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Solar panels often suffer from dust accumulation, significantly reducing their output, especially in desert regions where many of the world's largest solar plants are located. Here, an autonomous dust removal system for solar panels, powered by a wind-driven rotary electret generator is proposed. The generator applies a high voltage between one solar panel's output electrode and an upper mesh electrode to generate a strong electrostatic field. It is discovered that dust particles on the insulative glass cover of the panel can be charged under the high electrical field, assisted by adsorbed water, even in low-humidity environments. The charged particles are subsequently repelled from the solar panel with the significant Coulomb force. Two panels covered with sand dust are cleaned in only 6.6 min by a 15 cm diameter rotary electret generator at 1.6 m s-1 wind speed. Experimental results manifest that the system can work effectively in a wide range of environmental conditions, and doesn't impact the panel performance for long-term operation. This autonomous system, with its high dust removal efficiency, simplicity, and low cost, holds great potential in practical applications.

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Electrostatic generators show great potential for powering widely distributed electronic devices in Internet of Things (IoT) applications. However, a critical issue limiting such generators is their high impedance mismatch when coupled to electronics, which results in very low energy utilization efficiency. Here, we present a high-performance energy management unit (EMU) based on a spark-switch tube and a buck converter with an RF inductor. By optimizing the elements and parameters of the EMU, a maximum direct current output power of 79.2 mW m-2 rps-1 was reached for a rotary electret generator with the EMU, achieving 1.2 times greater power output than without the EMU. Furthermore, the maximum power of the contact-separated triboelectric nanogenerator with an EMU is 1.5 times that without the EMU. This excellent performance is attributed to the various optimizations, including utilizing an ultralow-loss spark-switch tube with a proper breakdown voltage, adding a matched input capacitor to enhance available charge, and incorporating an RF inductor to facilitate the high-speed energy transfer process. Based on this extremely efficient EMU, a compact self-powered wireless temperature sensor node was demonstrated to acquire and transmit data every 3.5 s under a slight wind speed of 0.5 m/s. This work greatly promotes the utilization of electrostatic nanogenerators in practical applications, particularly in IoT nodes.

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Monitoring the force of fingertip manipulation without disturbing the natural sense of touch is crucial for digitizing the skills of experienced craftsmen. However, conventional force sensors need to be put between the skin and the objects, which affects the natural sense of the skin. Here, we proposed a fingertip force sensing method based on changes of blood volume and designed a wearable photoelectric fingertip force sensing system (PFFS) for digitalization of traditional Chinese medicine (TCM) pulse diagnosis. The PFFS does not interfere with the fingertips' tactile sense while detecting fingertip force. This PFFS detects the change of blood volume in fingertip by photoelectric plethysmography and can obtain the change of output current under different fingertip forces. We also studied the effect of various factors on PFFS output signals, including emission lights of different wavelengths, ambient temperature, and the user's heartbeat artifact. We further established the relationship between the change of blood volume and fingertip force by combining experimental and theoretical methods. Moreover, we demonstrated the feasibility of the PFFS to detect fingertip forces under commonly used conditions in TCM pulse diagnosis without sensory interference. This PFFS also shows promise for perceiving the viscosity of objects and recognizing gestures in human-computer interaction. This work paves the way for the digitalization of fingertip forces during TCM pulse diagnosis and other fingertip forces under natural conditions.

Asunto(s)

Dedos , Dispositivos Electrónicos Vestibles , Humanos , Tacto , Fenómenos Mecánicos , Volumen Sanguíneo

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There is a growing but unmet need for point-of-care detection of prostate-specific antigen (PSA) in body fluid which may facilitate early diagnosis and therapy of prostate cancer in a cost-effective and user-friendly way. Low sensitivity and narrow detection range limits applications of point-of-care testing in practice. Here, an immunosensor is first presented based on shrink polymer and integrated into a miniaturized electrochemical platform for detecting PSA in clinical samples. The sensing electrode was prepared by sputtering a gold film on shrink polymer, followed by heating to shrink the electrode to a small size with wrinkles from nano-scale to micro-scale. These wrinkles can be directly regulated by the thickness of the gold film with high specific areas for enhancement of antigen-antibody binding (3.9 times). A distinct difference between electrochemical active surface area (EASA) and response to PSA of shrink electrodes was observed and discussed. The electrode was treated with air plasma and modified with self-assembled graphene to further enhance the sensor's sensitivity (10.4 times). The shrink sensor with gold 200 nm thick integrated into the portable system was validated by a label-free immunoassay for detection of PSA in 20 µL serum within 35 mins. It exhibited a limit of detection of 0.38 fg/mL, the lowest among label-free PSA sensors, and a wide linear response from 10 fg/mL to 1000 ng/mL. Moreover, the sensor demonstrated reliable assay results in clinical serums, comparable to the commercial chemiluminescence instrument, confirming its feasibility for clinical diagnosis.

