scispace - formally typeset
Search or ask a question

Showing papers in "Sensors and Actuators B-chemical in 2018"


Journal ArticleDOI
TL;DR: In this paper, a layer-by-layer self-assembled polyaniline (PANI)/graphene oxide (GO) film on quartz crystal microbalance (QCM) for humidity sensing is presented.
Abstract: This paper demonstrates a layer-by-layer self-assembled polyaniline (PANI)/graphene oxide (GO) film on quartz crystal microbalance (QCM) for humidity sensing. The morphological and compositional properties of PANI/GO composite films were examined by means of SEM, XRD and FT-IR. The humidity sensing properties of the PANI/GO nanocomposite-based QCM sensor were investigated by exposing to a broad range of 0–97%RH. The experimental results showed that the presented PANI/GO nanocomposite sensor has a high sensitivity, a good repeatability and fast response/recovery characteristics, which surpasses the previous reported counterparts. Moreover, the underlying humidity sensing mechanism of the PANI/GO-based QCM sensor was discussed by using Langmuir adsorption model. This work highlights the unique advantage of layer-by-layer self-assembled route for QCM sensor fabrication.

271 citations


Journal ArticleDOI
TL;DR: In this article, the development of cobalt nitride nanowire array on Ti mesh (Co 3 N NW/TM) was demonstrated as an efficient catalyst electrode for glucose oxidation in alkaline solutions and H 2 O 2 reduction in neutral solutions.
Abstract: It is highly attractive to develop non-noble-metal nanoarray architecture as a high-active catalyst electrode for molecular detection due to its large specific surface area and easy accessibility to target molecules. In this paper, we demonstrate the development of cobalt nitride nanowire array on Ti mesh (Co 3 N NW/TM) as an efficient catalyst electrode for glucose oxidation in alkaline solutions and H 2 O 2 reduction in neutral solutions. Electrochemical tests suggest that such Co 3 N NW/TM possesses superior non-enzymatic sensing ability toward rapid glucose and H 2 O 2 detection. As a glucose sensor, this fabricated electrode offers a high sensitivity of 3325.6 μA mM −1 cm −2 , with a wide linear range from 0.1 μM to 2.5 mM, a low detection limit of 50 nM (S/N = 3), and satisfactory stability and reproducibility. Its application in determining glucose in human blood serum is also successful. Amperometric H 2 O 2 sensing can also been realized with a sensitivity of 139.9 μA mM −1 cm −2 , a linear range from 2 μM to 28 mM, and a detection limit of 1 μM (S / N = 3). This nanoarray architecture holds great promise as an attractive sensing platform toward electrochemical small molecules detection.

266 citations


Journal ArticleDOI
Xing Gao1, Tong Zhang1
TL;DR: In this article, a review of recent efforts on engineering crystal structures with exposed high-energy facets of MOS nanomaterials and their improved gas-sensitive performance is provided, focusing on six kinds of common gas sensitive MOS including ZnO, SnO, TiO2, α-Fe2O3, NiO and Cu2O.
Abstract: Metal oxide semiconductor (MOS) gas sensors possess extensive applications due to their high sensitivity, low cost, and simplicity To boost their excellent sensing performance and meet the growing demand for applications, a series of strategies have been developed, such as the surface morphology engineering and function manipulation Recently, the controlled morphology with exposed high-energy facets and the facet-dependent sensing properties have attracted much attention Because of its abundant unsaturated active sites, the crystal planes with high surface energy usually serve as promising platform for gas sensing After a lot of survey of literature, the authors provide a review of recent efforts on engineering crystal structures with exposed high-energy facets of MOS nanomaterials and their improved gas-sensitive performance, emphasis on six kinds of common gas-sensitive MOS including ZnO, SnO2, TiO2, α-Fe2O3, NiO and Cu2O Also, the relationship between dangling bonds density and gas-sensing properties has been systematically discussed and used as one significant factor to evaluate superior sensing surface of MOS According to the research and calculation, surface engineering by selectively exposing high-energy facets provides an effective way to obtain MOS gas-sensitive materials with superior performance The understanding of the facet-dependent properties of MOS will assist in and guide the fabrication of more excellent gas sensors in the future

