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The present work envisages the development of a novel and low-cost self-mixing interferometry (SMI) technology-based single particle sensing system in a microchannel chip for real time single micro-scale particle sizing. We proposed a novel theoretical framework to describe the impulse SMI signal expression in the time domain induced by a flowing particle. Using Hilbert transform, the interferometric fringe number of the impulse SMI signal was retrieved precisely for particle size discrimination. For the ease of particle sensing, a hydrodynamic focusing microfluidic channel was employed by varying the flow rate ratio between the sample stream and the sheath liquid, and the particle stream of a controllable width was formed very easily. The experimental results presented good agreement with the theoretical values, providing a 300 nm resolution for the particle sizing measurement. [ABSTRACT FROM AUTHOR]

As a compact and simple sensing technique, optical feedback interferometry (OFI) can be a promising flowmetry method in various microfluidic applications. In this paper, OFI-based flowmetry sensor performance in a microscale flow scheme is studied theoretically and experimentally. An innovating model and different numerical methods are investigated, where the scattering light angle distribution is involved to predict the Doppler frequency distribution. For the first time, our model describes the influences of multiple OFI sensor system characteristics, such as flowing particle size, concentration, channel interface reflectivity and channel dimension, on the OFI signal spectral performances. In particular, a significant OFI signal level enhancement was achieved by deposing a high reflectivity gold layer on the rear channel interface due to the increased forward scattered light reflection. The consistent experimental validation associated with the simulations verifies this numerical simulation method's reliability. The numerical methods presented here provide a new tool to design novel microfluidic reactors and sensors. [ABSTRACT FROM AUTHOR]

In this work, we developed methane gas sensors based on zinc oxide nanorod (n-ZnO-NR) arrayed assembly, synthesized using aqueous phase deposition on p-Si(100) substrates, fabricated as pn junction besides chemical sensitization by Pd (Pd cat / n -ZnO-NR) and Pd-30 wt% Ag (Pd–Ag cat / n -ZnO-NR) forming Schottky junctions. These sensors are evaluated under reducing methane [CH 4 ] gas with varying concentration (100–10,000 ppm or 0.01–1.0%) mixed with synthetic air under optimum temperature (≤200–230 °C) for thermal activation and UV A (365 nm) light activation supplemented with 50–100 °C, following increased electrical conductivity, bandgap narrowing, decreased barrier height, under biasing operation. The performance metrics include a high response (R; 45–80%), low limit of detection (LOD; 80–270 ppm), fast response-recovery times (<1–67 s), and strong binding constants (0.012–0.021), quantified from saturation current, transient response, and Langmuir adsorption isotherm, respectively. Every factor inducing a change in oxygen content of analyte gas atmosphere above ZnO include: (1) surface chemical reaction with chemisorbed oxygen ions on pristine and Pd cat or Pd-Ag cat modified n-ZnO-NR yields electron donors increasing sensor conductance; (2) effective free carrier concentration and amplified interface-dipole allowing reduced barrier height and electron tunneling at high reverse bias prevailing depletion-driven mechanism; (3) faster electron transport shortening the response time due to weakened oxygen ion adsorption removed by analyte gas molecules; and finally, (4) in-depth study of thermal and UV activated processes is supported with space charge model and band-bending theory perspectives. • Assembled zinc oxide nanorod arrays pn junction using low temperature aqueous phase deposition. • Demonstrated high responsivity and faster detection of methane gas at moderate temperature. • Elucidated reduction in operating temperature under UV activation for Pd/Pd-Ag/ZnO-NR. • Leveraged higher reverse biasing operation for efficient electron transport via tunneling. • In-depth understanding of sensing mechanism by space charge model and band-bending theory. [ABSTRACT FROM AUTHOR]

[Display omitted] • More than 114 Schiff bases that provide detectable chromogenic and/or fluorogenic to sense Cu2+ were reviewed. • Structure and analytical parameters of the summarized sensors were discussed. • Different sensing mechanisms and applications were discussed. • Future scope on designing of Schiff bases for Cu2+ sensing is discussed. Cu2+ is an important essential trace metal ion and know to play numerous roles in biological systems. The deficiency and excess accumulation of Cu2+ in the human body can cause serious diseases. Therefore, different analytical techniques are developed for the detection of Cu2+ in various environmental, biological and industrial samples. The optical chemosensors based on UV–Vis absorption and fluorescence spectroscopic methods to detect Cu2+ are gaining wide interest due to their low-cost, simplicity, sensitivity and visual response for on-site detection. In designing chemosensors, Schiff bases are extensively explored owing to their facile synthesis, easy structural modification, unique optical and coordinative behaviour. This review compiled more than 114 Schiff bases that can be easily synthesized and provide detectable chromogenic and/or fluorogenic to sense Cu2+. Various analytical parameters, sensing mechanisms, sensing media, structure, chromo-fluorogenic parameters and applications of the summarized sensors are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Two new CdII/ZnII coordination polymers using the bis(pyridyl)-bis(amide) ligand as the main ligand and 1,2,4,5-benzenetetracarboxylic acid (H 4 BTEC) as the auxiliary ligand were designed and synthesized, which can sensitively detect biomarker 3-nitrotyrosine as fluorescence sensors. They have the advantages of excellent stability, anti-interference, recyclability and low limits of detection. [Display omitted] 3-Nitrotyrosine (3-NT), as a stable biomarker in the human body, is closely related to a variety of diseases. Therefore, the detection of 3-NT is of important significance for human disease monitoring. In addition, under the same dimension, the influence of CPs with different metals on 3-NT detection still has important research value. Herein, we successfully synthesized two new 2D coordination polymers (CPs), namely [M(L)(BTEC) 0.5 ]·H 2 O (M = Cd for CP 1 , M = Zn for CP 2), by using the bis(pyridyl)-bis(amide) ligand L [(E)-4,4′-(ethene-1,2-diyl)bis[(N -pyridin-3-yl)benzamide] as the main ligand and 1,2,4,5-benzenetetracarboxylic acid (H 4 BTEC) as the auxiliary ligand under hydrothermal conditions. CPs 1 – 2 can be used as fluorescent sensors to effectively detect 3-NT, and have the advantages of excellent stability, anti-interference, recyclability and low limits of detection (LODs). The influence of the different metals in the CPs on the fluorescence sensing 3-NT was discussed, and the difference of sensing mechanism and performance of CPs 1 – 2 on 3-NT were studied in detail, which provided a reference for the design of CPs and the influencing factors of 3-NT detection. [ABSTRACT FROM AUTHOR]