Asunto(s)

Técnicas Biosensibles , Nanopartículas del Metal , Masculino , Humanos , Antígeno Prostático Específico , Polímeros , Sistemas de Atención de Punto , Técnicas Biosensibles/métodos , Inmunoensayo/métodos , Electrodos , Oro , Técnicas Electroquímicas/métodos , Límite de Detección

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Traditional lithography plays a significant role in the fabrication of micro- and nanostructures. Nevertheless, the fabrication process still suffers from the limitations of manufacturing devices with a high aspect ratio or three-dimensional structure. Recent findings have revealed that shrink polymers attain a certain potential in micro- and nanostructure manufacturing. This technique, denoted as heat-induced shrink lithography, exhibits inherent merits, including an improved fabrication resolution by shrinking, controllable shrinkage behavior, and surface wrinkles, and an efficient fabrication process. These merits unfold new avenues, compensating for the shortcomings of traditional technologies. Manufacturing using shrink polymers is investigated in regard to its mechanism and applications. This review classifies typical applications of shrink polymers in micro- and nanostructures into the size-contraction feature and surface wrinkles. Additionally, corresponding shrinkage mechanisms and models for shrinkage, and wrinkle parameter control are examined. Regarding the size-contraction feature, this paper summarizes the progress on high-aspect-ratio devices, microchannels, self-folding structures, optical antenna arrays, and nanowires. Regarding surface wrinkles, this paper evaluates the development of wearable sensors, electrochemical sensors, energy-conversion technology, cell-alignment structures, and antibacterial surfaces. Finally, the limitations and prospects of shrink lithography are analyzed.

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Electrostatic generators as a kind of effective energy harvesters have attracted intensive attention. However, the output of the generators is highly dependent on the charge density. Here, we demonstrate an all-in-one rotary electrostatic nanogenerator based on the charge pumping and voltage multiplying strategy (CV-ESG), which achieves high output power in SF6 atmosphere. CV-ESG integrates a pumping electret generator, a main generator, and a voltage multiplying and stabilization circuit on a pair of rotator and stator. We analyze the breakdown effect and its influence on the insulating layer covered on the electrodes through experiments. The breakdown voltage is high in SF6 atmosphere, and the maximum average power of CV-ESG in SF6 is 37.29 mW at 750 rpm, which is 3.29 times that in air. There is no surface friction in CV-ESG, which avoids abrasion and reduces friction damping. And the pumping generator is integrated with the main generator, making CV-ESG compact and easy to assemble. This work provides the design strategy for a high-power rotary electrostatic generator with good performance.

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Early cancer diagnosis and treatment are crucial research fields of human health. One method that has proven efficient is biomarker detection which can provide real-time and accurate biological information for early diagnosis. This review presents several biomarker sensors based on electrochemistry, surface plasmon resonance (SPR), nanowires, other nanostructures, and, most recently, metamaterials which have also shown their mechanisms and prospects in application in recent years. Compared with previous reviews, electrochemistry-based biomarker sensors have been classified into three strategies according to their optimizing methods in this review. This makes it more convenient for researchers to find a specific fabrication method to improve the performance of their sensors. Besides that, as microfabrication technologies have improved and novel materials are explored, some novel biomarker sensors-such as nanowire-based and metamaterial-based biomarker sensors-have also been investigated and summarized in this review, which can exhibit ultrahigh resolution, sensitivity, and limit of detection (LoD) in a more complex detection environment. The purpose of this review is to understand the present by reviewing the past. Researchers can break through bottlenecks of existing biomarker sensors by reviewing previous works and finally meet the various complex detection needs for the early diagnosis of human cancer.

