Sensitive Sensor Research Articles

A Highly Sensitive, Conductive, and Flexible Hydrogel Sponge as a Discriminable Multimodal Sensor for Deep‐Learning‐Assisted Gesture Language Recognition

AbstractFlexible multimodal sensors have gained increasing popularity for applications in healthcare and extreme environment operations owing to their all‐around environmental perception and data acquisition capabilities. However, fabricating a magnetism‐mechanics‐humidity multimodal sensor that possesses high sensitivity without signal overlapping while in a facile methodology remains a great challenge. Herein, a highly sensitive, conductive, and flexible hydrogel sponge sensor with discriminable magnetism, mechanics, and humidity sensing capability is proposed, which shows stable pore size (19.30 µm) and satisfactory mechanical properties based on the synergistic hydrogen bonding among sodium alginate, poly(vinyl alcohol) and glycerol. The proposed sensors can not only display favorable humidity sensing ability with rapid response/recovery time (2.5/4 s) but also possess enhanced sensitivities (a gauge factor of 0.46 T−1 for magnetic field, −1.16 kPa−1 for pressure), superior stability and durability (over 8000 cycles). Benefiting from the separated capacitive and resistive response signals, the sensors can precisely distinguish the magnetic, mechanical, and humidity stimuli without cross‐talk. Further, the sensor arrays assisted by the deep learning algorithm are developed to realize gesture language recognition with a high accuracy of 99.17%. It can be believed that this high‐performance sensor will have good prospects in future soft electronics and human‐machine interaction systems.

Size Effects of Gold Nanoparticles on Surface Plasmon Resonance Assays for DNA Hybridization.

Recent advancements in signal amplifiers, such as biofunctionalized gold nanoparticles (AuNPs) have improved the surface plasmon resonance (SPR) performance. However, the correlation between the sizes of DNA-Au conjugates and the SPR chips remains elusive. We investigated how the size of AuNPs functioned with DNA detection probes (D-AuNPs) affect SPR signals in sandwich DNA hybridization assays. The effects of three sizes (5, 13, and 29 nm) of D-AuNPs with an equal surface probe density were systematically compared to delineate the relationship between signal amplification and steric hindrance. Sporadically adsorbed target DNA on sparse capture probe-coated chips led to a growth of signal amplification with larger D-AuNPs. In contrast, on dense capture probe-coated SPR chips, when the target DNA concentration was above 1.5 nM, the medium-sized 13-nm AuNPs displayed 1.7- and 1.3-fold enhancement factors than 5-nm and 29-nm ones, respectively. Our results indicate the steric hindrance disturbs the capture of D-AuNPs on dense target DNA-modified chips, rendering the surface density of captured D-AuNPs a determining factor of the sensor response. Alternatively, the sensor sensitivity to D-AuNP surface density is crucial on chips with sparse target DNA. These insights should stimulate and guide future research on surface functionalization toward SPR sensors and AuNPs.

Two-component heterojunction-based ambipolar field effect transistors for improved sensitivity of ammonia sensor

To improve the sensing response of ammonia (NH3) sensors, a two-dimensional configuration molecule 5,11-di-naphthalen-2-yl-6,12-dihydro-indolocarbazole (ICZ-NA) was designed and synthesized as the p-channel organic semiconductor material. Bilayer organic field-effect transistor (OFET) was constructed with ICZ-NA and N,N’-bis(n-octyl)-2,6-dicyanonaphthalene-1,4,5,8-bis(dicarboximide (NDI-8CN2) as p-type and n-type active semiconductor materials respectively, and the two-component devices exhibits excellent ambipolar FET performance. The thin film transistors based on single-component and two-component were further used as sensors for ammonia detection. Compared with the sensors based on NDI-8CN2, the sensitivity and selectivity of ammonia detection based on two-component sensors have been greatly improved, and the ratio of current change can still be maintained over 3.65 %, when the gas concentration lower to 10 ppb level. The higher sensing response and low limit of detection demonstrate that the two-component ambipolar configuration is a highly effective method for improving sensing response capability.