257 citations


Journal ArticleDOI
TL;DR: A review of the salinity measurement technology based on the optical fiber sensor is presented in this article, where the authors compare the performance of various sensing structures and analyses the advantages and disadvantages of different sensors.
Abstract: A review of the salinity measurement technology based on the optical fiber sensor is presented. The principles of optical fiber measurement, the structures of probes and the characteristics of various sensing structures are concerned. Firstly, this paper discusses the relationship between the salinity and refractive index, and the effect of ion pairs on the refractive index. Secondly, four methods of direct or non-direct measurements of salinity are summarized, including optical refraction method, optical fiber grating, optical interference and surface plasmon effect. Subsequently, the article compares performances of various sensing structures and analyses the advantages and disadvantages of different sensors. Finally, a prospect of salinity measurement requirement and the development direction of fiber-optic sensors in this area are addressed.

228 citations


Journal ArticleDOI
TL;DR: The review focuses on radio-based WCSs, and finds that ubiquitous wireless technologies are helping make analytical (bio)chemical sensing appropriate and realistic for mass market adoption, in particular for two major classes of chemical sensor – electrochemical and optical.
Abstract: Parallel advances in chemical sensing and wireless communication technologies have sparked the development of wireless chemical sensors (WCSs). These hybrid devices enable wireless determination, collection and distribution of (bio)chemical analytical information in a way that is significantly impacting the Sensor Internet of Things with applications in healthcare, defence, sport, the environment, and agriculture. Challenges and examples for each of the major chemical sensor and major radio technologies related to different application areas are reviewed, including the latest trends emerging from wearable sensors. The review focuses on radio-based WCSs, and finds that ubiquitous wireless technologies such as Bluetooth, ZigBee, radio-frequency identification (RFID) and near-field communication (NFC) are helping make analytical (bio)chemical sensing appropriate and realistic for mass market adoption, in particular for two major classes of chemical sensor – electrochemical and optical. The review provides an in-depth analysis of academic WCS research publications over the ten year period 2007–2017.

222 citations


Journal ArticleDOI
TL;DR: In this paper, a visual colorimetric sensor for ultrafast detecting H2O2 was constructed with a wide linear range of 20-700μm as well as a relative lower limit of detection (LOD) of 12.33μm.
Abstract: In this paper, FePt-Au ternary metallic hybrid nanaoparticles (FePt-Au HNPs) were prepared with FePt nanocubes as seeds and then the seeds were combined with Au(I) precursor through a facile hydrothermal approach. And the FePt-Au HNPs were characterized by a series of technical methods such as transmission electron microscopy (TEM), X-ray diffraction pattern (XRD) and UV–vis absorption spectra. Moreover, the as-prepared FePt-Au HNPs possessed the excellent peroxidase-like activity which could rapidly catalyze the oxidation reaction of substrate 3,3′,5,5′ −tetramethylbenzidine (TMB) to obtain a typical blue product which could be observed apparently by the naked eye only within 30 s. Notably, the color response is instant, due to the fast electron transfer between the substrate and H2O2 with the aid of FePt-Au HNPs. Based on the catalytic mechanism of fast electron transfer and the intrinsic peroxidase-like activity of FePt-Au HNPs, a visual colorimetric sensor for ultrafast detecting H2O2 was constructed with a wide linear range of 20–700 μM as well as a relative lower limit of detection (LOD) of 12.33 μM. Furthermore, the ultrafast sensor based on FePt-Au HNPs as peroxidase mimics was also successfully applied to detect H2O2 in milk samples.

210 citations


Journal ArticleDOI
TL;DR: In this paper, high sensitivity ammonia gas sensor based on Ag/ZnO composite (SZO) nanostructures and their structural, optical, morphological and gas sensing properties were investigated.
Abstract: High sensitivity ammonia gas sensor based on Ag/ZnO composite (SZO) nanostructures and their structural, optical, morphological and gas sensing properties were investigated. Field- emission scanning electron microscopy and high- resolution transmission electron microscopy revealed that pure ZnO flower-like nanorods transformed into nanoellipsoids upon adding of silver (Ag). Scanning transmission electron microscopy (STEM) analysis showed clear flower-like morphology of Ag/ZnO composite. STEM-mapping measurement showed that Zn, Ag and O were homogeneously distributed. The ammonia gas sensing analysis revealed that the Ag/ZnO (6 wt%) showed higher gas response compared with other content of Ag wt%. Ag/ZnO (6 wt%) exhibited the highest response of 29.5 when exposed to 100 ppm ammonia gas. Interestingly, Ag/ZnO (6 wt%) possessed good response and recovery property of 13 and 20 s at low concentration of ammonia at 10 ppm, respectively. The mechanism of gas sensing and enhanced gas response of pure ZnO and Ag/ZnO composite was discussed.

