Ultrafast Sensor Research Articles

Bioinspired Photoluminescent "Spider Web" as Ultrafast and Ultrasensitive Airflow-Acoustic Bimodal Sensor for Human-Computer Interaction and Intelligent Recognition.

Nature provides massive biomimetic design inspiration for constructing structural materials with desired performances. Spider webs can perceive vibrations generated by airflow and acoustic waves from prey and transfer the corresponding information to spiders. Herein, by mimicking the perception capability and structure of a spider web, an ultrafast and ultrasensitive airflow-acoustic bimodal sensor (HOF-TCPB@SF) is developed based on the postfunctionalization of hydrogen-bonded organic framework (HOF-TCPB) on silk film (SF) through hydrogen bonds. The "spider web-like" HOF-TCPB@SF possesses light weight and high elasticity, endowing this airflow sensor with superior properties including an ultralow detection limit (DL, 0.0076 m s-1), and excellent repeatability (480 cycles). As an acoustic sensor, HOF-TCPB@SF exhibits ultrahigh sensitivity (105140.77 cps Pa-1 cm-2) and ultralow DL (0.2980 dB), with the greatest response frequency of 375 Hz and the ability to identify multiple sounds. Moreover, both airflow and acoustic sensing processes show an ultrafast response speed (40 ms) and multiangle recognition response (0-180°). The perception mechanisms of airflow and acoustic stimuli are analyzed through finite element simulation. This bimodal sensor also achieves real-time airflow monitoring, speech recognition, and airflow-acoustic interoperability based on human-computer interaction, which holds great promise for applications in health care, tunnel engineering, weather forecasting, and intelligent textiles.

Ultrafast and Reproducible Fiber-Optic Hydrogen Sensor via a Tilted Fiber Grating With Pd/WO3 Nanocoating

Hydrogen, a high-density and clean energy, has been widely used in various critical applications. However, the safety risk caused by hydrogen leakage during storage and transportation is still a non-negligible issue. Therefore, it is necessary to offer hydrogen sensors with fast response and high repeatability, and it will be perfect for achieving in situ monitoring over the lifecycle of hydrogen production and utilization. Here, we propose a compact optical fiber sensor with a short section of the tilted Bragg fiber grating (TFBG) inscribed in the fiber core and a palladium and tungsten trioxide (Pd/WO3) combined film of 40 nm thickness over the fiber surface. The TFBG excites tens of narrow cladding resonances, part of which possess refractive indexes matching that of the Pd/WO3 coating and providing the high sensitivity to the surrounding hydrogen concentration change. The sensor offers improved sensing characteristics, including the fast response time (less than 10 s), high repeatability (over tens of measurement), and excellent linear response (higher than 99.6%) over the 0% to 3% concentration range.

Viscous terahertz photoconductivity of hydrodynamic electrons in graphene.

Light incident upon materials can induce changes in their electrical conductivity, a phenomenon referred to as photoresistance. In semiconductors, the photoresistance is negative, as light-induced promotion of electrons across the bandgap enhances the number of charge carriers participating in transport. In superconductors and normal metals, the photoresistance is positive because of the destruction of the superconducting state and enhanced momentum-relaxing scattering, respectively. Here we report a qualitative deviation from the standard behaviour in doped metallic graphene. We show that Dirac electrons exposed to continuous-wave terahertz (THz) radiation can be thermally decoupled from the lattice, which activates hydrodynamic electron transport. In this regime, the resistance of graphene constrictions experiences a decrease caused by the THz-driven superballistic flow of correlated electrons. We analyse the dependencies of the negative photoresistance on the carrier density, and the radiation power, and show that our superballistic devices operate as sensitive phonon-cooled bolometers and can thus offer, in principle, a picosecond-scale response time. Beyond their fundamental implications, our findings underscore the practicality of electron hydrodynamics in designing ultra-fast THz sensors and electron thermometers.

