Micro and Nano Systems Letters最新文献

Hydrogen sulfide (H₂S) is a colorless, flammable, and highly toxic gas that underscores the need for cost-effective, energy-efficient, simple, convenient, and durable detection methods. Resistive gas sensors based on inorganic conductive materials and organic conductive polymers can effectively address these requirements. This review discusses the hazards of H₂S gas and reviews sensors capable of detecting H₂S at room temperature, including those based on metal oxides, MXene/carbon materials, and p-type conductive polymers. It explores the mechanisms behind their enhanced response at room temperature, such as utilizing special structures (e.g., porous/hollow nanospheres, nanowires, nanotubes, and nanocapsules) to increase the effective surface area of the sensing materials, employing metal particles sensitization to improve gas adsorption, and leveraging heterojunctions to amplify the response. Additionally, this review highlights the limitations of these sensors and provides insights for the further development of low-power resistive H₂S gas sensors.

Omnidirectional wind energy harvesting has gained increasing attention as a means of harnessing the inherently variable and multidirectional flows encountered in real-world environments. Triboelectric nanogenerators (TENGs), which leverage contact electrification and electrostatic induction to convert mechanical motion into electrical power, are particularly well-suited for such applications due to their ability to operate effectively under low-speed and intermittent wind conditions. In this review, we first outline the fundamental triboelectric processes and operating modes that underpin TENG functionality, emphasizing how their low inertia and high-voltage outputs make them compatible with a wide range of wind profiles. We then discuss three predominant device classifications—rotary, aeroelastic, and rolling-based—highlighting their distinct mechanical configurations and capacities for omnidirectional capture. Key examples illustrate how strategically designed rotor geometries, flutter-driven films, and rolling elements can maximize contact–separation events and enhance triboelectric generation under complex airflow patterns. Finally, we examine the major obstacles faced by TENG-based harvesters, including durability, hybrid system design, and intelligent power management. Strategies to overcome these barriers involve wear-resistant materials, adaptive architectures, and advanced circuitry, offering TENG solutions that are feasible in micro- or off-grid scenarios.

The increasing demand for sustainable and eco-friendly technologies has recently led to the development of green and bio-based synthesis methods for a broad range of nanoparticles (NPs). This is because these methods are non-toxic, biocompatible, and cost-effective. Photosensitive nanoparticles (PSNPs) have gained popularity due to their photo-responsive properties. PSNPs have also been found to be promising nanomaterials with applications in optoelectronics, photocatalysis, photovoltaics, bioimaging, drug delivery, and cancer treatment. However, conventional synthesis methods for PSNPs raise concerns about their environmental impact. To address these challenges, researchers have explored alternative synthesis approaches for PSNPs. This review comprehensively evaluates green and bio-based synthesis methods and their advantages and limitations for PSNPs and highlights their unique properties and applications in various fields. It also covers general concepts about PSNPs, their mechanism of action, characterization techniques, and challenges that have not been discussed in detail in previous studies. Moreover, this review uniquely addresses the challenges and potential solutions for scaling up green synthesis methods, an aspect often overlooked in the existing literature. By connecting fundamental research with industrial-scale applications, this review offers a comprehensive perspective on the sustainable production and various applications of PSNPs, emphasizing their potential in multiple fields.

Graphical Abstract

With the advancements of industrialization and the Internet of Things (IoT), the demand for gas sensing technologies has grown significantly. However, conventional gas sensors, which rely on external power supplies, face limitations in lifespan, capacity, and replacement convenience. As a result, interest in self-powered solutions has grown, with triboelectric nanogenerators (TENGs) emerging as a promising alternative. TENG-based self-powered gas sensors utilize triboelectricity, enabling gas detection without external power. Notably, TENGs offer the unique advantage of integrating energy harvesting and gas detection into a single device. This review categorizes the sensing mechanisms of TENG-based gas sensors into two main types and introduces each mechanism in detail. Through case studies, it provides a comprehensive understanding of these gas sensors. Additionally, it aims to analyze the challenges faced by TENG-based gas sensors and offer new insights into research strategies, ultimately contributing to the advancement of this technology.

A lightweight resonance tracking system designed for precise monitoring of resonant frequency shifts in microcantilever sensors is introduced. The system integrates a Phase-Locked Loop (PLL)-based technique with a Python-based interface for real-time control and visualization. A tipless microcantilever sensor was tested under relative humidity (RH) conditions ranging from 63% to 90% to experimentally validate the system. The system demonstrated a sensitivity of 1.082 Hz/% RH and a Limit of Detection (LOD) of 1.89% RH. The silicon dioxide ((SiO_2)) surface of the microcantilever is hygroscopic, allowing water vapor adsorption and causing frequency shifts. This effect is more pronounced at high humidity levels (>80% RH) due to multilayer adsorption. These results confirm the reliability and precision of the system in detecting environmental changes. The findings highlight the potential of the developed system for applications in environmental monitoring, healthcare diagnostics, and industrial chemical sensing.

To investigate the effect of the surface roughness of 3D-metal-printed sub-THz components, the WR-10 3-inch-long waveguide and 24 dBi rectangular horn antenna were 3D-metal-printed using a titanium alloy powder and a high-resolution 3D metal printer. The characterized surface roughness of the printed components was 17.27 µm in RMS from a 3D optical surface profiler, and a nodule ratio of 7.89 µm and surface ratio of 1.52 for Huray model from the analyzed SEM images. The measured results of the 3D-metal-printed waveguide and rectangular horn antenna were compared with the ones of commercial waveguide and horn antenna having the same shapes. The 3D-metal-printed waveguide has 4.02 dB higher loss than the commercial waveguide, which may be caused by an ohmic loss of 0.85 dB and a surface roughness loss of 2.81 dB. The 3D-metal-printed horn antenna has 2 dB higher loss then the commercial horn antenna, which may be caused by an ohmic loss of 0.2 dB, surface roughness of 0.1 dB and fabrication tolerance loss of 1.7 dB. The loss separation was done from the EM simulation by changing the conductor material and surface roughness.

