High Response Time Research Articles

Ultra-Thin Highly Sensitive Electronic Skin for Temperature Monitoring

Electronic skin capable of reliable monitoring of human skin temperature is crucial for the advancement of non-invasive clinical biomonitoring, disease diagnosis, and health surveillance. Ultra-thin temperature sensors, with excellent mechanical flexibility and robustness, can conformably adhere to uneven skin surfaces, making them ideal candidates. However, achieving high sensitivity often demands sacrificing flexibility, rendering the development of temperature sensors combining both qualities a challenging task. In this study, we utilized a low-cost drop-casting technique to print ultra-thin and lightweight (thickness: approximately 3 µm, weight: 0.61 mg) temperature sensors based on a combination of vanadium dioxide and PEDOT:PSS at room temperature and atmospheric conditions. These sensors exhibit high sensitivity (temperature coefficient of resistance: −5.11%/°C), rapid response and recovery times (0.36 s), and high-temperature accuracy (0.031 °C). Furthermore, they showcased remarkable durability in extreme bending conditions (bending radius = 400 µm), along with stable electrical performance over approximately 2400 bending cycles. This work offers a low-cost, simple, and scalable method for manufacturing ultra-thin and lightweight electronic skins for temperature monitoring, which seamlessly integrate exceptional temperature-measuring capabilities with optimal flexibility.

Mode-locked soliton pulse generation using copper phthalocyanine absorber in long erbium-doped fibre laser cavity

We present the development of a mode-locked erbium-doped fibre laser (EDFL) utilizing Copper Phthalocyanine (CuPc) as a saturable absorber (SA). CuPc exhibits unique optical properties, including its high nonlinear optical response and rapid recovery time. To seamlessly integrate CuPc into the laser cavity, we employed a simple embedding technique within a polymer film. The SA demonstrates a modulation depth of 3.1% and a saturation intensity of 17 MW/cm2. Operating within a pump power range of 90.6 to 122.9 mW, the laser achieves mode-locked operation, producing a soliton pulse train with a fundamental frequency of 1.82 MHz and a pulse width of 6.4 ps at a wavelength of 1561.5 nm. It attains a maximum output power of 13.97 mW and a pulse energy of 7.67 nJ. These results underscore CuPc's potential as a promising material for generating mode-locked pulses, suggesting new avenues in ultrafast laser development for diverse applications.

Modelling and Experimentation of failure modes to obtain safe operating Range for improved Dielectric elastomer actuation performance

Abstract Dielectric elastomers (DEs) possess high energy density, lightweight, and low response time making them suitable material candidatures for electromechanical transducers (ET). Performance enhancement of ET necessitates escalated electrical load making prone to failure and subsequently hindering reliability and life cycle. Existing models towards failure mitigation focus on mechanical and electrical loads individually with constant relative permittivity, whereas DEs undergoes combined loading and stretch-electrostriction in real-time application. This study aims to identify safe design and operating parameters by addressing various modes of failures under combined loads and stretch-electrostriction. Under combined load, pre-strain emerges as a crucial parameter to reduce EMI, while extensive pre-strain leads to diminish thickness which in turn promotes electrical breakdown of elastomer. The optimized design for DEs exhibit substantial failure suppression at a pre-strain value of 1.7 (λpre) under maximum electrical load of 37.66 MV/m (Emax). The efficacy of optimized parameters for the failure suppression is verified through an in-house fabricated planar actuator. Operation within the identified range of parameters is observed to enhance the reliability and lifespan of DE-actuators, marking a noteworthy advancement in the field of soft robotics.

Improved transparency and charge matching of electrochromic devices with Ce-doped NiO counter electrode

