Ultrasensitive Detection of SARS-CoV‑2 by Flexible Metal Oxide Field-Effect Transistors

The pandemic of coronavirus disease 2019 (COVID-19) reflects the great significance of rapid and accurate detection of pathogens by new sensing technologies. Antibody based biosensors with high sensitivity comparable to golden standard polymerase chain reaction (PCR) and miniaturized device features allow the detection of pathogens in portable and flexible formats. Herein, flexible metal oxide electrolyte-gated field-effect transistors (EGFETs) are reported to serve as the biosensors for rapid and ultrasensitive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection. The semiconducting layer of the EGFETs associates with hybrid material of PEI doped metal oxides that not only improves the transistor performance, but also regulates microstructure forming higher surface-to-volume ratio, which brings more antibodies immobilization, resulting in higher sensitive, and faster response for detecting SARS-CoV-2. Comprehensive studies of materials and interfacing engineering of the EGFETs not only build the strong foundation for the EGFET sensors to show excellent sensitivity with a limit of detection from 0.14 fg ml⁻¹ for SARS-CoV-2 S1 proteins, and 0.09 copies µl⁻¹ for SARS-CoV-2 viruses, but also offer good mechanical properties to enable thin, soft flexible sensing platforms. This work provides a new strategy from materials to devices as innovative schemes for virus/pathogens detection.     

Stretchable Enzymatic Biofuel Cells Based on Microfluidic Structured Elastomeric Polydimethylsiloxane with Wrinkled Gold Electrodes

Various sensors and electronic devices are recently developed to monitor human health in mechanically flexible or even stretchable forms for intimate contact with non-flat curvilinear surfaces of the human body. For successful operation of these devices, finding a proper way to electrically power them is very important. In this work, glucose/oxygen fueled enzymatic biofuel cells (EBFCs) based on microfluidic structured elastomeric polydimethylsiloxane substrate with wrinkled gold (Au) electrodes are suggested for power supply. For doing that, firstly, bottom surface of microfluidic channel is covered with buckled Au electrodes for stretchability. By microfluidic design showing capillary imbibition through fluidic channels, loading of catalyts is promoted. Interestingly, buckled Au electrodes induce much better anodic and cathodic reaction rates than those of non-buckled Au electrodes by 25% and 33%, respectively. This is because surface area and the amount of catalyst loading in electrodes increase by Au wrinkling. In evaluations of EBFCs using the buckled Au electrodes, maximum power density reaches 7.1 ± 0.64 µW cm⁻², while they show decent performance of 5.4 ± 0.49 µW cm⁻² even under external stretching. Taken together, it is corroborated that such proposed stretchable EBFCs are alternative for providing electrical power in wearable or implantable devices.     

All-inkjet-printed dissolved oxygen sensors on flexible plastic substrates

Inkjet printing is a promising alternative manufacturing method to conventional standard microfabrication techniques for the development of flexible and low-cost devices. Although the use of inkjet printing for the deposition of selected materials for the development of sensor devices has been reported many times in literature, it is still a challenge and a potential route towards commercialization to completely manufacture sensor devices with inkjet technology. In this work is demonstrated the fabrication of a functional low-cost dissolved oxygen (DO) amperometric sensor with feature sizes in the micrometer range using inkjet printing. All the required technological steps for the fabrication of a complete electrochemical three electrodes system are discussed in detail. The working and counter electrodes have been printed using a gold nanoparticle ink, whereas a silver nanoparticle ink was used to print a pseudo-reference electrode. Both inks are commercially available and can be sintered at low temperatures, starting already at 120 °C, which allows the use of plastic substrates. In addition, a printable SU8 ink formulation cured by UV is applied as passivation layer in the sensor device. Finally, as the performance of analytical methods strongly depends on the working electrode material, is demonstrated the electrochemical feasibility of this printed DO sensor, which shows a linear response in the range between 0 and 8 mg L⁻¹ of DO, and affords a detection limit of 0.11 mg L⁻¹, and a sensitivity of 0.03 μA L mg⁻¹. The use of flexible plastic substrates and biocompatible inks, and the rapid prototyping and low-cost of the fabricated sensors, makes that the proposed manufacturing approach opens new opportunities in the field of biological and medical sensor applications.     

