Fast Signal Response Research Articles

One-base-mismatch CRISPR-based transistors for single nucleotide resolution assay

An effective strategy for accurately detecting single nucleotide variants (SNVs) is of great significance for genetic research and diagnostics. However, strict amplification conditions, complex experimental instruments, and specialized personnel are required to obtain a satisfactory tradeoff between sensitivity and selectivity for SNV discrimination. In this study, we present a CRISPR-based transistor biosensor for the rapid and highly selective detection of SNVs in viral RNA. By introducing a synthetic mismatch in the crRNA, the CRISPR-Cas13a protein can be engineered to capture the target SNV RNA directly on the surface of the graphene channel. This process induces a fast electrical signal response in the transistor, obviating the need for amplification or reporter molecules. The biosensor exhibits a detection limit for target RNA as low as 5 copies in 100 μL, which is comparable to that of real-time quantitative polymerase chain reaction (PCR). Its operational range spans from 10 to 5 × 105 copy mL–1 in artificial saliva solution. This capability enables the biosensor to discriminate between wild-type and SNV RNA within 15 min. By introducing 10 μL of swab samples during clinical testing, the biosensor provides specific detection of respiratory viruses in 19 oropharyngeal specimens, including influenza A, influenza B, and variants of SARS-CoV-2. This study emphasizes the CRISPR-transistor technique as a highly accurate and sensitive approach for field-deployable nucleic acid screening or diagnostics.

Development of high-performance organic photodetectors by understanding origin of dark current density with synthesis of photoconductive polymers

Photoconductive polymers (PCPs) are key materials that determine the static and dynamic performance of p-n bulk heterojunction organic photodetectors (OPDs). Herein, we developed benzo[1,2-d:4,5-d']bis(oxazole)-based novel PCPs with π-spacer molecular engineering to promote charge-transport while maintaining low dark-current densities (Jd) in OPDs. The origin of Jd was elucidated by measuring hole charge-transfer (CT) state energy. We found that the degree of hole accumulation at the CT state rather than the CT state energy was crucial to maintaining a low Jd and promoting a fast signal response in the devices. The optimized OPDs showed highly promising responsivity (R) of 0.43 A/W and specific detectivity (D*) of 6.85 × 1012 Jones at −1 V under 532 nm LED (5.0 mW cm−2) illumination, which are superior to those of the control device (R = 0.29 A/W and D* = 5.46 × 1011 Jones). In addition, the dynamic properties were significantly improved by the introduction of π-spacers on the PCPs. −3 dB cut-off frequency was 200.4 kHz, and the rising and falling response times was ultrafast as 2.3 and 2.8 μs, respectively. Understanding the origin of Jd through the molecular engineering of PCPs is expected to contribute greatly toward expanding the knowledge required to develop high-performance OPDs.

Precise simulation of drift chamber in the CEPC experiment

The Circular Electron Positron Collider (CEPC) is one of the future experiments which aims to precisely study the properties of the Higgs boson and to search for new physics beyond the Standard Model. To achieve that, it puts strict requirements on the particle reconstruction and identification ability of the CEPC detector. In order to obtain better particle identification performance, the drift chamber is chosen for the outer tracking detector which can provide information used by the cluster counting method for getting excellent particle identification performance. To evaluate the performance of the cluster counting method, it is necessary to develop a simulation tool that can be used to precisely simulate the response of the gaseous particle detector. This work proposes a new way to combine Geant4 and Garfield++ at the Geant4 step level for the drift chamber simulation. Due to the extreme time consumption of simulating the avalanche process in Garfield++, a fast signal response simulation method based on a neural network has been developed to replace detailed simulation. It shows the fast simulation can give consistent results with Garfield++ simulation and achieve the speedup by a factor of 200.

