Microsystems & Nanoengineering最新文献

Braille serves as an efficient means for visually impaired individuals to access textual information and engage in communication. However, the process of reading Braille can often be cumbersome and time-intensive, particularly in bidirectional human-machine interaction. In this work, a compact optical device for contactless detection of Braille is fabricated and characterized. The GaN-on-sapphire chip, which employs monolithic integration, serves as the core for both light emission and photodetection, significantly reducing its overall footprint. The incorporation of the semi-ellipsoid epoxy lens with optimized dimensions ensures consistent and accurate detection. The sensing device demonstrates high stability and fast response through its line-scanning capabilities on Braille codes. The captured signals are analyzed using a microcontroller, and the Braille recognition results are wirelessly transmitted to a portable mobile device, enabling the conversion into audio and visual formats. This innovative design not only facilitates Braille reading but also holds the potential to advance human-machine interaction.

Centrifugal microfluidic platforms are highly regarded for their potential in multiplexing and automation, as well as their wide range of applications, especially in separating blood plasma and manipulating two-phase flows. However, the need to use stroboscopes or high-speed cameras for monitoring these tasks hinders the extensive use of these platforms in research and commercial settings. In this study, we introduce an innovative and cost-effective strategy for using an array of light-dependent resistors (LDRs) as optical sensors in microfluidic devices, particularly centrifugal platforms. While LDRs are attractive for their potential use as photodetectors, their bulky size frequently restricts their ability to provide high-resolution detection in microfluidic systems. Here, we use specific waveguides to direct light beams from narrow apertures onto the surface of LDRs. We integrated these LDRs into electrified Lab-on-a-Disc (eLOD) devices, with wireless connectivity to smartphones and laptops. This enables many applications, such as droplet/particle counting and velocity measurement, concentration analysis, fluidic interface detection in multiphase flows, real-time monitoring of sample volume on centrifugal platforms, and detection of blood plasma separation as an alternative to costly stroboscope devices, microscopes, and high-speed imaging. We used numerical simulations to evaluate various fluids and scenarios, which include rotation speeds of up to 50 rad/s and a range of droplet sizes. For the testbed, we used the developed eLOD device to analyze red blood cell (RBC) deformability and improve the automated detection of sickle cell anemia by monitoring differences in RBC deformability during centrifugation using the sensors' signals. In addition to sickle cell anemia, this device has the potential to facilitate low-cost automated detection of other medical conditions characterized by altered RBC deformability, such as thalassemia, malaria, and diabetes.

Microfluidic contact lenses integrate microscale features that can efficiently and precisely manipulate, interact, and analyze the small volumes of tears available in the limited accessible space for the lens in the eye. The microfluidic network on contact lenses allows the miniaturization of biochemical operations on the wealth of physiological information available in the eye. Sensors integrated into channels enable real-time monitoring of ocular parameters, including glucose, pH, electrolytes, or other biomarkers. Additionally, microchannel-integrated contact lenses have demonstrated potential as power-free, continuous intraocular pressure monitoring platforms for the effective management of glaucoma. Furthermore, the controlled release of medications directly onto the eye from microfluidic contact lenses enhances therapeutic efficacy by increasing bioavailability. Despite current challenges such as scalable fabrication techniques, microfluidic contact lenses hold immense promise for ocular health, bridging the gap between diagnostics and treatment. This review summarizes the progress made in the design and fabrication of microfluidic contact lenses, with a special emphasis on the methods adopted to fabricate microfluidic contact lenses. Furthermore, the various applications of microfluidic contact lenses, ocular disease diagnosis, and drug delivery in particular are discussed in detail. Aside from outlining the state-of-the-art research activities in this area, challenges and future directions are discussed here.

