nanofluid exhibited better anti-friction and anti-wear properties under both immersion and electrostatic minimum quantity lubrication conditions. Moreover, the lower contact angle, surface tension and droplet size of nanofluids after charging improved the wettability on the frictional interface. The GO adsorption film formed on the friction interface protected the tribochemical reaction film of iron oxide and prevented the occurrence of sintering of base oil.

Simultaneous Dual-Wavelength Source Raman Spectroscopy with a Handheld Confocal Probe for Analysis of the Chemical Composition of In Vivo Human Skin.

Confocal Raman spectroscopy (CRS) is a powerful tool that has been widely used for biological tissue analysis because of its noninvasive nature, high specificity, and rich biochemical information. However, current commercial CRS systems suffer from limited detection regions (450-1750 cm-1), bulky sizes, nonflexibilities, slow acquisitions by consecutive excitations, and high costs if using a Fourier transform (FT) Raman spectroscopy with an InGaAs detector, which impede their adoption in clinics. In this study, we developed a portable CRS system with a simultaneous dual-wavelength source and a miniaturized handheld probe (120 mm × 60 mm × 50 mm) that can acquire spectra in both fingerprint (FP, 450-1750 cm-1) and high wavenumber (HW, 2800-3800 cm-1) regions simultaneously. An innovative design combining 671 and 785 nm lasers for simultaneous excitation through a compact and high-efficiency (>90%) wavelength combiner was implemented. Moreover, to decouple the fused FP and HW spectra, a first-of-its-kind precise Raman spectra separation algorithm (PRSSA) was developed based on the maximum a posteriori probability (MAP) estimate. The accuracy of spectra separation was greater than 99%, demonstrated in both phantom experiments and in vivo human skin measurements. The total data acquisition time was reduced by greater than 50% compared to other CRS systems. The results proved our proposed CRS system and PRSSA's superior capability in fast and ultrawideband spectra acquisition will significantly improve the integration of CRS in the clinical workflow.

An Investigation of Signal Preprocessing for Photoacoustic Tomography.

Photoacoustic tomography (PAT) is increasingly being used for high-resolution biological imaging at depth. Signal-to-noise ratios and resolution are the main factors that determine image quality. Various reconstruction algorithms have been proposed and applied to reduce noise and enhance resolution, but the efficacy of signal preprocessing methods which also affect image quality, are seldom discussed. We, therefore, compared common preprocessing techniques, namely bandpass filters, wavelet denoising, empirical mode decomposition, and singular value decomposition. Each was compared with and without accounting for sensor directivity. The denoising performance was evaluated with the contrast-to-noise ratio (CNR), and the resolution was calculated as the full width at half maximum (FWHM) in both the lateral and axial directions. In the phantom experiment, counting in directivity was found to significantly reduce noise, outperforming other methods. Irrespective of directivity, the best performing methods for denoising were bandpass, unfiltered, SVD, wavelet, and EMD, in that order. Only bandpass filtering consistently yielded improvements. Significant improvements in the lateral resolution were observed using directivity in two out of three acquisitions. This study investigated the advantages and disadvantages of different preprocessing methods and may help to determine better practices in PAT reconstruction.

The relationship between solid-liquid interface interaction and gelling capacity of h-BN 2D material: a rheological study.

Diurea modified h-BN nanosheet is a novel kind of 2D gelator that could gel the lubricating oils under the stimulus of ultrasound. Morphological analyzations in previous study confirmed that the ultrasound induced layer-by-layer (LBL) structure of BN gelator is critical for the gelation. However, the elastic response in LBL structure, which is crucial for the formation of a stable gel system, has not been explicitly illustrated yet. The challenge is that the LBL gelator structure is based on 2D material and thus lacks vertical linkage between gelator layers, which is significantly different from the traditional gel systems that generally possess highly crosslinked gelator network. In this work, by investigating the viscoelastic behavior of the BN-based gel via rheometer, it is found the solid-liquid interface interaction, which is regulated by the diurea molecular structure in the BN gelator, is the key factor for triggering the stable elastic response in the LBL structure, and the elasticity mainly originates from the interface interaction induced bending deformation of h-BN 2D material. The findings further elucidate the gelling mechanism of BN gelators and enlighten the structure design of ultrasound-responsive gelator based on 2D materials.