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Immunoagglutination assay is a promising approach for the detection of waterborne analytes like virus, cells, proteins with its advantages such as a smaller amount of reagents and easier operation. This paper presents a microfluidic agglutination assay on which all the assay processes including analyte capture, agglutination, and detection are performed. The chip integrates an on-chip pump for sample loading, a dynamic magnetic bead (MB) clump for analyte capture and agglutination, and a sheath-less flow cytometry for particle detection, sizing, and counting. The chip is tested with streptavidin-coated MBs and biotinylated bovine serum albumin as a model assay, which realizes a limit of detection (LOD) of 1 pM. Then, an antigen/antibody assay using rabbit IgG and goat anti-rabbit IgG coated MBs is tested and a LOD of 5.5 pM is achieved. At last, human ferritin in 10% fetal bovine serum is tested with Ab-functionalized MBs and the detection achieves a LOD of 8.5 pM. The whole procedure takes only 10 min in total.

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In this study, multi-functional nanocomposites with excellent mechanical, electrical and thermal properties were prepared through metal-ion coordination. Reduced graphene oxide (rGO) and hexagonal boron nitride (h-BN) interacted through calcium coordination bonding. Poly(ethylene oxide) (PEO) was added to bridge these two nanomaterials, providing more resistance to tensile deformation. The results of UV-Vis and FTIR spectra proved that coordination bonding was successfully formed among the three compounds. SEM images showed homogenous dispersions of the nanocomposite. After calcium-ion coordination, the mechanical, electrical and thermal properties of Ca2+-coordinated rGO/BN/PEO composite improved significantly, indicating that metal-ion coordination is a potential method for multi-functional nanocomposite fabrication.

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Cell disruption plays a vital role in detection of intracellular components which contain information about genetic and disease characteristics. In this paper, we demonstrate a novel microfluidic platform based on an on-chip micropump for mechanical cell disruption and sample transport. A 50 µl cell sample can be effectively lysed through on-chip multi-disruption in 36 s without introducing any chemical agent and suffering from clogging by cellular debris. After 30 cycles of circulating disruption, 80.6% and 90.5% cell disruption rates were achieved for the HEK293 cell sample and human natural killer cell sample, respectively. Profiting from the feature of pump-on-chip, the highly integrated platform enables more convenient and cost-effective cell disruption for the analysis of intracellular components.

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Single cell analysis has received increasing attention recently in both academia and clinics, and there is an urgent need for effective upstream cell sample preparation. Two extremely challenging tasks in cell sample preparation-high-efficiency cell enrichment and precise single cell capture-have now entered into an era full of exciting technological advances, which are mostly enabled by microfluidics. In this review, we summarize the category of technologies that provide new solutions and creative insights into the two tasks of cell manipulation, with a focus on the latest development in the recent five years by highlighting the representative works. By doing so, we aim both to outline the framework and to showcase example applications of each task. In most cases for cell enrichment, we take circulating tumor cells (CTCs) as the target cells because of their research and clinical importance in cancer. For single cell capture, we review related technologies for many kinds of target cells because the technologies are supposed to be more universal to all cells rather than CTCs. Most of the mentioned technologies can be used for both cell enrichment and precise single cell capture. Each technology has its own advantages and specific challenges, which provide opportunities for researchers in their own area. Overall, these technologies have shown great promise and now evolve into real clinical applications.

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To obtain 2D materials with large quantity, low cost, and little pollution, liquid-phase exfoliation of their bulk form in water is a particularly fascinating concept. However, the current strategies for water-borne exfoliation exclusively employ stabilizers, such as surfactants, polymers, or inorganic salts, to minimize the extremely high surface energy of these nanosheets and stabilize them by steric repulsion. It is worth noting, however, that the remaining impurities inevitably bring about adverse effects to the ultimate performances of 2D materials. Here, a facile and green route to large-scale production of impurity-free aqueous solutions of WS2 nanosheets is reported by direct exfoliation in water. Crucial parameters such as initial concentration, sonication time, centrifugation speed, and centrifugation time are systematically evaluated to screen out an optimized condition for scaling up. Statistics based on morphological characterization prove that substantial fraction (66%) of the obtained WS2 nanosheets are one to five layers. X-ray diffraction and Raman characterizations reveal a high quality with few, if any, structural distortions. The water-borne exfoliation route opens up new opportunities for easy, clean processing of WS2 -based film devices that may shine in the fields of, e.g., energy storage and functional nanocomposites owing to their excellent electrochemical, mechanical, and thermal properties.