Surface-enhanced spectroscopy technology based on metamaterials has flourished in recent years, and the use of artificially designed subwavelength structures can effectively regulate light waves and electromagnetic fields, making it a valuable platform for sensing applications. With the continuous improvement of theory, several effective universal modes of metamaterials have gradually formed, including localized surface plasmon resonance (LSPR), Mie resonance, bound states in the continuum (BIC), and Fano resonance. This review begins by summarizing these core resonance mechanisms, followed by a comprehensive overview of six main surface-enhanced spectroscopy techniques across the electromagnetic spectrum: surface-enhanced fluorescence (SEF), surface-enhanced Raman scattering (SERS), surface-enhanced infrared absorption (SEIRA), terahertz (THz) sensing, refractive index (RI) sensing, and chiral sensing. These techniques cover a wide spectral range and address various optical characteristics, enabling the detection of molecular fingerprints, structural chirality, and refractive index changes. Additionally, this review summarized the combined use of different enhanced spectra, the integration with other advanced technologies, and the status of miniaturized metamaterial systems. Finally, we assess current challenges and future directions. Looking to the future, we anticipate that metamaterial-based surface-enhanced spectroscopy will play a transformative role in real-time, on-site detection across scientific, environmental, and biomedical fields.

Silicon photonic switches are widely considered as a cost-effective solution for addressing the ever-growing data traffic in datacenter networks, as they offer unique advantages such as low power consumption, low latency, small footprint and high bandwidth. Despite extensive research efforts, crosstalk in large-scale photonic circuits still poses a threat to signal integrity. In this paper, we present two designs of silicon Mach-Zehnder Interferometer (MZI) switches achieving ultra-low-crosstalk, driven thermally and electrically. Each switch fabric is optimized at both the device and circuit level to suppress crosstalk and reduce system complexity. Notably, for the first time to the best of our knowledge, we harness the inherent self-heating effect in a carrier-injection-based MZI switch to create a pair of phase shifters that offers arbitrary phase differences. Such a pair of phase shifters induces matched insertion loss at each arm, thus minimizing crosstalk. Experimentally, an ultra-low crosstalk ratio below -40 dB is demonstrated for both thermo-optic (T-O) and electro-optic (E-O) switches. The T-O switch exhibits an on-chip loss of less than 5 dB with a switching time of 500 µs, whereas the E-O switch achieves an on-chip loss as low as 8.5 dB with a switching time of under 100 ns. In addition, data transmission of a 50 Gb/s on-off keying signal is demonstrated with high fidelity on the E-O switch, showing the great potential of the proposed switch designs.

Mode-localized sensors have attracted significant attention due to their exceptional sensitivity and inherent ability to reject common-mode noise. This high sensitivity arises from the substantial shifts in resonator amplitudes induced by energy confinement in weakly coupled resonators. Despite their promising attributes, there has been limited research on the mechanisms of energy confinement. This paper presents both qualitative and quantitative analyses of energy confinement within weakly coupled resonators and concludes them as the concept of modal dominance. This concept elucidates that mode frequencies are predominantly dictated by the natural frequencies of the internal resonators, facilitating spatial energy confinement. Based on this modal dominance, a novel concept of virtually coupled resonators is proposed, which obviates the need for physical coupling structures. Instead, energy confinement is achieved through a frequency offset between two independent resonators, resulting in a similar amplitude ratio output and enhanced sensitivity. To further enhance performance, a double-closed-loop control scheme is developed for virtually coupled resonators, expanding the bandwidth in comparison to weakly coupled resonators. Experimental results validate the feasibility of virtually coupled resonators and the double-closed-loop control, demonstrating a 2.7-fold improvement in amplitude ratio sensitivity and at least a four-fold enhancement in bandwidth relative to weakly coupled resonators with identical parameters.

Chronic kidney disease (CKD) significantly affects people's health and quality of life and presents a high economic burden worldwide. There are well-established biomarkers for CKD diagnosis. However, the existing routine standard tests are lab-based and governed by strict regulations. Creatinine is commonly measured as a filtration biomarker in blood to determine estimated Glomerular Filtration Rate (eGFR), as well as a normalization factor to calculate urinary Albumin-to-Creatinine Ratio (uACR) for CKD evaluation. In this study, we developed a passive flow microreactor for colorimetric urine creatinine measurement (uCR-Chip), which is highly amenable to integration with our previously developed microfluidic urine albumin assay. The combination of the 2-phase pressure compensation (2-PPC) technique and microfluidic channel network design accurately controls the fluidic mixing ratio and chemical reaction. Together with an optimized observation window (OW) design, a uniform and stable detection signal was achieved within 7 min. The color signal was measured by a simple USB microscope-based platform to quantify creatinine concentration in the sample. The combination of the custom in-house photomask production techniques and dry-film photoresist-based lithography enabled rapid iterative design optimization and precise chip fabrication. The developed assay achieved a dynamic linear detection range up to 40 mM and a lower limit of detection (LOD) of 0.521 mM, meeting the clinical precision requirements (comparable to existing point-of-care (PoC) systems). The microreactor was validated using creatinine standards spiked into commercial artificial urine that mimics physiological matrix. Our results showed acceptable recovery rate and low matrix effect, especially for the low creatinine concentration range in comparison to a commercial PoC uACR test. Altogether, the developed uCR-Chip offers a viable PoC test for CKD assessment and provides a potential platform technology to measure various disease biomarkers.