An ultrafast optical sensor for simultaneous detection of NH3 temperature and concentration based on ultraviolet absorption spectral redshift combined with spectral reconstruction

As a renewable and carbon-free fuel with high energy density, ammonia (NH3) is a promising alternative to fossil fuels. Real-time detection of its temperature and concentration is significant in improving NH3 combustion efficiency. In this paper, we report an optical sensor, which enables simultaneous measurement of temperature and concentration of NH3. The key idea is to acquire the temperature of NH3 through absorption spectral redshift, and determine its concentration by building three-dimensional field map combined with spectral reconstruction. Firstly, we explain the generation mechanism of temperature-induced redshift in ultraviolet differential absorption spectrum based on energy level distribution theory. The relationship between spectral redshift and temperature is then established using spectral autocorrelation algorithm. Secondly, a spectral reconstruction method based on absorbed intensity mapping wavelength is proposed to ensure real-time detection of NH3. Finally, a three-dimensional field map between temperature, reconstruction slope, and concentration is constructed to achieve the detection. Results indicated that the mean relative error in temperature measurement was 1.04% and the mean absolute error in concentration detection was 0.26mg/m3 in air. Additionally, the NH3 sensor enabled long-term detection with a detection limit of 15.50μg/m2, demonstrating its potential to broaden the application of NH3 as a fuel.

A Single-Pixel Event Photoactive Device for Real-Time, In-Sensor Spatiotemporal Optical Information Processing.

The increasing demand for energy-efficient, sophisticated optical sensing technologies in various applications, from machine vision to optical communication, highlights the necessity for innovations in spatiotemporal information sensing and processing at a nearly single-pixel scale. Traditional methods, including multi-pixel photodetector arrays and event-based camera systems, often fail to provide rapid, real-time detection and processing of dynamic events within the sensor. This shortcoming is particularly notable in handling high-dimensional spatiotemporal data, where the dependency on sequential data input and external processing tools leads to latency, reduced throughput, and heightened energy consumption, thereby impeding real-time parallel data processing capabilities. Here, a carrier-selective, single-pixel, position-sensitive planar photoactive device that integrates spatiotemporal event sensing with inherent short-term memory capabilities is introduced. The proof-of-concept single-pixel event photoactive device enables in-sensor spatiotemporal parallel optical information processing, efficiently managing multibit (>4 bit) data simultaneously and facilitating ultrafast (≈0.4µs) recognition of input patterns with low energy consumption (25 femtojoules). Additionally, by adjusting the operating speed from continuous to pulsed light illumination, the sensor array can detect trajectories and absolute position of events, offering in-sensor optical flow detection. This single-pixel event photodetector marks significant advancement toward developing compact, energy-efficient, ultrafast sensors suitable for a wide range of in sensor-based photonic applications.

Chemiresistive room temperature H2S gas sensor based on MoO3 nanobelts decorated with MnO2 nanoparticles

In this work, we develop ultrafast detection and reversible H2S gas sensor at room temperature (RT, 23 ℃). The optimized MoO3/MnO2 (MM-10) sensor exhibits remarkable sensitivity to H2S with a response of 32.51–100 ppm H2S at RT, which is approximately 21.82 times higher than that of the MoO3 sensor. Further, the MM-10 sensor demonstrates a fast response of 5.71–1000 ppb H2S with response/recovery times of 40/42 s at RT. More surprisingly, the theoretical limit of the MM-10 sensor for detecting H2S gas is as low as 4.58 ppb at RT, which addresses the limitation of binary heterojunction-based sensors in detecting ppb-level H2S gas at RT. After 49 days, the MM-10 sensor still demonstrates reliable stability, ensuring the long-term detection to ppb-level H2S at RT in practical applications. Notably, as the relative humidity increases from 30 % to 90 %, the response only decreases by about 17 %, indicating an excellent shielding ability against water molecules. Additionally, it is found that 1 % relative humidity change has a comparable effect on MM-10 sensor as approximately 5.58 ppb H2S gas. The significant enhancement mechanism on the sensing surface in the context of H2S/MoO3/MnO2 interaction is also thoroughly discussed.

Ultrafast response humidity sensor based on titanium dioxide quantum dots/silica and its multifunctional applications

Humidity sensors with ultrafast response and recovery speed are very popular for humidity monitoring in dynamic environments such as complex operating conditions and human body monitoring. In this work, we prepared titanium dioxide quantum dots by hydrothermal synthesis and silica microspheres by Stober method. In addition, the electrostatic self-assembly method was used to prepare the two films with ultrafast response for moisture sensitivity. Due to the superhydrophilic properties of TiO2 QDs, water molecules can be adsorbed and resolved quickly on their surface. While the addition of SiO2 microspheres further increases the specific surface area of moisture-sensitive films and improves the moisture-sensitive properties of TiO2 QDs. The TiO2 QDs/SiO2 resistive humidity sensors not only exhibit excellent stability and repeatability, but also have fast water adsorption/desorption capacity. Between 11 % and 97 % relative humidity, the resistance change of the sensor reaches 6 orders of magnitude. In order to simulate the actual application environment, an experimental platform was built to verify the ultrafast response of the humidity sensor, and the response/recovery time of the sensor was as short as 22.4 ms/40.8 ms, which can quickly detect the change of humidity. The TiO2 QDs/SiO2 ultrafast humidity sensors proposed in this paper have great application potential in rapidly changing humidity environments such as complex working conditions, human body detection, humidity alarm and voice recognition.

