Sensor Material Research Articles

Nanosized tin dioxide based semiconductor materials for creation of gas sensors

Nanosized initial semiconductor tin dioxide based material was synthesized by a sol-gel technique and characterized by XRD, IR-spectroscopy, DTA-DTG and TEM methods. Nanosized SnO2-based sensor materials were prepared using the pastes with different quantities of tin dioxide and carboxymethyl cellulose and formatted at various temperatures. It was found that the compositions of the pastes significantly affect the characteristics of the sensors obtained on their base. The characteristics of the sensors of different compositions were explained by necessity of the presence of sufficient number of contacts between the nanoparticles of the sensor material, which ensure the electrical conductivities of the sensors.

Specific temperature-modulated crab shell-derived porous carbon as a typical recycling material for nitrofurazone electrochemical sensor

Nitrofurazone (NFZ), a nitroimidazole antibiotic, can cause serious toxicity when overused, its quantification is crucial for human health. Herein, crab shell waste is converted into porous biochar at a high temperature, which can be employed for the establishment of an electrochemical sensor for the quantitative detection of NFZ. The morphological and structural properties of the crab shell carbon at different temperatures were characterized by SEM, XRD, FT-IR and N2 adsorption-desorption analyses. The crab shell carbon prepared at 500 °C (C-CS-500) and 700 °C (C-CS-700) is calcite-based and contains micro-fibrillar similar to chitin structure, while the crab shell carbon prepared at 900 °C (C-CS-900) is lime-based and lacks the similar structure. And the synergistic influence of calcite-based composition and micro-fibrillar structure of crab shell carbon offered strong electron-transport properties and a large electrode active at a higher carbonized temperature. The electrochemical signals demonstrated that the crab shell carbon prepared at 700 °C provided enhanced sensing capability for rapid NFZ detection with a wide linear range of 0.40–80 μM, a high sensitivity of 0.55 μA μM−1 and a low detection limit of 0.11 μM (S/N = 3), as compared to the crab shell carbon prepared at 500 °C and 900 °C. In addition, the sensor can also be utilized to quantify nitrofurazone in the real drug (compound cod liver oil ointment) with satisfactory recovery.

Environmentally friendly use of silver nanoparticles prepared with Anchusa azurea flower to detect mercury (II) ions

ABSTRACT In this study, the extract obtained from the flowers of the Anchusa azurea (AA) plant was mixed with silver nitrate to obtain silver nanoparticles. The ion sensing ability of the obtained bio-sourced silver nanoparticles in aqueous solutions was investigated and the presence of Hg2+ ions was determined colorimetrically. Silver nanoparticles (AgNPs) prepared on Green Chemistry method, which is both an environmentally friendly and cost-effective synthesis technique, were characterised using different analytical tools. The mean particle size of AA-AgNPs from transmission electron microscopy (TEM) images was determined to be 22 nm in diameter. XRD measurements showed that the crystallite sizes of the synthesised AgNPs were in the face-centred cubic crystal structure with an average size of 22 nm, which is consistent with TEM results. AA-AgNPs showed absorption at 435 nm, indicating that AgNPs exhibit a strong surface plasmon resonance (SPR) and play a role in stabilisation. AgNPs synthesised with Anchusa azurea flowers were observed using UV-vis spectroscopy to selectively and sensitively detect mercury ions (Hg2+). When Hg2+ in aqueous solution was added to the AgNPs, the overall absorbance dramatically decreased and the colour changed from yellow to colourless. This study shows that AA-AgNPs can be used as a cost-effective material in optical sensors for colorimetric determinations.