The ability to detect nanoscale objects is particular crucial for a wide range of applications, such as environmental protection, early-stage disease diagnosis and drug discovery. Photonic crystal nanobeam cavity (PCNC) sensors have attracted great attention due to high-quality factors and small-mode volumes (Q/V) and good on-chip integrability with optical waveguides/circuits. In this review, we focus on nanoscale optical sensing based on PCNC sensors, including ultrahigh figure of merit (FOM) sensing, single nanoparticle trapping, label-free molecule detection and an integrated sensor array for multiplexed sensing. We believe that the PCNC sensors featuring ultracompact footprint, high monolithic integration capability, fast response and ultrahigh sensitivity sensing ability, etc., will provide a promising platform for further developing lab-on-a-chip devices for biosensing and other functionalities.

Graphene quantum dots (GQDs) have received tremendous attention as fluorescent probes for detection of diverse heavy metal ions (HMIs). Nevertheless, the fluorescence sensing mechanisms of versatile GQDs with respect to different HMIs remain elusive. Herein, the fluorescence sensing behaviors and mechanisms of GQDs with amino and carboxyl groups toward commonly encountered Cr 6+ , Fe 3+ , Cu 2+ , Cr 3+ , Mn 2+ , Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ , and Hg 2+ under different pH conditions are systemically explored. The results show that the fluorescence of GQDs can be enhanced by Zn 2+ /Cd 2+ and quenched by other HMIs at pH 5.8, while it can be enhanced by HMIs except Cr 6+ /Fe 3+ /Cu 2+ at pH 2.0. Systematic studies verify that the fluorescence quenching/enhancing is mediated by the synergistic effect of the inner filter effect (IFE) and the photoinduced electron transfer (PET) or metal orbital-controlled chelation-quenched/enhanced fluorescence (CHQF/CHEF) effect. The strong and weak IFEs of Cr 6+ /Fe 3+ and Cr 3+ /Cu 2+ , respectively, are one of the reasons for the fluorescence quenching, while other HMIs have no IFE. Moreover, the PET effect caused by the interaction of GQDs with Hg 2+ at pH 5.8 and the CHQF/CHEF effect caused by the interaction of GQDs with other HMIs are also crucial for fluorescence quenching/enhancing. The findings suggest that the pH condition, the existing forms of functional groups on GQDs, and the complexation states of HMIs in aqueous systems dominate the PET and CHQF/CHEF effects. The elucidating of the fluorescence sensing mechanisms of GQDs toward different HMIs paves the way for developing versatile sensing platforms for monitoring of HMI contamination.

Abstract: Toxic gas detection and capture are two important topics, which are highly related with human health and environments. Recently, theoretical simulations based on first‐principles calculations have suggested two‐dimensional (2D) materials to be as ideal candidates for gas sensing and capturing due to the large surface–volume ratio and reactive surface. Starting from graphene, which was firstly proposed for 2D gas sensing, the family currently has been extended to transition metal dichalcogenides, phosphorene, silicene, germanene, MXene, and so on. In this review, we give a comprehensive overview of recent progress in computational investigations of 2D gas sensing/capture materials. We then offer perspectives on possible directions for further fundamental exploration of gas sensor and caption based on 2D materials, which are expected to offer tremendous new opportunities for future research and development. This article is categorized under: Structure and Mechanism > Computational Materials Science [ABSTRACT FROM AUTHOR]

Density Functional Theory (DFT) studies were conducted to evaluate the sensing mechanism between benzene and a polymeric sensing material, referred to as SXFA, which contains trifluoro-groups and OH-groups. These studies were undertaken to improve the understanding of how benzene and SXFA mechanistically interact based on their chemistry, information which can be used to more efficiently design polymeric sensing materials. We find that benzene adsorbed onto the OH-groups in SXFA rather than the trifluoro-groups as previously proposed. Specifically, we find that sorption results from electrostatic attraction between the negative benzene ring and the positive hydrogens of the OH-groups of SXFA. [ABSTRACT FROM AUTHOR]