Flexible Vanadium Dioxide Photodetectors for Visible to Longwave Infrared Detection at Room Temperature

Flexible optoelectronics is a rapidly growing field, with a wide range of potential applications. From wearable sensors to bendable solar cells, curved displays, and curved focal plane arrays, the possibilities are endless. The criticality of flexible photodetectors for many of these applications is acknowledged, however, devices that are demonstrated thus far are limited in their spectral range. In this study, flexible photodetectors are demonstrated using a VO_x nanoparticle ink, with an extremely broad operating wavelength range of 0.4 to 20 µm. This ink is synthesized using a simple and scalable wet-chemical process. These photodetectors operate at room temperature and exhibit minimal variance in performance even when bent at angles of up to 100 ° at a bend radius of 6.4 mm. In addition, rigorous strain testing of 100 bend and release cycles revealed a photoresponse with a standard deviation of only 0.55%. This combination of mechanical flexibility, wide spectral response, and ease of fabrication makes these devices highly desirable for a wide range of applications, including low-cost wearable sensors and hyperspectral imaging systems.     

Performance analysis of valveless micropump with disposable chamber actuated through Amplified Piezo Actuator (APA) for biomedical application

The precise manipulation of fluid through pumping systems has been the technological challenge in microfluidic applications. The biomedical applications call for precise and accurate delivery of fluid through miniaturized pumping systems. This paper presents a novel valveless micropump for biomedical applications operated by the Amplified Piezo Actuator. Integrating the disposable chamber and reusable actuator with the proposed micropump allows the actuator to be reused and eliminates the possibility of infection or contagion. The micropump was fabricated using low-cost polymeric materials like Polymethylmethacrylate (PMMA), Silicone rubber through CNC milling, Laser Cutting, conventional moulding operation. The micropump chamber, nozzle/diffusers, and a bossed diaphragm constituted disposable part and Amplified Piezo Actuator with structural support formed the reusable part of the micropump. The bossed diaphragm of the pump chamber consists of a central cylindrical protrusion to reduce the force of adhesion on the diaphragm and transmit force required for micropump actuation. A theoretical analysis was performed to assess the effect of diaphragm thickness and the bossed region on the effective stiffness of the diaphragm, which in turn influences the deflection achieved. Besides, an analytical approach has been presented to address the effect of adhesive force on the diaphragm surface due to the residual fluid and chamber depth. The experimental characterization of the micropump was carried out to determine the optimal performance parameters with water, fluids mimicking blood plasma, and whole blood. Based on the experimental results, the pumping rate and head developed by the micropump have been significantly affected by factors such as bossed ratio, diaphragm thickness, depth of the micropump chamber, and viscosity of the fluid. The optimum configuration of the micropump cosidered silicone rubber diaphragm with thickness of 0.20 mm having a bossed ratio of 0.33 and a chamber depth of 1.25 mm. With the optimal operating parameters of 150 V sinusoidal input of frequency 5 Hz, the proposed micropump was capable of delivering 7.192 ml/min, 6.108 ml/min, and 5.013 ml/min of water and blood plasma, whole blood mimicking fluid with the maximum backpressure of 294.00 Pa, 226.243 Pa, and 204.048 Pa respectively. The corresponding resolution, i.e., pumping volume/stroke of the micropump was about 23.972 µl, 20.358 µl, and 16.708 µl, respectively.     

微流控拉曼检测芯片的制备与应用

微流控芯片系统具有高效率、低损耗、高安全系数、高灵敏度等优势,表面增强拉曼散射(SERS)光谱具有灵敏度高以及指纹效应强等优点。从两方面对微流控拉曼检测芯片进行综述:微流控芯片通道和SERS基底的制备以及微流控拉曼检测芯片的集成与应用。最后讨论了SERS微流控芯片在便携化应用方面的挑战和机遇,并对整个领域的未来发展方向与前景进行了展望。     

微流控光学及其应用

微流控光学(optofluidics)通过融合微流控学和光学、光电子学技术合成新颖的功能器件和系统,微流控光学系统的主要特点在于结构的可调化、功能的集成化和系统的微型化.结构可调性为自适应光学提供了新的技术途径,光学检测与微流分析功能的集成将促进微型全分析系统技术的应用和发展,光学与微流控技术的融合则为传统光学器件的可调化和微型化提供了可能.介绍微流控光学这一前沿交叉学科的基本概念和应用前景.叙述了微流控自适应光学、微流控光学检测、微流控激光器以及微流控光学集成器件的近期研究成果和应用前景.     