Evaluating the effect of unidirectional loading on the piezoresistive characteristics of carbon nanoparticles

The piezoresistive effect of materials can be adopted for a plethora of sensing applications, including force sensors, structural health monitoring, motion detection in fabrics and wearable, etc. Although metals are the most widely adopted material for sensors due to their reliability and affordability, they are significantly affected by temperature. This work examines the piezoresistive performance of carbon nanoparticle (CNP) bulk powders and discusses their potential applications based on strain-induced changes in their resistance and displacement. The experimental results are correlated with the characteristics of the nanoparticles, namely, dimensionality and structure. This report comprehensively characterizes the piezoresistive behavior of carbon black (CB), onion-like carbon (OLC), carbon nanohorns (CNH), carbon nanotubes (CNT), dispersed carbon nanotubes (CNT-D), graphite flakes (GF), and graphene nanoplatelets (GNP). The characterization includes assessment of the ohmic range, load-dependent electrical resistance and displacement tracking, a modified gauge factor for bulk powders, and morphological evaluation of the CNP. Two-dimensional nanostructures exhibit promising results for low loads due to their constant compression-to-displacement relationship. Additionally, GF could also be used for high load applications. OLC’s compression-to-displacement relationship fluctuates, however, for high load it tends to stabilize. CNH could be applicable for both low and high loading conditions since its compression-to-displacement relationship fluctuates in the mid-load range. CB and CNT show the most promising results, as demonstrated by their linear load-resistance curves (logarithmic scale) and constant compression-to-displacement relationship. The dispersion process for CNT is unnecessary, as smaller agglomerates cause fluctuations in their compression-to-displacement relationship with negligible influence on its electrical performance.

Molecular receptors integrated bimodal porous polymer scaffolds as portable solid-state optical ion-sensors and extractors for the selective capturing of ultra-trace toxic copper ions

BackgroundEnvironmental contamination by heavy metal ions has caused growing ecological and public health concerns. In this line, monitoring of copper toxicity gains importance due to its application in industrial, agricultural, domestic, medical and technological sectors. Although noteworthy breakthroughs were made, critical issues, such as portability, the need for well-trained personnel, costly/complex instrumentations, long response time, and the introduction of secondary contaminants, required attention. Hence, developing a low-cost, user-friendly, real-time, portable analytical platform for rapid and on-site analysis remained imperative. Solid-state colorimetric sensors have gained widespread popularity due to their low cost, ease of use, and brilliant sensitivity/selectivity. ResultsWe have successfully unfolded an ultra-portable azomethine-infused structurally interwoven polymer monolith as the solid-state chromatic sensor for the quantitative naked-eye detection of ultra-trace Cu2+ in industrial/environmental samples. For the sensor fabrication, non-hygroscopic conjugated Schiff-base receptors, namely N-(1E,2E)-3-(4-dimethylamino)phenyl)allylidene)-3-nitrobenzohydrazide (DPAN) and 2,3-bis(((1E,2E)-3-(4-dimethylamino)phenyl)allylidene)amino)malononitrile (DPAM) were synthesized in-house and voluminously immobilized onto a crack-free porous poly(4VP-co-EGDMA) monolith framework. The topological structure and functionalities of the porous polymer monolith and chromatic sensor materials were examined using various surface analytical and microscopic techniques. The excellent surface area and intriguing interlaced porosity features of the tailor-made polymer monolith facilitated the voluminous anchoring of the chromatic receptors for the selective/sensitive targeting of Cu2+. The DPAN and DPAM receptor-loaded poly(4VP-co-EGDMA) sensors exhibited a linear range of 0–150 μg/L, with the limit of detection of 0.11 and 0.13 μg/L for Cu2+, respectively. The sensors manifested Cu2+ specificity amidst concomitant matrix ions to highlight the relevance of the proposed solid-state sensor. SignificanceThe sensor materials offered a reliable approach for detecting and quantifying environmentally toxic and industrially pertinent Cu2+ from aqueous samples, with the prospect of large-scale production, owing to the sensor's integrated compact design that can be reused for repeated real-time surveillance. The sensor's ability to sense/trap traces of toxic Cu2+ can provide an early warning about the growing toxicity in a particular resource, thereby providing an opportunity to initiate remediation protocols for speedy decontamination.