Pd doped SnO 2 nano-particles were synthesized using co-precipitation method. The resistances of the samples first decrease and then increase, which maybe influenced by the Pd doping and temperature effect. The CO response of SnO 2 was improved by doping with Pd. At low temperature range, the response decreases with increasing of operating temperature, which was caused by the physical adsorption. At higher operating temperature (160–400 °C), the response of Pd doped SnO 2 for CO increases at first, undergoes a maximum at 260 °C, and finally drops. The 1.5 wt.% PdO doping SnO 2 was verified to be significantly sensitive. The largest gas sensitive response of 6.59 was found at 260 °C in 400 ppm CO atmosphere. For 200 ppm CO, the response and recovery time were about 43 s and 10 s, respectively. The possible CO sensing mechanisms for Pd doped SnO 2 sensors were investigated with first principles calculations. The calculation results showed that CO molecule can grab O from the pre-adsorbed oxygen on Pd 4 cluster or the PdO cluster on the SnO 2 (110) surface forming CO 2 . These processes may play important role in CO sensing for Pd doped SnO 2 . The calculated result is a good explanation of the experimental observation. [ABSTRACT FROM AUTHOR]

As a compact and simple sensing technique, optical feedback interferometry (OFI) can be a promising flowmetry method in various microfluidic applications. In this paper, OFI-based flowmetry sensor performance in a microscale flow scheme is studied theoretically and experimentally. An innovating model and different numerical methods are investigated, where the scattering light angle distribution is involved to predict the Doppler frequency distribution. For the first time, our model describes the influences of multiple OFI sensor system characteristics, such as flowing particle size, concentration, channel interface reflectivity and channel dimension, on the OFI signal spectral performances. In particular, a significant OFI signal level enhancement was achieved by deposing a high reflectivity gold layer on the rear channel interface due to the increased forward scattered light reflection. The consistent experimental validation associated with the simulations verifies this numerical simulation method’s reliability. The numerical methods presented here provide a new tool to design novel microfluidic reactors and sensors.

The electrical response of sulfonated single-walled carbon nanotubes (SWCNTs) to NO and NO2, for gas sensing applications, at room temperature, is reported in this work. A specific configuration based on SWCNT deposition between double pair configuration gold electrodes, supported on a substrate, was considered for the sensing device; employed characterization technique where FTIR and SEM. The experimental results showed a p-type response of the sulfonated SWCNTs, with decrease in resistance, under exposure to NO gas (40–200 ppb) and NO2 (40–200 ppb). Also, the sensor responses to successive exposures at NO2 800 ppb together with investigation of long term stability, at 485 ppb for NO, are reported. The reaction mechanism in case of NO and NO2 detection with sulfonated SWCNTs is presented.

Gas analytes, or volatile organic compounds, interact with polymeric sensing materials through various sensing mechanisms. The dominant sensing mechanisms are discussed for different types of volatile organic compounds, which are categorized by their functional groups. Based on these sensing mechanisms, a systematic approach is used to design and tailor polymeric sensing materials for specific analytes and applications. This approach also takes into consideration other constraints determined by the target application. We include practical prescriptions on how to efficiently and cost-effectively design, tailor, and select potential polymeric sensing materials, as well as how to evaluate these sensing materials. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

As the main substrate participating in various physiological and pathological processes, the abnormal intracellular level of Cysteine (Cys) is closely associated with the occurrence and development of various diseases. Therefore, it is of great importance to establish a sensitive and efficient method for the precise exploration of Cys. Herein, we rationally designed and synthesized a water-soluble fluorescent nanoprobe Nano-PH1 for monitoring Cys in vitro and in vivo. The small molecular probe PH1 with 2,4-dinitrobenzene sulfonate (DNBS) as recognition moiety was constructed based on a phenothiazine derivative. To further improve the water solubility and selectivity of the probe , PH1 was assembled with an amphiphilic copolymer (mPEG-DSPE) to prepare a water-soluble fluorescent nanoprobe Nano-PH1. Fortunately, the nanoprobe preserves the excellent properties of small molecules and performs well in aqueous solution, as well as exhibiting a good selectivity only to Cys. Moreover, Nano-PH1 was successfully used to monitor Cys in living cancer cells and zebrafish larvae. We hope that this novel scaffold will provide a new reference for visualizing Cys in other biological systems. [Display omitted] • A water-soluble micellar nanoprobe was constructed for detecting Cys effectively. • Probe Nano-PH1 shows excellent selectivity only to Cys not to GSH and Hcy. • Cys in the living systems was successfully monitored with probe Nano-PH1. [ABSTRACT FROM AUTHOR]