Bifunctional Single-Atom Iron Cocatalysts Enable an Efficient Photoelectrochemical Fuel Cell for Sensitive Biosensing

Semiconductor-based photoelectrochemical (PEC) fuel cells offer a feasible solution for sustainable and environmentally friendly energy production by converting solar and chemical energy into electrical energy. However, the low PEC activities of PEC fuel cells have hindered their practical application due to rapid electron-hole recombination and slow interfacial reaction kinetics. To address this issue, a unique PEC fuel cell composed of dual photoelectrodes utilizing low-cost biomass, ascorbic acid, as an organic fuel is reported. Significantly, the integration of bifunctional iron single-atom catalysts (Fe SACs) and photoactive materials has effectively constructed a bridge for charge carrier transfer, boosting interfacial reaction kinetics and photoelectric conversion efficiency. Notably, the optimal dual-photoelectrode PEC fuel cell decorated with Fe SACs exhibits superior performance, delivering a maximum power density of 82.82 µW cm⁻². Taking advantage of the peroxidase-like activity of Fe SACs, the resultant self-powered PEC fuel cells are explored for sensitively detecting actual uric acid samples. This study provides a promising avenue to boost the energy conversion efficiency of PEC fuel cells for sensitive self-powered biosensing.     

An on-chip localized surface plasmon resonance-based biosensor for label-free monitoring of antigen–antibody reaction

The unique localized surface plasmon resonance (LSPR) property of gold nanoparticles has been used to design a label-free biosensor in a chip format. In this research, a sensitive and low-cost microfluidic integrated LSPR-based biosensor is developed. The gold nanoparticles were synthesized in solution and immobilized on quartz substrates by a silane layer as molecular glue. The gold nanoparticle-coated substrate was further integrated with a microfluidic chip. An automated sample introduction system was developed to perform a variety of processes including sample loading, chip washing and sample change. A refractive index resolution of 1 × 10⁻⁴ RIU (refractive index unit) was demonstrated by using the on-chip biosensor combined with the automated sampling system. This developed microfluidic integrated system is capable of transporting a specific amount of bio-samples into the sensing chambers to achieve sensitive and specific biosensing with decreased reaction time and less reagent consuming. Proof-of-concept detection of antigen/antibody (biotin/anti-biotin) binding was performed and was quantitatively detected.     

Vacuum-Assisted Microfluidic Technique for Fabrication of Guided Wave Devices

We report on a novel vacuum-assisted microfluidic (VAM) technique for guided wave device fabrication. Ultraviolet curable resins were used to demonstrate the effective VAM waveguide fabrication. Comparisons to a conventional soft molding technique demonstrate that the VAM approach results in lower propagation losses, lower crosstalk, and improved waveguide structures. More importantly, microscope analysis portrays improved device formation, sidewall edges, and the elimination of the polymer background residue inherent to traditional soft molding fabrication techniques. As a low-cost rapid prototyping technique, the VAM soft lithographic method allows guided wave devices to be implemented rapidly and inexpensively.     

A Low-Cost Test Methodology for Dynamic Specification Testing of High-Speed Data Converters

Testing high-speed A/D converters for dynamic specifications needs test equipment running at high frequency. In this paper, a methodology to test high-speed A/D converters using low-frequency resources is described. It is based on the alternate testing approach. In the proposed methodology, models are built to map the signatures of an initial set of devices, obtained on the proposed low-cost test set-up, to the dynamic specifications of the same devices, obtained using high-precision test equipment. During production testing, the devices are tested on the low-cost test set-up. The dynamic specifications of the devices are estimated by capturing their signatures on the low cost test set-up and processing them with the pre-developed models. As opposed to the conventional method of dynamic specification testing of data converters, the proposed approach does not require the tester resources running at a frequency higher than the device-under-test (DUT). The test methodology was verified in simulations as well as in hardware with specification estimation error of less than 5%.

Engineered Microneedles for Interstitial Fluid Cell‐Free DNA Capture and Sensing Using Iontophoretic Dual‐Extraction Wearable Patch

Interstitial fluid (ISF), as an emerging source of biomarkers, is unmistakably significant for disease diagnosis. Microneedles (MNs) provide a minimally invasive approach for extracting the desired molecules from ISF. However, existing MNs are limited by their capture efficiency and sensitivity, which impedes early disease diagnosis. Herein, an engineered wearable epidermal system is presented with a combination of reverse iontophoresis and MNs for rapid capture and sensing of Epstein‐Barr virus cell‐free DNA (an important biomarker of nasopharyngeal carcinoma). Owing to a dual‐extraction effect demonstrated by reverse iontophoresis and MNs, the engineered wearable platform successfully isolates the cell‐free DNA target from ISF within 10 min, with a threshold of 5 copies per µL and a maximum capture efficiency of 95.4%. The captured cell‐free DNA is also directly used in a recombinase polymerase amplification electrochemical microfluidic biosensor with a detection limit of 1.1 copies per µL (or a single copy). The experimental data from immunodeficient mouse models rationalizes the feasibility and practicality of the wearable system. Collectively, the developed method opens an innovative route for minimally invasive sampling of ISF for cell‐free DNA‐related cancer screening and prognosis.     