The development of electronic skin, soft robots, and smart wearables has significantly driven advances in flexible pressure sensing technology. However, traditional multilayer solid-structure flexible pressure sensors encounter challenges at temperatures between 100 °C and 150 °C due to high-temperature modal distortion. Changes in the conductivity of the sensor's conductive components interfere with accurate pressure measurement. In this research, a flexible pressure sensor with a convective liquid metal sensitive layer is proposed. The sensor uses a cyclic self-cooling mechanism to lower the temperature of its conductive components, reducing the impact of external high temperatures on the pressure measurement accuracy. At a 2.8 W thermal load, the flexible sensor, with liquid metal circulating at 2.0 mL/min, exhibits a sensitivity of 0.11 kPa⁻¹ within the pressure range from 0 to 12.5 kPa, and its maximum measurable pressure is 30 kPa. In addition, the resistance of the sensor is 18.5 mΩ less than that of a stationary liquid metal sensor, representing a 38.1% reduction. The sensor proposed in this research introduces a novel strategy for pressure measurement in high-temperature applications, extending the application scope to aircraft, special robots, and hydraulic oil circuits.

This work presents an integrated microsensor that combines the dual characterization capabilities of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). We integrated two pairs of thermocouples, heating resistors, and resonant drive/detection resistors into a single microcantilever, where the cantilever resonant frequency shifts respond to the mass change and the output voltage of the integrated thermocouples respond to the sample temperature. This integration enables programmable temperature control, temperature variation, and mass detection on a single chip. Our chip can achieve heating and cooling rates above 600 °C/min, which is significantly faster than commercial instruments with satisfactory measurement accuracy. The integrated polysilicon thermocouples bring high power responsivity of 6 V/W, making them suitable for highly sensitive DTA measurements on a chip. Moreover, the cantilever offers picogram (10^-12g) level mass resolution, reducing sample consumption from milligrams to nanogram levels. Additionally, the on-chip sample heating allows for easy observation of sample morphological evolution during heating under an optical microscope. We validated the dual functionality by conducting TGA measurements on a standard sample of calcium oxalate monohydrate (CaC₂O₄ ∙ H₂O) and DTA measurements on high-purity indium (In) and tin (Sn). The results indicate consistent measurements with the true values of the standard sample and high measurement efficiency. Our integrated cantilever chip is anticipated to have broad applications in high-performance and efficient TGA and DTA characterization.

This study presents the development and characterization of a nanomechanical gas sensor array with piezoresistive detectors for a wide range of applications. The sensors, made of silicon and polymers and integrated with the piezoresistive sensors on a silicon-on-insulator wafer, convert to electrical signals the stress caused by volume change of polymer induced by gas absorption. The fabrication of the sensors incorporates a process where Polymer A (Polyolefin), Polymer B (Fluorocarbon polymer) Polymer C (Acrylic resin), and Polymer D (Amino polymer), are deposited within silicon slits, demonstrating their distinct responses to various vapor species. These sensors show swift response times and efficient recovery periods, which makes them promising for real-time multiple gas and smell monitoring applications. An array of four nanomechanical sensors with polymers shows high repeatability and sensitivity when subjected to multiple gas exposure and turn-off cycles. The gas sensor arrays, effectively monitoring fish quality over several days, suggest a potential for determining optimal storage and early spoilage detection in perishables. The study demonstrates that the nanomechanical sensor array can accurately distinguish between different gas concentrations using principal component analysis, paving the way for real-time, automated multiple gas detection and analysis without human intervention.