Current research on gas sensors are focused toward developing cost-effective high-performance gas sensors at low operating temperature. Shortcomings of pristine semiconducting metal oxides (SMOs)-based high operating temperature sensors result in high power consumptions, high manufacturing cost, detonation risk for explosive gas detection and lack of long-term stability. These shortcomings could be diminished by designing suitable heterostructures to achieve superior sensing capabilities (high and faster response, high stability in environment) at room temperature. Herein, this review emphasizes on recent (last five years) advancement of SMOs-based heterostructures for room temperature gas sensors and various sensing mechanisms. The effects on different nano-junctions (p - n , n - n, p - p and Schottky), porosity, quantum dots and distinct facets have been explored for the modulation of charge depleted layers at interface, enhancing surface area, enabling more active sites etc. Diminution in sensor resistance and operating temperature can be realized by incorporating high conductive materials such as carbon nanotubes, graphene and activated carbon in SMOs. Several sensing mechanisms including heterojunction formation, Knudsen diffusion model, metal sulfuration, proton hopping, effusion effect and percolation effect have been elucidated for the correlation with high sensing performance gas sensors. Finally, a brief summary and future prospects have been addressed toward room temperature gas sensors. [Display omitted] • Designing suitable metal oxide based heterostructures for superior sensing capabilities at room temperature (RT). • Divergent ways of metal oxide heterojunctions (Schottky, p - n , p - p , n - n) formation to reduce sensor's operating temperature. • Enhanced RT sensing performances by blending carbon materials (CNT, graphene and activated carbon) in metal oxides. • Strategies to enhance surface area of metal oxides (morphology, facets, porosity) for RT gas sensing. • Numerous RT sensing mechanisms (metal sulfurtion, Knudsen effect, effusion, percolation etc.) are discussed. [ABSTRACT FROM AUTHOR]

Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions. [Display omitted] • Different chromogenic materials for the colorimetric detection of heavy metal ions. • Detailed sensing strategies and applications for each chromogenic material. • Current challenges and perspectives related to the colorimetry of heavy metal ions. [ABSTRACT FROM AUTHOR]

More attention is being paid to the environmental analysis because of the increasingly serious environmental pollution. Due to the superiority of low interference, excellent sensitivity, rapidness, and simple construction, chemiluminescence (CL) has evolved into a powerful technique for pollution analysis. Recently, nanomaterials such as MOFs, BPQDs, CDs, MoS 2 , LDHs, and noble metal NPs, have been exploited to further amplify the CL radiation, owing to their wide surface area, unique photoelectric properties, and excellent reactivity. Much encouraging progress in environmental analysis utilizing nanomaterial-based CL has been made. However, a comprehensive summary concentrated on the application of nanomaterial-based CL for environmental analysis is still lacking. In this review, the recent advances of nanomaterial-based CL in environmental pollutant analysis for typical harmful substances are summarized during the last 5 years, including inorganic ions, ROS, antibiotics, and pesticides, etc. Ultimately, the key challenges and further prospects in this exciting area are also highlighted to promote the advancement of environmental analysis. • Main types and sensing principles of nanomaterials used in chemiluminescence systems are summarized. • Applications of nanomaterial-based chemiluminescence in environmental pollutant analysis are reviewed. • Key challenges and further prospects of this nanomaterial-based chemiluminescence are proposed. [ABSTRACT FROM AUTHOR]

LaFeO 3 nanocrystalline powders prepared by sol–gel method with annealing at 800 °C for 4 h can sensitively detect low concentration of acetone. When exposed to 0.5 ppm acetone, the response of LaFeO 3 thick film at 260 °C is 2.068 with response time of 62 s and recovery time of 107 s, respectively. The possible acetone sensing mechanisms for LaFeO 3 sensor are investigated with first principles calculations. Calculated results demonstrate that acetone could release electrons to the surface of LaFeO 3 (010) pre-adsorbed with oxygen species O − and O 2 − . The acetone molecule reacts with oxygen species in the following ways: (1) adsorbs on oxygen species O − or (2) replaces of the weakly pre-adsorbed oxygen species O 2 − on Fe site, accompanying the formation of oxygen molecule. These above two processes may play important roles in acetone sensing for LaFeO 3 . We also find that the acetone molecule can be directly adsorbed on Fe site, transferring some electrons to the LaFeO 3 (010) surface. The latter processes may also provide additional contribution to acetone sensing. [ABSTRACT FROM AUTHOR]

An integrated SWCNT-Pt-P2O5-based sensor type was fabricated by direct deposition of the films on a commercial planar sensor substrate without any conventional coating and using the dropcast procedure. For the humidity sensing experimental work, two sensors were prepared by the authors using this facile solution and a system for data acquisition. The measurements showed that the integrated SWCNT sensors exhibit high and fast response (of approximately 25 s) toward a humidity range from 1% to 90% AH. The high sensitivity and dynamic reproducibility of these sensors materials reveal that the proposed composition and morphology can be applied to fabricate sensing devices for detecting water humidity in nitrogen gas from low to medium concentration range. The experimental results also confirm that the proposed solution fits in the class of proper structures for humidity sensing in inert gas and can show remarkable sensing and recovery capabilities for industrial usage. The sensing mechanism is attributed to the fact that electrical changes in sensors resistance, as a function of the AH, are related to the attraction and trapping of water molecules produced on the surface of the film. Due to this physical behavior, a resistive path is formed between the microelectrodes. The resistivity of the system increases as the AH increases, or decreases when the AH values decreases due to an electrolysis process taking place under sensors supply voltage and using Pt catalyst. [ABSTRACT FROM PUBLISHER]