The use of thiazole derivative molecules as sensor materials: Potentiometric determination of Cu(II) ions

AbstractIn this study, poly(vinyl chloride) (PVC)–membrane potentiometric sensors for the determination of copper(II) ions were prepared using 2‐acetamido‐4‐(2‐hydroxyphenyl)thiazole (L1), 2‐amino‐4‐(trifluoromethyl)thiazole‐5‐carboxylic acid (L2) and ethyl 2‐amino‐4,5,6,7‐tetrahydrobenzo[d]thiazole‐6‐carboxylate (L3) ionophores. It was determined that the potentiometric performance characteristics of the sensors prepared with L1 were superior to the others. Based on these properties, the optimum membrane composition was determined as 3.0% ionophore (L1), 64.0% bis(2–ethylhexyl)adipate (DEHA), 32.0% PVC and 1.0% potassium tetrakis (p–chlorophenyl) borate (KTpClPB). The newly developed sensor had a low detection limit of 6.74 × 10−7 mol L−1 over a wide concentration range of 1.0 × 10−1–1.0 × 10−6 mol L−1. Compared with different metal ions, the sensor showed good selectivity to copper(II) ions, had a repeatable, stable and fast response time. The copper(II)–selective sensor could work in a wide range without being affected by pH changes (5.0–9.0). It was used as indicator electrode for the potentiometric titration of copper(II) ions with ethylenediaminetetraacetic acid (EDTA), and successfully applied for the determination of copper(II) ions content in different water samples.

Sustainable Environmental Communication Project: Eco-Friendly and Sensory Materials for Museums

Sustainable Environmental Communication Project: Eco-Friendly and Sensory Materials for Museums

Shutters-Inspired metal ions coordination hydrogel Strain/Pressure sensor for joint behavior evaluation and flatfeet correction

The metal ions coordination hydrogels (MI-HG) that polymer gels serve as flexible substrates and metal ions as conductive media have emerged as flexible electronic sensor materials. Nevertheless, fabricating MI-HG by a traditional soaking method is difficult to guarantee the good permeation of metal ions, manifesting as the “core–shell” structure of MI-HG, which undoubtedly reduces their mechanical property, conductivity, and sensitivity. Inspired by the shutter opening and closing regulation mechanism, a strategy that completely opening the backbone layers of polymer gels facilitates metal ions permeation thus improving the whole performance of MI-HG, especially the mechanical property is proposed. Herein, poly(vinyl alcohol)(poly(acrylic acid)-polyacrylamide) (PVA(PAA-PAM)) is used as the typical polymer hydrogel (HG), trivalent aluminum ion (Al3+) as the metal salt, and N,N'-methylenebisacrylamide (MBAA) as the important regulation ‘rod’, fabricating a series of aluminum coordination hydrogels (Al-HGx%). The results indicate that the mechanical performances of Al-HG2% are significantly improved. For example, the toughness of Al-HG2% reaches 996.12 KJ/m3, approximately three times that of the Al-HG0% sample (354.45 KJ/m3). The combination of structural characterization as well as finite element analysis, the mechanism for the enhanced mechanical performances based on shutter’s completely open effect is elucidated, the product of which (Al-HG2%) has potential application in flexible strain/pressure sensor for joint behavior evaluation and flatfeet correction.

Influence of Be vacancy on 2D BeN4 single-layer for enhanced H2S sensing: prediction from first-principles simulations

