Micro and Nano Systems Letters最新文献

Metal oxide-based sensors have been widely used to detection biomarkers in exhaled breath for identification of various diseases such as asthma, diabetes, halitosis, and lung cancer. Herein, we proposed one step hydrothermal method for the preparation of SnO₂ nanospheres and reduced graphene oxide incorporated SnO₂ nanospheres for the detection of two important biomarkers such as decane and heptane from the exhaled breath of lung cancer patients. The as prepared materials are investigated in detail through various analytical techniques and the findings are consistent with each other. The sensing response of the proposed sensors were systematically investigated to enhance their sensing performance as a function of operating temperatures and gas concentration, and different analyte gases. The sensors showed maximum sensing response toward heptane and decane compared to other interfering gases such as hydrogen, carbon monoxide, acetone, ethanol, and methanol at 125 °C. The proposed sensors exhibit excellent detection range as low as 1 ppm with appreciably fast response and recovery time. Lung cancer patients may be easily screened using the proposed sensor, by detecting decane and heptane in their exhaled breath.

During deep reactive ion etching (DRIE), microscale etch masks with small opening such as trenches or holes suffer from limited aspect ratio because diffusion of reactive ions and free radicals become progressively difficult as the number of DRIE cycle increases. For this reason, high aspect ratio structures of microscale trenches or holes are not readily available with standard DRIE recipes and microscale holes are more problematic than trenches due to omnidirectional confinement. In this letter, we propose an optimization for fabrication of high aspect ratio microscale hole arrays with an improved cross-sectional etch profile. Bias voltage and inductively coupled plasma power are considered as optimization parameters to promote the bottom etching of the high aspect ratio hole array. In addition, flow rates of octafluorocyclobutane (C(_{4})F(_{8})) and sulfur hexafluoride (SF(_{6})) for passivation and depassivation steps, respectively, are considered as optimization parameters to reduce the etch undercut. As a result of optimization, the aspect ratio of 20 is achieved for 1.3 μm-diameter hole array and etch area reduction at the bottom relative to the top is improved to 21%.

A microarray detection method based on on-chip signal amplification using terminal deoxynucleotidyl transferase (TdT) was developed to visualize pathogenic genes. Cyclic olefin copolymer (COC) substrate for microarrays was treated with oxygen plasma to induce hydrophilic surface properties. The capture probe DNA was immobilized on the COC surface by UV irradiation. The 3ʹ end of the capture probe DNA immobilized on the COC surface was modified with a phosphate group to provide resistance against the TdT reaction. Therefore, the TdT reaction was triggered only when the capture probe DNA acquired the target gene, and biotin-11-deoxyuridine triphosphate (b-dUTP) was continuously added to the 3ʹ end of the target gene. Thereafter, streptavidin-conjugated gold nanoparticles (s-AuNPs) tagged the poly uridine tails by the biotin–streptavidin interaction. The visual signal was amplified by silver enhancement in the presence of the s-AuNPs. The usefulness of this detection method was confirmed by analyzing four pathogens and allowing their visual identification.

Silicon wet bulk micromachining is the most widely used technique for the fabrication of diverse microstructures such as cantilevers, cavities, etc. in laboratory as well as in industry for micro-electromechanical system (MEMS) application. Although, increasing the throughput remains inevitable, and can be done by increasing the etching rate. Furthermore, freestanding structure release time can be reduced by the improved undercutting rate at convex corners. In this work, we have investigated the etching characteristics of a non-conventional etchant in the form of hydroxylamine (NH₂OH) added sodium hydroxide (NaOH) solution. This research is focused on Si{100} wafer as this orientation is largely used in the fabrication of planer devices (e.g., complementary metal-oxide semiconductors) and microelectromechanical systems (e.g., inertial sensors). We have performed a systematic and parametric analysis without and with 12% NH₂OH in 10 M NaOH for improved etching characteristics such as etch rate, undercutting at convex corners, and etched surface morphology. 3D scanning laser microscope is used to measure average surface roughness (R_a), etch depth (d), and undercutting length (l). Morphology of the etched Si{100} surface is examined using optical and scanning electron microscopes. The addition of NH₂OH in NaOH solution remarkably exhibited a two-fold increment in the etching rate of a Si{100} surface. Furthermore, the addition of NH₂OH significantly improves the etched surface morphology and undercutting at convex corners. Undercutting at convex corners is highly prudent for the quick release of microstructures from the substrate. In addition, we have studied the effect of etchant age on etching characteristics. Results presented in this article are of large significance for engineering applications in both academic and industrial laboratories.

Soft devices that are mechanically flexible and stretchable are considered as the building blocks for various applications ranging from wearable devices to robotics. Among the many candidate materials for constructing soft devices, carbon nanomaterials such as carbon nanotubes (CNTs) and graphene have been actively investigated owing to their outstanding characteristics, including their intrinsic flexibility, tunable conductivity, and potential for large-area processing. In particular, hybrids of CNTs and graphene can improve the performance of soft devices and provide them with novel capabilities. In this review, the advances in CNT-graphene hybrid-based soft electrodes, transistors, pressure and strain sensors, and actuators are discussed, highlighting the performance improvements of these devices originating from the synergistic effects of the hybrids of CNT and graphene. The integration of multidimensional heterogeneous carbon nanomaterials is expected to be a promising approach for accelerating the development of high-performance soft devices. Finally, current challenges and future opportunities are summarized, from the processing of hybrid materials to the system-level integration of multiple components.