E-waste driven eco-friendly highly sensitive wearable capacitive sensors for physical activity monitoring and sign language recognition

Owing to the continual and rapid advancement in technology, there has been a significant surge in electronic waste (e-waste) in recent decades, resulting in a harmful impact on our environment. Due to the growing demand for battery-powered devices, non-rechargeable batteries are a significant source of e-waste. This study describes fabricating a paper-based graphite strain sensor that is eco-friendly, inexpensive, biodegradable, and sensitive to the applied strain. Readily accessible materials are employed to design and fabricate MIDC strain sensors. The Modified Interdigital Capacitor (MIDC) structure is formed on basic printing paper, and the conductive substance made with the ink of a gel pen and graphite from a drained dry cell is painted on the paper and used as electrode material. The suggested sensor has a high gauge factor value of 1998.578 and fast response and recovery time of 112 ms and 100 ms, respectively. The proposed prototype has also been utilized to inspect fitness exercises and physical activities on the human body, inspiring the potential for its integration into wearable systems for various applications. Reliable detection and differentiation of finger positions are achieved, highlighting the sensor's potential for more advanced sign language applications. It’s a good option to integrate the suggested strain sensor in wearable systems, such as telemedicine systems, electromechanical detection, healthcare, and physical activity monitoring of humans.

Novel oxygen vacancies-rich 3D porous ZnO for highly sensitive 3-hydroxy-2-butanone biomarker gas sensors

Listeriosis can cause human death via infection by Listeria monocytogenes (LMs) with a high fatality rate of 20–30 %. Detection of 3-hydroxy-2-butanone (3H-2B) biomarker of LMs can achieve estimation of LMs content, which is of great significance for human health. Exploring porous metal oxide semiconductors (MOSs) with rich vacancies towards 3H-2B sensing is quite promising for achieving this goal. Herein, we report a highly sensitive 3H-2B sensor based on novel 3D porous ZnO with rich oxygen vacancies which was facilely obtained by sacrificing Zn foam in oxalic acid and subsequent thermal decomposition. The ZnO sensor displays ultrahigh sensor response of Ra/Rg = 328@5 ppm, super-low detection limit of 0.001 ppm, excellent cycling stability and selectivity and good linear response at 120 °C, showing great potential for precise detection of 3H-2B biomarker. The porous structure and increased oxygen vacancies contribute greatly to the adsorption of active oxygen species therefore the sensing reactions on ZnO surface, which accounts for the high sensing performance. Our work provides an ingenious strategy to produce novel 3D ZnO with rich oxygen vacancies as well as new insights for boosting the detection of LMs.

Highly Stretchable Sensitive Multiscale Hydrogel Inspired by Biological Muscles for Wearing Sensors.

Hydrogels have attracted substantial research interest for application in wearable electronics due to their stretchability, elasticity, and compliance. However, most hydrogels could not satisfy the application requirements for high-performance wearable sensors due to their poor sensitivity, low mechanical properties, and sensing detection range until this day. Inspired by the fascia in biological muscles, we propose a strategy to form entangled "clusters" through the dense entanglement between highly cross-linked elastic hydrogel microspheres and polymer segments, and prepared a multiscale hydrogel with high sensitivity and mechanical toughness. This strategy embedded highly swollen hydrogel microspheres (with different pore sizes) to act as the microregions of dense entanglement in the soft matrix to adjust the microstructure of multiscale gel. When pressure was applied, this structure could provide a fast response due to the stack layer formed by microspheres and soft matrix produced effective stress distribution, resulting in the outstanding sensitivity of the multiscale hydrogel (S = 1.1 kPa-1) in the pressure range of 0-50 kPa. The distinct microspheres functioning as microscale joint areas significantly augment energy dissipation, culminating in exceptional mechanical stability, ultrastretchability (≈1050%), and high strength of the multiscale hydrogel. The most notable progress was that the synthesized multiscale hydrogel not only combined the above advantages but also simultaneously solved multiple dilemmas of tedious synthesis steps, high cost, and poor durability. Besides, the multiscale hydrogel also had excellent antibacterial properties and biocompatibility, which enabled them to have large-scale application potential in wearable and implantable electronic devices. Our research could provide a universal approach to the creation of robust, flexible, wearable, and sensitive sensors, significantly increasing the uses of stress sensors in wearable technology.