Self-Powered cobalt nanocluster decorated flexible graphene based Tribo-Sensors for respiratory diagnosis of critical asthma patient

Self-powered ultrafast sensors have received much attention for sustainable operation without any external power source in the Internet of Things (IoT) platform. This paper proposes faster responsive, highly sensitive triboelectric nanogenerator (TENG) sensors based on few layered nitrogen-doped graphene anchored with cobalt nanocluster (Co-N-Gr) to detect the relative concentration of target species, their proximity analysis, and monitor malfunction of human respiration in real-time. Herein, to understand the sensing mechanism, P-type behaviour of this active material is verified under the FET platform by reducing the leakage current density via the implementation of dual dielectric gate (NiO (200 nm)-SiO2 (10 nm)) oxides leading to better control over channel mobility. The device exhibits maximum sensitivity of around 4722 % at zero bias conditions with excellent response and recovery time of 1.16 s and 1.39 s, respectively which falls within the range of standard human breathing frequency. The triboelectric nature of the sensor device at 1 V bias under natural breathing exhibits a high sensitivity (39.56 %) towards relative humidity of 10–90 % with excellent stability over 13 h. In addition, our TENG sensor is highly sensitive towards NOx content upto ppb levelwhich can improve reliability towards asthma detection as NOx content is relatively higher in asthma patients. This approach provides an integrated platform not only towards selective detection of NOx content as well as to identify the individual breathing strength. Furthermore, as-fabricated self-powered device demonstrates its potential in differentiating various respiratory status and has the capability to detect acute exacerbation of chronic obstructive pulmonary disease (AECOPD) via a distinct pattern recognition. Therefore, the work paves the way to design a low-cost flexible device fabrication on Kapton substrate integrable with wearable appliances for commercialization.

High reflectivity, ultraflat-spectrum chirped fiber Bragg grating written using low energy UV femtosecond pulses

Chirped fiber Bragg gratings (CFBGs) have been extensively used in applications such as ultrafast lasers, fiber sensors, and fiber communications. This work presents a comprehensive investigation of CFBG written using a 257 nm femtosecond laser and a linear chirped phase mask. The CFBG, written on a hydrogen-loaded polarization-maintaining fiber, exhibited a center wavelength of 1031.7 nm and a bandwidth of 11.97 nm. The CFBG achieved an average reflectivity of 98.2 % within its bandwidth, demonstrating an ultrahigh flatness of the reflection spectrum with a low spectral reflectivity variance of 0.00003 (σ2). The high group velocity dispersion (GVD) of 60.7 ps2 signifies its potential in fiber chirped pulse amplification systems and dispersion compensation system. Meanwhile, the fs-laser + PM writing method shows advantages of high efficiency and low energy consumption (as low as 2 nJ), owing to the high photosensitivity of the fiber to the UV band, which holds significant promise in fiber grating inscription.

Ultrafast and low-hysteresis humidity sensors based on mesoporous LaFe0.925Ti0.075O3 perovskite

Humidity sensors are omnipresent. Thus, significant efforts have been undertaken to advance their performance, for example, to have a fast detection time, negligible hysteresis, and excellent stability. Despite numerous active research endeavors, establishing a sensor that excels in all these key performances is still challenging. Here, we address this challenge by designing a capacitive-based humidity sensor employing porous LaFeO3 perovskite. Integrating Ti into the perovskite using a sol-gel method, i.e., LaFe0.925Ti0.075O3, results in a 400% increase in specific surface area achieved through pore formation, translating to a 2094% response parameter. Furthermore, due to the rapid equilibrium between adsorption and desorption processes, the sensor achieves ultrafast 4.4 s response time and 1.4 s recovery time, with <1% hysteresis and excellent stability over 28 days, when assessed at 300 K. Our work significantly advances current humidity sensor performance and, in a broader context, emphasizes the efficacy of porous (perovskite) materials for high performance gas detection.

