AuPt Bimetal-Functionalized SnSe2 Microflower-Based Sensors for Detecting Sub-ppm NO2 at Low Temperatures

Fabrication of TeNT/TeO2 heterojunction based sensor for ultrasensitive detection of NO2

Tellurium nanotubes (TeNT) heterojunction with Tellurium oxide (TeO2) were prepared by in situ oxidation at elevated temperatures in air. The chemiresistive type NO2 sensor was then fabricated by depositing the synthesized TeNT/TeO2 on the integrated gold electrodes. The response of the TeNT/TeO2 based sensor to 600 ppb NO2 was 38.8 %, which was about 3.2 times higher than that of the single-phase TeNT based sensor (12.1 %). The response and recovery time are 39 s and 49 s, respectively, which are substantially reduced compared to those of the pristine TeNT based sensor (133 s and 336 s) and the results reported in literature. The sensor also exhibits good stability with a response deviation of less than 2 % for 45 days and a good resistance to environmental disturbances. The improved sensor performance can be attributed to the heterojunction formed between TeNT and TeO2. Density Functional Theory (DFT) calculations show that the formed TeNT/TeO2 heterojunction enhances the adsorption energy (-0.671 eV) and charge transfer (0.49 |e|) between NO2 and the TeNT/TeO2.

Phase Engineering of SnSeX (X = 1,2) Microstructures for High-Performance NO2 Chemiresistive Room-Temperature Sensor Systems: Toward Highly Reliable and Robust Detection Properties under Humidity and Interfering Gas Conditions

Two-dimensional SnSeX (X = 1, 2) has emerged as a promising candidate for a NO2 chemiresistive sensor due to a remarkable affinity to NO2 gas adsorption. Although their gas sensing mechanism primarily relies on direct charge transfer, the underlying mechanisms of SnSe and SnSe2 remain unclear, despite various reported successes in phase engineering of SnSeX. Here, we investigate phase engineering of SnSeX in a hydrothermal route via 1-dodecanethiol (1-DDT), which served as a phase stabilizer, and comprehensively demonstrate phase-dependent NO2 detection properties. As the 1-DDT concentration increases, we directly confirm that the SnSe structure was gradually transformed to the SnSe2 one. This transformation correlates with a gradual increase in NO2 gas responses from 45 to 1430%, the highest value reported among SnSeX-based NO2 gas sensors. The obtained SnSe2-based sensors also exhibit a good NO2 discrimination without configuration of sensor arrays, under an interfering gas atmosphere in humidity conditions. Our computational calculation also unveils that these outstanding detection performances are attributed to well-constructed SnSe2 coupled with a single Se vacancy to enhance a stronger NO2 adsorption than SnSe. Finally, we demonstrate a sensor module system based on SnSe2, enabling real-time monitoring of NO2 gas.

Recent Advances in Engineering of 2D Layered Metal Chalcogenides for Resistive-Type Gas Sensor

2D nanomaterials have triggered widespread attention in sensing applications. Especially for 2D layered metal chalcogenides (LMCs), the unique semiconducting properties and high surface area endow them with great potential for gas sensors. The assembly of 2D LMCs with guest species is an effective functionalization method to produce the synergistic effects of hybridization for greatly enhancing the gas-sensing properties. This review starts with the synthetic techniques, sensing properties, and principles, and then comprehensively compiles the advanced achievements of the pristine 2D LMCs gas sensors. Key advances in the development of the functionalization of 2D LMCs for enhancing gas-sensing properties are categorized according to the spatial architectures. It is systematically discussed in three aspects: surface, lattice, and interlayer, to comprehend the benefits of the functionalized 2D LMCs from surface chemical effect, electronic properties, and structure features. The challenges and outlooks for developing high-performance 2D LMCs-based gas sensors are also proposed.

SnTe/SnSe Heterojunction Based Ammonia Sensors with Excellent Withstand to Ambient Humidities

Non-invasive breath testing has gained increasing importance for early disease screening, spurring research into cheap sensors for detecting trace biomarkers such as ammonia. However, real-life deployment of ammonia sensors remains hindered by susceptibility to humidity-induced interference. The SnTe/SnSe heterojunction-based chemiresistive-type sensor demonstrates an excellent response/recovery to different concentrations of ammonia from 0.1 to 100 ppm at room temperature. The improved sensing properties of the heterojunctions-based sensors compared to single-phased SnTe or SnSe can be attributed to the stronger NH3 adsorptions, more Te vacancies, and hydrophobic surface induced by the formed SnTe/SnSe heterojunctions. The sensing mechanisms are investigated in detail by using in situ techniques such as diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), Kelvin probe, and a.c. impedance spectroscopy together with the Density-Function-Theory calculations. The formed heterojunctions boost the overall charge transfer efficiency between the ammonia and the sensing materials, thus leading to the desirable sensing features as well, with excellent resistance to ambient humidities.