The ubiquitous nature of anions has gained a bourgeoning interest among the supramolecular chemists to develop artificial receptors for the selective recognition and sensing of bioactive anions. Many excellent linear, dipodal, tripodal and multipodal anion receptors have been reported in the last two decades to recognize and detect anions of diverse geometry selectively. This review was narrated with the aim to summarize the C 3v -symmetric tripodal receptors reported for the chromogenic and fluorogenic sensing of anions using various flexible and rigid tripodal frameworks. Sensing mechanisms like ICT, PET, excimer-monomer formation, push-pull, rigidity effect etc., and the design concepts applied for the development of tripodal anion sensors have been discussed. [ABSTRACT FROM AUTHOR]

A systematic approach is used to design and tailor sensing materials for targeted analytes and specific applications. An example is used to demonstrate how potential sensing materials can be designed based on the chemical nature of both the target analyte and the sensing material, and thus predominant sensing mechanisms by which the two interact. The example analyte is a small, polar molecule able to hydrogen bond; therefore, a sensing material that targets the analyte should have polymer chains that pack tightly together, be polar, and be able to hydrogen bond. Any metal oxide dopants should be able to coordinate to both the target analyte and the polymer. Polyaniline and poly ( o-anisidine), along with nickel oxide and zinc oxide, are chosen as potential sensing materials and subsequently evaluated based on their ability to sorb the analyte in question. [ABSTRACT FROM AUTHOR]

Sensors based on thin film electroacoustic (TEA) devices have emerged as a promising alternative to quartz crystal microbalance and surface acoustic wave devices, in view of sensibility, miniaturization and easy integration. TEA devices include quasi-shear film bulk acoustic resonators (QS-FBAR) and S 0 mode Lamb wave resonators (S 0 -LWR) based on AlN films. Despite the work done on the application of TEA devices as in-liquid biological and chemical sensors, a theoretical framework for S 0 -LWRs properly describing their sensing mechanisms is still needed. Here we validate a finite element analysis model on QS-FBARs and study the sensing mechanisms of S 0 -LWRs in liquid media. We show that S 0 -LWRs can sense changes in the dielectric permittivity of the liquid and demonstrate different sensitivities to viscosity and density. A complementary assessment of the S 0 -LWRs losses, dependent in a non-specific manner on the square root of the density viscosity product, provides the ability to discriminate density from viscosity changes on the entire device surface. Finally, with an S 0 -LWR optimization study we show that resolution improves with the decrease of the membrane thickness; however, a trade-off between sensitivity, quality factor and membrane fragility has to be considered. [ABSTRACT FROM AUTHOR]

The utilization of clean hydrogen energy is becoming more feasible for the sustainable development of this society. Considering the safety issues in the hydrogen production, storage, and utilization, a sensitive hydrogen sensor for reliable detection is essential and highly important. Though various gas sensor devices are developed based on tin oxide, tungsten trioxide, or other oxides, the relatively high working temperature, unsatisfactory response time, and detection limitation still affect the extensive applications. In the current study, an amorphous tungsten trioxide (a-WO 3 ) layer is deposited on a phase-change vanadium dioxide film to fabricate a phase transition controlled Pd/a-WO 3 /VO 2 hydrogen sensor for hydrogen detection. Results show that both the response time and sensitivity of the hydrogen sensor are improved greatly if increasing the working temperature over the transition temperature of VO 2 . Theoretical calculations also reveal that the charge transfer at VO 2 /a-WO 3 interface becomes more pronounced once the VO 2 layer transforms to the metal state, which will affect the migration barrier of H atoms in a-WO 3 layer and thus improve the sensor performance. The current study not only realizes a hydrogen sensor with ultrahigh performance based on VO 2 layer, but also provides some clues for designing other gas sensors with phase-change material., (© 2022 Wiley-VCH GmbH.)

Rapid industrialization has inevitably led to serious air pollution problems, thus it is urgent to develop detection and treatment technologies for qualitative and quantitative analysis and efficient removal of harmful pollutants. Notably, the employment of functional nanomaterials, in sensing and photocatalytic technologies, is promising to achieve efficient in situ detection and removal of gaseous pollutants. Among them, carbon dots (CDs) have shown significant potential due to their superior properties, such as controllable structures, easy surface modification, adjustable energy band, and excellent electron-transfer capacities. Moreover, their environmentally friendly preparation and efficient capture of solar energy provide a green option for sustainably addressing environmental problems. Here, recent advances in the rational design of CDs-based sensors and photocatalysts are highlighted. An overview of their applications in air pollutants detection and photocatalytic removal is presented, especially the diverse sensing and photocatalytic mechanisms of CDs are discussed. Finally, the challenges and perspectives are also provided, emphasizing the importance of synthetic mechanism investigation and rational design of structures., (© 2022 Wiley-VCH GmbH.)

