Advanced operation of heated fluidic resonators via mechanical and thermal loss reduction in vacuum.

For simultaneous and quantitative thermophysical measurements of ultrasmall liquid volumes, we have recently developed and reported heated fluidic resonators (HFRs). In this paper, we improve the precision of HFRs in a vacuum by significantly reducing the thermal loss around the sensing element. A vacuum chamber with optical, electrical, and microfluidic access is custom-built to decrease the convection loss by two orders of magnitude under 10-4 mbar conditions. As a result, the measurement sensitivities for thermal conductivity and specific heat capacity are increased by 4.1 and 1.6 times, respectively. When differentiating between deionized water (H2O) and heavy water (D2O) with similar thermophysical properties and ~10% different mass densities, the signal-to-noise ratio (property differences over standard error) for H2O and D2O is increased by 9 and 5 times for thermal conductivity and specific heat capacity, respectively.

Massively parallel electro-optic sampling of space-encoded optical pulses for ultrafast multi-dimensional imaging.

High-speed and high-resolution imaging of surface profiles is critical for the investigation of various structures and mechanical dynamics of micro- and nano-scale devices. In particular, recent emergence of various nonlinear, transient and complex mechanical dynamics, such as anharmonic vibrations in mechanical resonators, has necessitated real-time surface deformation imaging with higher axial and lateral resolutions, speed, and dynamic range. However, real-time capturing of fast and complex mechanical dynamics has been challenging, and direct time-domain imaging of displacements and mechanical motions has been a missing element in studying full-field structural and dynamic behaviours. Here, by exploiting the electro-optic sampling with a frequency comb, we demonstrate a line-scan time-of-flight (TOF) camera that can simultaneously measure the TOF changes of more than 1000 spatial coordinates with hundreds megapixels/s pixel-rate and sub-nanometre axial resolution over several millimetres field-of-view. This unique combination of performances enables fast and precise imaging of both complex structures and dynamics in three-dimensional devices and mechanical resonators.

Nanomechanical Sensing Using Heater-Integrated Fluidic Resonators.

Micro/nanochannel resonators have been used to measure cells, suspended nanoparticles, or liquids, primarily at or near room temperature while their high temperature operation can offer promising applications such as calorimetric measurements and thermogravimetric analysis. To date, global electrothermal or local photothermal heating mechanisms have been attempted for channel resonators, but both approaches are intrinsically limited by a narrow temperature modulation range, slow heating/cooling, less quantitative heating, or time-consuming optical alignment. Here, we introduce heater-integrated fluidic resonators (HFRs) that enable fast, quantitative, alignment-free, and wide-range temperature modulation and simultaneously offer resistive thermometry and resonant densitometry. HFRs with or without a dispensing nozzle are fabricated, thoroughly characterized, and used for high throughput thermophysical properties measurements, microchannel boiling studies, and atomized spray dispensing. The HFR, without a doubt, opens a new avenue for nanoscale thermal analysis and processing and further encourages the integration of additional functions into channel resonators.

Correction to: Cellular and biomolecular detection based on suspended microchannel resonators.

[This corrects the article DOI: 10.1007/s13534-021-00207-7.].

PCA-based sub-surface structure and defect analysis for germanium-on-nothing using nanoscale surface topography.

Empty space in germanium (ESG) or germanium-on-nothing (GON) are unique self-assembled germanium structures with multiscale cavities of various morphologies. Due to their simple fabrication process and high-quality crystallinity after self-assembly, they can be applied in various fields including micro-/nanoelectronics, optoelectronics, and precision sensors, to name a few. In contrast to their simple fabrication, inspection is intrinsically difficult due to buried structures. Today, ultrasonic atomic force microscopy and interferometry are some prevalent non-destructive 3-D imaging methods that are used to inspect the underlying ESG structures. However, these non-destructive characterization methods suffer from low throughput due to slow measurement speed and limited measurable thickness. To overcome these limitations, this work proposes a new methodology to construct a principal-component-analysis based database that correlates surface images with empirically determined sub-surface structures. Then, from this database, the morphology of buried sub-surface structure is determined only using surface topography. Since the acquisition rate of a single nanoscale surface micrograph is up to a few orders faster than a thorough 3-D sub-surface analysis, the proposed methodology benefits from improved throughput compared to current inspection methods. Also, an empirical destructive test essentially resolves the measurable thickness limitation. We also demonstrate the practicality of the proposed methodology by applying it to GON devices to selectively detect and quantitatively analyze surface defects. Compared to state-of-the-art deep learning-based defect detection schemes, our method is much effortlessly finetunable for specific applications. In terms of sub-surface analysis, this work proposes a fast, robust, and high-resolution methodology which could potentially replace the conventional exhaustive sub-surface inspection schemes.