Time-domain photoacoustic waveform analysis for glucose measurement.

Photoacoustic (PA) effect is the product of light-ultrasound interactions and its time-domain waveform contains rich information. Besides optical absorption, the PA waveform inherently consists of other mechanical and thermal properties of the sample. They also have correlation with the target composition but have not been utilized in conventional PA spectroscopy. In this article, we propose a new concept named time-domain photoacoustic waveform spectroscopy (tPAWS) for chemical component quantification. It employs multiple variables inherently contained in the PA waveform excited by a single wavelength laser to extract informative features. The demonstration of glucose measurement in human blood serum (HBS) shows superior sensitivity and accuracy enhancement, compared to conventional amplitude-based PA measurement and NIR spectroscopy. Thanks to the sensitivity and accuracy of tPAWS, multiple wavelength sources and complex instrumentation used in conventional spectroscopic sensing methods can be avoided. TPAWS, as a novel physics-inspired sensing method, shows great potential for complementing or surpassing the current spectroscopic methods as a new sensing technique for chemical analysis.

Noninvasive Electromagnetic Wave Sensing of Glucose.

Diabetic patients need long-term and frequent glucose monitoring to assist in insulin intake. The current finger-prick devices are painful and costly, which places noninvasive glucose sensors in high demand. In this review paper, we list several advanced electromagnetic (EM)-wave-based technologies for noninvasive glucose measurement, including infrared (IR) spectroscopy, photoacoustic (PA) spectroscopy, Raman spectroscopy, fluorescence, optical coherence tomography (OCT), Terahertz (THz) spectroscopy, and microwave sensing. The development of each method is discussed regarding the fundamental principle, system setup, and experimental results. Despite the promising achievements that have been previously reported, no established product has obtained FDA approval or survived a marketing test. The limitations of, and prospects for, these techniques are presented at the end of this review.

Hybrid multi-wavelength nonlinear photoacoustic sensing and imaging.

Multi-wavelength photoacoustic (PA) imaging has been studied extensively to explore the spectroscopic absorption contrast of biological tissues. To generate strong PA signals, a high-power wavelength tunable pulsed laser source has to be employed, which is bulky and quite expensive. In this Letter, we propose a hybrid multi-wavelength PA imaging (hPAI) method based on the combination of a single-wavelength pulsed laser source and multi-wavelength continuous-wave (CW) laser sources. By carefully controlling the laser illumination sequence (pulse-CW-pulse) and extracting the PA signal difference before and after the heating of CW lasers, the optical absorption property of multi-wavelength light illumination could be obtained. Compared with conventional PA imaging, the proposed hPAI shows a much lower system cost due to the usage of single-wavelength pulsed lasers and multiple inexpensive CW lasers. As the preliminary results show in this Letter, hPAI imaging has the potential to provide another pathway for high spectroscopic optical absorption contrast in PA imaging.

Efficient Fog Harvesting Based on 1D Copper Wire Inspired by the Plant Pitaya.

The leaf of the plant pitaya shows excellent fog harvesting behavior through its 1D thorns with wire-like microstructures. The thorns of it cannot provide enough driving force for the droplet transportation by the special structure and chemistry gradient as the cactus thorns, but it showed efficient water supply which improved the fog harvesting greatly. The mechanism is studied based on 1D copper wire with similar 1D wire-like microstructure and wettability. This structure can significantly reduce the deviation of the fog-laden winds, and the surface intrinsic hydrophility makes water accumulate on it in the form of droplets, which endow it with an efficient water supply that is ∼100 times faster than that on a 2D-flat surface. In addition, it can also enhance the fog capture and water removal. The 3D fog collector composed of 1D microcopper wires has been fabricated which show a high fog harvesting efficiency of ∼13%. This work explains the role of 1D wire-like microstructure in efficient fog harvesting in a different view and provides new insight into the application of developing a more efficient fog collector.

Electromagnetic⁻Acoustic Sensing for Biomedical Applications.