Novel Ultraviolet and Ionizing Radiation Detectors Made From TiO Wide-Bandgap Semiconductor

We describe the fabrication and characterization of a novel ultraviolet (UV) and ionizing radiation detector using a polycrystalline TiO2 wide-bandgap semiconductor as the active material. The detector geometry we have developed and tested is a polycrystalline TiO2 thin film with planar electrode contacts for signal pickup. Several prototypes were fabricated using two single-step techniques. We present the dc characterization of these devices and the signal response to the UV light and low-energy proton beam irradiation. The detector prototypes show excellent dc characteristics and fast ac signal response at bias voltage as low as 50 V.

A ratiometric fluorescent aptamer homogeneous biosensor based on hairpin structure aptamer for AFB1 detection.

On the basis of aptamer (Apt) with hairpin structure and fluorescence resonance energy transfer (FRET), a ratio fluorescent aptamer homogeneous sensor was prepared for the determination of Aflatoxin B1 (AFB1). Initially, the Apt labeled simultaneously with Cy5, BHQ2, and cDNA labeled with Cy3 were formed a double-stranded DNA through complementary base pairing. The fluorescence signal of Cy3 and Cy5 were restored and quenched respectively. Thus, the ratio change of FCy3 to FCy5 was used to realized the detection of AFB1 with wider detection range and lower limit of detection (LOD). The response of the optimized protocol for AFB1 detection was wider linear range from 0.05 ng/mL to 100 ng/mL and the LOD was 12.6 pg/mL. The sensor designed in this strategy has the advantages of simple preparation and fast signal response. It has been used for the detection of AFB1 in labeled corn and wine, and has good potential for application in real samples.

A Chewing Gum Residue-Based Gel with Superior Mechanical Properties and Self-Healability for Flexible Wearable Sensor.

Chewing gum residue is hard to decompose and easy to cause pollution, which is highly desirable to realize recycling. In this paper, a chewing gum gel with enhanced mechanical properties and self-healing properties is prepared by using polyvinyl alcohol (PVA) as the backbone in chewing gum residue. The hydrogen bond and the borax ester bond are employed to construct reversible interaction to enhance the self-healing ability. The physical crosslinking is realized by further freeze-thaw treatment to improve its mechanical properties. The gel demonstrates high elongation at break of 610% and strength of 0.11MPa, as well as excellent self-healing performance and recyclable properties. In particular, the gel with a fast signal response is successfully applied as a wearable strain sensor to monitor different types of human motion. The gel as a sensor exhibits self-healing properties suggesting superior safety and stability, and displays wide linear sensitivity (the gauge factor is 0.417 and 0.170). The gel can be further served to explore temperature changes, implying the application in temperature monitoring. This study develops a novel approach for the recycle and reuse of chewing gum residue. The obtained gel may be a promising candidate for the fabrication of flexible wearable sensor.

A Super‐Stretchable and Highly Sensitive Carbon Nanotube Capacitive Strain Sensor for Wearable Applications and Soft Robotics

AbstractThe study of flexible and stretchable strain sensors is growing rapidly owing to the demands for human motion detection, human–machine interaction, and soft robotics. However, super‐stretchable and highly sensitive strain sensors with high linearity and low hysteresis are especially lacking, which therefore limits the use of soft strain sensors in varied practical applications. The stretchability and sensitivity of the capacitive strain sensor are constrained by the material characteristics and structure of parallel plate capacitor (theoretical gauge factor [GF] is 1). To address these limitations, a super‐stretchable and highly sensitive capacitive strain sensor composed of two strips of wrinkled carbon nanotubes‐based electrodes separated by a tape dielectric, is presented. By integrating nanomaterials and wrinkled film structure, this device achieves a GF of 2.07 at 300% strain with excellent linearity and negligible hysteresis. This is the first type of capacitive strain sensors that can achieve super‐stretchability and sensitivity simultaneously. Additionally, the sensor has a fast signal response time of ≈80 ms, and good mechanical durability during 1000 stretching and releasing cycles. The authors demonstrate the use of this sensor as a versatile wearable device for human motion tracking, and as a smart real‐time monitoring device for soft pneumatic robots.

