Microsystems & Nanoengineering最新文献

The localized surface plasmon resonance metasurface is a research hotspot in the sensing field since it can enhance the light-matter interaction in the nanoscale, but the wavelength sensitivity is far from comparable with that of prism-coupled surface plasmon polariton (SPP). Herein, we propose and demonstrate an ultrasensitive angular interrogation sensor based on the transverse electric mode surface lattice resonance (SLR) mechanism in an all-metal metasurface. In theory, we derive the sensitivity function in detail and emphasize the refraction effect at the air-solution interface, which influences the SLR position and improves the sensitivity performance greatly in the wide-angle. In the measurement, a broadband light source substitutes the single-wavelength laser generally used in traditional angular sensing, and the measured SLR wavelength of broadband illuminant at normal incidence is defined as the single wavelength, avoiding the sensitivity loss from the large angle. The experimental sensitivity can reach 4304.35°/RIU, promoting an order of magnitude compared to those of SPP-sensors. This research provides a novel theory as well as the corresponding crucial approach to achieving ultrasensitive angular sensing.

In conventional nondispersive infrared (NDIR) gas sensors, a wide-spectrum IR source or detector must be combined with a narrowband filter to eliminate the interference of nontarget gases. Therefore, the multiplexed NDIR gas sensor requires multiple pairs of narrowband filters, which is not conducive to miniaturization and integration. Although plasmonic metamaterials or multilayer thin-film structures are widely applied in spectral absorption filters, realizing high-performance, large-area, multiband, and compact filters is rather challenging. In this study, we propose and demonstrate a narrowband meta-absorber based on a planar metal-insulator-metal (MIM) cavity with a metallic ultrathin film atop. Nearly perfect absorption of different wavelengths can be obtained by controlling the thickness of the dielectric spacer. More significantly, the proposed meta-absorber exhibits angle-dependent characteristics. The absorption spectra of different gases can be matched by changing the incident angle of the light source. We also preliminarily investigate the CO₂ gas sensing capability of the meta-absorber. Afterward, we propose a tunable meta-absorber integrated with a microelectromechanical system (MEMS)-based electrothermal actuator (ETA). By applying a direct current (DC) bias voltage, the inclination angle of the meta-absorber can be controlled, and the relationship between the inclination angle and the applied voltage can be deduced theoretically. The concept of a tunable MEMS-based meta-absorber offers a new way toward highly integrated, miniaturized and energy-efficient NDIR multigas sensing systems.

Various hydrogels have been explored to create minimally invasive microneedles (MNs) to extract interstitial fluid (ISF). However, current methods are time-consuming and typically require 10-15 min to extract 3-5 mg of ISF. This study introduces two spiral-shaped swellable MN arrays: one made of gelatin methacryloyl (GelMA) and polyvinyl alcohol (PVA), and the other incorporating a combination of PVA, polyvinylpyrrolidone (PVP), and hyaluronic acid (HA) for fast ISF extraction. These MN arrays demonstrated a rapid swelling ratio of 560 ± 79.6% and 370 ± 34.1% in artificial ISF within 10 min, respectively. Additionally, this study proposes a novel method that combines MNs with a custom-designed Arduino-based applicator vibrating at frequency ranges (50-100 Hz) to improve skin penetration efficiency, thereby enhancing the uptake of ISF in ex vivo. This dynamic combination enables GelMA/PVA MNs to rapidly uptake 6.41 ± 1.01 mg of ISF in just 5 min, while PVA/PVP/HA MNs extract 5.38 ± 0.77 mg of ISF within the same timeframe. To validate the capability of the MNs to recover glucose as the target biomarker, a mild heating procedure is used, followed by determining glucose concentration using a D-glucose content assay kit. The efficient extraction of ISF and glucose detection capabilities of the spiral MNs suggest their potential for rapid and minimally invasive biomarker sensing.