Abstract: The gas sensor investigated is constituted by gold/vanadium–tin oxide (Au/V–SnO2) nanocomposite powders, prepared by a co-precipitation method, and evaluated for carbon monoxide detection at low temperature. The Au-loaded sensor exhibited a higher response and shorter response and recovery time than the V–Sn oxide sensor and had good stability. The responses obtained in both air and nitrogen atmospheres increased with increasing sensor temperatures or CO concentrations. X-ray photoelectron spectroscopy (XPS) revealed the presence of gold in the metallic state and vanadium cations with multiple valences on the oxide surface. The gold addition induced an interaction between gold and vanadium and enhanced oxygen adsorption on the sensor surface under electrical field, as indicated by electron paramagnetic resonance (EPR) and electrical analyses. Results demonstrate the viability of the Au/V–SnO2 sensor to detect CO gas in ambient and oxygen-deficient environments. It is postulated that gold and adjacent vanadium or oxygen vacancy sites facilitate oxygen activation for CO oxidation in air or CO chemisorption under nitrogen. Sensing mechanisms that discuss the roles of these active sites and oxygen in the CO detection are proposed. [Copyright &y& Elsevier]

Abstract: The semiconductor gas sensors investigated are constituted by vanadium-tin oxide nanoparticles, prepared by a co-precipitation method. They were evaluated for carbon monoxide detection at low temperatures. The sensing characteristics obtained are associated with the composition, structure and surface state of oxide semiconductor. XPS analysis revealed an electronic interaction between Sn and V atoms in the mixed oxide structure and the formation of vanadium cations with multiple valences. Combined XRD and FTIR analyses showed that the tin oxide crystallinity decreased with increasing vanadium loadings. Lower levels of vanadium dopants in tin oxide enhanced response to CO gas in air because they facilitated oxygen adsorption by scavenging electrons to form reactive oxygen ions on the surface, as indicated by electrical and EPR measurements. The response to CO gas in nitrogen atmosphere was observed, and increased with increasing CO concentrations. Sensing mechanisms that discuss the roles of the vanadium redox pairs and oxygen vacancies in the CO detection process are proposed. [Copyright &y& Elsevier]

In recent years, considerable research efforts have been devoted to the development of wearable multi-functional sensing technology to fulfill the requirements of healthcare smart detection, and much progress has been achieved. Due to the appealing characteristics of flexibility, stretchability and long-term stability, the sensors have been used in a wide range of applications, such as respiration monitoring, pulse wave detection, gait pattern analysis, etc. Wearable sensors based on single mechanisms are usually capable of sensing only one physiological or motion signal. In order to measure, record and analyze comprehensive physical conditions, it is indispensable to explore the wearable sensors based on hybrid mechanisms and realize the integration of multiple smart functions. Herein, we have summarized various working mechanisms (resistive, capacitive, triboelectric, piezoelectric, thermo-electric, pyroelectric) and hybrid mechanisms that are incorporated into wearable sensors. More importantly, to make wearable sensors work persistently, it is meaningful to combine flexible power units and wearable sensors and form a self-powered system. This article also emphasizes the utility of self-powered wearable sensors from the perspective of mechanisms, and gives applications. Furthermore, we discuss the emerging materials and structures that are applied to achieve high sensitivity. In the end, we present perspectives on the outlooks of wearable multi-functional sensing technology. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is a wide bandgap semiconductor material that has been widely explored for countless applications, including in biosensing. Among its interesting properties, its remarkable photoluminescence (PL), which typically exhibits an intense signal at room temperature (RT), arises as an extremely appealing alternative transduction approach due to the high sensitivity of its surface properties, providing high sensitivity and selectivity to the sensors relying on luminescence output. Therefore, even though not widely explored, in recent years some studies have been devoted to the use of the PL features of ZnO as an optical transducer for detection and quantification of specific analytes. Hence, in the present paper, we revised the works that have been published in the last few years concerning the use of ZnO nanostructures as the transducer element in different types of PL-based biosensors, namely enzymatic and immunosensors, towards the detection of analytes relevant for health and environment, like antibiotics, glucose, bacteria, virus or even tumor biomarkers. A comprehensive discussion on the possible physical mechanisms that rule the optical sensing response is also provided, as well as a warning regarding the effect that the buffer solution may play on the sensing experiments, as it was seen that the use of phosphate-containing solutions significantly affects the stability of the ZnO nanostructures, which may conduct to misleading interpretations of the sensing results and unreliable conclusions. [ABSTRACT FROM AUTHOR]

Abstract: The sorption of water vapour and gaseous ammonia into polyacrylic acid (PAA) induces a mass uptake and changes the electrochemical properties of the material. In order to review and confirm phenomenological models describing these processes, systematic infrared (IR) studies have been performed. The IR spectra are taken in the 400–4000cm−1 wavenumber range and the IR spectrum of the polymer in dry air is taken as the reference for calculation of the absorbance spectra. The interpretation of increasing and decreasing bands in the IR spectra draws a consistent picture of the processes in the polymer, so that the models can be confirmed and, additionally, more detailed information is gained. [Copyright &y& Elsevier]