The quest for cost-effective and efficient electrochromic electrodes, featuring high color contrast and rapid response times, has sparked increasing interest in research of metal oxides for electrochromic applications. In this study, nickel oxide thin films with various cerium dopant concentrations are synthesized, with the optimized doping concentration identified as 1 at%. X-ray diffraction analysis confirmed that the dopant successfully reduces crystal size and alters the preferred orientation to (111). The 1 % Ce:NiO thin film exhibits enhanced electrochromic performance, with a transmittance modulation increase of 27.4 % at 633 nm, a 27.1 % rise in coloration efficiency and faster response time (tb=9.64 s and tc=6.76 s) compare to the undoped NiO. Importantly, the charge density of 1 % Ce:NiO thin film increases from 4.86 to 8.14 mC cm−2, representing a 67.5 % improvement, which becomes a better charge matching with WO3 in electrochromic devices. The incorporation of Ce into the NiO thin films not only leads to increased transmittance in the bleached state and optical modulation in the electrochromic devices but also contributes to a rise in the optical band gap of the NiO thin films and improved charge balance matching. These results underscore the positive impact of cerium doping on microstructure and electrochromic performance, indicating a promising future for electrochromic devices.

Sulfuration-induced enhancement of photodetection performance of photoconductive detector based on Bi2O2Se thin film

Significant interlayer transmission obstacles and numerous interface barriers in two-dimensional material thin films impede charge transfer, degrading device performance. However, appropriate impurity ions can enhance charge mobility by creating transfer channels and regulating interface defect states. Herein, a series of Bi2O2SxSe1-x films were prepared by a one-step hydrothermal sulfurization method. The XRD and XPS measurement and analysis can confirm that the Se atoms have been replaced by the S atoms. The introduction of S atoms can effectively enhance the number of defects in Bi2O2Se, resulting in an increase in carrier concentration, thereby improving the conductivity of Bi2O2Se film. The photoconductive detectors fabricated from these Bi2O2SxSe1-x films showed improved detection performance compared to those made from the pristine Bi2O2Se film, and the responsivity is increased by nearly 1000 times. Notably, the detector based on Bi2O2S0.37Se0.63 film has high responsivity (47.7 mA/W) and fast response time (15 ms/25 ms). The simple thin film preparation method and good device performance make it have great potential for large-scale preparation.

A commercially available dye as a highly versatile colorimetric fluoride sensor

Reported herein is the successful use of the commercially available organic dye bromocresol green (compound 1) for high-performing and practical fluoride detection. This dye responds to fluoride anion with high selectivity (virtually no response to other halide anions), excellent sensitivity (limits of detection as low as 0.22 ppm) and rapid response times, and maintains functionality when it is adsorbed on filter paper. Mechanistic studies determined that the fluoride-induced colorimetric changes were due to intermolecular hydrogen bonding between compound 1 and fluoride. Finally, the broad applicability of this sensor was demonstrated through the colorimetric response of compound 1 – functionalized paper to fluoride in commercial mouthwash. These findings underscore compound 1’s potential as a practical and commercially viable fluoride sensor, in addition to compound 1’s better-known role as a colorimetric pH indicator.

Fabrication of surface functionalized QCM sensor for BTX detection at ambient conditions

Developing optimized gas sensors for detecting low concentrations of Benzene, Toluene, and Xylene (BTX) in ambient conditions is advantageous for health and environment monitoring applications. This study reports on the feasibility of using Quartz Crystals Microbalance (QCM) coated by Tungsten Oxide (WO3) to detect BTX compounds. A WO3 layer was deposited on the QCM surface using DC magnetron sputtering. Optical Profilometry (OP), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) were employed to analyze sensor surface morphology and structure. Adsorption properties were studied through the Langmuir adsorption isotherm. Thermal stability was evaluated by thermogravimetric analysis. The response to BTX vapours was investigated using a laboratory-designed gas-sensing setup in ambient conditions. The optimized film thickness was 200.81 ± 0.39 nm for 540 s of sputtering. XRD pattern confirms the amorphous nature, and SEM images of WO3 show the granular microstructure with 200 nm diameter. The developed sensor shows the highest sensitivity for xylene (5.10 ± 0.08 Hz/ppm), followed by toluene (5.69 ± 0.22 Hz/ppm) and benzene (3.36 ± 0.24 Hz/ppm). The limit of detection for BTX was 1.48 ppm, 0.79 ppm, and 0.33 ppm, respectively. The sensor exhibited faster response times of 30 s, 32 s, and 43 s for BTX, respectively. Repeatability of 99 % and reproducibility of 98 % were observed for BTX vapours. The fabricated WO3-coated QCM sensor can detect BTX vapour at room temperature with high sensitivity and response time. Thus, it can play a significant role in detecting BTX in the workplace for health and environment monitoring systems.