Radiation hard monolithic CMOS sensors with small electrodes for High Luminosity LHC

The upgrade of the tracking detectors for the High Luminosity-LHC (HL-LHC) requires the development of novel radiation hard silicon sensors. The development of Depleted Monolithic Active Pixel Sensors targets the replacement of hybrid pixel detectors with radiation hard monolithic CMOS sensors. We designed, manufactured and tested radiation hard monolithic CMOS sensors in the TowerJazz 180 nm CMOS imaging technology with small electrodes pixel designs. These designs can achieve pixel pitches well below current hybrid pixel sensors (typically 50 × 50μm) for improved spatial resolution. Monolithic sensors in our design allow to reduce multiple scattering by thinning to a total silicon thickness of only 50μm. Furthermore monolithic CMOS sensors can substantially reduce detector costs. These well-known advantages of CMOS sensor for performance and costs can only be exploited in pp-collisions at HL-LHC if the DMAPS sensors are designed to be radiation hard, capable of high hit rates and have a fast signal response to satisfy the 25 ns bunch crossing structure of LHC. Through the development of the MALTA and Mini-MALTA sensors we show the necessary steps to achieve radiation hardness at 1015 neq/cm2 for DMAPS with small electrode designs. The sensors combine high granularity (pitch 36.4x36.4μm2), low detector capacitance (<5fF/pixel) of the charge collection electrode (3μm), low noise (ENC≈10 e−) and low power operation (1μW/pixel) with a fast signal response (25 ns bunch crossing). The sensors feature arrays of 512 × 512 (MALTA) and 16 × 64 (Mini-MALTA) pixels. To cope with high hit rates expected at HL-LHC (>200 MHz/cm2) we have implemented a novel high-speed asynchronous readout architecture. The paper summarises the optimisation of the pixel design to achieve radiation hard pixel designs with full efficiency after irradiation at >98% after 1015 neq/cm2).

Wrinkle-Enabled Highly Stretchable Strain Sensors for Wide-Range Health Monitoring with a Big Data Cloud Platform.

Flexible and stretchable strain sensors are vital for emerging fields of wearable and personal electronics, but it is a huge challenge for them to possess both wide-range measurement capability and good sensitivity. In this study, a highly stretchable strain sensor with a wide strain range and a good sensitivity is fabricated based on smart composites of carbon black (CB)/wrinkled Ecoflex. The sensor exhibits a maximum recoverable strain of up to 500% and a high gauge factor of 67.7. It has a low hysteresis, a fast signal response (as short as 120 ms), and a high reproducibility (up to 5000 cycles with a strain of 150%). The sensor is capable of detecting and capturing wide-range human activities, from speech recognition and pulse monitoring to vigorous motions. It is also applicable for real-time monitoring of robot movements and vehicle security crash in an anthropomorphic field. More importantly, the sensor is successfully used to send signals of a volunteer's breathing data to a local hospital in real time through a big data cloud platform. This research provides the feasibility of using a strain sensor for wearable Internet of things and demonstrates its exciting prospect for healthcare applications.

A graphite nanoplatelet-based highly sensitive flexible strain sensor

Flexible strain sensors, as crucial components in smart wearable devices, have recently drawn considerable attention due to their long-term monitoring abilities and facile interaction with the human body. However, low sensitivity, sluggish response, poor repeatability, sophisticated, and expensive fabrication process have notoriously limited their further deep applications. Herein, a graphite nanoplatelet (GNP) based capacitive-type strain sensor has been developed by a cost-effective gap coating method. The prepared sensors can be stretched up to 30%, and unlike other traditional capacitive-type strain sensors which have a limited theoretical maximum gauge factor of 1, it exhibits an interesting negative gauge factor, whose absolute value can go up to ∼3.5. Additionally, this work also investigated the layout design of shunt capacitors, and the pseudo-interdigital capacitor sensor demonstrated a substantial increase in the cyclic stability compared to the parallel plate capacitor. Furthermore, the as-prepared sensor has a fast signal response, whose response time is less than ∼140 ms and recovery time less than ∼90 ms. Also, the cyclic stability test of stretching proves the long-term durability of the sensor. Moreover, a microcontroller unit (MCU) system has been developed in the circuit level to realize the real-time control of a robotic hand.