Cellular and biomolecular detection based on suspended microchannel resonators.

Suspended microchannel resonators (SMRs) have been developed to measure the buoyant mass of single micro-/nanoparticles and cells suspended in a liquid. They have significantly improved the mass resolution with the aid of vacuum packaging and also increased measurement throughput by fast resonance frequency tracking while target objects travel through the microchannel without stopping or even slowing down. Since their invention, various biological applications have been enabled, including simultaneous measurements of cell growth and cell cycle progression, and measurements of disease associated physicochemical change, to name a few. Extension and advancement towards other promising applications with SMRs are continuously ongoing by adding multiple functionalities or incorporating other complementary analytical metrologies. In this paper, we will thoroughly review the development history, basic and advanced operations, and key applications of SMRs to introduce them to researchers working in biological and biomedical sciences who mostly rely on classical and conventional methodologies. We will also provide future perspectives and projections for SMR technologies.

Effect of seasonal succession of algal communities on fouling of MF membrane.

An emerging threat to membrane application is the seasonal proliferation of algae in water sources such as rivers, reservoirs and lakes. This study investigated the link between feed parameters and the membrane performance of a pilot-scale microfiltration (MF) plant for 7 months. The seasonal succession of algae in relation to temperature dynamics was monitored. Temperature-dependent seasonal patterns for algae species were observed. The water temperatures during the dominance of cyanobacteria, especially Microcystis, were relatively higher (over 25 °C) than those during the dominance of diatoms. Diatoms did not much affect membrane performance (less than 0.2 kgf/cm2), however, under the cyanobacterial dominance condition, especially Microcystis sp., transmembrane pressure (TMP) reached up to the limited level (0.4 kgf/cm2) within one month. Concurrently UV absorbance at 254 nm wavelength and dissolved organic carbon values increased significantly during the Microcystis bloom and the build-up rate of TMP increased up to 0.005 kgf/cm2/day. Membrane autopsy also showed that during the dominance of diatom, application of cleaning agents can fully remove foulants on the membrane surface. However, during the dominance of cyanobacteria, there is a lot of Al, Si and organic complex on the fouled membrane, indicating the formation of Al-organic complexes that contributed to the residual membrane fouling. It is suggested that the irrecoverable fouling layer still contained some Al, mostly in complex with organics. Thus, organic matter originated from cyanobacteria may cause a serious impact on membrane fouling by forming the complex with metal ions originated from coagulant.

Complex Exercise Improves Anti-Inflammatory and Anabolic Effects in Osteoarthritis-Induced Sarcopenia in Elderly Women.

We investigated the effects of a 15-week complex exercise program on osteoarthritis and sarcopenia by analyzing anabolic effects and the impact on the activities of daily living (ADLs). Nineteen women aged ≥60 years with sarcopenia (SEG, n = 9) or diagnosed with osteoarthritis with sarcopenia (OSEG, n = 10) were enrolled and underwent an exercise program. Insulin-like growth factor 1 (IGF-1), irisin, myostatin, interleukin-10 (IL-10), and tumor necrosis factor alpha (TNF-a) levels were analyzed pre- and post-intervention. Thigh cross-sectional area (TCSA) was measured pre- and post-intervention via computed tomography. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Short Physical Performance Battery (SPBB) were assessed pre- and post-interventions to assess ADL. There was a significant interaction effect between SEG and OSEG at the IGF-1 level post-intervention. Irisin increased and myostatin decreased post-intervention in both groups. IL-10 increased and TNF-α decreased post-intervention with a significant interaction effect in the OSEG group. TCSAs increased post-intervention in both groups. There was a significant interaction between the two groups. OSEG showed a greater WOMAC decrease and SPPB increase post-intervention, and there was a significant interaction effect. Combined exercise may be effective in improving biochemical factors, anabolic effects, and ADL in elderly women with osteoarthritis and sarcopenia.

Tailoring the Spectral Absorption Coefficient of aBlended Plasmonic Nanofluid Using a CustomizedGenetic Algorithm.

