Recent Advances in Flexible Temperature Sensors: Materials, Mechanism, Fabrication, and Applications

Flexible electronics is an emerging and cutting-edge technology which is considered as the building blocks of the next generation micro-nano electronics. Flexible electronics integrate both active and passive functions in devices, driving rapid developments in healthcare, the Internet of Things (IoT), and industrial fields. Among them, flexible temperature sensors, which can be directly attached to human skin or curved surfaces of objects for continuous and stable temperature measurement, have attracted much attention for applications in disease prediction, health monitoring, robotic signal sensing, and curved surface temperature measurement. Preparing flexible temperature sensors with high sensitivity, fast response, wide temperature measurement interval, high flexibility, stretchability, low cost, high reliability, and stability has become a research target. This article reviewed the latest development of flexible temperature sensors and mainly discusses the sensitive materials, working mechanism, preparation process, and the applications of flexible temperature sensors. Finally, conclusions based on the latest developments, and the challenges and prospects for research in this field are presented.

Wearable sensor supports in-situ and continuous monitoring of plant health in precision agriculture era

Plant health is intricately linked to crop quality, food security and agricultural productivity. Obtaining accurate plant health information is of paramount importance in the realm of precision agriculture. Wearable sensors offer an exceptional avenue for investigating plant health status and fundamental plant science, as they enable real-time and continuous in-situ monitoring of physiological biomarkers. However, a comprehensive overview that integrates and critically assesses wearable plant sensors across various facets, including their fundamental elements, classification, design, sensing mechanism, fabrication, characterization and application, remains elusive. In this study, we provide a meticulous description and systematic synthesis of recent research progress in wearable sensor properties, technology and their application in monitoring plant health information. This work endeavours to serve as a guiding resource for the utilization of wearable plant sensors, empowering the advancement of plant health within the precision agriculture paradigm.

Constructing high-density crack-microstructures within MXene interlayers for ultrasensitive and superhydrophobic cellulosic fibers-based sensors

Incorporating biopolymers into two-dimensional transition metal carbides and/or nitrides (2D MXene) has been demonstrated as an effective strategy to improve the mechanical behaviors of MXene-based composites. However, the insulate nature of biopolymers inevitably deteriorated the electrical conductivity and the sensitivity of assembled sensors. Herein, a novel cellulose nanofiber (CNF)/MXene/carbon black (CB) composite was demonstrated as the conductive layer in eco-friendly cellulose paper-based sensors by intercalating the CB into the MXene/CNF interlayer, followed by coating hydrophobic SiO2 for encapsulation. Befitting from the high-density crack-microstructures between CB and MXene, the fabricated superhydrophobic paper CB/CNF/MXene/SiO2 sensor delivered ultrahigh sensitivity of 729.52 kPa-1, low detect limit of 0.29 Pa, rapid response time of 80 ms and excellent stability over 10,000 cycles. Moreover, the fabricated sensor was capable of detecting the physiological parameter of human (e.g. huge/subtle movements) and spatial pressure distribution. Furthermore, the presence of SiO2 layer endowed the sensor with superhydrophobic performance (water contact angle ∼158.2 o) and stable electrical signals under high moisture conditions or even under water. Our work proposed a novel strategy to boost the sensitivity of MXene-based conductive layer in flexible electronic devices.

Wide-range soft anisotropic thermistor with a direct wireless radio frequency interface

Temperature sensors are one of the most fundamental sensors and are found in industrial, environmental, and biomedical applications. The traditional approach of reading the resistive response of Positive Temperature Coefficient thermistors at DC hindered their adoption as wide-range temperature sensors. Here, we present a large-area thermistor, based on a flexible and stretchable short carbon fibre incorporated Polydimethylsiloxane composite, enabled by a radio frequency sensing interface. The radio frequency readout overcomes the decades-old sensing range limit of thermistors. The composite exhibits a resistance sensitivity over 1000 °C-1, while maintaining stability against bending (20,000 cycles) and stretching (1000 cycles). Leveraging its large-area processing, the anisotropic composite is used as a substrate for sub-6 GHz radio frequency components, where the thermistor-based microwave resonators achieve a wide temperature sensing range (30 to 205 °C) compared to reported flexible temperature sensors, and high sensitivity (3.2 MHz/°C) compared to radio frequency temperature sensors. Wireless sensing is demonstrated using a microstrip patch antenna based on a thermistor substrate, and a battery-less radio frequency identification tag. This radio frequency-based sensor readout technique could enable functional materials to be directly integrated in wireless sensing applications.