Study of Ion-to-Electron Transducing Layers for the Detection of Nitrate Ions Using FPSX(TDDAN)-Based Ion-Sensitive Electrodes.

The development of ISE-based sensors for the analysis of nitrates in liquid phase is described in this work. Focusing on the tetradodecylammonium nitrate (TDDAN) ion exchanger as well as on fluoropolysiloxane (FPSX) polymer-based layers, electrodeposited matrixes containing double-walled carbon nanotubes (DWCNTs), embedded in either polyethylenedioxythiophene (PEDOT) or polypyrrole (PPy) polymers, ensured improved ion-to-electron transducing layers for NO3- detection. Thus, FPSX-based pNO3-ElecCell microsensors exhibited good detection properties (sensitivity up to 55 mV/pX for NO3 values ranging from 1 to 5) and acceptable selectivity in the presence of the main interferent anions (Cl-, HCO3-, and SO42-). Focusing on the temporal drift bottleneck, mixed results were obtained. On the one hand, relatively stable measurements and low temporal drifts (~1.5 mV/day) were evidenced on several days. On the other hand, the pNO3 sensor properties were degraded in the long term, being finally characterized by high response times, low detection sensitivities, and important measurement instabilities. These phenomena were related to the formation of some thin water-based layers at the polymer-metal interface, as well as the physicochemical properties of the TDDAN ion exchanger in the FPSX matrix. However, the improvements obtained thanks to DWCNT-based ion-to-electron transducing layers pave the way for the long-term analysis of NO3- ions in real water-based solutions.

Solid-state Batteries: Overcoming Challenges and Harnessing Opportunities for a Sustainable Energy Future

Herein we reviewed solid-state batteries (SSBs) as an emerging and promising alternative to conventional lithium-ion batteries, offering enhanced energy density, safety, and longevity. Solid-state batteries (SSBs) use a solid electrolyte instead of the liquid or gel electrolytes found in conventional lithium-ion batteries. SSBs can achieve energy densities of up to 500 Wh/kg, compared to 350 Wh/kg for conventional lithium-ion batteries. This paper explores the potential of SSBs to revolutionize grid stability and energy storage. The unique characteristics of SSBs, including their solid-state electrolytes (SSEs) and absence of liquid components, significantly mitigate safety concerns associated with traditional batteries. Moreover, SSBs exhibit higher faster charging rates, making them ideal for applications demanding high energy storage capacity and rapid response times. The paper further discusses the key challenges and advancements in SSB development, including material selection, manufacturing processes, and cost reduction. It also highlights the anode and cathode materials but also the interface challenges faced during the design and development of SSBs. By addressing the limitations of current energy storage solutions, SSBs offer a promising pathway toward a more resilient and sustainable energy future.

Dual design strategy for carboxymethyl cellulose-polyaniline composite hydrogels as super-sensitive amphibious sensors

Conductive hydrogels as ideal candidate materials for flexible sensors have exhibited many promising applications. However, complex application environments, such as low temperatures or underwater conditions, have introduced new requirements for hydrogel sensors. Herein, a high-performance conductive hydrogel based on carboxymethyl cellulose-polyaniline (CMC-PANI) submicron spheres, poly (vinyl alcohol) (PVA) and phytic acid (PA) was designed and fabricated via a dual design strategy. CMC-PANI particles were introduced to not only empower the good electromechanical performance to the hydrogels, but also enhance the mechanical properties. The obtained hydrogel exhibited good mechanical property, anti-freezing, anti-swellable behavior and recyclable performance. Resistive-type strain sensors assembled by the prepared hydrogels exhibited high pressure sensitivity (34.17×10−2 kPa−1) and fast response time (100 ms), which can clearly detect the pulse beats. Moreover, the hydrogel sensors can achieve long-term stability, high sensitivity and fatigue resistance as an underwater sensor. Based on these favorable performances, the conductive polymer hydrogels may open up an enticing avenue for functional soft materials in health diagnostic and electronic components.