Design of monitoring system for material vibration screening equipment

In order to effectively reduce the failure rate of vibrating screens, a vibration monitoring system design was proposed based on the structure and working principle. The system should be able to monitor the operating state of the vibrating screen in real time, including vibration amplitude, frequency, axial displacement, etc., and be able to detect abnormal conditions in time and give warning prompts. The key hardware of the monitoring system was designed, including acceleration sensor, power module, signal filtering circuit, etc. The sensitivity of the acceleration sensor was measured using comparative method and accurately completed parameter calibration. The eccentric block was used to simulate different deviation of excitation force for system vibration signal test and calibration. The results show that under normal operating conditions, the amplitude of each frequency of the vibrating screen is less than 0.04 g. Under the condition of excitation force deviation, the amplitude of 16 Hz is obviously lower than that of other frequencies, which means that the vibrating screen is currently experiencing lateral oscillation.

Supramolecular Luminescent Copper-Nanocluster-Based Dough with Excellent Electrical Conductivity Sensing Properties.

In recent years, the rapid advancement of flexible conductive materials has significantly increased the demand for dough materials that offer high flexibility and conductivity for diverse applications. Here, we developed a flexible, stretchable, and self-healing dough utilizing hydrogen-bonding interactions between glutathione-stabilized copper nanoclusters (GSH-Cu NCs) and poly(acrylic acid) (PAA). The dough materials can be kneaded, readily reshaped, and further processed to create bulk materials of arbitrary form factors. The incorporation of PAA not only preserved the vibrant blue emission of GSH-Cu NCs but also enhanced their electrical conductivity and stretchability. The dough can be stretched up to 25 times its initial length and achieves complete self-healing in a short time. Moreover, the dough can automatically repair physical damage and return to its initial conductivity levels after healing. Surprisingly, the electrical conductivity of the dough can reach as high as 2.97 S/m, which is relatively superior compared to that of conventional conductive materials. This study presents a dough that serves as a highly sensitive strain sensor, capable of effectively monitoring human movement across a broad range of strains.

Advancements in healthcare through 3D- printed micro and nanosensors: Innovation, application, and prospects

Integrating 3D printing technology with micro and nanoscale sensors has emerged as a transformative approach in healthcare, offering unparalleled opportunities for innovation and application. This review paper comprehensively explores the recent advancements in this interdisciplinary field, focusing on the synthesis, fabrication techniques, applications, and prospects of 3D- Printed micro and nanosensors in healthcare. The ideal manufacturing of sensors with intricate geometries and unique capabilities is made possible by combining 3D printing technology with micro and nanoscale sensors, completely changing the healthcare industry. This transformational strategy has resulted in the creation of highly sensitive, selective, and biocompatible sensors that enable real-time monitoring, early illness detection, and tailored drug delivery. These developments improve results, alter patient care, and optimize treatment approaches. Applications include medication administration, point-of-care testing, and diagnostics. Innovations such as portable lab-on-a-chip devices are improving these areas. Future work will concentrate on improving sensor flexibility and incorporating AI to forecast and treat new medical diseases.

Ultrasoft Conducting Polymer Hydrogels with Large Biaxial Strain and Conformal Adhesion for Sensitive Flexible Sensors

Ultrasoft Conducting Polymer Hydrogels with Large Biaxial Strain and Conformal Adhesion for Sensitive Flexible Sensors

Biofunctionalized magnetic nanoparticles incorporated MoS2 nanocomposite for enhanced n-butanol sensing at room temperature

N-butanol is well known to be a flammable and harmful liquid that is a potential threat to human health and property. Therefore, it is important to monitor the concentration of n-butanol in the surroundings. The need for highly efficient toxic gas detection is urgent and has been driving the research on gas sensors for practical applications. Molybdenum disulfide (MoS2) has been attracting significant interest for gas detection at room temperature. Herein, we report biofunctionalized magnetic nanoparticles incorporated MoS2 for sensing n-butanol. The biosynthesized magnetite nanoparticles (CT-Fe3O4) were synthesized by the addition of Cinnamomum Tamala (CT) leaf extract, and subsequently, the nanocomposite was synthesized using a hydrothermal method. Highly sensitive sensors based on MoS2-CT-Fe3O4 were fabricated and tested for sensing different concentrations of n-butanol. The nanocomposites showed a good sensing performance (Δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta$$\\end{document} R/Rair %) of 72% towards 20 ppm of n-butanol, indicating the potential use of MoS2-CT-Fe3O4 nanocomposite for sensing n-butanol at room temperature.