Abstract A notable surge in research interest directed towards the exploration and development of two-dimensional materials, specifically in the realm of advancing nano-devices, with a special focus on applications in gas detection, has been observed. Among these materials, the spotlight has fallen on a newly synthesized single-layered Dirac Semimetal, known as BeN4, which holds great promise as a potential candidate for an efficient gas sensor. The current investigation uses first-principles calculations to examine the H2S detection capability of pristine and point-defect-tempted BeN4 single-layers. The H2S molecule has been observed to be weakly adsorbed on pure BeN4 through weak van der Waals interaction exhibiting very low adsorption energy of −0.0726 eV and insignificant charge transport. The impact of the Be vacancy point defect in BeN4 was the surge in H2S adsorption energy to −0.582 eV, manifested by enhanced charge transmission (0.02 e) from the H2S molecule to the BeN4 with Be defects. The reasonable physical steadiness and modest recovery time (6 ms) at ambient conditions indicate the possibility of Be point-defected BeN4 being a contender as a sensor material for designing and developing a robust H2S gas sensor. In addition, the sensor exhibited a selective response towards the H2S gas molecules. Our findings will provide a reference line for the fabrication of innovative H2S detectors, showcasing the practical implications of the observed enhancements in H2S adsorption energy and charge transmission in Be point-defected BeN4 structures.

Indium-Doped SnO2 Based Surface Acoustic Wave Gas Sensor with Ba0.6Sr0.4TiO3 Film

SnO2-based gas sensors have been widely synthesized and used for the detection of various hazardous gases. However, the use of doped SnO2 in sensing applications has recently attracted increased interest due to the formation of a synergistic effect between the dopant and the host. Moreover, in the case of a surface acoustic wave (SAW) sensor, the piezoelectric material used in the fabrication of the sensor plays a crucial role in defining the response of the SAW sensor. As a ferroelectric material, barium strontium titanate (Ba0.6Sr0.4TiO3) has recently been studied due to its intriguing dielectric and electromechanical properties. Its high acoustic velocity and coupling coefficient make it a promising candidate for the development of acoustic devices; however, its use as a piezoelectric material in SAW sensors is still in its infancy. In this paper, we present the design, fabrication and validation of an indium doped SnO2-based SAW gas sensor on Ba0.6Sr0.4TiO3 thin film for room temperature (RT) applications. Pulsed laser deposition was used to deposit thin films of Ba0.6Sr0.4TiO3 and indium-doped SnO2. Different characterization techniques were employed to analyze the morphology and crystallization of the films. The performance of the fabricated sensor was validated by exposing it to different concentrations of ethanol and then analyzing the recorded frequency shift. The sensor exhibited fast response (39 s) and recovery (50 s) times with a sensitivity of 9.9 MHz/Δ. Moreover, the sensor had good linear response and reproducibility. The fabricated indium-doped SnO2-based SAW gas sensor could be suitable for practical room temperature applications.

Efficient Multi-stimulus-Responsive Luminescent Eu(III)-Modified HOFs Materials: Detecting Thiram and Caffeic Acid and Constructing a Flexible Substrate Anti-counterfeiting Platform.

The powerful capability of multi-stimulus-responsive luminescent hydrogen-bonded organic frameworks (HOFs) to respond to external chemical or physical stimuli in various manners makes them appealing in the luminescence anti-counterfeiting field. Herein, a novel Eu3+-functionalized HOF (Eu@GC-2) that combines the emission of HOFs with the characteristic emission of Eu3+ ions has been successfully synthesized, which can generate various fluorescence at different excitation wavelengths. Eu@GC-2 has enormous potential as a raw material for a paper-based sensor that is designed for detecting the pesticides thiram and caffeic acid in crops with favorable selectivity, anti-interference, and high efficiency. Based on the above excellent properties, Ln3+-functionalized HOFs (Ln@GC-2) were then employed to produce four luminescent anti-counterfeiting inks. With the incorporation of back-propagation neural network and Gray code conversion functions, a multi-stimulus-responsive luminescent anti-counterfeiting platform, coregulated by the excitation light and the chemical reagent, has been constructed. This approach can not only achieve multiple encryptions and fast information identification but also enhance the code-breaking complexity, making it an efficient strategy for information encryption and decryption.