Self-Assembled and Multilayer-Overlapped ESM-PDA@rGO Nanofilm-Based Flexible Wearable Sensor for Real-Time Body Temperature Monitoring

There is an urgent need for wearable sensors that continuously monitor human physiological conditions in real time. Herein, an ESM-PDA@rGO-based flexible wearable temperature sensor was successfully constructed by integrating an eggshell membrane (ESM) with reduced graphene oxide (rGO) through dopamine (DA) polymerization. Depending on the "bridge effect" of diversified polydopamine (PDA) chains, on the one hand, a staggered arrangement of PDA-rGO frameworks and a lot of conductive pathways were produced and acted as an active layer. On the other hand, PDA-rGO frameworks were linked with ESM by PDA chains as a flexible sensing nanofilm. As a result, these mechanical merits of the ESM-PDA@rGO exhibited a 1.8-fold increase in Young' s modulus and 1.4-fold increase in tensile strength. Thereby, the conformability and performance of the temperature sensor were greatly enhanced, showing excellent sensitivity (-2.23%/°C), good linearity (R2 = 0.979), as well as stability. Especially, the flexible sensing nanofilm is evolved from the staggered arrangement of PDA-rGO frameworks, which endows it with rapid response (only 4-8 s), high resolution (0.1 °C), as well as excellent long-term durability (10 weeks). More importantly, the temperature sensor demonstrates insensitivity to bending deformation, ensuring reliable wearing stability. The sensor allows for online, real-time monitoring of human body temperature, encompassing both core (forehead, temple, cochlea, and exhale gas) and shell (palm and back of the hand, fingertip, and instep) temperatures. Particularly, it can accurately assess minor changes in peripheral body temperature before and after exercise, and it is capable of mapping daily patterns of body temperatures. The developed temperature sensor will provide us new materials design concepts and holds considerable promise in the fields of e-skin, disease surveillance, prediction, and diagnose.

Recent advances in smart wearable sensors as electronic skin

Flexible and multifunctional electronic devices and soft robots inspired by human organs, such as skin, have many applications. However, the emergence of electronic skins (e-skins) or textiles in biomedical engineering has made a great revolution in a myriad of people's lives who suffer from different types of diseases and problems in which their skin and muscles lose their appropriate functions. In this review, recent advances in the sensory function of the e-skins are described. Furthermore, we have categorized them from the sensory function perspective and highlighted their advantages and limitations. The categories are tactile sensors (including capacitive, piezoresistive, piezoelectric, triboelectric, and optical), temperature, and multi-sensors. In addition, we summarized the most recent advancements in sensors and their particular features. The role of material selection and structure in sensory function and other features of the e-skins are also discussed. Finally, current challenges and future prospects of these systems towards advanced biomedical applications are elaborated.

Twisted Optical Micro/Nanofibers Enabled Detection of Subtle Temperature Variation

The detection of subtle temperature variation plays an important role in many applications, including proximity sensing in robotics, temperature measurements in microfluidics, and tumor monitoring in healthcare. Herein, a flexible miniaturized optical temperature sensor is fabricated by embedding twisted micro/nanofibers in a thin layer of polydimethylsiloxane. Enabled by the dramatic change of the coupling ratio under subtle temperature variation, the sensor exhibits an ultrahigh sensitivity (-30 nm/°C) and high resolution (0.0012 °C). As a proof-of-concept demonstration, a robotic arm equipped with our sensor can avoid undesired collisions by detecting the subtle temperature variation caused by the existence of a human. Moreover, benefiting from the miniaturized and engineerable sensing structure, real-time measurement of subtle temperature variation in microfluidic chips is realized. These initial results pave the way toward a category of optical sensing devices ranging from robotic skin to human-machine interfaces and implantable healthcare sensors.

