Search Results (23)

High-entropy alloys (HEAs), composed of five or more principal elements in near-equimolar ratios, have emerged as a groundbreaking class of materials for next-generation flexible electronics. This review systematically examines the unique potential of HEAs as sensing materials, moving beyond their traditional role as structural components. We first elucidate the fundamental mechanisms—core effects including lattice distortion, sluggish diffusion, and the cocktail effect—that endow HEAs with an exceptional synergy of high strength, good ductility, tunable electrical resistivity, and superior electrocatalytic activity. Subsequently, we critically analyze the state-of-the-art strategies for processing HEA-based micro/nano structures, including mechanical alloying, wet-chemical synthesis, and non-equilibrium deposition techniques, with an emphasis on their compatibility with flexible substrates. The core of the review categorizes and discusses the latest advances in HEA-based flexible sensors for strain/stress, gas, and electrochemical (e.g., glucose, biomarkers, heavy metals) detection, highlighting the structure–property–performance relationships. Representative studies have demonstrated that HEA flexible strain sensors achieve a temperature coefficient of resistance as low as 45.59 ppm/K with no signal drift over 6000 stretching cycles; room-temperature hydrogen sensors reach a detection limit down to 31 ppb with a response time of 19 s; and non-enzymatic glucose sensors deliver a sensitivity up to 3043 μA·mM⁻¹·cm⁻². Finally, we summarize the key challenges—such as manufacturing scalability, long-term stability under dynamic deformation, and cost-effectiveness—and provide a forward-looking perspective on promising research directions, including high-throughput compositional screening, multi-functional sensor arrays, and the integration of machine learning for rational material design. Full article

The rapid advancement of humanoid robotics has spurred researchers’ interest in flexible sensors for wide linear range detection. In response, we report a capacitive flexible pressure sensor based on a multi-walled carbon nanotubes/titanium dioxide/polydimethylsiloxane (MWCNTs/TiO₂/PDMS) composite. A micro-hemispherical structure array formed on the composite surface via a templating method reduces the initial capacitance value. Modified carbon nanotubes (F-MWCNTs) were prepared using 2 wt%, 5 wt% and 10 wt% γ-aminopropyltriethoxysilane (APTES), significantly enhancing dispersion and interfacial bonding strength. The synergistic effect of microstructures and MWCNTs surface functionalization further enhances sensing performance. The F-MWCNTs/TiO₂/PDMS pressure sensor modified with 2 wt% APTES exhibits outstanding sensing capabilities: it demonstrates dual-stage sensitivity across a broad linear range of 0–95 kPa (0–13 kPa segment: 1.89 ± 0.49 kPa⁻¹; 13–95 kPa segment: 7.08 ± 0.63 kPa⁻¹), with a response time of 200 milliseconds, maintaining stability over 2500 cyclic loadings. In practical application exploration, this sensor has demonstrated strong adaptability, confirming its significant potential in micro-pressure detection, wearable electronics, and array sensing applications. Full article

Rapid developments in intelligent interfaces across service, healthcare, and industry have led to unprecedented demands for advanced tactile perception systems. Traditional tactile sensors often struggle with adaptability on curved surfaces and lack sufficient feedback for delicate interactions. Flexible and wearable tactile sensors are emerging as a revolutionary solution, driven by innovations in flexible electronics and micro-engineered materials. This paper reviews recent advancements in flexible tactile sensors, focusing on their mechanisms, multifunctional performance and applications in health monitoring, human–machine interactions, and robotics. The first section outlines the primary transduction mechanisms of piezoresistive (resistance changes), capacitive (capacitance changes), piezoelectric (piezoelectric effect), and triboelectric (contact electrification) sensors while examining material selection strategies for performance optimization. Next, we explore the structural design of multifunctional flexible tactile sensors and highlight potential applications in motion detection and wearable systems. Finally, a detailed discussion covers specific applications of these sensors in health monitoring, human–machine interactions, and robotics. This review examines their promising prospects across various fields, including medical care, virtual reality, precision agriculture, and ocean monitoring. Full article

Glove-based human–machine interfaces (HMIs) offer a natural, intuitive way to capture finger motions for gesture recognition, virtual interaction, and robotic control. However, many existing systems suffer from complex fabrication, limited sensitivity, and reliance on external power. Here, we present a flexible, self-powered glove HMI based on a minimalist triboelectric nanogenerator (TENG) sensor composed of a conductive fabric electrode and textured Ecoflex layer. Surface micro-structuring via 3D-printed molds enhances triboelectric performance without added complexity, achieving a peak power density of 75.02 μW/cm² and stable operation over 13,000 cycles. The glove system enables real-time LED brightness control via finger-bending kinematics and supports intelligent recognition applications. A convolutional neural network (CNN) achieves 99.2% accuracy in user identification and 97.0% in object classification. By combining energy autonomy, mechanical simplicity, and machine learning capabilities, this work advances scalable, multi-functional HMIs for applications in assistive robotics, augmented reality (AR)/(virtual reality) VR environments, and secure interactive systems. Full article