PVC plasticized membranes modified with Fe3O4 nanoparticles for potentiometric sensing of sulfate

Potentiometric sensing is one of the most wide spread platforms for analysis of aqueous solutions. The development of potentiometric sensors for hydrophilic anions such as sulfate, phosphate and bicarbonate is a challenging problem, since their high hydration energy results in a low affinity for non-polar polymer membranes – a standard material for potentiometric sensor production.In this study we propose a new type of polymeric sensor membranes for ion-selective sensors with pronounced selectivity to hydrophilic anions. The membranes are based on inorganic Fe3O4 nanoparticles (NP) embedded into plasticized poly(vinyl chloride). Six different formulations of membranes with various combinations of Fe3O4 nanoparticles and other membrane-active components were synthesized and characterized with a wide range of physico-chemical methods. Contact angle measurements, FTIR spectra, SEM and AFM imaging, magnetization hysteresis curves, ZFC/FC studies were performed. The obtained results proved the formation of nanocomposites and demonstrated a structure with “cavities” in membranes with embedded nanoparticles. Potentiometric sensitivity and selectivity of the developed sensors in aqueous solutions of SO42−, HPO42−, HCO3−, H2PO4−, NO3− and Cl−anions were studied. The developed sensors showed high sensitivity to sulfate ion (-22 mV/dec in the concentration range from 10−5 to 10−3 M) and low sensitivity to the typical interfering anions – chloride and nitrate (-14 mV/dec). The optimized sensor membrane composition demonstrated sulfate selectivity higher than that of commercially available ion-selective sensor formulations. The novel sensors were tested for quantification of SO42− in real samples of natural mineral water and the obtained content of sulfate was in a good agreement with the reference data (relative error < 3 %)

Application of Sensing Devices in the Detection of Oral, Pulmonary, and Gastrointestinal Diseases

Biomedical sensing technology is developing at a tremendous pace and is expected to become an effective clinical tool for the diagnosis and monitoring of human health. The development of sensing devices has successfully transformed the specific sensor prototype designed in the laboratory into a commercially feasible clinical disease detection device. Recently, sensing devices have been accelerated and extended to various fields beyond disease detection, including the measurement of gastrointestinal physiological parameters such as pH, VOC detection, small-molecule gas sensing, and noninvasive screening of oral and lung diseases such as oral cancer, gastric cancer, and other major diseases. In this review, the applications of sensors and electronic nose devices in the diagnosis and monitoring of oral, pulmonary, and gastrointestinal diseases are reviewed, as well as the design and application of sensor materials in disease markers and in situ detection. This article also introduces the practical application of sensing devices in human disease detection, critically analyzes their detection mechanisms and clinical utility, and discusses their future development in medicine. We believe that this review will help readers, especially practitioners in the medical field, provide ideas for the development of sensing devices.

Solid-state real-time colorimetric sensing of ultra-trace copper ions using aqueous compatible chromatic probe imbued porous polymer monolithic sensor

In this work, we design an aqua-compatible and sustainable chromatic sensor for the selective detection of copper ions in aqueous solutions for application in industrial quality control and environmental analysis. The solid-state chromatic sensor is fabricated through the uniform decoration of an indigenously synthesized unique chromoionophoric probe (TMAP), i.e., (2,2′-(((1E,1′E)-thiophene-2,5-diylbis(methaneylylidene)) bis(azaneylylidene))diphenol) onto a bimodal macro-/meso‑porous polymer monolith, poly(2VP-co-DVB), i.e., poly(2vinylpyridine-co-divinylbenzene), to exploit the possibility of solid-state colorimetric ion sensing. The polymer monolith and sensor materials' topography and morphology are characterized through p-XRD, FE-SEM, XPS, EDX, TEM, SAED, TGA, FT-IR and BET/BJH analysis. The ion-sensing is accompanied by a discernible color transition from vivid yellow to subdued red, with a detection and quantification limit value of 0.20 and 0.51 μg/L for Cu2+, respectively. The sensor affirms a fast detection (≤60 s) for Cu2+, with a linear signal/colorimetric response in the concentration range of 3–100 μg/L. The parameters such as sensor dosage, chromatic receptor dose, pH, temperature, sensing kinetics and reusability are optimized for reliable and reproducible ion-sensing. The solid-state sensor reveals excellent selectivity and sensitivity for Cu2+, and its practical utility with environmental/industrial samples proves its utility as a portable sensor kit for real-time on-site analysis for ultra-trace Cu2+.