Recently, plasmonic nanofluids (i.e., a suspension of plasmonic nanoparticles in a base fluid) have been widely employed in direct-absorption solar collectors because the localized surface plasmon supported by plasmonic nanoparticles can greatly improve the direct solar thermal conversion performance. Considering that the surface plasmon resonance frequency of metallic nanoparticles, such as gold, silver, and aluminum, is usually located in the ultraviolet to visible range, the absorption coefficient of a plasmonic nanofluid must be spectrally tuned for full utilization of the solar radiation in a broad spectrum. In the present study, a modern design process in the form of a genetic algorithm (GA) is applied to the tailoring of the spectral absorption coefficient of a plasmonic nanofluid. To do this, the major components of a conventional GA, such as the gene description, fitness function for the evaluation, crossover, and mutation function, are modified to be suitable for the inverse problem of tailoring the spectral absorption coefficient of a plasmonic nanofluid. By applying the customized GA, we obtained an optimal combination for a blended nanofluid with the desired spectral distribution of the absorption coefficient, specifically a uniform distribution, solar-spectrum-like distribution, and a step-function-like distribution. The resulting absorption coefficient of the designed plasmonic nanofluid is in good agreement with the prescribed spectral distribution within about 10% to 20% of error when six types of nanoparticles are blended. Finally, we also investigate how the inhomogeneous broadening effect caused by the fabrication uncertainty of the nanoparticles changes their optimal combination.

Absorption characteristics of a metal-insulator-metal nanodisk for solar thermal applications.

Due to their ability to confine light in a sub-wavelength scale and achieve coherent absorption, plasmonic nanostructures have been intensively studied for solar energy harvesting. Although nanoparticles generating localized surface plasmon resonance (LSPR) have been thoroughly studied for application in a direct absorption solar collector (DASC), nanoparticles exciting magnetic polaritons (MP) for use in a DASC have not drawn much attention. In this work, we report a metal-insulator-metal (MIM) nanodisk that can excite MP peaks apart from the LSPR in the solar spectrum. It was found that the MIM nanodisk generates a broader and relatively more uniform absorption band compared to a pure metallic nanodisk. The MP peaks were also found to cause less significant scattering compared to those associated with the LSPR. We finally showed that the peaks induced by the MIM nanodisk are highly tunable by varying the particle dimensions, making the proposed MIM nanodisk a potential candidate for solar thermal applications.

Intense Pulsed Light-Treated Near-Field Electrospun Nanofiber on a Quartz Tuning Fork for Multimodal Gas Sensors.

Accurate and portable gas sensors are required for environmental monitoring, locating leakages, and detecting trace chemical vapors or gases. Although many sensors have been developed, few can rapidly and selectively detect parts per million (ppm) concentration changes. In this work, we fabricate multimodal gas sensors by depositing a single nanocomposite fiber between the prongs of a quartz tuning fork (QTF). The resulting sensors are portable and integrate multimodal approaches by applying both chemo-mechanical sensing for sensitivity and electrochemical sensing for selectivity. Near-field electrospinning (NFES) produces a flexible and semiconductive nanocomposite fiber with ∼500 nm diameter that can be integrated into electronic systems as environmental gas sensors. Intense pulsed light (IPL) and sputter coating improve adhesion of the nanocomposite fiber onto a QTF. Furthermore, IPL offers improved sensing performance due to the higher specific surface area and reduction in polymer content. In this study, hydrogen gas (H2) is chosen as a target gas since it is a common energy source in fuel cell applications and byproduct in chemical reactions. An electrospinning solution containing polyaniline, multiwalled carbon nanotubes, and platinum nanoparticles is used to test H2 gas sensing performance. The resulting multimodal sensors are selective to hydrogen versus other gases and vapors including methane, hexane, toluene, ammonia, ethanol, carbon dioxide, and oxygen. Furthermore, the sensors detect ppm levels of hydrogen gas even in the presence of high humidity that typically hinders gas sensor performance. The development of this sensor leads to a new method for compact and portable multimodal gas sensing.

Micropipette Resonator Enabling Targeted Aspiration and Mass Measurement of Single Particles and Cells.