This paper reviews the theories and applications of electromagnetic⁻acoustic (EMA) techniques (covering light-induced photoacoustic, microwave-induced thermoacoustic, magnetic-modulated thermoacoustic, and X-ray-induced thermoacoustic) belonging to the more general area of electromagnetic (EM) hybrid techniques. The theories cover excitation of high-power EM field (laser, microwave, magnetic field, and X-ray) and subsequent acoustic wave generation. The applications of EMA methods include structural imaging, blood flowmetry, thermometry, dosimetry for radiation therapy, hemoglobin oxygen saturation (SO2) sensing, fingerprint imaging and sensing, glucose sensing, pH sensing, etc. Several other EM-related acoustic methods, including magnetoacoustic, magnetomotive ultrasound, and magnetomotive photoacoustic are also described. It is believed that EMA has great potential in both pre-clinical research and medical practice.

Noninvasive photoacoustic measurement of glucose by data fusion.

We proposed a novel noninvasive method for glucose detection using a photoacoustic (PA) technique utilizing both the peak-to-peak value and peak arrival time delay information. Without increasing apparatus and system complexity, we demonstrated the accuracy enhancement of 29.5% and 33.63% for high (0-7 g dL-1) and low (0-350 mg dL-1) concentration of glucose solution, compared to conventional amplitude-based prediction.

Remarkable In Vivo Nonlinear Photoacoustic Imaging Based on Near-Infrared Organic Dyes.

Two near-infrared dyes featuring good dispersion and light-harvesting property present a remarkable nonlinear photoacoustic response in vitro and in vivo comparing with conventional gold nanorods. This study benefits the fabrication of drug delivery platforms with accurate targeting and control effect under photoacoustic image guidance.

Hybrid Photoacoustic Ultrasound Imaging System for Cold-Induced Vasoconstriction and Vasodilation Monitoring.

Lewis hunting reaction refers to the alternating cold-induced vasoconstriction and dilation in extremities, whose underlying mechanism is complex. While numerous studies reported this intriguing phenomenon by measuring cutaneous temperature fluctuation under cold exposure, few of them tracked peripheral vascular responses in real-time, lacking a non-invasive and quantitative imaging tool. To better monitor hunting reaction and diagnose relevant diseases, we developed a hybrid photoacoustic ultrasound (PAUS) tomography system to monitor finger vessels' dynamic response to cold, together with simultaneous temperature measurement. We also came out a standard workflow for image analysis with self-defined indices. In the small cohort observational study, vascular changes in the first cycle of hunting reaction were successfully captured by the image series and quantified. Time difference between vasodilation and temperature recovery was noticed and reported for the first time, thanks to the unique capability of the PAUS imaging system in real-time and continuous vascular monitoring. The developed imaging system and indices enabled more objective and quantitative monitoring of peripheral vascular activities, indicating its great potential in numerous clinical applications.

A portable optical pulsatile flowmetry demonstrates strong clinical relevance for diabetic foot perfusion assessment.

We present a robust, cost-effective (<2000 USD), and portable optical diffuse speckle pulsatile flowmetry (DSPF) device with a flexible handheld probe for deep tissue blood flow measurement in the human foot as well as a first-in-man observational clinical study using the proposed optical device for tissue ischemia assessment and peripheral artery disease (PAD) diagnosis. Blood flow in tissue is inherently pulsatile in nature. However, most conventional methods cannot measure deep tissue-level pulsatile blood flow noninvasively. The proposed optical device can measure tissue-level pulsatile blood flow ∼6 mm underneath the skin surface. A new quantitative tissue perfusion index (TPIDSPF) based on frequency domain analysis of the pulsatile blood flow waveform is defined to assess tissue ischemia status. Through a clinical study involving 66 subjects, including healthy individuals and diabetes patients with and without PAD, TPIDSPF demonstrated strong correlations of 0.720 with transcutaneous tissue partial oxygen pressure (TcPO2) and 0.652 with toe-brachial index (TBI). Moreover, among the three methods, TPIDSPF demonstrated the highest area under the curve for PAD diagnosis among diabetes patients, with a notable value of 0.941. The promising clinical results suggest that the proposed optical method has the potential to be an effective clinical tool for identifying PAD among the diabetic cohort.