Phthalocyanine and Porphyrin Derivatives and Their Hybrid Materials in Optical Sensors Based on the Phenomenon of Surface Plasmon Resonance

In this review, the state of research over the past fifteen years in the field of the applications of metal phthalocyanines and porphyrin derivatives as well as their hybrid materials with carbon nanotubes, metal oxides, and polymers in optical sensors based on the phenomenon of surface plasmon resonance (SPR) is analyzed. The first chapter of the review presents an analysis of works on the use of porphyrins and phthalocyanines in classical SPR sensors for the detection of gases and volatile organic vapors, as well as their improved modifications, such as total internal reflection ellipsometry (TIRE) and magneto-optical SPR (MOSPR) methods, while the second chapter is devoted to their application for the detection of various analytes in solutions. The third chapter of the review summarizes publications describing recent advances in the use of porous materials based on hybrids of carbon nanotubes and oxides with metal phthalocyanines. The fourth chapter describes two-dimensional metal-organic frameworks (MOFs) based on metal porphyrin derivatives as SPR sensitizers.

Multifunctional Optical Sensing with Lanthanide-Doped Upconverting Nanomaterials: Improving Detection Performance of Temperature and Pressure in the Visible and NIR Ranges.

Temperature and pressure are fundamental physical parameters in the field of materials science, making their monitoring of utmost significance for scientists and engineers. Here, the NaSrY(MoO4)3:0.02Er3+/0.01Tm3+/0.15Yb3+ nanophosphor is developed as an optical sensor material. Under 975 nm laser excitation, the upconversion characteristics and optical detection performance of the multifunctional sensing platform of temperature and pressure (vacuum) are investigated. We have successfully developed a novel detection platform that enables optical detection of pressure (vacuum) and temperature. This platform utilizes thermally coupled levels (TCLs) and non-TCLs of Er3+ and Tm3+ to achieve ratiometric detection. The multimodal optical temperature and pressure detection based on TCLs and non-TCLs is successfully realized by using different emission bands of double emission centers, which makes it possible for self-referencing optical temperature and pressure measurement modes. These results indicate that the developed nanophosphor is a promising candidate for optical sensors, and our findings suggest potential strategies for modulating the sensor properties of luminescent materials doped with rare-earth ions.

Multifunctional polyphosphazene grafted with triphenylamine and aminostilbene chromophore for electrochromic and sensor application

In this paper, a sequence of polyphosphazenes (PPZs) as electrochromic (EC) and sensor materials have been designed and synthesized by introducing chromophores, (4-(diphenyl amino)phenyl) methanol (CH1) for PPZ1, 3-(4-(dimethyl amino) phenyl)-2-(4hydroxyphenyl) acrylonitrile (CH2) for PPZ2, and CH1 and CH2 for PPZ3 into the main chain. In terms of EC performance, PPZ1 shows the best EC performance among the three PPZs which can achieve 60 % optical contrast at 690 nm with good cyclic stability within 1000 s and fast switching response time (tcolor/tbleach = 1.2 s/0.6 s). Compared to PPZ1, the oxidation potential of PPZ3 is reduced compared to PPZ1. PPZ2 and PPZ3 as sensors are more sensitive for the detection of 2,4,6-trinitrophenol (TNP) and trifluoroacetic acid (TFA) compared to PPZ1. What's more, PPZs can be used in memory devices with non-volatile flash memory performance and switching current ratios of 103:102.4:1, 104.7:101.3:1 and 103.5.:100.6:1 respectively. Therefore, PPZs have the promising prospect in optoelectronic field.