Ultrasensitive Thin-Film Pressure Sensors with a Broad Dynamic Response Range and Excellent Versatility Toward Pressure, Vibration, Bending, and Temperature

Flexible pressure sensors with high sensitivity and wide pressure response range are attracting considerable research interest for their potential applications as e-skins. Nowadays, it seems a dilemma to realize high-performance, multifunctional pressure sensors with cost-effective, scalable strategy, which can simplify wearable sensing systems without additional signal processing, enabling device miniaturization and low power consumption. Herein, pressure sensors with ultrahigh sensitivity and broad response pressure range are developed with a low-cost, facile method by combining strain-induced percolation behavior and contact area contributions. Due to their special surface structure and strain induced conductive network formation behavior, these unique pressure sensors exhibit wide sensing range of 1 Pa-500 kPa, ultra-high sensitivity (1×106 kPa-1and 3.1×104 kPa-1 in the pressure ranges of 1 Pa-20 kPa and 20-500 kPa, respectively), fast signal response (< 50 ms), low detect limit (1 Pa) and high stability over 500 loading/unloading cycles. These characteristics allow the devices work as e-skins to monitor human pulse signals and finger touch. Moreover, these sensors illustrate precise electrical response to mechanical vibration, bending and temperature stimuli, which afford the ability of detecting cell phone call-in vibration signals, joint bending and spatial pressure & temperature distributions, indicating promising applications in next-generation wearable, multifunctional e-skins.

Novel optical composite material for efficient vanadium(III) capturing from wastewater

The high-efficient detection and recovery of vanadium (V(III)) using organic ligand embedded inorganic-organic mesoporous composite material (MeCM) was studied in this work. After 2‑methyl‑8‑quinolinol immobilization onto the porous silica, the MeCM was confirmed the high surface area, large pore diameters and ordered morphological homogeneity. The MeCM was exhibited fast and specific signal response to V(III) ion, and the color was observed by naked-eye based on the charge-transfer stable complexation mechanism. The MeCM was influenced by the solution pH and pH 3.50 was selected for the highest detection and adsorption ability. The limit of detection was 0.27 μg/L, which was remarkably low as defined. The MeCM was also exhibited comparatively high kinetic performances as the equilibrium adsorption was observer within short contact time. The adsorption data were fitted with the Langmuir isotherm model as expected from the MeCM morphology. The maximum capacity was found to be 192.16 mg/g with the monolayer adsorption coverage. The presence of diverse metal ion was not affected significantly during the detection and adsorption operations. The V(III) ion desorbed from the MeCM using 0.15 M HCl and then simultaneously regenerated into the initial functionality for next operation as revealed from the several cycles reuses study. Therefore, the proposed MeCM is allowed to the sensitive, selective, easy to use, cost-effective, high efficiency, fast kinetics and stable capturing of V(III) ion even in the presence of diverse competing ion. In addition, there was no more secondary sludge production due to the reusability and makes it a potential candidate in better replacement technology for capturing V(III) ion in a wide range of practical purposes.

Application Research of the Non-Destructive Testing Using Optical Fiber Sensor

In this paper, an optical fiber sensor is designed by using optical Faraday effect. It is composed of fiber collimator, polarizer, magneto-optical crystal and mirror. Based on the magnetic flux leakage (MFL) theory, The optical fiber sensor was placed between two permanent magnets with the N-pole. Therefore, the optical fiber sensing system was built to detect the defective ferromagnetic objects. Theoretical and experimental studies shown that the system can identify a little defects, such as irons’ blind hole (diameter φ = 3mm , depth t = 4mm ), irons’ grooves (length l= 30mm , width ω = 10mm ), hole (φ = 3mm ) and crackle etc. The system has the characteristics of small size, high sensitivity, fast signal response and high resolution. In terms of the defective oil and gas pipelines detection, The optical fiber sensing system is used in non-destructive testing, which will be valuable and meaningful.