Flexible tactile sensors with biomimetic microstructures: Mechanisms, fabrication, and applications

In recent years, flexible devices have gained rapid development with great potential in daily life. As the core component of wearable devices, flexible tactile sensors are prized for their excellent properties such as lightweight, stretchable and foldable. Consequently, numerous high-performance sensors have been developed, along with an array of innovative fabrication processes. It has been recognized that the improvement of the single performance index for flexible tactile sensors is not enough for practical sensing applications. Therefore, balancing and optimization of overall performance of the sensor are extensively anticipated. Furthermore, new functional characteristics are required for practical applications, such as freeze resistance, corrosion resistance, self-cleaning, and degradability. From a bionic perspective, the overall performance of a sensor can be optimized by constructing bionic microstructures which can deliver additional functional features. This review briefly summarizes the latest developments in bionic microstructures for different types of tactile sensors and critically analyzes the sensing performance of fabricated flexible tactile sensors. Based on this, the application prospects of bionic microstructure-based tactile sensors in human detection and human-machine interaction devices are introduced.

Multifunctional Motion Sensing Enabled by Laser-Induced Graphene

The development of flexible sensors based on laser-induced graphene (LIG) has recently attracted much attention. It was commonly generated by laser-ablating commercial polyimide (PI). However, the weak mechanical extensibility of PI limits the development and diversified applications of LIG-based sensors. In this work, we adopted medical polyurethane (PU) tapes to peel off the LIG generated on PI and developed flexible and wearable sensors based on the proposed LIG/PU composite structure. Compared with other methods for LIG transfer, PU tape has many advantages, including a simplified process and being less time-consuming. We characterized the LIG samples generated under different laser powers and analyzed the property differences introduced by the transfer operation. We then studied the impact of fabrication mode on the strain sensitivity of the LIG/PU and optimized the design of a LIG/PU-based strain sensor, which possessed a gauge factor (GF) of up to 263.6 in the strain range of 75-90%. In addition, we designed a capacitive pressure sensor for tactile sensing, which is composed of two LIG/PU composite structures and a PI space layer. These LIG flexible devices can be used for human motion monitoring and tactile perception in sports events. This work provides a simple, fast, and low-cost way for the preparation of multifunctional sensor systems with good performance, which has a broad application prospect in human motion monitoring.

Flexible thin film thermocouples: From structure, material, fabrication to application

Flexible thin-film thermocouples (TFTCs) have been garnering interest as temperature sensors due to the advantages of being flexible, ultrathin, and ultralight. Additionally, they have fast response times and enable detection of temperature. These properties have made them suitable for applications such as wearable electronics, healthcare, portable personal devices, and smart detection systems. This review presents the progress in the development of flexible TFTCs. The mechanism, structural design, materials, fabrication methods, and related applications of flexible TFTCs are also elaborated. Finally, future development directions of flexible TFTCs are discussed such as wide-range temperature measurement, multiple sensor integration, and achieving reliable cold-end compensation systems.

A low-power and flexible bioinspired artificial sensory neuron capable of tactile perceptual and associative learning

Biomimetic haptic neuron systems have received a lot of attention from the booming artificial intelligence industry for their wide applications in personal health monitoring, electronic skin, and human-machine interfaces. In this work, inspired by the human tactile afferent nerve, we developed a flexible and low energy consumption artificial tactile neuron, which was constructed by combining a dual network (DN) hydrogel-based sensor and a low power memristor. The tactile sensor (ITO/PAM:CS-Fe³⁺ hydrogel/ITO) serves as E-skin, with mechanical properties including pressure and stretching. The memristor (Ti:ITO/BiFeO₃/ITO) serving as an artificial synapse has low power (∼3.96 × 10^-7 W), remarkable uniformity, a large memory window of 500 and excellent plasticity. Remarkably, the pattern recognition simulation based on a neuromorphic network is conducted with a high recognition accuracy of ∼89.81%. In the constructed system, the artificial synapse could be activated by the electrical information from the E-skin induced by an external pressure, to generate excitatory postsynaptic currents. The system shows functions of perception and memory functions, and it also enables tactile associative learning. The present work is important for the development of empowering robots and prostheses with the capability of perceptual learning, and it provides a paradigm for next-generation artificial sensory systems with low-power, wearable and low-cost features.

