Micro and Nano Systems Letters最新文献

For more than five decades, vibrating tube resonators have evolved from fragile laboratory devices into versatile platforms used in industrial metrology, biomedical research, and education. This technology originated with glass U-tube densitometers, which established the foundation for resonance-based density measurements. Later, metallic tubes extended operation to harsh conditions, including high pressure, elevated temperature, and cryogenic environments, enabling applications ranging from supercritical fluid studies to aerospace propulsion. The vibrating tube principle also inspired Coriolis flowmeters, which can monitor both density and mass flow. Miniaturization through microelectromechanical systems (MEMS) has led to microchannel resonators that can weigh biomolecules, nanoparticles, and cells with high sensitivity. Subsequent innovations improved readout using piezoresistive and piezoelectric schemes, increased throughput with array architectures, and integrated heaters for thermal property measurements. More recent advances include integrating capacitive electrodes, enabling access to electrical and dielectric properties of liquids. Meanwhile, renewed interest in glass and metallic tube resonators has highlighted their robustness, scalability, and utility for handling larger biological entities and for educational purposes. Macro- and micro-scale approaches complement each other, ensuring continuity across scales and pointing toward future integration with optical, magnetic, and quantum modalities.

Nanofillers are one of the most important additives in the creation of natural fibre reinforced polymer composite (NFRPC), as they greatly improve the properties of the material even at low doses. Such Nanofillers enhance the bonding of fibers and matrix that result in an increase of the mechanical and functional properties of composite. Clays, nanomaterials of carbon, metal and metal oxide nanoparticles, cellulose nanocrystals are some of the most prevalent Nano fillers. NFRPC, with the current advantages of low cost, renewability, biodegradability, and desirable specific properties, have taken off as an alternative to synthetic composites in biomedical applications. Although such composites present the advantage of desirable mechanical strength, thermal stability, and acoustic performance, the addition of Nanofillers enhances the performance further by increasing structure-property associations and processing. Also, Nano filler-enhanced composites have a promising biomedical future, especially when used in tissue engineering, wound healing, antimicrobial systems, and load bearing implants. The review is a compilation of recent developments of natural and synthetic nano filler applications in combination of natural fibers and is therefore a complete reference to any researcher or scientist who will be interested in designing high-performance composites by the synergistic combination of fibers, polymer matrices, and Nanofillers.

Flexible piezoresistive pressure sensors have emerged as vital components for wearable electronics, soft robotics, and biomedical monitoring. However, simultaneously achieving high sensitivity, a wide detection range, and long-term durability for these sensors remains challenging. Among the various approaches, freeze-casted aerogel-based sensors have garnered significant attention owing to their exceptional properties, such as ultralow density, high porosity, and customizable microstructures. This review summarizes the recent advances in such sensors, with emphasis on material selection, structural design, and practical applications. The integration of one-dimensional, two-dimensional, and hybrid nanomaterials offers synergistic enhancements in electrical conductivity, mechanical robustness, and sensing performance. Advanced structural engineering strategies, including anisotropic pore alignment, gradient architecture, and biomimetic designs, have enabled improved sensitivity, a broader detection range, and enhanced durability. Representative applications in real-time physiological monitoring and human–machine interfaces demonstrate the potential of these sensors in real-world scenarios. This review provides insight into rational design strategies that harness both materials and architecture to improve the performance and applicability of next-generation aerogel-based pressure sensors.

Hydrogel-based strain sensors are highly promising for wearable electronics; however, their practical application is often limited by their low sensitivity and tendency to dehydrate. This paper reports on the development of a high-performance strain sensor that addresses these limitations simultaneously through a synergistic material and structural design. A conductive hydrogel composed of a polyvinyl alcohol matrix, multiwalled carbon nanotube filler, and borax cross-linker is encapsulated using a simple and effective lamination process with a self-adhesive, transparent acrylic elastomer film. This facile encapsulation method provides a robust hermetic seal that ensures environmental stability without compromising device flexibility. The resulting device exhibits a remarkable gauge factor of approximately 172 in the high-strain regime (30–100%), negligible signal drift, and stable performance over prolonged cyclic loading. Furthermore, the encapsulated sensor maintains durability and reliable adhesion under humid or saline conditions, validating its suitability for wearable use. The combination of superior sensitivity, long-term stability, and a scalable, low-temperature fabrication process establishes this work as a practical route toward robust hydrogel-based sensors for soft robotics and human-motion monitoring.

This study presents the fabrication and characterization of a MEMS-based hot arm actuator that utilizes Joule heating-induced thermal expansion for lateral displacement. The actuator was fabricated through a series of micro-fabrication processes including photolithography, e-beam evaporation, and plasma ashing. Electro-thermal and electro-thermo-mechanical characteristics were experimentally analyzed and compared with finite element analysis (FEA) simulations. The actuator demonstrated fast thermal response (~100 μs), high repeatability, and effective displacement (> 10 μm) under low-voltage operation (< 0.6 V). These findings highlight its potential application in fast-switching optical MEMS systems.