Through-Layer Buckle Wavelength-Gradient Design for the Coupling of High Sensitivity and Stretchability in a Single Strain Sensor.

Recent years have witnessed a breathtaking development of wearable strain sensors. Coupling high sensitivity and stretchability in a strain sensor is greatly desired by emerging wearable applications but remains a big challenge. To tackle this issue, a through-layer buckle wavelength-gradient design is proposed and a facile and universal fabrication strategy is demonstrated to introduce such a gradient into the sensing film with multilayered sensing units. Following this strategy, strain sensors are fabricated using graphene woven fabrics (GWFs) as sensing units, which exhibit highly tunable electromechanical performances. Specifically, the sensor with 10-layer GWFs has a gauge factor (GF) of 2996 at a maximum strain of 242.74% and an average GF of 327. It also exhibits an extremely low minimum detection limit of 0.02% strain, a fast signal response of less than 90 ms, and a high cyclic durability through more than 10 000 cycling test. Such excellent performances qualify it in accurately monitoring full-range human activities, ranging from subtle stimuli (e.g., pulse, respiration, and voice recognition) to vigorous motions (finger bending, walking, jogging, and jumping). The combination of experimental observations and modeling study shows that the predesigned through-layer buckle wavelength gradient leads to a layer-by-layer crack propagation process, which accounts for the underlying working mechanism. Modeling study shows a great potential for further improvement of sensing performances by adjusting fabrication parameters such as layers of sensing units ( n) and step pre-strain (εsp). For one thing, when εsp is fixed, the maximum sensing strain could be adjusted from >240% ( n = 10) to >450% ( n = 15) and >1200% ( n = 20). For the other, when n is fixed, the maximum sensing strain could be adjusted from >240% (εsp = 13.2%) to >400% (εsp = 18%) and >800% (εsp = 25%).

Core-shell diode array for high performance particle detectors and imaging sensors: status of the development

We propose a novel high performance radiation detector and imaging sensor by a ground-breaking core-shell diode array design. This novel core-shell diode array are expected to have superior performance respect to ultrahigh radiation hardness, high sensitivity, low power consumption, fast signal response and high spatial resolution simultaneously. These properties are highly desired in fundamental research such as high energy physics (HEP) at CERN, astronomy and future x-ray based protein crystallography at x-ray free electron laser (XFEL) etc.. This kind of detectors will provide solutions for these fundamental research fields currently limited by instrumentations. In this work, we report our progress on the development of core-shell diode array for the applications as high performance imaging sensors and particle detectors. We mainly present our results in the preparation of high aspect ratio regular silicon rods by metal assisted wet chemical etching technique. Nearly 200 μm deep and 2 μm width channels with high aspect ratio have been etched into silicon. This result will open many applications not only for the core-shell diode array, but also for a high density integration of 3D microelectronics devices.

Antibody-based SAW sensor for the detection of explosives

A robust and sensitive method for the detection of the explosive trinitrotoluene (TNT) was developed. The detection limit was determined to be around 0.5 µg/L. The fast signal response of less than 1 minute shows that this approach is suitable for security and other time-critcal applications. In addition, the very low cross-reactivity highly reduces the number of false-positives in relation to competing techniques, including sniffer dogs. Due to the multianalyte ability of the SAW system, several explosives might be detected in parallel.