We present a versatile platform for label-free magnetic separation of plasma, tailored to accommodate diverse environments. This innovative device utilizes an advanced long-short alternating double Halbach magnetic array, specifically engineered for optimal magnetic separation. The array's adaptability allows for seamless integration with separation channels of varying sizes, enabling static separation of whole blood. The platform has a highly flexible processing throughput, spanning from 100 μL to 3 mL per separation cycle without sacrificing separation efficiency. A key aspect of this device is its power-free operation throughout the separation process, obviating the complexity of conventional separation devices. Its effectiveness is demonstrated by the extraction of 40 μL of plasma from 100 μL of rat whole blood within 8 min. The separated plasma proved effective for subsequent analysis of antibody concentration and size in the separated plasma for pharmacokinetic investigations, yielding results on par with those obtained via centrifugation. Furthermore, the device's high-throughput capability was validated using human whole blood, achieving 3 mL of plasma separation in just 1 min. In a follow-up study on COVID-19 IgG antibody detection, the results matched those from centrifugation. The device demonstrates a separation efficiency of 99.9% for cells larger than 1 μm in both rat and human blood samples, with a plasma recovery rate of 72.7%. In summary, our magnetic separation device facilitates rapid plasma extraction from whole blood, with a capacity of up to 3 mL per minute in human blood, without compromising subsequent plasma-based analyses, thereby highlighting its broad applicability across diverse settings.

This work presents air-coupled piezoelectric micromachined ultrasonic transducers (pMUTs) with high sound pressure level (SPL) under low-driving voltages by utilizing sputtered potassium sodium niobate K_0.34Na_0.66NbO₃ (KNN) films. A prototype single KNN pMUT has been tested to show a resonant frequency at 106.3 kHz under 4 V_p-p with outstanding characteristics: (1) a large vibration amplitude of 3.74 μm/V, and (2) a high acoustic root mean square (RMS) sound pressure level of 105.5 dB/V at 10 cm, which is 5-10 times higher than those of AlN-based pMUTs at a similar frequency. There are various potential sensing and actuating applications, such as fingerprint sensing, touch point, and gesture recognition. In this work, we present demonstrations in three fields: haptics, loudspeakers, and rangefinders. For haptics, an array of 15 × 15 KNN pMUTs is used as a non-contact actuator to provide a focal pressure of around 160.3 dB RMS SPL at a distance of 15 mm. This represents the highest output pressure achieved by an airborne pMUT for haptic sensation on human palms. When used as a loudspeaker, a single pMUT element with a resonant frequency close to the audible range at 22.8 kHz is characterized. It is shown to be able to generate a uniform acoustic output with an amplitude modulation scheme. In the rangefinder application, pulse-echo measurements using a single pMUT element demonstrate good transceiving results, capable of detecting objects up to 2.82 m away. As such, this new class of high-SPL and low-driving-voltage pMUTs could be further extended to other applications requiring high acoustic pressure and a small form factor.

Nanoelectromechanical systems (NEMS) incorporating atomic or molecular layer van der Waals materials can support multimode resonances and exotic nonlinear dynamics. Here we investigate nonlinear coupling of closely spaced modes in a bilayer (2L) molybdenum disulfide (MoS₂) nanoelectromechanical resonator. We model the response from a drumhead resonator using equations of two resonant modes with a dispersive coupling term to describe the vibration induced frequency shifts that result from the induced change in tension. We employ method of averaging to solve the equations of coupled modes and extract an expression for the nonlinear coupling coefficient (λ) in closed form. Undriven thermomechanical noise spectral measurements are used to calibrate the vibration amplitude of mode 2 (a₂) in the displacement domain. We drive mode 2 near its natural frequency and measure the shifted resonance frequency of mode 1 (f_1s) resulting from the dispersive coupling. Our model yields λ = 0.027 ± 0.005 pm^-2 · μs^-2 from thermomechanical noise measurement of mode 1. Our model also captures an anomalous frequency shift of the undriven mode 1 due to nonlinear coupling to the driven mode 2 mediated by large dynamic tension. This study provides a direct means to quantifying λ by measuring the thermomechanical noise in NEMS and will be valuable for understanding nonlinear mode coupling in emerging resonant systems.