Abstract: The origin of work-function changes induced in polymer/metal structures (polyacrylic acid (PAA), ammonium and sodium polyacrylate) upon ammonia exposure is studied. To understand and explain the mechanism systematic measurements of uncoated and polymer coated metals are performed in Kelvin Probe (KP) setups. Additional data have been acquired through gravimetric and electrochemical experiments (cyclic voltammetry (CV)). The results obtained confirm that the field effect sensitive processes are taking place at the metal/polymer interface and allow their modelling. The intrinsic sensitivity of metallic samples upon ammonia exposure is influenced by the presence of coating polymers, by their ability to sorb water and to keep the metal surface wet or dry. [Copyright &y& Elsevier]

Abstract: Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses are described to study the CO2 sensing mechanisms in LaOCl wet chemically synthesized nanopowders. In order to establish a connection between resistance values and DRIFTS spectra, the two measurements were made simultaneously. A PLS data treatment was then applied to identify which of the absorbed specimens contribute essentially to resistance changes. Furthermore, the obtained results are discussed in light of the overall available information. From this discussion, a sensing mechanism is suggested in agreement with sensor performance and characteristics. [Copyright &y& Elsevier]

The paper investigates the gas response of nanocrystalline SnO2 based thick film sensors upon exposure to carbon monoxide (CO) in changing water vapour (H2O) and oxygen (O2) backgrounds. The sensing materials were undoped, Pt- and Pd-doped SnO2. We found that in the absence of oxygen, the sensor signal (defined as the ratio between the resistance in the background gas, R0 and the resistance in the presence of the target gases, R, namely R0/R) have the highest values. These values are higher for doped materials than for the undoped ones. The presence of humidity increases dramatically the sensor signal of the doped materials. In the presence of oxygen, the sensor signal decreases significantly for all sensor materials. The results indicate that there is a competitive adsorption between O2 and H2O related surface species and, as a result, different sensing mechanisms can be observed for CO. [Copyright &y& Elsevier]

[Display omitted] • This review covers fluorometric and colorimetric probes for water and humidity, reported in the last 10 years. • Probes are divided on the basis of types of scaffold/signaling unit used. • Sensing mechanisms have been discussed. • Applications of these sensors have been highlighted wherever possible. Detection of trace quantities of water in laboratory and industrial processes is very crucial. Monitoring humidity is of vital importance in maintaining ambient atmosphere in places like hospitals, in climate sciences, automated devices, intelligent systems, etc. Development of optical detection systems for water and humidity entails real time progress in industrial processing and storage, human–machine interactions, clinical diagnosis and security solutions and many more. This review provides a comprehensive study of developments made in the field of optical sensing of water and humidity in the last decade. The compilation has been segmented into various sub-sections based on various molecular scaffolds. It covers a library of structural motifs containing anthracene, rhodamine, coumarin, bodipy, pyrene, naphthalene, naphthalimide, anthraquinone, tetraphenylethene, triphenylamine, thioxanthone, triarylmethane, etc. These have followed versatile mechanistic pathways like intramolecular charge transfer, photo-induced electron transfer, aggregation induced emission, solvatochromism, forster resonance energy transfer, hydrogen bonding interactions, reaction- based formation or cleavage of bonds, etc. to respond to presence of water in organic solvents or atmosphere by colorimetry or fluorimetry. All the reported probes have been dealt in a case by case manner with respect to their working mechanisms, advantages, limitations and applications. The detection limit and quantification limit values have been assembled to compare the efficacies of different probes. Real life applications of the sensors have been demonstrated, which shows that the scope of employing chemosensors in solving various real-time problems is huge and bright. It outlays concretely the opportunities and scope for future works. [ABSTRACT FROM AUTHOR]

Laser-induced graphene (LIG) is produced rapidly by directly irradiating carbonaceous precursors, and it naturally exhibits as a three-dimensional porous structure. Due to advantages such as simple preparation, time-saving, environmental friendliness, low cost, and expanding categories of raw materials, LIG and its derivatives have achieved broad applications in sensors. This has been witnessed in various fields such as wearable devices, disease diagnosis, intelligent robots, and pollution detection. However, despite LIG sensors having demonstrated an excellent capability to monitor physical and chemical parameters, the systematic review of synthesis, sensing mechanisms, and applications of them combined with comparison against other preparation approaches of graphene is still lacking. Here, graphene-based sensors for physical, biological, and chemical detection are reviewed first, followed by the introduction of general preparation methods for the laser-induced method to yield graphene. The preparation and advantages of LIG, sensing mechanisms, and the properties of different types of emerging LIG-based sensors are comprehensively reviewed. Finally, possible solutions to the problems and challenges of preparing LIG and LIG-based sensors are proposed. This review may serve as a detailed reference to guide the development of LIG-based sensors that possess properties for future smart sensors in health care, environmental protection, and industrial production.