207 citations


Journal ArticleDOI
TL;DR: The classic and current protocols used to synthesize QDs, as well as the adaptability of QD surfaces for versatile bioconjugation are discussed, aswell as the recent advances in the detection of heavy metal ions, pathogens, and cancer biomarkers are highlighted in this review.
Abstract: Luminescent semiconductor nanocrystals or quantum dots (QDs) provide exquisite electro-optical properties that are ideal for biological sensing applications. Unlike traditional fluorescent dyes that lack in long-term stability and the ability to detect multiple signals simultaneously, QDs have overcome these obstacles, and thus, their potential use as in vivo and in vitro fluorophores has greatly advanced since their discovery in the 1980’s. In this review article, we discuss the classic and current protocols used to synthesize QDs, as well as the adaptability of QD surfaces for versatile bioconjugation. Energy transfer mechanisms represent the basis for the strong attraction of QDs to the biosensing community and thus, we examine the parameters that are required for efficient fluorescence resonance energy transfer, bioluminescence resonance energy transfer, and chemiluminescence resonance energy transfer. In addition, the recent advances in the detection of heavy metal ions, pathogens, and cancer biomarkers are also highlighted in this review. While QDs have shown much progress, the materials selection and commercialization of QDs for biological applications remain an ambitious challenge.

206 citations


Journal ArticleDOI
TL;DR: In this article, the authors consider state-of-the-art amperometric NO2 gas sensors based on carbon nanomaterials with respect to their dimensionalities, and discuss the enhanced gas-sensing performance achieved by using composite materials.
Abstract: Nitrogen dioxide (NO2) detection is critical because NO2 is a typical toxic gas that is harmful to humans as well as the environment. Over the last few decades, various nanomaterials such as nanowires, nanoparticles, carbon nanotubes, and graphene have been widely utilized to construct the platform (i.e., supporting material) of NO2 gas sensors. Among these materials, carbon nanomaterials (e.g., graphene and carbon nanotubes) have received increasing attention owing to their outstanding physical and electrical properties required for NO2 detection. Recently, many attempts have been made to blend the carbon nanomaterials with other materials, resulting in the creation of composite materials with enhanced electrical conductivity and physical properties for highly sensitive and selective detection of NO2 gas. As such, blended or stacked carbon composite materials offer higher efficiency (i.e., improved sensitivity and response/recovery time) for detecting NO2 gas in comparison with pristine carbon nanomaterials. In this review, we consider state-of-the-art amperometric NO2 gas sensors based on carbon nanomaterials with respect to their dimensionalities, and we discuss the enhanced gas-sensing performance achieved by using composite materials.

201 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed an AgNPs/graphene@AuNPs system with three-dimensional hot spots and tunable nanometer gap by changing the layer of graphene with a simple and facile method.
Abstract: Hot spots have been considered as a dominant role in surface enhancement Raman scattering (SERS). Its generation cannot be separated from the ultra-small nanogaps, which will tremendously contribute to the strong electromagnetic field. We propose a AgNPs/graphene@AuNPs system with three-dimensional hot spots and tunable nanometer gap by changing the layer of graphene with a simple and facile method. The excellent SERS behaviors of the proposed AgNPs/graphene@AuNPs substrate are demonstrated experimentally using rhodamine 6G (R6G) and crystal violet (CV) as probe molecules and theoretically using commercial COMSOL software. The excellent SERS behaviors can be attributed to the electromagnetic mechanism (EM) in all three dimensions introduced by the lateral nanogaps (AgNP-AgNP) and the vertical nanogaps (AgNP-AuNPs), and the chemical enhancement mechanism (CM) induced by the graphene film. For practical application, the prepared sensitive AgNPs/graphene@AuNPs SERS substrate was used to detect Malachite green (MG) in sea water, which provides a bran-new avenue for the detection of biological and chemical molecule.