Optomechanical sensors provide a platform for probing acoustic/vibrational properties at the micro-scale. Here, we used cavity optomechanical sensors to interrogate the acoustic environment of adjacent air bubbles in water. We report experimental observations of the volume acoustic modes of these bubbles, including both the fundamental Minnaert breathing mode and a family of higher-order modes extending into the megahertz frequency range. Bubbles were placed on or near optomechanical sensors having a noise floor substantially determined by ambient medium fluctuations, and which are thus able to detect thermal motions of proximate objects. Bubble motions could be coupled to the sensor through both air (i.e., with the sensor inside the bubble) and water, verifying that sound is radiated by the high-order modes. We also present evidence for elastic-Purcell-effect modifications of the sensor's vibrational spectrum when encapsulated by a bubble, in the form of cavity-modified linewidths and line shifts. Our results could increase the understanding of bubble acoustics relevant to a variety of fields such as lab-on-a-chip microfluidics and biosensing, and could also inform future efforts to optimize the properties of micro-mechanical oscillators.

Microscopic imaging is a critical tool in scientific research, biomedical studies, and engineering applications, with an urgent need for system miniaturization and rapid, precision autofocus techniques. However, traditional microscopes and autofocus methods face hardware limitations and slow software speeds in achieving this goal. In response, this paper proposes the implementation of an adaptive Liquid Lens Microscope System utilizing Deep Reinforcement Learning-based Autofocus (DRLAF). The proposed study employs a custom-made liquid lens with a rapid zoom response, which is treated as an "agent." Raw images are utilized as the "state", with voltage adjustments representing the "actions." Deep reinforcement learning is employed to learn the focusing strategy directly from captured images, achieving end-to-end autofocus. In contrast to methodologies that rely exclusively on sharpness assessment as a model's labels or inputs, our approach involved the development of a targeted reward function, which has proven to markedly enhance the performance in microscope autofocus tasks. We explored various action group design methods and improved the microscope autofocus speed to an average of 3.15 time steps. Additionally, parallel "state" dataset lists with random sampling training are proposed which enhances the model's adaptability to unknown samples, thereby improving its generalization capability. The experimental results demonstrate that the proposed liquid lens microscope with DRLAF exhibits high robustness, achieving a 79% increase in speed compared to traditional search algorithms, a 97.2% success rate, and enhanced generalization compared to other deep learning methods.

Metasurface with natural static structure limits the development of dynamic metasurface holographic display with rapid response and broadband. Currently, liquid crystal (LC) was integrated onto the metasurface to convert the passive metasuface into an active one. But, majority of LC-assisted active metasurfaces often exhibit trade-offs among degree of freedom (DoF, typically less than 2), information capacity, response speed, and crosstalk. Herein, at first time, we experimentally demonstrate a cascaded device with polymer dispersed liquid crystal (PDLC) and broadband metasurface, enabling dynamic three-dimensional (3D) holographic display with ultra-high contrast, rapid response and continuous regulation. The PDLC droplets enable modulation of scattering state of incident light by high-speed dynamic control system for electric scanning. Based on self-addressing, rapid response and multi-channel PDLC-metasurface device, the dynamic holographic effect of monochrome holographic images switching and color-changing holographic display with broadband, low-crosstalk and high contrast, has been achieved. Our approach offers a novel perspective on dynamic metasurface.

Piezoelectric resonance sensors are essential to many diverse applications associated with chemical and biological sensing. In general, they rely on continuously detecting the resonant frequency shift of piezoelectric resonators due to analytes accreting on their surfaces in vacuum, gas or fluid. Resolving the small analyte changes requires the resonators with a high quality factor. Here, we propose theoretically and demonstrate experimentally a scheme using a physics concept, i.e., a Fano resonance, to enhance the quality factor rather than optimizing the structure and material of the resonator itself though these are important. The Fano resonance arises due to the interference between a discrete mode and a continuum of modes, leading to the asymmetric and steep dispersion. In our scheme, the as-fabricated piezoelectric sensors are put into the Fano resonance by connecting an external shunt capacitor to them. As a verification case, one-port surface acoustic wave (SAW) resonators on LiNbO₃ substrate, incorporating a composite of polymethyl methacrylate (PMMA) and graphene oxide (GO) for humidity sensing, have been fabricated and characterized. We enhance the quality factor by up to a factor of about 8, from 929 for the as-fabricated sensor to 7682 for that with the external shunt capacitor. Our results pave the way for the practical development of piezoelectric resonance sensors with high quality factor.