Minimum Quantity Lubrication Jet Noise: Passive Control.

Jet noise is a common problem in minimum quantity lubrication (MQL) technology. This should be given great attention because of its serious impacts on the physical and mental health of the operators. In this study, a micro-grooved nozzle is proposed based on the noise reduction concept of biological micro-grooves. The flow field and acoustic characteristics of an original nozzle and a micro-grooved nozzle were investigated numerically to help better understand the noise reduction mechanism. The reasons for noise generation and the effects of the length (L), width (W) and depth (δ) of the micro-grooves on noise reduction were analyzed. It was found that jet noise is generated by the large-scale vortex ring structure and the pressure fluctuations caused by its motion. The overall sound pressure level (OASPL) decreased with the increases in W and δ, and increased with the increase in L. Among of them, δ has the greatest effect on noise reduction. The maximum noise reduction achieved was 6.66 dB, as verified by the OASPL test. Finally, the noise reduction mechanism was discussed in terms of the flow field, vorticity and the frequency characteristics. Micro-grooves can enhance the mixing of airflow inside the nozzle and accelerate the process of large-scale vortices breaking into smaller-scale vortices. It also reduces the sound pressure level (SPL) of middle frequencies, as well as the SPL of high frequencies on specific angles.

Effects of the Electric Double Layer Characteristic and Electroosmotic Regulation on the Tribological Performance of Water-Based Cutting Fluids.

The electroosmosis effect is a complement to the theory of the traditional capillary penetration of cutting fluid. In this study, based on the electric double layer (EDL) characteristics at friction material/solution interfaces, the influences of additives and their concentrations on capillary electroosmosis were investigated, and a water-based cutting-fluid formulation with consideration to the electroosmosis effect was developed. The lubrication performance levels of cutting fluids were investigated by a four-ball tribometer. The results show that the EDL is compressed with increasing ionic concentration, which suppresses the electroosmotic flow (EOF). The specific adsorption of OH- ions or the dissociation of surface groups is promoted as pH rises, increasing the absolute zeta potential and EOF. The polyethylene glycol (PEG) additive adsorbed to the friction material surface can keep the shear plane away from the solid surface, reducing the absolute zeta potential and EOF. The electroosmotic performance of cutting fluid can be improved by compounding additives with different electroosmotic performance functions. Furthermore, electroosmotic regulators can adjust the zeta potential by the electrostatic adsorption mechanism, affecting the penetration performance of cutting fluid in the capillary zone at the friction interface. The improvement in the tribological performance of cutting fluid developed with consideration given to the electroosmosis effect is attributed to the enhancement of the penetration ability of the cutting fluid and the formation of more abundant amounts of lubricating film at the interface.

Applications of Optical Fiber in Label-Free Biosensors and Bioimaging: A Review.

Biosensing and bioimaging are essential in understanding biological and pathological processes in a living system, for example, in detecting and understanding certain diseases. Optical fiber has made remarkable contributions to the biosensing and bioimaging areas due to its unique advantages of compact size, immunity to electromagnetic interference, biocompatibility, fast response, etc. This review paper will present an overview of seven common types of optical fiber biosensors and optical fiber-based ultrasound detection in photoacoustic imaging (PAI) and the applications of these technologies in biosensing and bioimaging areas. Of course, there are many types of optical fiber biosensors. Still, this paper will review the most common ones: optical fiber grating, surface plasmon resonance, Sagnac interferometer, Mach-Zehnder interferometer, Michelson interferometer, Fabry-Perot Interferometer, lossy mode resonance, and surface-enhanced Raman scattering. Furthermore, different optical fiber techniques for detecting ultrasound in PAI are summarized. Finally, the main challenges and future development direction are briefly discussed.

Handheld Multifunctional Fluorescence Imager for Non-invasive Plant Phenotyping.