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Microfiltration is a compelling method to separate particles based on their distinct size and deformability. However, this approach is prone to clogging after processing a certain number of particles and forming bubbles in the separation procedure, which often leads to malfunctioning of devices. In this work, we report a bubble-free and clogging-free microfluidic particle separation platform with high throughput. The platform features an integrated bidirectional micropump, a hydrophilic microporous filtration membrane and a hydrophobic porous degassing membrane. The bidirectional micropump enables the fluid to flow back and forth repeatedly, which flushes the filtration membrane and clears the filtration micropores for further filtration, and to flow forward to implement multi-filtration. The hydrophobic porous membrane on top of the separation channel removes air bubbles forming in the separation channel, improving the separation efficiency and operational reliability. The microbead mixture and undiluted whole blood were separated using the microfluidic chip. After 5 cycles of reverse flushing and forward re-filtration, a 2857-fold enrichment ratio and an 89.8% recovery rate of 10 µm microbeads were achieved for microbead separation with 99.9% removal efficiency of 2 µm microbeads. After 8 cycles, white blood cells were effectively separated from whole blood with a 396-fold enrichment ratio and a 70.6% recovery rate at a throughput of 39.1 µl min-1, demonstrating that the platform can potentially be used in biomedical applications.

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We report the aluminothermic reduction enabled synthesis of silicon hollow microspheres from commercialized silica nanoparticles by controlled transformation and organization. The synergistically integrated merits of a simple process and delicate structural design lay a basis for developing an industrially viable silicon anode with optimized electrochemical performances.

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Uncooled infrared (IR) focal-plane-array (FPA) with both large sensing range and high sensitivity is a great challenge due to the limited dynamic range of the detected signals. A coaxial dual-wavelength interferometric system was proposed here to detect thermal-induced displacements of an ultrasensitive FPA based on polyvinyl-chloride(PVC)/gold bimorph cantilevers and carbon nanotube (CNT)-based IR absorbing films. By alternately selecting the two displacement measurements performed by λ1 (=640 nm) and λ2 (=660 nm), the temperature measuring range with greater than 50% maximum sensitivity can be extended by eight-fold in comparison with the traditional single-wavelength mode. Meanwhile, the relative measurement error over the full measuring range is below 0.4%. In addition, it offers a feasible approach for on-line and on-wafer FPA characterization with great convenience and high efficiency.

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Developing an industrially viable silicon anode, featured by the highest theoretical capacity (4200 mA h g(-1)) among common electrode materials, is still a huge challenge because of its large volume expansion during repeated lithiation-delithiation as well as low intrinsic conductivity. Here, we expect to address these inherent deficiencies simultaneously with an interesting hybridization design. A facile self-assembly approach is proposed to decorate silicon hollow nanospheres with SnO2 nanowires. The two building blocks, hand in hand, play a wonderful duet by bridging their appealing functionalities in a complementary way: (1) The silicon hollow nanospheres, in addition to the major role as a superior capacity contributor, also act as a host material (core) to partially accommodate the volume expansion, thus alleviating the capacity fading by providing abundant hollow interiors, void spaces, and surface areas. (2) The SnO2 nanowires serve as a conductive coating (shell) to enable efficient electron transport due to a relatively high conductivity, thereby improving the cyclability of silicon. Compared to other conductive dopants, the SnO2 nanowires with a high theoretical capacity (790 mA h g(-1)) can contribute outstanding electrochemical reaction kinetics, further adding value to the ultimate electrochemical performances. The resulting novel Si@SnO2 core-shell heterostructures exhibit remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1869 mA h g(-1)@500 mA g(-1) after 100 charging-discharging cycles.