Pd@Pt Core-Shell Nanocrystal-Decorated ZnO Nanosheets for ppt-Level NO2 Detection

Bimetallic nanocrystals (NCs) have obtained significant attention due to their unique advantages of the intrinsic properties of individual metals and synergistic enhancements resulting from the electronic coupling between two constituent metals. In this work, Pd@Pt core-shell NCs were prepared through a facile one-pot solution-phase method, which had excellent dispersion and uniform size. Concurrently, ZnO nanosheets were prepared via a hydrothermal method. To explore their potential in nitrogen dioxide (NO2) gas sensing applications, sensitive materials based on ZnO nanosheets with varying mass percentages of Pd@Pt NCs were generated through an impregnation process. The sensor based on 0.3 wt % Pd@Pt-ZnO exhibited remarkable performance, demonstrating a substantial response (Rg/Ra = 60.3) to 50 ppb of NO2 at a low operating temperature of 80 °C. Notably, this sensor reached an outstanding low detection limit of 300 ppt. The enhancement in gas sensing capabilities can be attributed to the sensitization and synergistic effects imparted by the exceptional catalytic activity of Pd@Pt NCs, which significantly promoted the reaction. This research introduces a novel approach for the utilization of core-shell structured bimetallic nanocrystals as modifiers in metal-oxide-semiconductor (MOS) materials for NO2 detection.

Oxygen Vacancy-Rich Bimetallic Au@Pt Core-Shell Nanosphere-Functionalized Electrospun ZnFe2O4 Nanofibers for Chemiresistive Breath Acetone Detection

Sensitive and selective acetone detection is of great significance in the fields of environmental protection, industrial production, and individual health monitoring from exhaled breath. To achieve this goal, bimetallic Au@Pt core-shell nanospheres (BNSs) functionalized-electrospun ZnFe2O4 nanofibers (ZFO NFs) are prepared in this work. Compared to pure NFs-650 analogue, the ZFO NFs/BNSs-2 sensor exhibits a stronger mean response (3.32 vs 1.84), quicker response/recovery speeds (33 s/28 s vs 54 s/42 s), and lower operating temperature (188 vs 273 °C) toward 0.5 ppm acetone. Note that an experimental detection limit of 30 ppb is achieved, which ranks among the best cases reported thus far. Besides the demonstrated excellent repeatability, humidity-enhanced response, and long-term stability, the selectivity toward acetone is remarkably improved after BNSs functionalization. Through material characterizations and DFT calculations, all these improvements could be attributed to the boosted oxygen vacancies and abundant Schottky junctions between ZFO NFs and BNSs, and the synergistic catalytic effect of BNSs. This work offers an alternative strategy to realize selective subppm acetone under high-humidity conditions catering for the future requirements of noninvasive breath diabetes diagnosis in the field of individual healthcare.

Enhanced Acetone Sensing Properties Based on Au-Pd Decorated ZnO Nanorod Gas Sensor

The mature processes of metal oxide semiconductors (MOS) have attracted considerable interest. However, the low sensitivity of metal oxide semiconductor gas sensors is still challenging, and constrains its practical applications. Bimetallic nanoparticles are of interest owing to their excellent catalytic properties. This excellent feature of bimetallic nanoparticles can solve the problems existing in MOS gas sensors, such as the low response, high operating temperature and slow response time. To enhance acetone sensing performance, we successfully synthesized Au-Pd/ZnO nanorods. In this work, we discovered that Au-Pd nanoparticles modified on ZnO nanorods can remarkably enhance sensor response. The Au-Pd/ZnO gas sensor has long-term stability and an excellent response/recovery process. This excellent sensing performance is attributed to the synergistic catalytic effect of bimetallic AuPd nanoparticles. Moreover, the electronic and chemical sensitization of noble metals also makes a great contribution. This work presents a simple method for preparing Au-Pd/ZnO nanorods and provides a new solution for the detection of acetone based on metal oxide semiconductor.