Alkaline phosphatase (ALP), an important enzyme in living organisms, plays significant roles in the hydrolysis of phosphate groups from nucleic acids, proteins, and other substrates. Abnormal level of ALP in serum is related to a variety of diseases. Low expression of ALP can cause blood diseases, such as anemia and leukemia, while over-expression of ALP can lead to disorders in liver, prostate, endocrine system, and bone tissues. Therefore, to monitor the ALP level in physiological and pathological events, it is in urgent need to develop a rapid, accurate, sensitive, and non-invasive approach, which can also be of great significance for the improvement of corresponding clinical agents. With the development of fluorescent probes, many advantages of fluorescent probes for ALP detection, such as simple operation, non-invasive, real-time imaging, economy, fast response, and so on, have been gradually highlighted. In this review, we enumerated almost all the ALP fluorescent probes from 2009 to now and summarized their respective characteristics, in order to provide a unified platform for their standardized evaluation. Meanwhile, we tried to systematically review the research progress of ALP fluorescent probes, including both small-molecule and nanoscale ones. Logically, we focused on the structures, reaction mechanisms, and biological applications of ALP fluorescent probes. In addition, the prospects of ALP in the near future have also been foreseen. We hope that this review will be helpful for the investigators who are interested in ALP-associated biological procedures, and even in the regulation of more extensive enzyme levels. • Alkaline phosphatase (ALP) fluorescent probes possess respective characteristics. • Different combinations between fluorophores and detection mechanisms of small-molecule fluorescent probes. • ALP nano probes included noble metal nanoparticles, metal-organic frameworks, AIEgens, quantum dots, terbium chelates, etc. • ALP level was crucial for diagnosis of diseases in clinical medicine. • ALP can hydrolysis 5′-phosphate residues from nucleic acid molecules in biology. [ABSTRACT FROM AUTHOR]

The active sulfur small molecules such as biothiols, hydrogen sulfide, hydrogen polysulfides and sulfur dioxide are closely related to various diseases in the biological system and have important physiological and pathological functions. Small-molecule fluorescent probes enable to detect and image active sulfur small molecules by virtue of their non-invasiveness, fast response times, and real-time in situ detection capability. Based on the inherent characteristics of active sulfur small molecules, many fluorescent probes have been reported to detect and image them. In this review, we classify the fluorescent probes according to the different type reaction of each small molecule, and summarize the reaction mechanism in detail. Moreover, we also emphasize the challenges of active sulfur small molecules-responsive fluorescent probes, hoping to provide a general implication for future research. • Summarised the latest developments in fluorescent probes for detecting small active sulfur molecules. • Classification was based on different reaction mechanism, and discussed the sensing mechanism of probes in detail. • Summarised a list of the involved probes, and compared the related sensing performance of the reported probes. • 147 references were contained and 104 probes were discussed. [ABSTRACT FROM AUTHOR]

Recently, more and more attention has been focused on the construction and analytical applications of optical nanoassembly through combining carbon dots (CDs) with various other functional nanomaterials. The rational design and manufacture of CDs-based optical nanoassembly will be critical to meeting the needs of analytical science. The last decade has witnessed the immense potential of CDs-based optical nanoassembly in multiple sensing applications owing to their controlled optical properties, adjustable surface chemistry and microscopic morphology. This feature article collects the recent advances in the research and development of CDs-based optical nanoassembly and their applications in analytical sensors, aiming to provide vital insights and suggestions to inspire their broad sensing applications. Image 1 • Optical nanoassembly combining CDs with various other functional nanomaterials displays outstanding sensing performance. • The construction and analytical applications of CDs-based optical nanoassembly have been summarized. • The advances, limitations and future aspects of CDs-based optical nanoassembly are discussed. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) sensing is a newly emerged and fast-developing analytical method using photoactive materials that are excited by external light to produce photocurrent readout signal. In recent years, two-dimensional (2D) layered materials have attracted increasing interest in PEC sensing due to their unique structure and fascinating photoelectric properties. Herein, an overview of the rapidly emerging 2D materials and their PEC sensing applications are summarized, including graphene, graphitic carbon nitride, transition metal dichalcogenides, Mxene, oxides, etc. Particularly, the different roles played by these 2D materials in a PEC sensor, the various strategies for improving photoelectric activity, and the preparation methods of 2D materials are discussed. Furthermore, some sensing mechanisms and signal amplification techniques frequently used in the PEC sensing area are also introduced in the review. Finally, the existing challenges and some future perspectives of this field are proposed. • Recent advances in 2D layered materials for photoelectrochemical sensing. • Various strategies for improving photoelectric activity of 2D materials. • The widely used preparation methods of 2D materials. • Some challenges and opportunities of 2D materials in terms of PEC sensing. [ABSTRACT FROM AUTHOR]

• The fluorescent probes, chemiluminescent probes and bioluminescent probes for sensing NTRs were reviewed. • The design strategies of those modes were discussed based on different probes. • The advantages and drawbacks of those detection modes were discussed. • A prospect for the detection of NTRs activity was proposed. As one of the most representative hypoxic enzymes, nitroreductases (NTRs) play momentous roles in malignant tumor progression, metastasis, invasion and angiogenesis. They are also a key hallmark of highly aggressive disease in various hypoxic tumor cells. In addition, NTRs participate in essential processes of detoxification, pro-drug activation as well as radiation therapy. Thus, the detection of NTRs has great importance for theranostic and drug development. In this review, we focused on the design principles, sensing mechanisms and biological applications of small-molecule probes for NTRs detection over the past ten years (2010–2020). We also highlighted the challenges and future directions in this rapidly developing field. Significantly, we hope that some insights and inspiration for future research work will be provided to surmount the Achilles' Heels of the small-molecule probes, such as limited application, for detecting NTRs. [ABSTRACT FROM AUTHOR]