This paper reports micropipette resonators, mechanical resonator-integrated micropipettes, which enable selective aspiration and mass measurement of particles or cells suspended in liquids with two orthogonal vibration modes. A custom pipette pulling system is built to provide power-modulated linear heating on a rotating glass capillary to make an asymmetric cross section with extended uniformity.A glass capillary is stretched with the custom puller, cut within the pulled region, polished, mounted on a machined metallic jig, and then coated with a metal. As a result, a doubly clamped tube resonator-integrated micropipette is made. For simultaneous frequency readouts of two orthogonal modes, an optical pickup, originally developed for optical data storage, is configured closely above and properly aligned to the micropipette resonator and two digital phase-locked loops are employed. For mass responsivity calibration, frequency shifts of the micropipette resonator are measured with various liquids and glass microparticles. Buoyant masses of unicellular organisms, Paramecium aurelia, freely swimming in a culture dish are successfully measured with two orthogonal modes.

Design of a Broadband Solar Thermal Absorber Using a Deep Neural Network and Experimental Demonstration of Its Performance.

In using nanostructures to design solar thermal absorbers, computational methods, such as rigorous coupled-wave analysis and the finite-difference time-domain method, are often employed to simulate light-structure interactions in the solar spectrum. However, those methods require heavy computational resources and CPU time. In this study, using a state-of-the-art modeling technique, i.e., deep learning, we demonstrate significant reduction of computational costs during the optimization processes. To minimize the number of samples obtained by actual simulation, only regulated amounts are prepared and used as a data set to train the deep neural network (DNN) model. Convergence of the constructed DNN model is carefully examined. Moreover, several analyses utilizing an evolutionary algorithm, which require a remarkable number of performance calculations, are performed using the trained DNN model. We show that deep learning effectively reduces the actual simulation counts compared to the case of a design process without a neural network model. Finally, the proposed solar thermal absorber is fabricated and its absorption performance is characterized.

Soft and Deformable Sensors Based on Liquid Metals.

Liquid metals are one of the most interesting and promising materials due to their electrical, fluidic, and thermophysical properties. With the aid of their exceptional deformable natures, liquid metals are now considered to be electrically conductive materials for sensors and actuators, major constituent transducers in soft robotics, that can experience and withstand significant levels of mechanical deformation. For the upcoming era of wearable electronics and soft robotics, we would like to offer an up-to-date overview of liquid metal-based soft (thus significantly deformable) sensors mainly but not limited to researchers in relevant fields. This paper will thoroughly highlight and critically review recent literature on design, fabrication, characterization, and application of liquid metal devices and suggest scientific and engineering routes towards liquid metal sensing devices of tomorrow.

Optical Detection of Small Metabolites for Biological Gas Conversion by using Metal Nanoparticle Monolayers Produced by Capillary-Assisted Transfer.

Detection of small metabolites is essential for monitoring and optimizing biological gas conversion. Currently, such detection is typically done by liquid chromatography with offline sampling. However, this method often requires large equipment with multiple separation columns and is at risk of serious microbial contamination during sampling. Here we propose real-time optical detection of small metabolites using uniform plasmonic nanoparticles monolayers produced by capillary-assisted transfer. We reproducibly fabricate metal nanoparticles monolayers with a diameter of ∼1 mm for the detection of acetate, butyrate, and glucose by a glass capillary tube. Metal nanoparticles monolayers are not only uniform in terms of average interparticle distance but also structurally stable under dynamic fluidic conditions. The monolayers resistant to fluid shear stress with surface-enhanced Raman scattering are able to reversibly monitor the concentration of acetate and sensitively detect acetate and glucose at levels as low as 10 µM, which is more than 2 orders of magnitude lower than the concentration range of typical biological gas conversion. In addition, structurally similar metabolites such as acetate and butyrate, when mixed, become distinguishable by our method.

Super-contrast-enhanced darkfield imaging of nano objects through null ellipsometry.

We rediscover the null ellipsometry principle for an outstanding image-contrast enhancement method for darkfield imaging. Simply by adding polarizers, compensators, and a photodiode sensor to a conventional darkfield imaging system and applying the null principle, Si nano-cylinder structures as small as D20 nm (H20 nm) on non-patterned wafer, and gap defects as small as 14.6 nm and bridge defects as small as 21.9 nm on 40 nm line and 40 nm space patterns (H40 nm), which are invisible in conventional darkfield imaging, can be distinguished from scattered noise. To the best of our knowledge, no method has been successful for identifying such small non-metal (silicon) nanoscale objects with such low magnification (×20) optics.

Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS2 multilayers.