Fabrication of Temperature Sensors with High-Performance Uniformity through Thermal Annealing

It is considered to be of great significance to monitor human health and track the effect of drugs by measuring human temperature mapping through flexible temperature sensors. In this work, we found that the thermal annealing of flexible temperature sensors based on graphite-acrylate copolymer composites can not only improve the temperature coefficient of resistance (TCR) values of the devices, but also greatly improve the uniformity of the performance of the devices prepared in parallel. The best results were obtained when the devices were annealed at 100 °C, which is believed to be due to the rearrangement of graphite particles to generate more uniform and numerous conductive channels within the conductive composite. We believe this finding might promote the practical development of flexible temperature sensors in body temperature sensing for health maintenance and medical applications.

Flexible and Stretchable Carbon-Based Sensors and Actuators for Soft Robots

In recent years, the emergence of low-dimensional carbon-based materials, such as carbon dots, carbon nanotubes, and graphene, together with the advances in materials science, have greatly enriched the variety of flexible and stretchable electronic devices. Compared with conventional rigid devices, these soft robotic sensors and actuators exhibit remarkable advantages in terms of their biocompatibility, portability, power efficiency, and wearability, thus creating myriad possibilities of novel wearable and implantable tactile sensors, as well as micro-/nano-soft actuation systems. Interestingly, not only are carbon-based materials ideal constituents for photodetectors, gas, thermal, triboelectric sensors due to their geometry and extraordinary sensitivity to various external stimuli, but they also provide significantly more precise manipulation of the actuators than conventional centimeter-scale pneumatic and hydraulic robotic actuators, at a molecular level. In this review, we summarize recent progress on state-of-the-art flexible and stretchable carbon-based sensors and actuators that have creatively added to the development of biomedicine, nanoscience, materials science, as well as soft robotics. In the end, we propose the future potential of carbon-based materials for biomedical and soft robotic applications.

Fast-Response Flexible Temperature Sensors with Atomically Thin Molybdenum Disulfide

Real-time thermal sensing on flexible substrates could enable a plethora of new applications. However, achieving fast, sub-millisecond response times even in a single sensor is difficult, due to the thermal mass of the sensor and encapsulation. Here, we fabricate flexible monolayer molybdenum disulfide (MoS₂) temperature sensors and arrays, which can detect temperature changes within a few microseconds, over 100× faster than flexible thin-film metal sensors. Thermal simulations indicate the sensors' response time is only limited by the MoS₂ interfaces and encapsulation. The sensors also have high temperature coefficient of resistance, ∼1-2%/K and stable operation upon cycling and long-term measurement when they are encapsulated with alumina. These results, together with their biocompatibility, make these devices excellent candidates for biomedical sensor arrays and many other Internet of Things applications.

Fabrication of a graphene-based sensor to detect the humidity and the temperature of a metal body with imprecise data analysis

Graphene is a 2D material with remarkable properties. The present study demonstrates the fabrication of a graphene-based sensor for measuring the temperature and humidity of a metal body. The graphene sensor was fabricated by depositing a thin film of graphene nanoparticles between silver electrodes (separated by ∼50 μm) on a glass substrate. The graphene thin film was characterized by XRD, Raman spectroscopy and UV-vis techniques. The capacitance and resistance for both the relative humidity (in the range of 0-100% RH) and temperature (in the range of 230-310 K) were measured using an LCR meter at 1 kHz in a controlled chamber. The graphene-based sensor expressed high sensitivity with fast response and recovery times for both humidity and temperature with long stability and low hysteresis curves. The sensor was also tested on a metal body, which expressed a good response time. Moreover, the measured data of capacitance and resistance was analyzed with classical and neutrosophic analysis as an application of modern material statistics. It was observed that neutrosophic analysis is more flexible for analyzing the capacitance and resistance of the fabricated sensor.