Fluorescence imaging has shown great potential in non-invasive plant monitoring and analysis. However, current systems have several limitations, such as bulky size, high cost, contact measurement, and lack of multifunctionality, which may hinder its applications in a wide range of settings including indoor vertical farming. Herein, we developed a compact handheld fluorescence imager enabling multipurpose plant phenotyping, such as continuous photosynthetic activity monitoring and non-destructive anthocyanin quantification. The compact imager comprises of pulse-amplitude-modulated multi-color light emitting diodes (LEDs), optimized light illumination and collection, dedicated driver circuit board, miniaturized charge-coupled device camera, and associated image analytics. Experiments conducted in drought stressed lettuce proved that the novel imager could quantitatively evaluate the plant stress by the non-invasive measurement of photosynthetic activity efficiency. Moreover, a non-invasive and fast quantification of anthocyanins in green and red Batavia lettuce leaves had excellent correlation (>84%) with conventional destructive biochemical analysis. Preliminary experimental results emphasize the high throughput monitoring capability and multifunctionality of our novel handheld fluorescence imager, indicating its tremendous potential in modern agriculture.

A Review of Emerging Electromagnetic-Acoustic Sensing Techniques for Healthcare Monitoring.

Conventional electromagnetic (EM) sensing techniques such as radar and LiDAR are widely used for remote sensing, vehicle applications, weather monitoring, and clinical monitoring. Acoustic techniques such as sonar and ultrasound sensors are also used for consumer applications, such as ranging and in vivo medical/healthcare applications. It has been of long-term interest to doctors and clinical practitioners to realize continuous healthcare monitoring in hospitals and/or homes. Physiological and biopotential signals in real-time serve as important health indicators to predict and prevent serious illness. Emerging electromagnetic-acoustic (EMA) sensing techniques synergistically combine the merits of EM sensing with acoustic imaging to achieve comprehensive detection of physiological and biopotential signals. Further, EMA enables complementary fusion sensing for challenging healthcare settings, such as real-world long-term monitoring of treatment effects at home or in remote environments. This article reviews various examples of EMA sensing instruments, including implementation, performance, and application from the perspectives of circuits to systems. The novel and significant applications to healthcare are discussed. Three types of EMA sensors are presented: (1) Chip-based radar sensors for health status monitoring, (2) Thermo-acoustic sensing instruments for biomedical applications, and (3) Photoacoustic (PA) sensing and imaging systems, including dedicated reconstruction algorithms were reviewed from time-domain, frequency-domain, time-reversal, and model-based solutions. The future of EMA techniques for continuous healthcare with enhanced accuracy supported by artificial intelligence (AI) is also presented.

How does caffeine influence memory? Drug, experimental, and demographic factors.

Caffeine is a widely used nootropic drug, but its effects on memory in healthy participants have not been sufficiently evaluated. Here we review evidence of the effects of caffeine on different types of memory, and the associated drug, experimental, and demographical factors. There is limited evidence that caffeine affects performance in memory tasks beyond improved reaction times. For drug factors, a dose-response relationship may exist but findings are inconsistent. Moreover, there is evidence that the source of caffeine can modulate its effects on memory. For experimental factors, past studies often lacked a baseline control for diet and sleep and none discussed the possible reversal of withdrawal effect due to pre-experimental fasting. For demographic factors, caffeine may interact with sex and age, and the direction of the effect may depend on the dose, individual tolerance, and metabolism at baseline. Future studies should incorporate these considerations, as well as providing continued evidence on the effect of caffeine in visuospatial, prospective, and implicit memory measures.

A Portable Ultrawideband Confocal Raman Spectroscopy System with a Handheld Probe for Skin Studies.

Confocal Raman spectroscopy (CRS) has shown potential in non-invasive skin analysis. However, current CRS systems have various limitations including a narrow detection band, large size, non-flexibility, slowness, and complexity, which hinder their clinical applications. Herein, we developed a portable ultrawideband CRS system with a fiber-based handheld probe to acquire the Raman spectra in both fingerprint and high wavenumber regions in a fast and quasi-simultaneous way. Dual-wavelength excitation with a dual-passband laser cleaning filter and high-speed fiber array multiplexer was adopted instead of a specialized grating and detector to achieve instant switching between the detection regions and improve system robustness. Preliminary in vivo results demonstrated its depth profiling capability in an ultrawide detection range for stratum corneum thickness, natural moisturizing factor, and water content quantification, indicating its great potential in a wide range of clinical and cosmeceutical applications.