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Rapid separation of white blood cells from whole blood sample is often required for their subsequent analyses of functions and phenotypes, and many advances have been made in this field. However, most current microfiltration-based cell separation microfluidic chips still suffer from low-throughput and membrane clogging. This paper reports on a high-throughput and clogging-free microfluidic filtration platform, which features with an integrated bidirectional micropump and commercially available polycarbonate microporous membranes. The integrated bidirectional micropump enables the fluid to flush micropores back and forth, effectively avoiding membrane clogging. The microporous membrane allows red blood cells passing through high-density pores in a cross-flow mixed with dead-end filtration mode. All the separation processes, including blood and buffer loading, separation, and sample collection, are automatically controlled for easy operation and high throughput. Both microbead mixture and undiluted whole blood sample are separated by the platform effectively. In particular, for white blood cell separation, the chip recovered 72.1% white blood cells with an over 232-fold enrichment ratio at a throughput as high as 37.5 µl/min. This high-throughput, clogging-free, and highly integrated platform holds great promise for point-of-care blood pretreatment, analysis, and diagnosis applications.

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h-BN, as an isoelectronic analogue of graphene, has improved thermal mechanical properties. Moreover, the liquid-phase production of h-BN is greener since harmful oxidants/reductants are unnecessary. Here we report a novel hybrid architecture by employing h-BN nanosheets as 2D substrates to load 0D Fe3O4 nanoparticles, followed by phenol/formol carbonization to form a carbon coating. The resulting carbon-encapsulated h-BN@Fe3O4 hybrid architecture exhibits synergistic interactions: 1) The h-BN nanosheets act as flexible 2D substrates to accommodate the volume change of the Fe3O4 nanoparticles; 2) The Fe3O4 nanoparticles serve as active materials to contribute to a high specific capacity; and 3) The carbon coating not only protects the hybrid architecture from deformation but also keeps the whole electrode highly conductive. The synergistic interactions translate into significantly enhanced electrochemical performances, laying a basis for the development of superior hybrid anode materials.

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Homogeneous assays possess important advantages that no washing or physical separation is required, contributing to robust protocols and easy implementation which ensures potential point-of-care applications. Optimizing the detection strategy to reduce the number of reagents used and simplify the detection device is desirable. A method of homogeneous bead-agglutination assay based on micro-chip sheathless flow cytometry has been developed. The detection processes include mixing the capture-probe conjugated beads with an analyte containing sample, followed by flowing the reaction mixtures through the micro-chip sheathless flow cytometric device. The analyte concentrations were detected by counting the proportion of monomers in the reaction mixtures. Streptavidin-coated magnetic beads and biotinylated bovine serum albumin (bBSA) were used as a model system to verify the method, and detection limits of 0.15 pM and 1.5 pM for bBSA were achieved, using commercial Calibur and the developed micro-chip sheathless flow cytometric device, respectively. The setup of the micro-chip sheathless flow cytometric device is significantly simple; meanwhile, the system maintains relatively high sensitivity, which mainly benefits from the application of forward scattering to distinguish aggregates from monomers. The micro-chip sheathless flow cytometric device for bead agglutination detection provides us with a promising method for versatile immunoassays on microfluidic platforms.

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Due to the diversity of carbon nanotubes (CNTs), polymers, and the preparation processes of the composites, CNT-filled polymeric composites present various piezoresistive properties. One puzzling issue is the concurrence of a negative piezoresistive effect and a positive piezoresistive effect in composites with different polymer matrixes. In this paper, we present a microscopic view of the nature of the positive piezoresistive effect and its dependence on the polymer matrix types based on the model in our previous study, in which the piezoresistive behavior was tailored by a parameter-the average junction gap variation (AJGV)-describing the statistical property of the CNT conductive network. The microscopic movement process of CNTs embedded in a polymer matrix was analyzed and then the Poisson's ratio of the polymer matrix was determined as a key factor that is in charge of negative or positive piezoresistive properties. The obstacle effect of polymer chains on the movement of CNTs was also found to be responsible for the positive piezoresistive effect as it affects the AJGV in compressive strain. Based on numerical simulations of CNT network deformation with different Poisson's ratios and minimum junction gaps caused by the obstacle effect, the positive piezoresistive effect was found resulted from the obstacle effect on CNT junction gap variations that exceeds the initial value of the AJGV caused by the CNT network deformation, and only occur under the precondition of the polymer matrixes with a large Poisson's ratio close to 0.5. The conclusions were then verified experimentally using composites with two kinds of polymer matrixes with significantly different Poisson's ratios.