Paper-based electronics have emerged as a sustainable, low-cost, and flexible alternative to traditional substrates for electronics, particularly for disposable and wearable applications. This review outlines recent developments in paper-based devices, focusing on sensors and paper-based field-effect transistors (PFETs). Key fabrication techniques such as laser-induced graphene, inkjet printing, and screen printing have enabled the creation of highly sensitive and selective devices on various paper substrates. Material innovations, especially the integration of graphene, carbon-based materials, conductive polymers, and other novel micro- and nano-enabled materials, have significantly enhanced device performance. This review discusses modern applications of paper-based electronics, with a particular emphasis on biosensors, electrochemical and physical sensors, and PFETs designed for flexibility, low power, and high sensitivity. Advances in PFET architectures have further enabled the development of logic gates and memory systems on paper, highlighting the potential for fully integrated circuits. Despite challenges in durability and performance consistency, the field is rapidly evolving, driven by the demand for green electronics and the need for decentralized, point-of-care diagnostic tools. This paper also identifies detection strategies used in paper-based sensors, reviews limitations in the current fabrication methods, and outlines opportunities for the scalable production of multifunctional paper-based systems. This review addresses a critical gap in the literature by linking device-level innovation with real-world sensor applications on paper substrates. Full article

Detecting urea is crucial for diagnosing related health conditions and ensuring timely medical intervention. The addition of machine learning (ML) technologies has completely changed the field of biochemical sensing, providing enhanced accuracy and reliability. In the present work, an ML-assisted screen-printed, flexible, electrochemical, non-enzymatic biosensor was proposed to quantify urea concentrations. For the detection of urea, the biosensor was modified with a multi-walled carbon nanotube-zinc oxide (MWCNT-ZnO) nanocomposite functionalized with copper oxide (CuO) micro-flowers (MFs). Further, the CuO-MFs were synthesized using a standard sol-gel approach, and the obtained particles were subjected to various characterization techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Fourier transform infrared (FTIR) spectroscopy. The sensor’s performance for urea detection was evaluated by assessing the dependence of peak currents on analyte concentration using cyclic voltammetry (CV) at different scan rates of 50, 75, and 100 mV/s. The designed non-enzymatic biosensor showed an acceptable linear range of operation of 0.5–8 mM, and the limit of detection (LoD) observed was 78.479 nM, which is well aligned with the urea concentration found in human blood and exhibits a good sensitivity of 117.98 mA mM⁻¹ cm⁻². Additionally, different regression-based ML models were applied to determine CV parameters to predict urea concentrations experimentally. ML significantly improves the accuracy and reliability of screen-printed biosensors, enabling accurate predictions of urea levels. Finally, the combination of ML and biosensor design emphasizes not only the high sensitivity and accuracy of the sensor but also its potential for complex non-enzymatic urea detection applications. Future advancements in accurate biochemical sensing technologies are made possible by this strong and dependable methodology. Full article

The characteristics of the surface and interface of nanocomposites are important for exerting multi-functional properties and widening interdisciplinary applications. These properties are mainly depending on the electronic structures of materials. Some key factors, such as the surface, interface, grain boundaries, and defects take vital roles in the contribution of desired properties. Due to the excellent sensitivity of the QCM (quartz crystal microbalance) device, the surface and interface features of the nanocomposite were studied with the aid of the gas-response of the sensors (Sensor’s Gas-Sensitivity) in this work. To make full use of the visible light and part of NIR, a ZnO/MnS_x nanocomposite was constructed using hydrothermal synthesis for narrowing the bandgap width of wide bandgap materials. The results indicated that the absorbance of the resulting nanocomposite was extended to part of the NIR range due to the introduction of impurity level or defect level, although ZnO and MnS belonged to wide bandgap semiconductor materials. To explore the physical mechanism of light activities, the photoconductive responses to weak visible light (650 nm, etc.) and NIR (near-infrared) (808 nm, 980 nm, and 1064 nm, etc.) were studied based on interdigital electrodes of Au on flexible PET (polyethylene terephthalate) film substrate with the casting method. The results showed that the on/off ratio of ZnO/MnS_x nanocomposite to weak visible light and part of NIR light were changed by about one to five orders of magnitude, with changes varying with the amount of MnS_x nanoparticle loading due to defect-assisted photoconductive behavior. It illustrated that the ZnO/MnS_x nanocomposite easily produced photo-induced free charges, effectively avoiding the recombination of electrons/holes because of the formation of strong built-in electrical fields. To examine the surface and interface properties of nanocomposites, chemical prototype sensor arrays were constructed based on ZnO, ZnO/MnS_x nanocomposite, and QCM arrays. The adsorption response behaviors of the sensor arrays to some typical volatile compounds were examined under a similar micro-environment. The results exhibited that in comparison to ZnO nanosheets, the ZnO nanosheets/MnS_x nanocomposite increased adsorption properties to some typical organic volatile compounds significantly. It would have good potential applications in photo-catalysts, self-cleaning films, multi-functional coatings, and organic pollutants treatment (VOCs) of environmental fields for sustainable development. It provided some reference value to explore the physical mechanism of materials physics and photophysics for photo-active functional nanocomposites. Full article