200 citations


Journal ArticleDOI
TL;DR: In this article, the first application of a Co-based porous metal-organic framework (MOF) ZIF-67 as the glucose electrochemical sensor was demonstrated, and the results indicated that with the Ag contents increasing from 0% to 0.5%, the response time of the modified electrode was shorten by more than two times, and sensitivity was increased by two times and a half.
Abstract: In this paper, we demonstrated the first application of a Co-based porous metal-organic framework (MOF) ZIF-67 as the glucose electrochemical sensor. The ZIF-67 modified glassy carbon electrode (GCE) showed an excellent catalytic activity towards glucose oxidation. Meanwhile, to improve the electrocatalytic performance of the modified electrode, a novel Ag@ZIF-67 nanocomposite was fabricated through a sequential deposition-reduction method. The Ag@ZIF-67/GCE exhibited an enhanced catalytic activity towards glucose oxidation. The electrocatalytic performance of Ag@ZIF-67 with different Ag loadings was investigated, and the results indicated that with the Ag contents increasing from 0% to 0.5%, the response time of the modified electrode was shorten by more than two times, and the sensitivity was increased by two times and a half. The Ag-0.5%@ZIF-67GCE exhibited excellent electrocatalytic performances in the glucose concentration range of 2–1000 μM, including a high sensitivity of 0.379 μA μM−1 cm−2, a low detection limit of 0.66 μM (S/N = 3) as well as good selectivity and stability.

Journal ArticleDOI
TL;DR: This study focuses on the concise classification, underlying principles on the optical transducer, optical (surface) analytical techniques as a part of biosensing and use of nanostructures in optical sensors, and the recent advances in label-free optical biosensors based on the target analytes.
Abstract: Safety of food is a scientific domain requiring advanced handling, preparation, and storage. Food is a paramount need for growth of microorganisms it serves as a medium for proliferation and contamination. The primary historical techniques for food analysis are time-consuming and laborious whereas biosensors have an easier control over these limitations. Biosensor technology is a powerful tool for food analysis. Optical sensors reveal higher calibre for analysis of drugs, pesticide residues, pathogens, heavy metals, toxic substances as well as for overall hygiene monitoring in the food system. Label-free operations altogether acquired a well-established need for the characterization and identification of molecular components. We review the recent advances in label-free optical biosensors based on the target analytes. This study focuses on the concise classification, underlying principles on the optical transducer, optical (surface) analytical techniques as a part of biosensing and use of nanostructures in optical sensors. The main highlights include characterisation of localized surface plasmon and surface plasmon resonance based biosensors. Additionally, other optical biosensors such as bioluminescent optical fibre biosensors, evanescent wave fluorescence, ellipsometric, surface-enhanced Raman scattering and light-addressable potentiometric sensors are also well explained and characterized for food and environmental applications.

Journal ArticleDOI
TL;DR: In this paper, a dual-functional platform for detection and removal of antibiotic tetracycline (TC) is developed by a highly stable luminescent zirconium-based MOF (PCN-128Y).
Abstract: Antibiotic tetracycline (TC) is a sort of main contaminates in water, and of adverse effect on ecosystems and human health. The development of simple and efficient methods for both detection and removal of TC in water is highly desirable but remains challenging. Herein, a dual-functional platform for detection and removal of antibiotic tetracycline (TC) is developed by a highly stable luminescent zirconium-based MOF (PCN-128Y). The detection is based on the efficient luminescence quenching of the PCN-128Y toward TC. Theoretical/experimental studies reveal that the luminescence quenching can be attributed to a combined effect of the strong absorption of TC at the excitation wavelength and the photo-induced electron transfer process from the ligand of PCN-128Y to TC. The strong cheating metal-ligand bonding between Zr6 nodes and TC through solvent-assisted ligand incorporation is suggested to mainly account for the high adsorption capability of PCN-128Y toward TC in water. The preconcentration of TC within the pores of PCN-128Y induced by the adsorption process makes TC contact with the framework more sufficient, thus significantly enhances the efficiency of TC sensing. This work is the first example demonstrating that MOF materials can integrate the functions of detection and removal of antibiotic TC in water, which highlights the opportunity of luminescent MOFs in the application of wastewater treatment.