The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting 1-3 . A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification 2 . Here, we show that continuous direct-current (d.c.) with a maximum density of 106 A m-2 can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS2). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (105-106 V m-2) at the conductive nanoscale tip 4 . We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.

Electrophoresis assisted time-of-flow mass spectrometry using hollow nanomechanical resonators.

This report discusses the first demonstration of electrophoresis assisted time-of-flow mass spectrometry using 'U' shaped hollow nanomechanical resonators (HNR). Capillary electrophoresis was coupled with the HNR based mass detection to overcome low ionic conductivity of channels embedded in the HNR preventing direct in-situ electrophoretic separation. The flow of analytes through the HNR was achieved by balancing the hydrodynamic pressure to override the electromotive force and inhibit the motion of analytes towards the anode for capillary electrophoresis. The resonance frequency shifts of the HNR vibrating around 1.5 MHz were correlated with the time of the passage of the protein bands to construct the mass spectrum. The proposed concept was demonstrated by constructing a mass spectrum of egg white proteins in the molecular weight range of 14-250 kDa. When compared to regular polyacrylamide gel electrophoresis, our method not only provides a precise and fast readout but also avoids the use of chemical staining. This study paves a new route for low-cost and on-chip mass spectrometers with ultra-miniaturized dimensions.

Increase in brain activation due to sub-tasks during driving: fMRI study using new MR-compatible driving simulator.

BACKGROUND: Several studies have used functional magnetic resonance imaging (fMRI) to show that neural activity is associated with driving. fMRI studies have also elucidated the brain responses associated with driving while performing sub-tasks. It is important to note that these studies used computer mouses, trackballs, or joysticks to simulate driving and, thus, were not comparable to real driving situations. In order to overcome these limitations, we used a driving wheel and pedal equipped with an MR-compatible driving simulator (80 km/h). The subjects drove while performing sub-tasks, and we attempted to observe differences in neuronal activation. METHODS: The experiments consisted of three blocks and each block consisted of both a control phase (1 min) and a driving phase (2 min). During the control phase, the drivers were instructed to look at the stop screen and to not perform driving tasks. During the driving phase, the drivers either drove (driving only condition) or drove while performing an additional sub-task (driving with sub-task condition) at 80 km/h. RESULTS: Compared to when the drivers were focused only on driving, when the drivers drove while performing a sub-task, the number of activation voxels greatly decreased in the parietal area, which is responsible for spatial perception. Task-performing areas, such as the inferior frontal gyrus and the superior temporal gyrus, showed increased activation. Performing a sub-task simultaneously while driving had affected the driver's driving. The cingulate gyrus and the sub-lobar region (lentiform nucleus, caudate, insula, and thalamus), which are responsible for error monitoring and control of unnecessary movements (e.g., wheel and pedal movements), showed increased activation during driving with sub-task condition compared to driving only condition. CONCLUSIONS: Unlike simple driving simulators (joysticks, computer mouses, or trackballs) used in previous research, the addition of a driving wheel and pedals (accelerator and brake) to the driving simulator used in this study closely represents real driving. Thus, the number of processed movements was increased, which led to an increased number of unnecessary movements that needed to be controlled. This in turn increased activation in the corresponding brain regions.

Pulled microcapillary tube resonators with electrical readout for mass sensing applications.

This paper reports a microfabrication-free approach to make hollow channel mass sensors by pulling a glass capillary and suspending it on top of a machined jig. A part of the pulled section makes simple contact with an actuation node and a quartz tuning fork (QTF) which acts as a sensing node. The two nodes define a pulled micro capillary tube resonator (PµTR) simply supported at two contacts. While a piezo actuator beneath the actuation node excites the PµTR, the QTF senses the resonance frequency of the PµTR. The proposed concept was validated by electrical and optical measurements of resonant spectra of PµTR. Then, different liquid samples including water, ethanol, glycerol, and their binary mixtures were introduced into the PµTR and the resonance frequency of the PµTR was measured as a function of liquid density. Density responsivity of -3,088 Hz-g-1 cm3 obtained is comparable to those of microfabricated hollow resonators. With a micro droplet generation chip configured in series with the PµTR, size distribution of oil droplets suspended in water was successfully measured with the radius resolution of 31 nm at the average droplet radius, 28.47 µm. Overall, typical off-the-shelf parts simply constitute a resonant mass sensing system along with a convenient electrical readout.