Dual source-powered multifunctional Pt/FePc@Mn-MOF spindle-like Janus nanomotors for active CT imaging-guided synergistic photothermal/chemodynamic therapy

Nanomaterials capable of dual therapeutic effects of chemodynamic therapy (CDT) and photothermal therapy (PTT) is an efficacious strategy in cancer treatment. It is still a challenge to achieve complete apoptosis of tumor tissue in CDT/PTT due to the poor permeability of nanomaterials in tumor tissue. Herein, we prepared a dual-source driven Pt/FePc@Mn-MOF spindle-like Janus nanomotor by a facile oriented connection growth method for computed tomography (CT) imaging-guided CDT and PTT. The high catalase (CAT)-like activity of nanomotors allows the generation of oxygen (O2) bubbles by catalyzing the decomposition of endogenous H2O2, which alleviates the hypoxic state of the tumor microenvironment (TME) and simultaneously drive nanomotors. Pt/FePc@Mn-MOF nanomotor with excellent photothermal conversion efficiency exhibited dual peroxidase (POD)-like and oxidase (OXD)-like activities, which can produce large amounts of ROS to obtain PTT enhanced CDT. Meanwhile, near-infrared light, as "optical brakes", can trigger Janus nanomotor to realize self-thermophoretic movement. Chemical/NIR-assisted autonomous propulsion can significantly improve the accumulation of Janus nanomotors in solid tumors and enhance their ability to penetrate tumor tissue, thus brings synergistic enhancement effect to PTT and CDT. Moreover, Mn-MOF in nanomotor can deplete the antioxidant GSH by redox reaction to release massive Mn2+, which introduce Mn2+-based CT imaging properties. This novel dual-source controlled Janus nanomotor offers great potential for multimodal therapeutic medical applications.

Electronic Modulation of MoS2 Nanosheets by N-Doping for Highly Sensitive NO2 Detection at Room Temperature

Transition metal dichalcogenide (TMD) materials hold great promise for gas sensors working at room temperature (RT). But the low response and slow dynamics derived from pristine TMDs remain a challenge toward their real applications. In this work, we report an efficient N-doping strategy to modulate the electronic structure of MoS2 nanosheets (N-MoS2) to achieve improved detection toward NO2. The effect of N-doping on the sensor properties, which has been rarely investigated, is elucidated by both experimental and computational studies. Due to N-doping, the Fermi level of N-MoS2 decreased from -5.29 to -5.33 eV and the band gap was reduced from 1.79 to 1.65 eV. The smaller band gap indicated the reduced resistance of N-MoS2 compared to that of original MoS2. As a result, the response of the MoS2 sensor to 10 ppm of NO2 was improved from 1.23 to 2.31 at RT. The sensor also has a limit of detection (LOD) of 62.5 ppb. To explain the effect of N-doping, density functional theory (DFT) calculations were conducted to figure out the important roles played by N-doping. This work demonstrates a pathway to modulate the chemical and electronic structures of TMD materials for advanced sensors.

One-pot synthesis of AuPt@FexOy nanoparticles with excellent peroxidase-like activity for development of ultrasensitive colorimetric lateral flow immunoassay of cardiac troponin I

Detection of cardiac troponin I (cTnI) plays a critical role in diagnosing acute myocardial infarction (AMI). In this report, a new kind of spherical AuPt@FexOy core@shell nanoparticles (termed as AuPt@FexOy NPs) were one-pot synthesized by a redox interaction-engaged strategy (RIES) without the addition of any surfactants or reducing agents. The as-synthesized AuPt@FexOy NPs not only retain the plasmonic activity of gold nanoparticles (AuNPs), but also possess excellent catalytic activities of platinum nanoparticles (PtNPs) and FexOy nanoclusters. The features of AuPt@FexOy NPs enable greatly enhance the colorimetric detection sensitivity of lateral flow immunoassay (LFIA) through integrating AuPt@FexOy NPs labeling procedure and catalyzing oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) signal amplification strategy. The as-developed colorimetric LFIA (termed as AuPt@FexOy-LFIA) exhibits the limit of detection (LOD) as 26.0 pg mL-1 cTnI under the TMB signal amplification mode. In particular, the detection results of cTnI in 40 clinical seral samples by AuPt@FexOy-LFIA are correlated well with those of cTnI in the same samples by commercial enzyme-linked immunosorbent assay (ELISA) detection kit (R2 = 0.97, slope = 1), demonstrating the highly reliable analytical performance and good application prospect of AuPt@FexOy-LFIA.