Respiration-based human-machine interface for aphasic patients with limited physical mobility

Communication between aphasic patients and health care professionals (HCPs) is often difficult, which is even more complex for aphasic patients with limited physical mobility. In this study, we have proposed a C60-OH/PDDA/SiO2-based humidity sensor with an extremely short response/recovery time (13 ms/30 ms). This is closely related to the electrostatic adsorption of PDDA which effectively alleviates the aggregation of C60-OH and the introduction of SiO2 microspheres which increases the diffusion space of water molecules. The fast response and recovery rates gave the sensor good respiratory monitoring capability, which can be used to develop a human–machine interface (HMI) to assist aphasic patients for semantic expression. In this HMI, aphasia patients can generate different respiratory signals through the ultrafast humidity sensors to express specific semantics (such as thirst, hunger, etc.). In contrast to traditional semantic expression devices, this interface does not require the user to have vocal or physical movement, and therefore is extremely friendly to aphasic patients with limited mobility.

Unlocking stray light mysteries in the CoRot baffle with the time-of-flight method

Stray light (SL) has emerged as a primary limiting factor for space telescopes. Pre-launch testing is essential for validating performance and identifying potential issues. However, traditional methods do not enable the decomposition and identification of individual SL contributors. Consequently, when problems arise, resolving them often involves a cumbersome and risky trial-and-error approach. The time-of-flight (ToF) method was recently introduced, employing a pulsed laser source and ultrafast sensor to characterize individual SL contributors. A proof of concept was achieved using a simple three-lens system. In this paper, we apply the ToF method to a real space optical system: the spare model of the CoRoT baffle. We successfully measured individual SL contributors over a dynamic range of 10−11, identifying direct scattering on vane edges and two-step scattering paths. Our results provide a performance breakdown, differentiating intrinsic baffle SL from contributions arising from experimental conditions. Notably, the ToF method allowed us to discriminate air scattering, eliminating the need for expensive vacuum testing. The ToF provides unparallel insights, including defects identification. For instance, we identified the presence of localized dust particles causing significant SL. These results confirm the utility of the ToF method even for the most challenging space systems.

Ultrafast, Flexible, and Selective Water Sensor Based on Multiwalled Carbon Nanotubes/Poly(vinylidene fluoride) Screen-Printed on Cotton Fabric

Ultrafast, Flexible, and Selective Water Sensor Based on Multiwalled Carbon Nanotubes/Poly(vinylidene fluoride) Screen-Printed on Cotton Fabric

Interconnected SnO2 nanoflakes decorated WO3 composites as wearable and ultrafast sensors for real-time wireless sleep quality tracking and breath disorder detection

Monitoring human breath is critical for determining human well-being. Most reported humidity sensors are unsuitable for breath monitoring because of their long response and recovery time, poor stability, and high operating temperature. To address these challenges, robust tungsten oxide (WO3) and tin oxide (SnO2) composite sensors were fabricated, and their humidity-sensing properties were investigated. The SnO2/WO3 composites were optimized by altering the SnO2 fraction to achieve high humidity sensitivity. The SnO2/WO3 composite exhibited superior sensing performance (88) than pristine WO3 and SnO2 under 97 % relative humidity. The sensor demonstrated good linearity while altering humidity from 15 % to 97 %, with an R2 = 0.9729. The sensor's rapid response (0.6 s) and recovery (0.6 s) time allow for breath rate monitoring and breath disorder detection. The wearable sensor demonstrated multifunctional human breath detections such as varied breath rates (5–60 breaths per minute), nose blocking for separate nostrils, wireless sleep quality tracking for more than 7 h continuously, and sleep apnea-hypopnea detection via a smartphone. The capabilities of the humidity sensor allow for robust application in sleep quality, sleep apnea, and hypopnea detection.

Time-resolved X-ray diffraction diagnostic development for the National Ignition Facility.

We present the development of an experimental platform that can collect four frames of x-ray diffraction data along a single line of sight during laser-driven, dynamic-compression experiments at the National Ignition Facility. The platform is comprised of a diagnostic imager built around ultrafast sensors with a 2-ns integration time, a custom target assembly that serves also to shield the imager, and a 10-ns duration, quasi-monochromatic x-ray source produced by laser-generated plasma. We demonstrate the performance with diffraction data for Pb ramp compressed to 150GPa and illuminated by a Ge x-ray source that produces ∼7 × 1011, 10.25-keV photons/ns at the 400μm diameter sample.

Light-driven ultrafast sensor based on biocompatible solvatochromic metal-organic framework

The design of fast, endurant, and biocompatible porous frameworks with solvatochromism, aimed to address the multiple visual sensing of chemicals, yet remains a challenge. Here, we report on a solvatochromic...