Here, we report a novel, easy-to-implement scalable single-step procedure for the fabrication of a solid-state surface-enhanced photoluminescence (SEPL) sensor via the direct femtosecond (fs) laser patterning of monocrystalline Si wafers placed under the layer of functionalizing solution simultaneously containing a metal salt precursor (AgNO₃) and a photoluminescent probe (d114). Such laser processing creates periodically modulated micro- and nanostructures decorated with Ag nanoparticles on the Si surface, which effectively adsorbs and retains the photoluminescent sensor layer. The SEPL effect stimulated by the micro- and nanostructures formed on the Si surface localizing pump radiation within the near-surface layer and surface plasmons supported by the decorating Ag nanoparticles is responsible for the intense optical sensory response modulated by a small amount of analyte species. The produced SEPL sensor operating within a fluidic device was found to detect sub-nanomolar concentrations of Hg²⁺ in water which is two orders of magnitude lower compared to this molecular probe sensitivity in solution. The fabrication technique is upscalable, inexpensive, and flexible regarding the ability to the control surface nano-morphology, the amount and type of loading noble-metal nanoparticles, as well as the type of molecular probe. This opens up pathways for the on-demand development of various multi-functional chemosensing platforms with expanded functionality. Full article

Due to the lack of efficient bioelectronic interfaces, the communication between biology and electronics has become a great challenge, especially in constructing bioelectronic sensing. As natural polysaccharide biomaterials, chitosan-based hydrogels exhibit the advantages of flexibility, biocompatibility, mechanical tunability, and stimuli sensitivity, and could serve as an excellent interface for bioelectronic sensors. Based on the fabrication approaches, interaction mechanisms, and bioelectronic communication modalities, this review divided chitosan-based hydrogels into four types, including electrode-based hydrogels, conductive materials conjugated hydrogels, ionically conductive hydrogels, and redox-based hydrogels. To introduce the enhanced performance of bioelectronic sensors, as a complementary alternative, the incorporation of nanoparticles and redox species in chitosan-based hydrogels was discussed. In addition, the multifunctional properties of chitosan-based composite hydrogels enable their applications in biomedicine (e.g., smart skin patches, wood healing, disease diagnosis) and food safety (e.g., electrochemical sensing, smart sensing, artificial bioelectronic tongue, fluorescence sensors, surface-enhanced Raman scattering). We believe that this review will shed light on the future development of chitosan-based biosensing hydrogels for micro-implantable devices and human–machine interactions, as well as potential applications in medicine, food, agriculture, and other fields. Full article

Ionic conductive hydrogels used as flexible wearable sensor devices have attracted considerable attention because of their easy preparation, biocompatibility, and macro/micro mechanosensitive properties. However, developing an integrated conductive hydrogel that combines high mechanical stability, strong adhesion, and excellent mechanosensitive properties to meet practical requirements remains a great challenge owing to the incompatibility of properties. Herein, we prepare a multifunctional ionic conductive hydrogel by introducing high-modulus bacterial cellulose (BC) to form the skeleton of double networks, which exhibit great mechanical properties in both tensile (83.4 kPa, 1235.9% strain) and compressive (207.2 kPa, 79.9% strain) stress–strain tests. Besides, the fabricated hydrogels containing high-concentration Ca²⁺ show excellent anti-freezing (high ionic conductivities of 1.92 and 0.36 S/m at room temperature and −35 ${}^{\circ }$C, respectively) properties. Furthermore, the sensing mechanism based on the conductive units and applied voltage are investigated to the benefit of the practical applications of prepared hydrogels. Therefore, the designed and fabricated hydrogels provide a novel strategy and can serve as candidates in the fields of sensors, ionic skins, and soft robots. Full article