TES X-ray microcalorimeters for X-ray astronomy and material analysis

TES X-ray microcalorimeter arrays provide not only high-energy resolution (FWHM < 10eV) in X-ray spectroscopy but also imaging and high-counting-rate capabilities. They are very promising spectrometer for X-ray astronomy and material analysis. In this paper, we report our recent progress. For material analysis, we have fabricated 8 × 8 format array with a fast signal response ( 40 µs) and proved the energy resolution of 5.8 eV FWHM at 5.9 keV. We developed common biasing scheme to reduce number of wirings from room temperature to the cryogenic stage. From measurements using the newly-designed common-bias SQUID array amplifier chips, and from numerical simulations, we demonstrated that signal cross talks due to the common bias is enough small. For space applications, we are developing frequency-division signal multiplexing system. We have fabricated a baseband feedback system and demonstrated that the noise added by the feedback system is about 4 eV FWHM equivalent for 16 ch multiplexing system. The digital to analog converter (DAC) dominates the noise, and needs be reduced by a factor of four for future astronomy missions.

Core–shell diodes for particle detectors

High performance particle detectors are needed for fundamental research in high energy physics in the exploration of the Higgs boson, dark matter, anti-matter, gravitational waves and proof of the standard model, which will extend the understanding of our Universe. Future particle detectors should have ultrahigh radiation hardness, low power consumption, high spatial resolution and fast signal response. Unfortunately, some of these properties are counter-influencing for the conventional silicon drift detectors (SDDs), so that they cannot be optimized simultaneously. In this paper, the main issues of conventional SDDs have been analyzed, and a novel core–shell detector design based on micro- and nano-structures etched into Si-wafers is proposed. It is expected to simultaneously reach ultrahigh radiation hardness, low power consumption, fast signal response and high spatial resolution down to the sub-micrometer range, which will probably meet the requirements for the most powerful particle accelerators in the near future. A prototype core–shell detector was fabricated using modern silicon nanotechnology and the functionality was tested using electron-beam-induced current measurements. Such a high performance detector will open many new applications in extreme radiation environments such as high energy physics, astrophysics, high resolution (bio-) imaging and crystallography, which will push these fields beyond their current boundaries.

Synthesis and photo-property of 2-cyano boron-dipyrromethene and the application for detecting fluoride ion

Three 2-cyano boron-dipyrromethene (BODIPY) based derivatives (CB1–CB3) have been synthesized and characterized. The photophysical properties of these compounds are investigated by means of UV/Vis absorption and fluorescence spectroscopy. CB1–CB3 exhibit small Stokes shift and high fluorescence quantum yield. Noticeably, CB2 with styrene moieties at 5-position of BODIPY displays absorption alternation with maximum of 120 nm red-shift upon addition of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) as a base, giving remarkable color change which can be detected by naked eye. Meanwhile, the compound CB3 shows high selectivity toward fluoride ion via fluorescence quenching mechanism by release of the masked phenolate form of CB2 through fluoride ion induced deprotection reaction. It also exhibits fast signal response time (30 s) and excellent selectivity over other competing analytes, making it a good candidate as colorimetric sensor for fluoride sensing.

Rational design of a low-affinity peptide for the detection of cystatin C in a fast homogeneous immunoassay.

Immunoassays play an essential role in current research and diagnostics resulting in a variety of detection principles. Thereby, homogeneous assays are often used for a fast signal response as demanded for example in point-of-care diagnostics. These systems often rely on a competitive assay design where the sample analyte and the corresponding dye-labeled substance are competing for binding sites on an antibody present in limited amounts. Due to the similar affinities of the antibody towards the sample analyte and the competitor, both sensitivity and assay time are limited. As a consequence, a competitor with a slightly reduced affinity towards the antibody can potentially overcome these drawbacks. Here, we present the rational design of a low-affinity peptide (donor peptide) as a specific analyte competitor for a FRET-based homogeneous immunoassay for the analysis of the protein cystatin C. Thereby, the strategy of peptide-induced antibody generation was combined with the selective variation of the immunization sequence in order to achieve a lower affinity towards the antibody. We could show that shortened donor peptides improved the resulting quenching efficiency in the immunoassay. In addition, the substitution of small hydrophobic amino acids by those with a higher steric demand appeared to be the most promising strategy providing a fast assay response for cystatin C of only 90s.