Pt-functionalized Amorphous RuOx as Excellent Stability and High-activity Catalysts for Low Temperature MEMS Sensors

The unsaturated coordination and abundant active sites endow amorphous metals with tremendous potential in improving metal oxide semiconductors' gas-sensing properties. However, the amorphous materials maintain the metastable status and easily transfer into the lower-active crystals during the gas-sensing process at high working temperatures, significantly limiting their further applications. Here, a bimetal amorphous PtRu catalyst is developed by accurately regulating the introduction of Pt species into amorphous RuOx supports to realize the highly active and stable H2 S gas-sensing detection. It is found that incorporation of low-concentration Pt species can effectively maintain the amorphous state of initial RuOx and delay the crystallization temperature as high as 100 °C. Further, ex situ XPS and in situ Raman spectroscopy analysis confirm that active Pt species can facilitate H2 S adsorption by strong Pt-S coordination and dissociate the sulfur species to the surrounding support, which contribute to the chemisorption and sensitization of H2 S. Meanwhile, electron transport at the interface between Pt, RuOx and ZnO further activates the reaction process at the surface of the gas-sensitive material. The final PtRu-modified ZnO (PtRu/ZnO) sensor enables the detection of H2 S in the ultra-low concentration range of 15-2000 ppb with remarkable stability.

Activating ultralow upconversion nanothermometry in neodymium sublattice for heart tissue imaging rapid-responsive

The fields of biosensitivity and biological imaging have received a lot of attention from rare earth-doped upconversion nanoparticles (UCNPs). However, owing to the relatively large energy difference of rare earth ions, biological sensitivity based on UCNPs is restricted to detect at low temperature. Here, we design core-shell-shell NaErF₄:Yb@Nd₂O₃@SiO₂ UCNPs as a dual-mode bioprobe that produces blue, green, and red multi-color upconversion emissions at extremely low temperatures between 100 K and 280 K. Based on the thermally coupled energy levels (TCELs) of Er³⁺ (²H_11/2 and ⁴S_3/2) and Nd³⁺ (⁴F_5/2 and ⁴F_3/2) at 100 K, the greatest relative sensitivity (S_R) approaches 12.7% K^-1. NaErF₄:Yb@Nd₂O₃@SiO₂ injection is used to achieve blue upconversion emission imaging of frozen heart tissue, showing that this UCNP can serve as a low-temperature sensitive biological fluorescence.

Advances in Noble Metal-Decorated Metal Oxide Nanomaterials for Chemiresistive Gas Sensors: Overview

Highly sensitive gas sensors with remarkably low detection limits are attractive for diverse practical application fields including real-time environmental monitoring, exhaled breath diagnosis, and food freshness analysis. Among various chemiresistive sensing materials, noble metal-decorated semiconducting metal oxides (SMOs) have currently aroused extensive attention by virtue of the unique electronic and catalytic properties of noble metals. This review highlights the research progress on the designs and applications of different noble metal-decorated SMOs with diverse nanostructures (e.g., nanoparticles, nanowires, nanorods, nanosheets, nanoflowers, and microspheres) for high-performance gas sensors with higher response, faster response/recovery speed, lower operating temperature, and ultra-low detection limits. The key topics include Pt, Pd, Au, other noble metals (e.g., Ag, Ru, and Rh.), and bimetals-decorated SMOs containing ZnO, SnO2, WO3, other SMOs (e.g., In2O3, Fe2O3, and CuO), and heterostructured SMOs. In addition to conventional devices, the innovative applications like photo-assisted room temperature gas sensors and mechanically flexible smart wearable devices are also discussed. Moreover, the relevant mechanisms for the sensing performance improvement caused by noble metal decoration, including the electronic sensitization effect and the chemical sensitization effect, have also been summarized in detail. Finally, major challenges and future perspectives towards noble metal-decorated SMOs-based chemiresistive gas sensors are proposed.