Synthesis of Metal–Organic Frameworks Quantum Dots Composites as Sensors for Endocrine-Disrupting Chemicals

Hazardous chemical compounds such as endocrine-disrupting chemicals (EDCs) are widespread and part of the materials we use daily. Among these compounds, bisphenol A (BPA) is the most common endocrine-disrupting chemical and is prevalent due to the chemical raw materials used to manufacture thermoplastic polymers, rigid foams, and industrial coatings. General exposure to endocrine-disrupting chemicals constitutes a serious health hazard, especially to reproductive systems, and can lead to transgenerational diseases in adults due to exposure to these chemicals over several years. Thus, it is necessary to develop sensors for early detection of endocrine-disrupting chemicals. In recent years, the use of metal–organic frameworks (MOFs) as sensors for EDCs has been explored due to their distinctive characteristics, such as wide surface area, outstanding chemical fastness, structural tuneability, gas storage, molecular separation, proton conductivity, and catalyst activity, among others which can be modified to sense hazardous environmental pollutants such as EDCs. In order to improve the versatility of MOFs as sensors, semiconductor quantum dots have been introduced into the MOF pores to form metal–organic frameworks/quantum dots composites. These composites possess a large optical absorption coefficient, low toxicity, direct bandgap, formidable sensing capacity, high resistance to change under light and tunable visual qualities by varying the size and compositions, which make them useful for applications as sensors for probing of dangerous and risky environmental contaminants such as EDCs and more. In this review, we explore various synthetic strategies of (MOFs), quantum dots (QDs), and metal–organic framework quantum dots composites (MOFs@QDs) as efficient compounds for the sensing of ecological pollutants, contaminants, and toxicants such as EDCs. We also summarize various compounds or materials used in the detection of BPA as well as the sensing ability and capability of MOFs, QDs, and MOFs@QDs composites that can be used as sensors for EDCs and BPA.

Research Progress on the Preparation and Applications of Laser-Induced Graphene Technology

Graphene has been regarded as a potential application material in the field of new energy conversion and storage because of its unique two-dimensional structure and excellent physical and chemical properties. However, traditional graphene preparation methods are complicated in-process and difficult to form patterned structures. In recent years, laser-induced graphene (LIG) technology has received a large amount of attention from scholars and has a wide range of applications in supercapacitors, batteries, sensors, air filters, water treatment, etc. In this paper, we summarized a variety of preparation methods for graphene. The effects of laser processing parameters, laser type, precursor materials, and process atmosphere on the properties of the prepared LIG were reviewed. Then, two strategies for large-scale production of LIG were briefly described. We also discussed the wide applications of LIG in the fields of signal sensing, environmental protection, and energy storage. Finally, we briefly outlined the future trends of this research direction.

Pyrrol-Anthracene: Synthesis, Characterization and Its Application as Active Material in Humidity, Temperature and Light Sensors

This work reports on the synthesis of small molecular semiconductor 2-(1H-pyrrol-1-yl)-anthracene-9,10-dione (PAD) via wet chemical precipitation route method for its possible potential applications in sensors. Thin film characterization of the synthesized PAD is carried out by studying its surface morphology, bond dynamics, and optical properties. For studying sensing characteristics of the PAD, its 100 nm thick film is thermally deposited on pre-patterned silver (Ag) electrodes over glass substrate having ~45 µm inter-electrode gaps to prepare Ag/PAD/Ag sensor. The effects of humidity (%RH), temperature (T), and illumination of light (Ev) on the fabricated Ag/PAD/Ag sensor are studied by changing one of the three (%RH, T, and Ev) parameters at a time and measuring the corresponding variations in capacitance (C) and capacitive reactance (X) of the device. As C and X also depend on frequency, sensing properties of the Ag/PAD/Ag sensor are measured at two different frequencies (120 Hz and 1 kHz) to find the optimum sensitivity conditions. To investigate reproducibility and repeatability of Ag/PAD/Ag sensor, each measurement is taken several times and also hysteresis loops of %RH vs. C are plotted at 120 Hz and 1 kHz to find the percent errors in each cycle of measurements. The sensor is active to sense humidity, temperature, and illumination within a broad range, i.e., from 15–93%RH, 293–382 K, and 1500–20,000 lx, respectively. Other key parameters of the sensor i.e., the humidity response time (TRes) and recovery time (TRec), are measured, which are 5 and 7 s, respectively, whereas for light sensing the values of TRes and TRec are measured to be 3.8 and 2.6 s, respectively. The measured values of TRes and TRec for the fabricated Ag/PAD/Ag sensor are shorter and better as compared to those of previously reported for similar kind of small molecular based sensors. The sensing properties of Ag/PAD/Ag device exhibit the potential of PAD for humidity, temperature, and light sensing applications.