Control resonant excitation of surface plasmon polariton in quantum-dot molecule system via tunneling induced transparency and Autler–Townes splitting

Electromagnetic induced transparency (EIT) and Autler–Townes splitting (ATS) both produce a transparency window in an absorption profile, yet EIT is distinct in that it can create a transparency window for a weak control field. To elucidate the distinct physical mechanisms underlying EIT and ATS effects, we explore the controlled resonant excitation of surface plasmon polaritons (SPPs) within these regimes. Our setup is composed of three layers: a top vacuum or air layer, a central metal film, and a bottom layer of dielectric medium based on the quantum-dot molecules (QDMs) system. Unlike typical systems, that employ prism or grating coupling scheme, our setup takes advantage of the unique features of the QDMs medium to investigate the direct resonance excitation of SPPs. A weak probe and a strong control field are carried through air or vacuum to the top layer. Our results demonstrate that the permittivity of the bottom medium displays tunneling induced transparency (TIT) if the tunneling strength (Te) and the decay rate of the direct exciton (Γ1) follow the condition Te/Γ1⩽0.5; otherwise, it represents the ATS effect. In both instances, the permittivity of the QDMs medium satisfy the low-loss (high transmission) criteria, i.e., Re [ɛd]<1 and Im [ɛd]≪1, providing a framework for exploring the control resonant excitation of SPPs. We simulate the reflection and transmission spectra using the Fresnel’s formula and noticed sharp dips in reflection and peaks in the transmission spectra, which are the signature of coupler free resonance excitation of SPPs. We noticed that the narrow peak in TIT allows for strong light transmission and thus a high peak in SPP resonance excitation, resulting in higher sensitivity in plasmonic sensors. Conversely, the large spacing between the two peaks in the ATS effect broadens the range of effective excitation frequencies for SPPs, increasing the system’s adaptability and efficiency in applications requiring broad spectrum responses.

SiO2-capped ZnO quantum dot based highly sensitive optical fiber humidity sensor with potential applications in human breath monitoring and voice print recognition

This article describes the development and characterization of an optical fiber humidity sensor employing intensity modulation via the evanescent wave (EW) absorption technique. For the development of the sensor, SiO2-capped ZnO quantum dot (QDs) thin film is synthesized over the decladded portion of plastic cladding silica (PCS) fiber via the sol-gel method. A thorough experimental investigation was conducted by varying the thickness of the sensing film to optimize the sensor’s response. The sensing probe with optimized film thickness of 891 nm demonstrates a linear response over 30.5%–92.5%RH with an enhanced sensitivity of 46.2 mV/%RH (0.0138RH−1). Very fast response and recovery times of 2 s and 2.5 s are observed during humidification and dehumidification for the optimized sensing probe. The maximum resolution recorded during the short stability test is ±0.12%RH. Additionally, the proposed sensor demonstrates a very high degree of repeatability, reversibility, and stability. The proposed sensor has also been tested for human breath monitoring and voice print recognition. The result shows the sensor is able to detect minute humidity fluctuations in exhaled air during breathing and speaking.

Tailored Porous Conductive Elastomer Composites for Highly Sensitive Flexible Pressure Sensors over a Wide Range

Tailored Porous Conductive Elastomer Composites for Highly Sensitive Flexible Pressure Sensors over a Wide Range

Self-Powered Tactile Sensors Embedded with Self-Healing Electrodes for Multifunctional Applications.