An efficient electrochemical biosensor based on double-conductive hydrogel as antifouling interface for ultrasensitive analysis of biomarkers in complex serum medium

Electrochemical biosensors are suitable for trace detection of biomarkers in serum due to their high sensitivity and fast response time. However, the extensive adsorption of non-specific biomolecules may affect detection results and reduce the operating life of sensors. Herein, an efficient electrochemical biosensor based on double-conductive antifouling hydrogel was developed for ultrasensitive detection of carcinoembryonic antigen (CEA) in serum. Specifically, the antifouling hydrogel was designed with MXene as the conductive framework, and its inherent surface hydrophilicity made it have good antifouling ability. Meanwhile, the introduction of conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) further improved the conductivity and stability and of antifouling hydrogel. Furthermore, the prepared MXene nanosheets exhibited large surface area, which could load a large amount of [Ru(NH3)6]3+ as internal standards. Importantly, the encapsulation of [Ru(NH3)6]3+ in hydrogel can not only eliminate the environmental and instrument errors, but also realize the integration of antifouling and internal standards, thus simplifying the construction process and improving the detection accuracy of the biosensor. Based on this, the proposed signal “on-off” electrochemical antifouling biosensor realized trace detection of CEA in a wide linear range (1 pg/mL ∼ 1 μg/mL), with a detection limit as low as 0.41 pg/mL (3δ/k). This study broadens the application of hydrogels in electrochemical antifouling systems, providing a positive reference for sensitive and accurate determination of biomarkers in serum samples.

Fast Responsive and Highly Sensitive Ethanol Gas Sensors Designed by Agar‐Laponite Hybrid Hydrogels

AbstractLaponite, a synthetic nanosilicate clay and agar, a natural polysaccharide, both imbibe large amount of water and form into hydrogels. Various physical and chemical stimuli elicit the hydrogel response, which has been applied in designing diverse sensors and biomedical systems. In this work, we exploit the change in hydrogel's ionic conductivity due to volatile organic compounds (VOCs) (e. g. ethanol) interaction with the surfaces of Laponite‐Agar hybrid hydrogel films. Gas sensing studies are carried out on silicon (Si) and flexible polyethylene terephthalate (PET) substrates by monitoring the resistance changes. Pristine Laponite hydrogel has shown increase in resistance as it interacted with the ethanol, whereas pure agar and Laponite‐Agar have shown decrease in resistance. Moreover, Laponite‐Agar gel films have exhibited high sensitivity, fast response (4 s) and recovery time (15 s) with lowest detection limit of 6 ppm. Selectivity test carried shows high ethanol sensing response and exhibited very good reproducibility. Observed responses and sensing mechanism are discussed based on changes in ionic conduction resulted due to interacting ethanol with the gel surface network structure. Present study paves the way for understanding and designing low cost, soft and flexible hydrogel gas sensors.

Synergistic effects of anionic surfactant doping on dielectric and electro-optical properties of nematic liquid crystals by cyano-ionic interactions

Modern research has long focused on controlling and optimizing the dielectric, electro-optical and optical attributes of liquid crystals (LCs) to increase their technological value. Numerous approaches have been investigated for this reason in an effort to overcome various issues such as high response time, high driving voltage requirements, low dielectric anisotropy and limited operating temperature range, etc. The strategy utilizing binary/multicomponent systems is the most investigated and seems to have the most potential out of all the other techniques. In keeping with the same subject, the influence of anionic surfactant on the dielectric, electro-optical, and optical properties of nematic LC (NLC) has been examined. Precisely, dodecane-1-sulfonic acid sodium salt (SDS) which is an anionic surfactant was dispersed in a room temperature NLC E7 at various concentrations. Our findings reveal a significant alteration in the electro-optical behavior resulting from the introduction of an anionic surfactant, extending well beyond the instance of electrode polarization, albeit with a detrimental impact on performance within the low-frequency range as a result of increased ionic contribution. The main findings of this study include a 17.5%% increase in dielectric anisotropy, an appreciable reduction of about 30%% in threshold voltage and rotational viscosity, and approximately 64% reduction in response time in the host NLC due to the addition of anionic salt in it. A significant photoluminescence quenching of about 64%% is observed after dispersion of 3.0% by weight anionic surfactant in E7. These findings offer potential pathways for the development of future technologies in various domains, including photonic devices, biological imaging, light-emitting diodes (LEDs), and luminescent markers.