A state-of-the-art review on graphene-based nanomaterials to determine antibiotics by electrochemical techniques

Antibiotics might build up into the human body by foodstuff metabolism, posing a serious threat to human health and safety. Establishing simple and sensitive technology for quick antibiotic evaluation is thus extremely important. Nanomaterials (or NMTs) with the advantage of possessing merits such as remarkable optical, thermal, mechanical, and electrical capabilities have been highlighted as a piece of the best promising materials for rising new paths in the creation of the future generation biosensors. This paper presents the most recent advances in the use of graphene NMTs-based biosensors to determine antibiotics. Gr-NMTs (or graphene nanomaterials) have been used in the development of a biosensor for the electrochemical signal-transducing process. The rising issues and potential chances of this field are contained to give a plan for forthcoming research orientations. As a result, this review provides a comprehensive evaluation of the nanostructured electrochemical sensing approach for antibiotic residues in various systems. In this review, various electrochemical techniques such as CV, DPV, Stripping, EIS, LSV, chronoamperometry, SWV were employed to determine antibiotics. Additionally, this also demonstrates how graphene nanomaterials are employed to detect antibiotics.

Temperature-dependent resistance of carbon nanotube fibers

Carbon nanotube fibers are highly recommended in the field of temperature sensor application owing to their excellent electrical conductivity and thermal conductivity. Here, this work demonstrated the rapid thermal response behaviour of CNT fibers fabricated by floating catalyst CVD method, which was measured by anin situtechnique based on the CNT film electric heater with excellent electrothermal response properties. The temperature dependences of resistance and structure were both explored. Experimental investigation indicates that the reduction in the inter-CNT interspace in the fibers caused by thermally driven actuation was dominantly responsible for the decrease of the fibers resistance during the heating process. Especially, the heated fibers showed 7.2% decrease in electrical resistance at the applied square-wave voltage of 8 V, and good temperature sensitivity (-0.15% °C^-1). The as-prepared CNT fibers also featured a rapid and reversible electrical resistance response behaviour when exposed to external heating stimulation. Additionally, with the increment of temperature and twist-degree, the generated contraction actuation increased, which endowed the CNT fibers with more decrease in electrical resistance. These observations further suggested that the temperature-dependent conduction behavior of the CNT fibers with a high reversibility and repeatability was strongly correlated with their structure response to heat stimulation. As a consequence, the temperature-conduction behavior described here may be applied in other CNT-structured fibers and facilitated the improvement in their temperature-sensing applications.

Porous Polydimethylsiloxane Elastomer Hybrid with Zinc Oxide Nanowire for Wearable, Wide-Range, and Low Detection Limit Capacitive Pressure Sensor

We propose a flexible capacitive pressure sensor that utilizes porous polydimethylsiloxane elastomer with zinc oxide nanowire as nanocomposite dielectric layer via a simple porogen-assisted process. With the incorporation of nanowires into the porous elastomer, our capacitive pressure sensor is not only highly responsive to subtle stimuli but vigorously so to gentle touch and verbal stimulation from 0 to 50 kPa. The fabricated zinc oxide nanowire-porous polydimethylsiloxane sensor exhibits superior sensitivity of 0.717 kPa-1, 0.360 kPa-1, and 0.200 kPa-1 at the pressure regimes of 0-50 Pa, 50-1000 Pa, and 1000-3000 Pa, respectively, presenting an approximate enhancement by 21-100 times when compared to that of a flat polydimethylsiloxane device. The nanocomposite dielectric layer also reveals an ultralow detection limit of 1.0 Pa, good stability, and durability after 4000 loading-unloading cycles, making it capable of perception of various human motions, such as finger bending, calligraphy writing, throat vibration, and airflow blowing. A proof-of-concept trial in hydrostatic water pressure sensing has been demonstrated with the proposed sensors, which can detect tiny changes in water pressure and may be helpful for underwater sensing research. This work brings out the efficacy of constructing wearable capacitive pressure sensors based on a porous dielectric hybrid with stress-sensitive nanostructures, providing wide prospective applications in wearable electronics, health monitoring, and smart artificial robotics/prosthetics.