The Phlomis bracteosa Royle ex Benth. is one of the medicinal plants used by the people of the north-western Himalayan region, India. Initially, phytochemical components of this plants have been evaluated by estimating total phenolic, flavonoid and tannin contents, and also by GCMS analysis in acetone and methanol solvents, which listed twenty-four compounds in acetone and twenty-two in methanol extract with different percentage peak areas. Later, silver nanoparticles (SNPs) were biogenically synthesized from the acetone extract of the same plant. The formation of SNPs was observed with UV-vis spectroscopy with surface plasmon resonance (SPR) at 438 nm. Further, the Fourier transform infrared spectroscopy suggested the presence of carbonyls, nitrogenous compounds and different types of hydrocarbons in SNPs. The field emission scanning electron microscopy (FESEM) and the high-resolution transmission electron microscopy suggested the spherical shape of SNPs with average size of 43.53 ± 0.71 nm. On the other hand, the energy dispersive X-ray spectroscopy depicted Ag as major element, the selected area electron diffraction and the X-ray diffraction supported crystalline nature of synthesized SNPs. The antimicrobial and antioxidant activities of both extracts (acetone and methanol) and SNPs were also studied. For the antimicrobial activity analysis, disk diffusion and broth microdilution methods were selected which displayed that plant extracts (PEs) exhibited better activity against Gram-positive bacteria and were inactive against Escherichia coli, while synthesized SNPs displayed better antimicrobial activity against all selected microorganisms. In case of antioxidant activity, by following two methods i.e., DPPH radicle scavenging and reducing power methods again SNPs expressed better antioxidant property with lower IC₅₀ value (40.55 µg/mL) than PEs i.e., 93.48 µg/mL (acetone) and 92.57 µg/mL (methanol). Therefore, biosynthetic SNPs can be a useful strategy in the biomedical sector.

Metal-Assisted Chemical Etching (MACE) is a technique for precisely forming nanostructures on semiconductor substrates, and it is actively researched in various fields such as electronic devices, optoelectronic devices, energy storage, and conversion systems. This process offers economic efficiency and effectiveness because it can be performed in a simple chemical laboratory environment without the need for expensive equipment. Particularly, MACE is recognized as an excellent technology for forming various nanostructures due to its advantage of precisely controlling the shape, size, and orientation of nanostructures compared to traditional etching techniques. MACE operates by inducing electrochemical reactions using a metal catalyst, selectively etching the semiconductor surface in a mixed solution of hydrofluoric acid (HF) and hydrogen peroxide ((hbox {H}_2hbox {O}_2)). The metal catalyst reacts with the oxidant to generate holes, which are injected into the semiconductor substrate to promote oxidation reactions. The oxidized material is then dissolved by HF, progressing the etching process. Precise nanostructures are formed only in the areas with the metal catalyst, and the etching results vary depending on the type, thickness, and deposition method of the catalyst. In this study, we comprehensively review the mechanism of the MACE process, the patterns of nanostructure formation according to the characteristics of catalysts and substrates, and the influence of process variables. We also analyze application cases of MACE in various semiconductor substrates such as silicon (Si), germanium (Ge), indium phosphide (InP), and gallium arsenide (GaAs), and examine the latest research trends and applications utilizing MACE. Nanostructures formed through MACE have the potential to maximize the performance of next-generation semiconductor and optoelectronic devices, and research in this area is expected to greatly contribute to the future development of the semiconductor industry.

Brain-on-a-chip is an emerging field involving microfluidic devices capable of mimicking the structure and function of the human brain. Existing research often focuses on single barriers, such as the blood–brain barrier or blood–cerebrospinal fluid barrier (BCSFB). However, the brain has both barriers working together, and mimicking this dual system is crucial for better understanding of brain (patho)physiology. In this work, we present a four-channel microfluidic chip model that incorporates both the BBB and BCSFB, to reproduce physiologically correct architecture. Using computer simulations, we demonstrate that this model can mimic both healthy and diseased states by adjusting the shear stress experienced by the barriers, which is a key factor in their function. These findings offer valuable insights for designing future brain-on-a-chip devices with improved accuracy. This improved technology could contribute to wider advancements in tissue engineering and the study of brain function and diseases.

Organoids are three-dimensional cell clusters derived from stem cells and closely resemble the physiological characteristics of human tissues. As the next-generation biological model, organoids provide new opportunities for drug discovery, disease modeling, and personalized medicine. To fully harness the potential of organoids, real-time monitoring of biological states and functional evaluation of organoids are crucial. This review highlights recent advances in real-time, in situ biosensing technologies, including microelectrode arrays for electrophysiological recordings, chemical sensors for biochemical detection, and strain sensors for monitoring mechanical properties. While the development of miniature sensors for non-invasive, long-term, and real-time monitoring of organoids is in the early stage, these sensors are an essential part of organoid technology which would provide new insights into human developmental biology, pathophysiology, and drug discovery. After reviewing the seminal works on the microfabricated sensors for organoids, we also provide an outlook of the field including a discussion on the remaining challenges and future directions with a focus on integration of multiple sensors to facilitate organoid research and applications.