Electrochromic Reflective Displays Based on In Situ Photo-Crosslinked PEDOT:PSS Patterns

Electrochromic (EC) technology is regarded as one of the most promising candidates for next-generation reflective displays, owing to its advantages of outstanding color adjustability, low energy consumption, vivid color, and flexibility, etc. However, current EC reflective displays are seriously restricted by the complicated and expensive patterned methods. Herein, a facile and low-cost route is developed to achieve the EC reflective displays, which is fabricated based on the combination of an easily-obtained EC material of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and an efficient photo-crosslinked additive (2,4-hexadiyne-1,6-diol, HDDO). The micrometer-scale patterns (<50 µm) can be achieved by the in situ photo-crosslinked process. As-prepared EC devices show great performances containing fast response (<0.5 s), good reversibility (>10 000 cycles) and high coloration efficiency (274.75 cm² C⁻¹). More importantly, the applications in the EC logo, QR code, and price tag are demonstrated successfully. Overall, the current exploration suggests an efficient, low-cost, and facile method to produce patterned EC devices with high performance, which can undoubtedly promote the further development and application of EC reflective displays.     

Bio-Inspired Differential Capillary Migration of Aqueous Liquid Metal Ink for Rapid Fabrication of High-Precision Monolayer and Multilayer Circuits

Manipulating liquid metal inks to create conductive microstructures has attracted widespread interest as liquid metal microstructures are turning into influential components in flexible electronics. However, it is challenging to prevent the issues with low precision, low efficiency, and residue caused by sedimentation, free diffusion, and the Marangoni effect. Inspired by the water transport in plants, the wetting-induced assembly method based on the differential capillary effect for liquid metal ink is created to realize the facile and rapid manufacture of liquid metal conductive microstructures. The single-micron accuracy circuits with a minimum of ≈4 µm straight lines are fabricated to a centimeter scale. This method can also be extended to the preparation of multilayer circuits (minimum 5 µm through hole). The resulting entirely flexible stretchable circuits make it possible to construct highly stretchable devices, such as flexible transparent conductors and stretching sensors. Transparent conductors exhibit excellent mechanical (maximum ≈750% tensile rupture limit) and optoelectronic properties (the transmittance reaches ≈87% and the sheet resistance is ≈0.5 Ω/□)|making them suitable for optically-clear electromagnetic shielding. This study offers a fresh and plain approach to solving the assembly problem of liquid metal inks, paving the way for the creation of flexible electronic devices     

Laser-recrystallized silicon thin-film transistors on expansion-matched 800°C glass

Laser-recrystallized silicon thin-film transistors (TFT's) have been fabricated, for the first time, on a novel, potentially low-cost glass substrate, The 0.5-µm-thick silicon films were deposited along with appropiate dielectric layers on Corning Code 1729 glass substrates and recrystallized using an argon ion laser. The n-channel enhancement-mode transistors were made using conventional IC device fabrication procedures modified to have a maximum processing temperature of 800°C. Transistor's made in the recrystallized silicon show field-effect electron mobilities as high as 270 cm²/V.s, approximately 15 times that of comparable devices made in as-deposited polycrystalline-silicon films. The recrystallized silicon devices also exhibit lower threshold voltages and lower leakage currents than do comparable polycrystalline-silicon devices.     

Fully-Depleted PdTe2/WSe2 van der Waals Field Effect Transistor with High Light On/Off Ratio and Broadband Detection

Due to its unique band structure and topological properties, the 2D topological semimetal exhibits potential applications in photoelectric detection, polarization sensitive imaging, and Schottky barrier diodes. However, its inherent large dark current hinders the further improvement of the performance of the semimetal-based photodetectors. In this study, a van der Waals (vdWs) field effect transistor (FET) composed of semimetal PdTe₂ and transition metal dichalcogenides (TMDs) WSe₂ is fabricated, which exhibits high sensitivity photoelectric detection performance in a wide band from visible light (405 nm) to mid-infrared (5 µm). The dark current and the noise level in the device are greatly suppressed by the effective control of the gate. Benefiting from the extremely low dark current (1.2 pA), the device achieves an optical on/off ratio up to 10⁶, a high detectivity of 9.79 × 10¹³ Jones and a rapid response speed (219 and 45 µs). This research demonstrates the latent capacity of the 2D topological semimetal/TMDs vdWs FET for broadband, high-performance, and miniaturized photodetection.     