Microbial synthesis of antimony sulfide to prepare catechol and hydroquinone electrochemical sensor by pyrolysis and carbonization

The application of antimony sulfide sensors, characterized by their exceptional stability and selectivity, is of emerging interest in detection research, and the integration of graphitized carbon materials is expected to further enhance their electrochemical performance. This study represents a pioneering effort in the synthesis of carbon-doped antimony sulfide materials through the pyrolysis of the mixture of microorganisms and their synthetic antimony sulfide. The prepared materials are subsequently applied to electrochemical sensors for monitoring the highly toxic compounds catechol (CC) and hydroquinone (HQ) in the environment. Via cyclic voltammetry (CV) and impedance testing, we concluded that the pyrolytic product at 700 °C (Sb-700) demonstrated the best electrochemical properties. Differential pulse voltammetry (DPV) revealed impressive separation when utilizing Sb-700/GCE for simultaneous detection of CC and HQ, exhibiting good linearity within the concentration range of 0.1–140 μM. The achieved sensitivities of 24.62 μA μM−1 cm−2 and 22.10 μA μM−1 cm−2 surpassed those of most CC and HQ electrochemical sensors. Meanwhile, the detection limits for CC and HQ were as low as 0.18 μM and 0.16 μM (S/N = 3), respectively. Additional tests confirmed the good selectivity, reproducibility, and long-term stability of Sb-700/GCE, which was effective in detecting CC and HQ in tap water and river water, with recovery rates of 100.7%–104.5% and 96.5%–101.4%, respectively. It provides a method that combines green microbial synthesis and simple pyrolysis for the preparation of electrode materials in CC and HQ electrochemical sensors, and also offers a new perspective for the application of microbial synthesized materials.

Current Landscape of the Robotic Tactile Array Sensors and Algorithm‐Based Performance Enhancement

The automated robots utilizing the traditional rigid tactile sensors have achieved significant success in effective task execution. Advancing into the era of service robots and humanoids that should perform sophisticated works in daily life, recent research trends in robotic tactile sensors have been shifting from the conventional rigid sensors to flexible/stretchable sensors. Over the past decade, the flexible/stretchable tactile sensors with human skin‐like mechanical compliance and stimulation perceptions have seen considerable advances. However, there are many substantial remaining challenges to produce practically useful flexible/stretchable tactile sensors such as the signal hysteresis originating from sensor material and the limited spatial resolution resulting from excessive addressing lines and signal interferences. Incorporation of learning‐based algorithms and data analysis techniques have been introduced recently and made remarkable successes in improving the challenges. Because most robotic tactile sensors are fabricated using the electronic sensing mechanisms or platforms, this article presents a concise overview on recent flexible/stretchable tactile sensors. This article introduces a brief discussion on the sensor performance parameters and sensing mechanisms, and the algorithmic approaches. In addition, it addresses existing challenges associated with current tactile array sensors and algorithms, then discusses prospects, and proposes a research direction for immediate practical uses in robots.

Bioinspired Touch-Responsive Hydrogels for On-Demand Adhesion on Rough Surfaces.

Reversible adhesives are widely needed in our daily lives and industrial applications. However, robust and switchable adhesion on rough surfaces with on-demand attachment and detachment remains highly challenging. Here, we report a snail-mucus-inspired touch-responsive hydrogel (TRH), whose universal and robust adhesion is triggered by simple contact with the attaching surface. TRH is composed of a polymeric hydrogel and saturated sodium acetate (NaAc) and is prepared by one-pot synthesis. At room temperature, TRH remains in an amorphous and soft state, which allows it to conformally adapt to rough surfaces. The contact with the target surface triggers the crystallization of NaAc, which increases the modulus of TRH by an order of magnitude and interlocks with the target surfaces, achieving an adhesion of up to 204.84 ± 53.98 kPa. Upon heating, TRH returns to a soft state, facilitating easy detachment with adhesion of 5.12 ± 1.34 kPa. Meanwhile, the detached TRH is ready for the next adhesion without the need to be maintained at high temperature. TRH finds applications as a smart material for light-triggered adhesion switching, information encryption, and temperature sensors.