Tactile-based sensing technology represents one of the most promising methods for interacting with their surrounding environment. Consequently, flexible tactile sensing has garnered significant attention from researchers worldwide. In this study, triboelectricity and piezoelectricity were combined to propose a multifunctional self-powered tactile sensor (MSPTS). Notably, new and innovative self-healing electrodes were embedded and synthesized from HPDMS (poly(dimethylsiloxane)) and boric acid in the MSPTS, MSPTS demonstrated a linear detection range of 0.25-5 kPa with a sensitivity of 246.28 mV/kPa, indicating substantial improvements in sensor sensitivity, output performance, and anti-interference capability. Our method of forming hydrogen bonds between a self-healing material (SHM) and a liquid metal (LM) effectively addressed the issue of LM leakage within the flexible matrix under pressure, thus preventing sensor failure. The borate dynamic bonding conferred self-healing properties to the electrode when it was damaged. The MSPTS was successfully applied to pressure detection, material identification, and human body movement detection, significantly broadening the application range of flexible electronic devices.

Analysis and experiment of structural geometry for improved strain sensitivity of FBG sensors

AbstractThis paper presents analysis and experimental studies to significantly enhance the strain sensitivity of fiber Bragg grating (FBG) sensors by suitably modifying the host structure used for mounting the FBG. The proposed host structure is a novel, compact flexure beam-based design, specially engineered to amplify and convert horizontal strain into vertical strain more effectively. Its unique geometry includes circular sections for hinge connections, resulting in improved displacement amplification and reduced stress across the structure. Using ANSYS calculations and finite element analysis, simulations were conducted to evaluate the vertical deformation, stress, and longevity of the sensor's mechanical structure. Results from these simulations indicate an enhanced strain sensitivity of approximately 15.633 pm/με, a significant improvement over the 1.191 pm/με sensitivity observed with bare FBGs. Experimental tests were carried out on fabricated sensor structures to validate the enhancement in strain sensitivity. FBGs utilized in the experiments were inscribed using a 255 nm UV beam generated from a second harmonic copper vapour laser. The strain sensitivity of FBGs mounted on the optimized structure was found to increase up to 9.95 pm/με. The difference between simulation and experimental results are attributed to the partial absorption of strain by the adhesive used to affix FBGs.

3D Network Spacer-Embedded Flexible Iontronic Pressure Sensor Array with High Sensitivity over a Broad Sensing Range.

Microstructure construction is a common strategy for enhancing the sensitivity of flexible pressure sensors, but it typically requires complex manufacturing techniques. In this study, we develop a flexible iontronic pressure sensor (FIPS) by embedding an isolated three-dimensional network spacer (3DNS) between an ionic gel and a flexible Ti3C2Tx MXene electrode, thereby avoiding complex microstructure construction techniques. By leveraging substantial deformation of the 3DNS and the high capacitance density resulting from the electrical double layer effect, the sensor exhibits high sensitivity (87.4 kPa-1) over a broad high-pressure range (400-1000 kPa) while maintaining linearity (R2 = 0.998). Additionally, the FIPS demonstrates a rapid response time of 46 ms, a low limit of detection at 50 Pa, and excellent stability over 10 000 cycles under a high pressure of 600 kPa. As practical demonstrations, the FIPS can effectively monitor human motion such as elbow bending and assist a robotic gripper in accurately sensing gripping tasks. Moreover, a real-time, adaptive 7 × 7 sensing array system is built and can recognize both numeric and alphabetic characters. Our design philosophy can be extended for fabricating pressure sensors with high sensing performance without involving complex techniques, facilitating the applications of flexible sensors in human motion monitoring, robotic tactile sensing, and human-machine interaction.

Composite Janus film based on the synergistic interactions of π-π stacking and dynamic covalent bond toward direction recognition sensing