Characterization of SnO2-based gas sensors to analyze diesel and biodiesel blends

This study analyzed biodiesel blends using sensors constituted by SnO2 pellets with gold interdigitated contacts deposited on the surface. Tin dioxide was synthesized by the polymeric precursor method with further calcination treatment at 500°C, conformed and sintered at three temperatures to form three different samples: 700°C (Sn1), 900°C (Sn2) and 1100°C (Sn3). The samples were analyzed by X-Ray Diffraction, FEG-SEM (Field Emission Gun - Scanning Electron Microscopy), Raman spectroscopy, and electrical measurements. Results confirmed the formation of rutile-type tetragonal cassiterite phase, with quasi-spherical particles a moderate degree of heterogeneity in particle size 30-90 nm). Raman vibrational modes and infrared spectrum also confirmed the presence of tin oxide in high purity rutile phase. Sensorial measurements showed high sensitivity, response, and recovery time in tests with biodiesel/ethanol mixtures, allowing to distinguish between blends with a wide range of composition and serving as a potential device to detect adulterated fuel.

Hydrothermally Grown Globosa-like TiO2 Nanostructures for Effective Photocatalytic Dye Degradation and LPG Sensing.

The rapid expansion of industrial activities has resulted in severe environmental pollution manifested by organic dyes discharged from the food, textile, and leather industries, as well as hazardous gas emissions from various industrial processes. Titanium dioxide (TiO2)-nanostructured materials have emerged as promising candidates for effective photocatalytic dye degradation and gas sensing applications owing to their unique physicochemical properties. This study investigates the development of a photocatalyst and a liquefied petroleum gas (LPG) sensor using hydrothermally synthesized globosa-like TiO2 nanostructures (GTNs). The synthesized GTNs are then evaluated to photocatalytically degrade methylene blue dye, resulting in an outstanding photocatalytic activity of 91% degradation within 160 min under UV light irradiation. Furthermore, these nanostructures are utilized to sense liquefied petroleum gas, which attains a superior sensitivity of 7.3% with high response and recovery times and good reproducibility. This facile and cost-effective hydrothermal method of fabricating TiO2 nanostructures opens a new avenue in photocatalytic dye degradation and gas sensing applications.

Construction of a dual “off-on” near-infrared fluorescent probe for bioimaging of HClO in rheumatoid arthritis

Hypochlorous acid (HClO) serves as a critical biomarker in inflammatory diseases such as rheumatoid arthritis (RA), and its real-time imaging is essential for understanding its biological functions. In this study, we designed and synthesized a novel probe, RHMB, which ingeniously integrates rhodamine B and methylene blue fluorophores with HClO-specific responsive moieties into a single molecular framework. Upon exposure to HClO, RHMB exhibited significant dual-channel fluorescence enhancement characterized by high sensitivity (LODs of 2.55 nM and 14.08 nM), excellent selectivity, and rapid response time (within 5 s). Notably, RHMB enabled reliable imaging of both exogenous and endogenous HClO in living cells and in zebrafish, employing a unique duplex-imaging turn-on approach that highlighted its adaptability across various biological contexts. Furthermore, RHMB effectively monitored HClO fluctuations in an RA mouse model and assessed the therapeutic efficacy of diclofenac (Dic) in alleviating RA symptoms. These findings underscore the potential of RHMB as an invaluable tool for elucidating the biological roles of HClO in various diseases.

High performance PVC/ [AMI]mNTF2 ionic gel sensors for smart wearable applications

Plasticized polyvinyl chloride (PVC) gel as an electroactive polymer material has attracted increasing interest for the construction of flexible devices with the integration of actuation and self-sensing. However, the insufficient sensing ability of traditional PVC gels limits their applications. In this paper, a PVC ionic gel sensor based on the physical blending of PVC gel and the ionic liquid 1-allyl-3-methylimidazolium bisimide ([AMI]mNTF2) is presented. With the addition of ionic liquids, the PVC molecular chains and ions formed stable conductive pathways, resulting in increased conductivity and sensing performance of the PVC gel. The proposed sensor exhibits excellent sensing properties of high resolution (0.12 %) and fast response time (95 ms), along with high sensitivity (GF=27.8), which is more than seven times that of the traditional PVC gel. Furthermore, it was successfully utilized for human motion detection and remote control of a robotic hand, demonstrating the feasibility of the sensor for smart wearable applications in the future.