Adsorption properties of small gas molecules on SnSe2 monolayer supported with transition metal: first-principles calculations

The adsorption properties of CH₄, H₂S, SO₂, CO, H₂O and NO molecules on transition metal-supported SnSe₂ surface are investigated by the first-principles method. The calculation results show that the transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) has the lowest adsorption energy when supporting at the Sn site of SnSe₂, indicating the system is relatively stable. Also, we find that CH₄, SO₂ and H₂O molecules tend to adsorb on Sc-supported SnSe₂ surface, H₂S and NO molecules prefer to adsorb on V-supported SnSe₂ surface, while CO molecule and Fe-supported SnSe₂ surfaces have strong interaction. And, CH₄, H₂S and H₂O molecules act as donors to provide electrons to the substrate, while SO₂, CO and NO molecules act as acceptors to gain electrons from the substrate. An analysis of charge difference density and density of states reveals that the adsorption energies of gas molecules are related to charge transfer and orbital hybridization. We hope that this work not only provides a promising sensor material, but also provides a new idea for the rational design of two-dimensional materials.

Revealing the alloying and dealloying behaviours in AuAg nanorods by thermal stimulus

Binary metallic nanocrystals are attractive as they offer an extra degree of freedom for structure and phase modulation to generate synergistic effects and extraordinary properties. However, whether the binary structures and phases at the nanoscale still follow the rules established on the bulk counterparts remains unclear. In this work, AuAg nanorods were used as a sample to probe into this issue. An in situ heating method by combining aberration-corrected transmission electron microscopes with a chip-based heating holder was employed to perform the heating experiments. It was found that the AuAg nanorods, which initially possessed heterostructures, can be designed and engineered to be gradient phase alloys with thermal pulses over 350 °C. Atomic diffusion inside the rod structures did not alter the shape of the rods but provided a route to fine-tune their properties. At higher temperatures, the discrepant sublimation behaviours between Au and Ag lead to dealloying of the nanorods. Durative sublimation of the Ag element can continuously tailor the lengths of the nanorods while concentrating the Au composition simultaneously. Especially, nearly pure Au nanocrystals can be obtained with the depletion of Ag by sublimation. These findings give insights into the nanoscale structure and phase behaviours in binary alloys and provide an alternative way to fine-tune their structure, phase, and properties.

MXene/SnS2 Heterojunction for Detecting Sub-ppm NH3 at Room Temperature

Detection of ultralow concentrations of ammonia is very important in many applications such as fishing, poultry, agriculture, industry, biomedicine, and clinical diagnosis. However, detecting sub-ppm NH₃ remains a challenge for chemiresistive-type gas sensors. Two-dimensional (2D) materials display tremendous potential for effective gas detectors that can be used in these applications. The as-developed MXene/SnS₂ heterojunction-based chemiresistive-type sensor presents superior gas-sensing performance toward sub-ppm ammonia at room temperature. The sensor can detect NH₃ concentrations down to 10 ppb at room temperature. It also displays excellent long-term stability, with a decline in the response at ∼3.4% for 20 days. The developed sensor also displays good selectivity toward NH₃ relative to some potential interferents, such as HCHO, C₂H₅OH, CH₃OH, C₃H₆O, benzene, and NO₂. The measured in situ diffuse-reflectance infrared Fourier transform (DRIFT) spectra confirm that the products of nitric oxides during the chemical reactions occurred at the surface of MXene/SnS₂. Density functional theory (DFT) based on the first principles was implemented to compute the adsorption ability of NH₃ at the surface of the MXene/SnS₂ heterostructure. This indicates that the enhancement in the sensing properties of the MXene/SnS₂ heterostructure-based chemosensor could be ascribed to the stronger NH₃ adsorption, better catalytical activity, and more effective charge transfer bestowed by the formed heterostructure and the electron-redistribution-assisted stronger extraction of electrons from the sensing material.

Oxygen Plasma-Assisted Defect Engineering of Graphene Nanocomposites with Ultrasmall Co3O4 Nanocrystals for Monitoring Toxic Nitrogen Dioxide at Room Temperature

Functional adjustment of graphene with metal oxide can in fact progress the affectability of graphene-based gas sensors. However, it could be a huge challenge to upgrade the detecting execution of nitrogen dioxide (NO₂) sensors at room temperature. The ultrasmall size of nanocrystals (NCs) and copious defects are two key variables for moving forward gas detecting execution. Herein, we provide an effective strategy that the hydrothermal reaction is combined with room-temperature oxygen plasma treatment to prepare Co₃O₄ NCs and reduced graphene oxide (RGO) nanohybrids (Co₃O₄-RGO). Among all of Co₃O₄-RGO nanohybrids, Co₃O₄-RGO-60 W exhibits the most superior NO₂ sensing properties and achieves the low-concentration detection of NO₂. The sensitivity of Co₃O₄-RGO-60 W to 20 ppm NO₂ at room temperature is the highest (72.36%). The excellent sensing properties can mainly depend on the change in the microstructure of Co₃O₄-RGO. Compared with Co₃O₄-RGO, Co₃O₄-RGO-60 W with oxygen plasma treatment shows more favorable properties for NO₂ adsorption, including the smaller size of Co₃O₄ NCs, larger specific surface area, pore size, and more oxygen vacancies (OVs). Especially, OVs make the surface of NCs have a unique chemical state, which can increase active sites and improve the adsorption property of NO₂. Besides, the agreeable impact of the p-p heterojunction (Co₃O₄ and RGO) and the doping of N molecule contribute to the improved NO₂ detecting properties. It is demonstrated that the Co₃O₄-RGO-60 W sensor is expected to monitor NO₂ at room temperature sensitively.