Although flexible strain sensors have made important advancements recently, most of them are unable to recognize the direction of motion, which greatly limits their application in fields such as human-machine interaction. This paper presents the fabrication of a bilayer asymmetric composite film that exhibits Janus dual-sided characteristics and interfacial properties. Specifically, the two sides possess different chemical compositions and surface features. The strong π-π stacking interaction between carbon nanotubes (CNTs) and pyrene enables a tight coating on the surface of poly(glycidyl propyl urethane) (PGPU), resulting in excellent sensing capabilities and electromagnetic shielding properties for the composite material. This composite film can effectively monitor the amplitude and direction of motion. Firstly, pyrene-grafted polyurethane (PGPU) was synthesized including on dynamic covalent bonds. The tensile strength of different samples can reach up to 19.69 MPa, and the strain at break is up to 501.95 %. Furthermore, PGPU/CNTs conductive composite films were fabricated by spray-coating carbon nanotubes (CNTs) onto PGPU, and the pyrene units in PGPU can effectively interact with CNTs via π-π stacking, ensuring that stable adhesion of CNTs layer during long-term usage. Due to the dynamic covalent bonds and hydrogen bonds inside PGPU, PGPU and PGPU/CNTs both exhibit well-performed self-healing capability. Notably, the Janus structure of PGPU/CNTs can adjust the positive and negative values of relative resistance based on stretchable and compressive status of CNTs layer. Thus, PGPU/CNTs are directionally sensitive and self-healing flexible wearable sensor, which might apply in human-machine interaction field.

A highly sensitive and selective ZnO-based ammonia sensor: Fe- doping effect

Abstract This study investigates the gas sensing capabilities of ZnO and Fe-doped ZnO films prepared via a cost-effective spin coating method. The films were characterized optically, structurally, and morphologically. X-ray diffraction revealed good crystal quality with a polycrystalline nature, and wurzite structure, though crystal quality and crystallite size decreased with Fe doping. Optical measurements indicated an increased optical band gap from 3.205 ± 0.002 to 3.220 ± 0.002 eV after Fe doping. Scanning electron microscope images confirmed spherical grainy structures with reduced grain sizes after Fe doping. Gas sensing measurements at room temperature (RT) at an exposure of vapors of various toxic chemicals (acetone, ethanol, propanol, methanol, and ammonia), demonstrated a highly selective nature of ZnO and Fe-ZnO towards the ammonia. The Fe-doping into ZnO improved the ammonia sensing capability of ZnO film. The Fe-ZnO film exhibited a gas response of 388.8 ± 5.5 at 400 ppm ammonia exposure, which was nearly 10 times larger than that of ZnO film with a response/recovery time of 22/51 s, good stability, and good repeatability. The Fe-ZnO film’s higher response is attributed to its smaller grain sizes and surplus of charge carriers after Fe doping which promote the adsorption of extra oxygen ions onto the film’s surface and the subsequent interaction between the adsorbed oxygen ions ammonia molecules. It could detect up to the lower limit of 1 ppm ammonia with a response of 24.2 ± 0.9, which is better than the previous reports. These results reveal the Fe-ZnO film as a viable material for developing a cost-effective and efficient ammonia sensor at room temperature.

Advancements in Flexible and Stretchable Electronics for Resistive Hydrogen Sensing: A Comprehensive Review.

Flexible and stretchable electronics have emerged as a groundbreaking technology with wide-ranging applications, including wearable devices, medical implants, and environmental monitoring systems. Among their numerous applications, hydrogen sensing represents a critical area of research, particularly due to hydrogen's role as a clean energy carrier and its explosive nature at high concentrations. This review paper provides a comprehensive overview of the recent advancements in flexible and stretchable electronics tailored for resistive hydrogen sensing applications. It begins by introducing the fundamental principles underlying the operation of flexible and stretchable resistive sensors, highlighting the innovative materials and fabrication techniques that enable their exceptional mechanical resilience and adaptability. Following this, the paper delves into the specific strategies employed in the integration of these resistive sensors into hydrogen detection systems, discussing the merits and limitations of various sensor designs, from nanoscale transducers to fully integrated wearable devices. Special attention is paid to the sensitivity, selectivity, and operational stability of these resistive sensors, as well as their performance under real-world conditions. Furthermore, the review explores the challenges and opportunities in this rapidly evolving field, including the scalability of manufacturing processes, the integration of resistive sensor networks, and the development of standards for safety and performance. Finally, the review concludes with a forward-looking perspective on the potential impacts of flexible and stretchable resistive electronics in hydrogen energy systems and safety applications, underscoring the need for interdisciplinary collaboration to realize the full potential of this innovative technology.