Facile construction of nanocubic Mn3[Fe(CN)6]2@Pt based electrochemical DNA sensors for ultrafast precise determination of SARS-CoV-2

Owing to the high mortality and strong infection ability of COVID-19, the early rapid diagnosis is essential to reduce the risk of severe symptoms and the loss of lung function. In clinic, the commonly used detection methods, including the computed tomography (CT) and reverse transcription-polymerase chain reaction (RT-PCR), are often time-consuming with bulky instruments, which normally require more than one hour to report the results. To shorten the analytical period for testing the COVID-19 virus (SARS-CoV-2), we proposed an ultrafast and ultrasensitive DNA sensors to achieve an accurate determination of the DNA sequence by the RNA reverse transcription (rtDNA) of the SARS-CoV-2. A nanocubic architecture of the MnFe@Pt crystals was constructed to integrate both electrocatalysis and conductivity to greatly improve the biosensing performance. After the immobilization of a specific capture and report DNA on above nanocomposite, the rtDNA can be rapidly caught to the DNA sensor to form a double-helix structure, thus generating the current signal change. Within only 10 min, the as-prepared DNA sensors exhibited ultralow detection limit (1 × 10−20 M) and wide linear detection range, together with an outstanding selectivity among various interfering substances.

Ultrafast Electrochemical Sensor Based on Electrical Potential-Assisted Hybridization for Non-Amplification Determination of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) by Differential Pulse Voltammetry (DPV)

A highly ultrafast and sensitive electrochemical sensor based on electrical potential-assisted hybridization was developed for the determination of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The electrode was modified with multi-walled carbon nanotubes (MWCNTs) and Au nanoparticles (AuNPs) for excellent electrochemical performance. The constant electric field was applied to rapidly and efficiently enrich the capture probes to the electrode surface in 60 s. Meanwhile, pyrene as the backfill reagent resulted in a significant reduction of nonspecific adsorption. The electrochemical properties of the modified electrode were investigated via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The analytical response was measured by differential pulse voltammetry (DPV). The sensor achieved the ultrafast hybridization of nucleic acids at the electrode interface within 90 s, substantially reducing the reaction time from hours to minutes. Under optimal conditions, the sensor exhibited a superior detection limit of 60 fM and showed satisfactory specificity toward single-base mismatch. Additionally, the proposed sensor realized sensitive determination of SARS-CoV-2 in throat swabs. The enzyme-free and non-amplification sensing strategy showed promising potential for application in point-of-care testing (POCT).

Advantages of Slow Sensing for Ambient Monitoring: A Practical Perspective

Air pollution is a ubiquitous threat, affecting 99% of the global populace and causing millions of premature deaths annually. Monitoring ambient air quality is essential, aiding policymakers and environmental agencies in timely interventions. This study delves into the advantages of slower gas sensors over their ultrafast counterparts, with a keen focus on their practicality in real-world scenarios. Slow sensors offer accurate time-averaged exposure assessments, harmonizing with established regulatory benchmarks. Their heightened precision and reliability, complemented by their cost-effectiveness, render them eminently suitable for large-scale deployment. The slow sensing ensures compatibility with regulations, fostering robust risk management practices. In contrast, ultrafast sensors, while claiming rapid detection, despite touting swift detection capabilities, grapple with formidable challenges. The sensitivity of ultrafast sensors to uncontrolled atmospheric effects, fluctuations in pressure, rapid response times, and uniform gas dispersion poses significant hurdles to their reliability. Addressing these issues assumes paramount significance in upholding the integrity of air quality assessments.

Bimodal Gating Mechanism in Hybrid Thin-Film Transistors Based on Dynamically Reconfigurable Nanoscale Biopolymer Interfaces.

In recent years, increased control over naturally-derived structural protein formulations and their self-assembly has enabled the application of high-resolution manufacturing techniques to silk-based materials, leading to bioactive interfaces with unprecedented miniaturized formats and functionalities. We present here a hybrid biopolymer-semiconductor device obtained by integrating nanoscale silk layers in a well-established class of inorganic field-effect transistors (silk-FETs). The devices offer two distinct modes of operation - either traditional field-effect or electrolyte-gated - enabled by the precisely controlled thickness, morphology and biochemistry of the integrated silk layers. The different operational modes are selectively accessed by dynamically modulating the free-water content within the nanoscale protein layer from the vapor phase. The utility of these hybrid devices is illustrated in a highly sensitive and ultrafast breath sensor, highlighting the opportunities offered by the integration of nanoscale biomaterial interfaces in conjunction with traditional semiconductor devices, enabling functional outcomes at the intersection between the worlds of microelectronics and biology. This article is protected by copyright. All rights reserved.