The vanadium redox flow battery (VRFB) system is an emerging energy storage technology with many advantages, such as high efficiency, long life, and high safety. However, during the power-generation process, if local high temperature is generated, the rate of ions passing through the membrane will increase. In addition, it will also cause vanadium pentoxide molecules (V₂O₅) to exist in the solid state. Once the solid is formed, it will affect the flow of the vanadium electrolyte, which will eventually cause the temperature of the VRFB to continue to rise. According to the various physical parameters of VRFB shown in the literature, they have a significant impact on the efficiency and life of VRFB. Therefore, this research proposes to develop flexible multifunction (voltage, current, temperature, and flow) micro-sensors using micro-electro-mechanical systems (MEMS) technology to meet the need for real-time micro-diagnosis in the VRFB. The device is embedded in the VRFB of real-time microscopic sensing and diagnosis. Its technical advantages are: (1) it can simultaneously locally measure four physical quantities of voltage, current, temperature, and flow; (2) due to its mall size it can be accurately embedded; (3) the high accuracy and sensitivity provides it with a fast response time; and (4) it possesses extreme environment resistance. Full article

With the rising demand for wearable, multifunctional, and flexible electronics, plenty of efforts aiming at wearable devices have been devoted to designing sensors with greater efficiency, wide environment tolerance, and good sustainability. Herein, a thin film of double-network ionic hydrogel with a solution replacement treatment method is fabricated, which not only possesses excellent stretchability (>1100%) and good transparency (>80%), but also maintains a wide application temperature range (−10~40 °C). Moreover, the hydrogel membrane further acts as both the flexible electrode and a triboelectric layer, with a larger friction area achieved through a micro-structure pattern method. Combining this with a corona-charged fluorinated ethylene propylene (FEP) film, an electret/hydrogel-based tactile sensor (EHTS) is designed and fabricated. The output performance of the EHTS is effectively boosted by 156.3% through the hybrid of triboelectric and electrostatic effects, which achieves the open-circuit peak voltage of 12.5 V, short-circuit current of 0.5 μA, and considerable power of 4.3 μW respectively, with a mentionable size of 10 mm × 10 mm × 0.9 mm. The EHTS also demonstrates a stable output characteristic within a wide range of temperature tolerance from −10 to approximately 40 °C and can be further integrated into a mask for human breath monitoring, which could provide for a reliable healthcare service during the COVID-19 pandemic. In general, the EHTS shows excellent potential in the fields of healthcare devices and wearable electronics. Full article

Stretchable optical fiber sensors (SOFSs), which are promising and ultra-sensitive next-generation sensors, have achieved prominent success in applications including health monitoring, robotics, and biological–electronic interfaces. Here, we report an ultra-sensitive multi-functional optical micro/nanofiber embedded with a flexible polydimethylsiloxane (PDMS) membrane, which is compatible with wearable optical sensors. Based on the effect of a strong evanescent field, the as-fabricated SOFS is highly sensitive to strain, achieving high sensitivity with a peak gauge factor of 450. In addition, considering the large negative thermo-optic coefficient of PDMS, temperature measurements in the range of 30 to 60 °C were realized, resulting in a 0.02 dBm/°C response. In addition, wide-range detection of humidity was demonstrated by a peak sensitivity of 0.5 dB/% RH, with less than 10% variation at each humidity stage. The robust sensing performance, together with the flexibility, enables the real-time monitoring of pulse, body temperature, and respiration. This as-fabricated SOFS provides significant potential for the practical application of wearable healthcare sensors. Full article

Flexible, highly sensitive, easy fabricating process, low-cost pressure sensors are the trend for flexible electronic devices. Inspired by the softness, comfortable, environmental friendliness and harmless of natural latex mattress, herein, we report an agile approach of constructing a flexible 3D-architectured conductive network by dip-coating silver nanowires (AgNWs) on the natural rubber latex foam (NRLF) substrate that provide the 3D micro-network structure as the skeleton. The variation of the contact transformed into the electrical signal among the conductive three-dimensional random networks during compressive deformation is the piezoresistive effect of AgNWs/NRLF pressure sensors. The resulting AgNWs/NRLF pressure sensors exhibit desirable electrical conductivity (0.45–0.50 S/m), excellent flexibility (58.57 kPa at 80% strain), good hydrophobicity (~128° at 5th dip-coated times) and outstanding repeatability. The AgNWs/NRLF sensors can be assembled on a glove to detect hand motion sensitively such as bending, touching and holding, show potential application such as artificial skin, human prostheses and health monitoring in multifunctional pressure sensors. Full article

To realize the practical applications of flexible pressure sensors, the high performance (sensitivity and response time) as well as more functionalities are highly desired. In this work, we fabricated a piezoresistive pressure sensor based on the micro-structured composites films of multi-walled carbon nanotubes (MWCNTs) and poly (dimethylsiloxane) (PDMS). In addition, we establish efficient strategies to improve key performance of our pressure sensor. Its sensitivity is improved up to 474.13 kPa⁻¹ by minimizing pressure independent resistance of sensor, and response time is shorten as small as 2 μs by enhancing the elastic modulus of polymer elastomer. Benefiting from the high performance, the functionalities of sensors are successfully extended to the accurate detection of high frequency mechanical vibration (~300 Hz) and large range of air pressure (6–101 kPa), both of which are not achieved before. Full article