Wearable electronic devices such as mobile communication devices, portable computers, and various sensors are the latest significant innovations in technology which use the Internet of Things (IoT) to track personal data. Wearable energy harvesters are required to supply electricity to such devices for the convenience of users. In this study, a textile-type triboelectric nanogenerator (T-TENG), produced using commercial electrode fibers, was fabricated to generate electrical energy using external mechanical stimulation. The commercial fiber was an electrode coated with Teflon on a copper wire with a diameter of ~ 320 μm. Using this commercial fiber, a T-TENG was easily fabricated by knitting and weaving. The performance of the T-TENG was analyzed to understand the effect of force and frequency. It was observed that the performance of the T-TENG did not degrade even under harsh conditions and treatment. The textile-type TENG possessed an energy harvesting capability with an output power density of ~ 0.36 W/m² and could operate electronic devices by charging a capacitor.

Precise sensing of pressure is essential for various mechanical and electrical systems. The recent emergence of flexible pressure sensors has enabled novel applications, such as human–machine interfaces, soft robotics, and wearable devices. Specifically, the piezoresistive sensing scheme is widely adapted for flexible pressure sensors as it is simple and exhibits outstanding measurement sensitivity and stability. The sensing properties of piezoresistive pressure sensors mainly depends on the materials and contact morphologies at the interface. This paper proposes a flexible pressure sensor based on multi-height microstructures in which the measurement sensitivity and detection range are tunable. Such tunability is due to the sequential contact of micropyramids with different heights. The multi-height micropyramid structured PDMS layer with stamp-coated multi-walled carbon nanotubes (MWCNTs) acts as a conductive active layer and a gold interdigitated electrode (IDE) patterned polyimide (PI) layer works as the bottom electrode. The fabricated sensor exhibits a sensitivity of 0.19 kPa⁻¹, a fast response speed of 20 ms, and a detection range of up to 100 kPa. The sensor is applied to a robotic gripper for object recognition and integrated into a shoe to track walking motions.

We propose a scheme to establish a surrogate model for optimizing the annealing duration of the self-assembled membrane-cavity structures from hole patterned silicon wafers. Although it has been reported that the design space of post-annealing shape can be extended by increasing the dimensions of hole arrays, the annealing duration for large hole arrays has not been well examined. A two-dimensional axisymmetric phase-field model in commercial FEM software is employed to establish the surrogate model with respect to three variables (i.e., radius, aspect ratio (AR), and normalized spacing). The established surrogate model based on the neural network indicates that the hole radius dominantly affects annealing duration and the temperature elevation (i.e., acceleration of diffusion speed) is necessary to achieve the practical annealing duration when the hole radius is larger than 1 μm.

The phytosynthesis method was used to prepare ZnO nanoparticles (ZnO NPs) via Senna alata L. leaf extract (SALE) by involving alkaloids, which play an essential role as a source of weak bases during the formation reaction of NPs. ZnO NPs on glassy carbon electrodes (GCE/ZnO NP) have been introduced to investigate its electrochemical activity towards the antiretroviral drug, lamivudine (3TC). Several characterization techniques, such as Fourier Transform Infra-Red (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and Dynamic Light Scattering (DLS) techniques were employed to analyze the properties of GCE/ZnO NPs. As a result, ZnO NPs in spherical shape showed a high purity crystalline hexagonal wurtzite structure with a particle diameter of 40–60 nm. A Cyclic Voltammetry (CV) measurement confirmed that the electrochemical reduction of 3TC on GCE/ZnO NPs exhibited an excellent linear range of 10–300 µM with a detection limit of 1.902 µM, quantitation limit of 6.330 µM, and sensitivity of 0.0278 µA/µM. Thus, this research suggests a facile method for the preparation of material-based ZnO NPs as a promising antiretroviral drug sensors due to their excellent electrochemical properties.

Gaseous ethanol detection has attracted significant interest owing to its practical applications such as in breath analysis, chemical process monitoring, and safety evaluations of food packaging. In this study, titanium dioxide (TiO₂) nanoparticles functionalized with cobalt porphyrin (CoPP) are utilized as resistive ethanol-sensing materials, and are integrated with a suspended micro-heater for low power consumption. The micro-heater with the suspended structure inhibits substrate heat transfer, resulting in power consumption as low as 18 mW when the operating temperature is approximately 300 °C. CoPP functionalization allows an enhanced response (197.8%) to 10 ppm ethanol compared to that of pristine TiO₂ nanoparticles. It is confirmed that the sensor response is reliable upon exposure to 10 ppm ethanol for three cycles. In addition, responses of different magnitude are obtained under exposure to ethanol at various concentrations from 9 to 1 ppm, indicating that the resistance change originates from a charge transfer between the sensing materials and target gas. The sensing mechanism of CoPP-functionalized TiO₂ in relation to charge transfer is analyzed, and the performance of the proposed sensor with previously reported TiO₂-based ethanol sensors is compared. Considering that it is processed by batch fabrication, consumes low power, and offers high sensitivity, the proposed sensor is promising for use as a portable sensor in the distributed monitoring of gaseous ethanol.