Plasmonic bowtie nanostructures have been widely used to enhance electric fields by concentrating the electromagnetic field within nanoscale gaps. Various structural modifications of the bowtie geometry have been proposed to achieve stronger light confinement within the nanogaps. Among them, bowtie structures with curved arms have demonstrated a significantly higher enhancement factor (EF) compared to those with linear arms. However, although tip sharpness plays a critical role in electric field enhancement, the tip sharpness of the curved bowtie has not been systematically examined. In this study, we investigated the influence of tip sharpness on the EF of curved bowtie nanostructures using finite-difference time-domain (FDTD) simulations. We systematically optimized four structural parameters, including the tip sharpness and curvature of the side arms, and evaluated their impact on the resulting EF. The curved bowtie with sharp tips showed substantial increases in the EF (5.33 × 10³), which is approximately 26% higher than that of the normal bowtie with sharp tips (4.23 × 10³), whereas the bowtie with blunt tips exhibited an even lower EF than those with linear arms. These results highlight the critical role of the tip sharpness in achieving high-field enhancement. This study underscores the need for advanced nanofabrication techniques, such as domino lithography, to realize sharp tips, which are often limited by proximity effects in conventional photolithography and electron-beam lithography (EBL). Our findings provide valuable insight into the design of high-performance plasmonic nanostructures and pave the way for their practical applications in biosensing and nanophotonic technologies.

The evolution of human–machine interfaces (HMI) toward more immersive and intuitive forms, such as wearable devices and augmented reality systems, demands the development of high-performance flexible electronics. Heterogeneous integration, which combines diverse inorganic materials and functional devices onto unconventional substrates, is the core strategy for realizing these next-generation systems. The success of this approach, however, critically hinges on the ability to precisely transfer and assemble vast quantities of micro-scale components. This paper reviews the state-of-the-art in inorganic thin-film transfer technologies, which are the essential enablers for this paradigm shift. We systematically categorize and discuss the mechanisms, advantages, and drawbacks of three primary approaches: physical, chemical, and self-assembly transfer methods. Furthermore, we introduce recent applications of semiconductor devices developed via these techniques. The continued advancement of these transfer technologies is poised to catalyze transformative innovations in how users interact with the digital world, fundamentally reshaping applications in medicine, personal computing, and beyond.

The escalating global plastic production (~ 390 million tons in 2022) and subsequent environmental release of microplastics necessitate urgent advancements in real-time detection technologies. While optical methods (Raman spectroscopy, FTIR) dominate current microplastic analysis, their reliance on bulky instrumentation limits field applications. This study presents a portable surface acoustic wave (SAW) sensor system for real-time microplastic detection in beverages. A biocompatible aluminum interdigital transducer (IDT) array (40 pairs, 30 μm gap) was fabricated on piezoelectric substrates (InGaN and PMN-PT), with SU-8 passivation selectively exposing sensing regions to minimize liquid-phase interference. Material characterization confirmed substrate crystallinity and composition, revealing InGaN’s superior sensitivity, estimated to be ~ 0.168 MHz/(mg/mL) than the PMN-PT-based device. The integrated system employs an InGaN-based oscillator circuit resonating at 39.06 MHz, enabling standalone operation without external signal generators. A threshold-driven LED interface (red/green for ≥ / < 0.25 mg) provides intuitive readouts, while universal printed circuit board (PCB) integration ensures portability. This work demonstrates a scalable platform for on-site microplastic monitoring, addressing critical gaps in consumer safety and environmental health.

Wearable electrochemical biosensors based on solid-contact ion-selective electrodes (SC-ISEs) have emerged as a promising platform for non-invasive, real-time monitoring of sweat electrolytes. However, conventional ion-selective biosensors often suffer from potential drift and long-term instability due to the formation of undesired aqueous layers and interference from other ions. To overcome these challenges, we present a flexible and highly stable SC-ISE patch sensor for simultaneous detection of Na⁺ and K⁺ ions in sweat. The sensor employs a laser-induced graphene (LIG) electrode patterned directly onto a Ti₃C₂T_x -MXene/PVDF nanofiber mat, which was fabricated using electrospinning followed by CO₂ laser carbonization. The MPNFs/LIG@TiO₂ hybrid structure exhibits excellent electrical conductivity, high electrochemical surface area, and enhanced hydrophobicity, all contributing to reduced potential drift and improved signal stability.

Ion-selective membranes (ISMs) based on a PVC-SEBS blend were drop-cast onto the LIG electrode to achieve selective ion recognition, while a double-sided PET tape substrate ensured mechanical flexibility and skin conformity. The addition of TiO₂ nanoparticles during the thermal laser oxidation process induced π-π interactions within the composite, resulting in a robust 3D porous electrode architecture with enhanced ion transport and interfacial contact. The fabricated Na⁺ and K⁺ sensors demonstrated near-Nernstian sensitivities of 48.8 mV/decade and 50.5 mV/decade, respectively, within physiologically relevant sweat concentration ranges. Additionally, the sensors showed excellent long-term stability with minimal potential drift (0.04 mV/h for Na⁺ and 0.08 mV/h for K⁺), along with rapid response and high accuracy. The use of scalable, low-cost laser engraving and solution casting techniques enables reliable batch fabrication, making the proposed sensor patch a strong candidate for integration into wearable platforms aimed at continuous electrolyte monitoring during physical activity.

This study aims to develop and evaluate a wearable sensing and monitoring system for the diagnosis and therapy of obstructive sleep apnea (OSA), a disorder characterized by recurrent upper airway collapse during sleep that leads to sleep fragmentation and oxygen desaturation. The proposed system integrates multivariate biosensor modules—including flow, acceleration, temperature, humidity, and pH sensors—into an oral appliance designed to maintain the mandible in a forward position, thereby preventing airway collapse. A convolutional neural network was employed to analyze biosignals for detecting OSA-related events, bruxism, sleeping posture, and sleep patterns. In feasibility tests, the system accurately classified body postures, monitored heart rate variations, detected bruxism with up to 94% accuracy in non-bruxism segments and 89.47% in bruxism segments, and quantified sleep quality over extended monitoring periods. These results demonstrate that the proposed system offers a practical, non-invasive, and cost-effective alternative to conventional polysomnography or continuous positive airway pressure therapy, enabling continuous at-home screening and management of OSA, particularly in mild-to-moderate cases.