Tin Diselenide (SnSe2) Van der Waals Semiconductor: Surface Chemical Reactivity, Ambient Stability, Chemical and Optical Sensors

Tin diselenide (SnSe2) is a layered semiconductor with broad application capabilities in the fields of energy storage, photocatalysis, and photodetection. Here, we correlate the physicochemical properties of this van der Waals semiconductor to sensing applications for detecting chemical species (chemosensors) and millimeter waves (terahertz photodetectors) by combining experiments of high-resolution electron energy loss spectroscopy and X-ray photoelectron spectroscopy with density functional theory. The response of the pristine, defective, and oxidized SnSe2 surface towards H2, H2O, H2S, NH3, and NO2 analytes was investigated. Furthermore, the effects of the thickness were assessed for monolayer, bilayer, and bulk samples of SnSe2. The formation of a sub-nanometric SnO2 skin over the SnSe2 surface (self-assembled SnO2/SnSe2 heterostructure) corresponds to a strong adsorption of all analytes. The formation of non-covalent bonds between SnO2 and analytes corresponds to an increase of the magnitude of the transferred charge. The theoretical model nicely fits experimental data on gas response to analytes, validating the SnO2/SnSe2 heterostructure as a suitable playground for sensing of noxious gases, with sensitivities of 0.43, 2.13, 0.11, 1.06 [ppm]-1 for H2, H2S, NH3, and NO2, respectively. The corresponding limit of detection is 5 ppm, 10 ppb, 250 ppb, and 400 ppb for H2, H2S, NH3, and NO2, respectively. Furthermore, SnSe2-based sensors are also suitable for fast large-area imaging applications at room temperature for millimeter waves in the THz range.

Gate-controlled gas sensor utilizing 1D-2D hybrid nanowires network

Novel gas sensors that work at room temperature are attracting attention due to their low energy consumption and stability in the presence of toxic gases. However, the development of sensing characteristics at room temperature is still a primary challenge. Diverse reaction pathways and low adsorption energy for gas molecules are required to fabricate a gas sensor that works at room temperature with high sensitivity, selectivity, and efficiency. Therefore, we enhanced the gas sensing performance at room temperature by constructing hybridized nanostructure of 1D-2D hybrid of SnSe2 layers and SnO2 nanowire networks and by controlling the back-gate bias (Vg = 1.5 V). The response time was dramatically reduced by lowering the energy barrier for the adsorption on the reactive sites, which are controlled by the back gate. Consequently, we believe that this research could contribute to improving the performance of gas sensors that work at room temperature.

A nanozyme-catalysis-based ratiometric electrochemical sensor for general detection of Cd2+

AuPt–rGO showed good peroxidase-like activity for the oxidation of OPD to DAP (a novel internal reference) and achieved sensitive and reliable detection of Cd2+ based on a ratiometric strategy.

Au-Decorated WS2 Microflakes Based Sensors for Selective Ammonia Detection at Room Temperature

Gold nanoparticles decorated WS2 microflakes (Au/WS2) have been synthesized by an in situ chemical reducing process. A chemiresistive-type sensor using as-synthesized Au/WS2 heterostructures as sensing materials shows an improved response to different concentrations of ammonia compared to pure WS2 at room temperature. As the concentrations of gold nanoparticles increased in heterostructures, response/recovery speeds of the sensors became faster although the sensitivity of the sensor was compromised compared to the sensitivity of the sensor with lower concentrations of Au. In addition, the Au/WS2-based sensor indicated excellent selectivity to formaldehyde, ethanol, benzene and acetone at room temperature. The improved performance of the sensors was attributed to the synergistic effect of electronic sensitization and chemical sensitization between WS2 and Au.