Rapid isothermal processing with electron beams of small-geometry CMOS devices

Small-geometry CMOS devices with shallow n⁺and p⁺source-drain regions formed by arsenic and boron difluoride ion implantation, respectively, have been studied. Activation of implants was produced by a single rapid isothermal anneal using the multiple-scan electron-beam approach. Transistor and circuit simulations were used to determine a requirement for the source-drain region of a sheet resistance of < 100 Ω/square with a junction depth of less than 0.2 µm in 1-µm channel length devices. These values cannot be obtained by conventional furnace annealing at 950°C, but can be achieved by a single heat treatment With an e-beam. E-beam-annealed devices have a reverse-bias junction leakage similar to furnace-annealed control samples, and show improvements in short-channel effects such as short-channel threshold voltage shifts and punchthrough, without introducing other deleterious effects.     

A kappa projection algorithm (KPA) for programming to femtoampere currents in standard CMOS floating-gate elements

We present an algorithm that enables programming of standard CMOS floating-gate devices into ultra-low current levels. This paper looks at the limitations of conventional programming schemes for these devices, as well as new methods to achieve ultra-low current levels, reliably, in these devices. Currents range from 1 µA down to 100 fA. We present measured results programming an array of bandpass filters using floating-gate transistors using the Kappa Projection Algorithm (KPA) from 10 Hz to 48 kHz. We program out device offsets and mismatches to result in very precise device behavior within the circuit elements. Experimental data is presented from circuits fabricated on a 0.5 µm nwell CMOS process available through MOSIS.     

Wireless,Flexible, Ionic,Perspiration-Rate Sensor System with Long-Time and High Sweat Volume Functions Toward Early-Stage,Real-Time Detection of Dehydration

Flexible sensors that can be attached to the body to collect vital data wirelessly enable real-time, early-stage diagnosis for human health management. Wearable sweat sensors have received considerable attention for real-time physiological monitoring. Unlike conventional methods that require blood-drawing in a clinic, sweat analyses may enable noninvasive tracking of health conditions for early-stage diagnosis. Even though a variety of studies to monitor metabolites and other substances have been conducted, automatic, continuous, long-term, simultaneous monitoring of perspiration rate and electrolytes, which are important parameters in dehydration, has yet to be achieved because of challenges related to sensor design. Here a wireless, wearable, integrated, microfluidic sensor system that can continuously measure these parameters in real-time for prolonged periods are presented. The proposed sensors are systematically characterized, and machine learning is used to predict device tilt angle to calibrate sensor output signals. Using the sensor design to form a water droplet in a fluidic channel, high-volume perspiration rate is continuously monitored for more than 7000 s (total sweat volume >170 µL). By testing 10 subjects, physiological responses to ingestion of a sports drink are confirmed by measuring perspiration rhythm changes extracted from real-time, continuous sweat impedance and rate.     

A HiPAD Integrated with rGO/MWCNTs Nano-Circuit Heater for Visual Point-of-Care Testing of SARS-CoV-2

Nowadays, the main obstacle for further miniaturization and integration of nucleic acids point-of-care testing devices is the lack of low-cost and high-performance heating materials for supporting reliable nucleic acids amplification. Herein, reduced graphene oxide hybridized multi-walled carbon nanotubes nano-circuit integrated into an ingenious paper-based heater is developed, which is integrated into a paper-based analytical device (named HiPAD). The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still raging across the world. As a proof of concept, the HiPAD is utilized to visually detect the SARS-CoV-2 N gene using colored loop-mediated isothermal amplification reaction. This HiPAD costing a few dollars has comparable detection performance to traditional nucleic acids amplifier costing thousands of dollars. The detection range is from 25 to 2.5 × 10¹⁰ copies mL⁻¹ in 45 min. The detection limit of 25 copies mL⁻¹ is 40 times more sensitive than 1000 copies mL⁻¹ in conventional real-time PCR instruments. The disposable paper-based chip could also avoid potential secondary transmission of COVID-19 by convenient incineration to guarantee biosafety. The HiPAD or easily expanded M-HiPAD (for multiplex detection) has great potential for pathogen diagnostics in resource-limited settings.