Sustainable Synthesis of MIL-53(Al)-Cys Based Chemosensor for the Fluoro-Chromogenic Detection of Copper

Copper is the third most abundant heavy metal in the environment important for human survival. However, in excess it can have deleterious effects on aquatic as well as terrestrial beings. The detection of Cu2+ has huge significance in food safety and environment monitoring. The conventional detection methods are costly and complex. Therefore, we have designed a waste derived material for Cu2+ determination in complex samples. Our work is based on the eco-friendly synthesis of waste derived Al-MOF with remarkable properties grafted with L-Cysteine to develop the novel MIL-53(Al)-Cys sensor. The formation of the sensing probe was verified by various characterization techniques including FE-SEM, HR-TEM, PXRD, FTIR, UV-Vis and Photoluminescence spectroscopies. The developed waste-derived probe showed multifunctional properties with the visual and fluorescent detection of Cu2+ ions with high sensitivity and fast response time. The proposed waste-derived fluoro-chromogenic sensor exhibited a “turn of” detection response mechanism with a visual color change only the presence of Cu2+ ions. The results showed reproducible, selective and stable response with a LOD of 0.2 ng/mL, which is lower than the permissible levels. Therefore, the observed results highlight the potential of developed waste-derived MIL-53(Al)-Cys chemosensor as a promising platform in water remediation applications.

High sensitivity gas detection based on Au waveguide

Hydrogen, as a representative of the new energy source, has great potential for development, and the detection of the low concentration of hydrogen plays a crucial role in process safety control. In this paper, a gas sensor based on a metal-insulator-metal (MIM) structure with high sensitivity and low response time is proposed. The sensor is bilaterally coupled with a ring resonant cavity and a metal nanopillar, and the outgoing field superposition is achieved by bilaterally coupling the resonant cavity to achieve a lower transmittance, which facilitates detection. The symmetry of the structure was broken by different methods, and the results showed that the complexity and response time of the structure increased significantly after breaking the symmetry, but the transmittance appeared to decrease and the transmission characteristic curve was independent of the coupling phase. The waveguide structure shows a highly linear relationship between resonance wavelength and refractive index with a maximum sensitivity of 2433.00 nm/RIU when used for refractive index sensing, and a maximum sensitivity of −2.61 nm/% when used for hydrogen gas sensing. For methane gas sensing, the maximum sensitivity is −9.22 nm/%.

A review on development of enzymatic biosensors for industrial applications

Enzymatic biosensors are vital tools across various industries due to their high specificity, sensitivity, and rapid response times. They are extensively used in medical diagnostics for monitoring biomarkers like glucose and lactate, environmental monitoring to detect pollutants, food safety and quality assurance, bioprocess control in industrial fermentation, pharmaceutical drug development and quality control, soil health and agrochemical detection in agriculture, and for identifying biological warfare agents. However, several challenges limit their broader adoption and effectiveness in industrial settings. Key challenges include enzyme stability, as enzymes can denature under extreme environmental conditions, reducing sensor lifespan and performance. Variability in enzyme activity and immobilization techniques also leads to inconsistencies, affecting sensor reproducibility and reliability. Complex sample matrices, such as those in environmental and food samples, introduce interference that can affect sensor accuracy. Integrating biosensors into existing industrial processes is another significant challenge, requiring compatibility with automated systems and real-time data processing capabilities. Additionally, high production costs and scalability issues hinder widespread adoption. Regulatory and standardization barriers further complicate the development and deployment of enzymatic biosensors. Despite these limitations, advancements in materials science, nanotechnology, and bioengineering are paving the way for more robust and reliable biosensors. Innovations such as nanomaterial-based enzyme immobilization, synthetic biology for enzyme engineering, and advanced data analytics integration hold promise for overcoming current limitations. Collaborative efforts among researchers, industry stakeholders, and regulatory bodies are essential to accelerate the development and application of enzymatic biosensors in industrial settings. While enzymatic biosensors offer significant potential, addressing these challenges through ongoing research and technological advancements is crucial for their widespread implementation and optimization.