Femtomolar detection of dopamine using surface plasmon resonance sensor based on chitosan/graphene quantum dots thin film

Due to the crucial role of dopamine (DA) in health and peripheral nervous systems, it is particularly important to develop an efficient and accurate sensor to monitor and determine DA concentrations for diagnostic purposes and diseases prevention. Up to now, using surface plasmon resonance (SPR) sensors in DA determination is very limited and its application still at the primary stage. In this work, a simple and ultra-sensitive SPR sensor was constructed for DA detection by preparation of chitosan- graphene quantum dots (CS-GQDs) thin film as the sensing layer. Other SPR measurements were conducted using different sensing layers; GQDs, CS for comparison. The proposed thin films were prepared by spin coating technique. The developed CS-GQDs thin film-based SPR sensor was successfully tested in DA concentration range from 0 fM to 1 pM. The designed SPR sensor showed outstanding performance in detecting DA sensitively (S = 0.011°/fM, R² = 0.8174) with low detection limit of 1.0 fM has been achieved for the first time. The increased angular shift of SPR dip, narrow full width half maximum of the SPR curves, excellent signal-to-noise ratio and figure of merit, and a binding affinity constant (K_A) of 2.962 PM^-1 demonstrated the potential of this sensor to detect DA with high accuracy. Overall, it was concluded that the proposed sensor would serve as a valuable tool in clinical diagnostic for the serious neurological disorders. This in turns has a significant socio-economic impact.

Development and Progress in Sensors and Technologies for Human Emotion Recognition

With the advancement of human-computer interaction, robotics, and especially humanoid robots, there is an increasing trend for human-to-human communications over online platforms (e.g., zoom). This has become more significant in recent years due to the Covid-19 pandemic situation. The increased use of online platforms for communication signifies the need to build efficient and more interactive human emotion recognition systems. In a human emotion recognition system, the physiological signals of human beings are collected, analyzed, and processed with the help of dedicated learning techniques and algorithms. With the proliferation of emerging technologies, e.g., the Internet of Things (IoT), future Internet, and artificial intelligence, there is a high demand for building scalable, robust, efficient, and trustworthy human recognition systems. In this paper, we present the development and progress in sensors and technologies to detect human emotions. We review the state-of-the-art sensors used for human emotion recognition and different types of activity monitoring. We present the design challenges and provide practical references of such human emotion recognition systems in the real world. Finally, we discuss the current trends in applications and explore the future research directions to address issues, e.g., scalability, security, trust, privacy, transparency, and decentralization.

The Application of Nanomaterials for the Electrochemical Detection of Antibiotics: A Review

Antibiotics can accumulate through food metabolism in the human body which may have a significant effect on human safety and health. It is therefore highly beneficial to establish easy and sensitive approaches for rapid assessment of antibiotic amounts. In the development of next-generation biosensors, nanomaterials (NMs) with outstanding thermal, mechanical, optical, and electrical properties have been identified as one of the most hopeful materials for opening new gates. This study discusses the latest developments in the identification of antibiotics by nanomaterial-constructed biosensors. The construction of biosensors for electrochemical signal-transducing mechanisms has been utilized in various types of nanomaterials, including quantum dots (QDs), metal-organic frameworks (MOFs), magnetic nanoparticles (NPs), metal nanomaterials, and carbon nanomaterials. To provide an outline for future study directions, the existing problems and future opportunities in this area are also included. The current review, therefore, summarizes an in-depth assessment of the nanostructured electrochemical sensing method for residues of antibiotics in different systems.