Journal ArticleDOI
TL;DR: In this paper, the gas sensing properties of these nanofibers were investigated systematically, and the results indicated that the response to 50ppm acetone of 0.5 mol% Rh-doped SnO2 nanofibrers was 60.6, which was 9.6 times higher than that of undoped nanofiber.
Abstract: Undoped and 0.2-1.0 mol% Rh-doped SnO2 nanofibers were fabricated using electrospinning combined with calcination treatment. The fibrous morphology of these nanofibers were maintained and the grain size of the SnO2 nanocrystals were greatly decreased after Rh doping. Sensors based on these nanofibers were fabricated through a hot pressing mathod. The gas sensing properties of these nanofibers were investigated systematically. The results indicated that the response to 50 ppm acetone of 0.5 mol% Rh-doped SnO2 nanofibers was 60.6, which was 9.6 times higher than that of undoped SnO2 nanofibers. In addition, the Rh-doped SnO2 nanofibers showed a decreased cross-response to ethanol, whereas pure SnO2 naofibers did not show selective detection of ethanol and acetone gases. The doping of Rh ions into SnO2 nanocrystals modulates the electron concentration, and induces the changes of the oxygen vacancies and chemisorbed oxygen of SnO2 naofibers. Thus, the doping of Rh3+ into SnO2 nanofibers should be a promising method for designing and fabricating acetone gas sensor with high gas sensing performance.

Journal ArticleDOI
TL;DR: In this paper, advances in polyaniline-based ammonia detection sensors are summarized, with a special focus on progresses in polymer modification techniques to achieve enhanced sensing performance, including template synthesis, interfacial and high dilution syntheses, multifunctional dopants, template synthesis and self-oxidizing template synthesis.
Abstract: Recently, there is an increasing interest in ammonia sensing and detection for a wide range of applications, including food, automotive, chemical, environmental, and medical sectors. A major challenge is to obtain selective, sensitive and environmentally stable sensing polymer/chemical materials that can meet the stringent performance requirements of these application areas. Among various polymer-based sensing materials, polyaniline has emerged as a preferred choice owing to its cost-effectiveness, facile preparation steps, and superior sensing performance towards ammonia. In this review, advances in polyaniline based ammonia detection sensors are summarized, with a special focus on progresses in polyaniline modification techniques to achieve enhanced sensing performance. These techniques utilize interfacial and high dilution syntheses, multifunctional dopants, template synthesis, self-oxidizing template synthesis, etc. , methods. Most up-to-date developments in combining polyaniline with other ammonia sensing materials, including polyaniline nanocomposites with metal oxides, graphene, carbon nanotubes and other carbon nanomaterials, are included. These novel nanocomposites have special capabilities of forming p - n nanojunctions or electron interphase interactions for superior detection sensitivity and selectivity. In addition, existing challenges toward understanding, reproducing, and optimizing the design of polyaniline based ammonia sensors are discussed.

Journal ArticleDOI
TL;DR: In this paper, the synthesis, characterization, and gas sensing applications of Pt nanoparticles-decorated SnO 2 nanoneedles synthesized through a facile hydrothermal process were reported.
Abstract: Herein, we report the synthesis, characterization, and gas sensing applications of Pt nanoparticles-decorated SnO 2 nanoneedles synthesized through a facile hydrothermal process. The synthesized nanoneedles were characterized for their morphological, structural, compositional and sensing properties using different characterization techniques. The morphological and structural characterizations confirmed the synthesis of well crystalline Pt nanoparticles decorated SnO 2 nanoneedles with tetragonal rutile crystal phase. X-ray photoelectron spectroscopic analysis (XPS) confirmed the spatial distribution of Pt metal into SnO 2 nanoneedles. Further, gas sensor applications of the synthesized nanoneedles were studies at different operating temperatures and concentrations of the CO gas. The detailed CO gas sensing analysis revealed that at an optimized temperature of 250 °C, the sensor exhibited 23.18 gas response with the response and recovery times of 15 s and 14 s, respectively. The long-term stability and the selectivity of the 3.125 at% Pt-decorated SnO 2 nanoneedles were also explored. Finally, a plausible gas sensing mechanism was also proposed.

Journal ArticleDOI
TL;DR: In this paper, a novel ozone gas sensor made with ca. 0.5μm yolk-shelled ZnCo2O4 microstructures synthesized via an eco-friendly, co-precipitation method and subsequent annealing was presented.
Abstract: The need to improve the sensitivity, selectivity and stability of ozone gas sensors capable of monitoring the environment to prevent hazard to humans has sparked research on binary metal oxides. Here we report on a novel ozone gas sensor made with ca. 0.5 μm yolk-shelled ZnCo2O4 microstructures synthesized via an eco-friendly, co-precipitation method and subsequent annealing. With these ZnCo2O4 microspheres, ozone concentrations down to 80 parts per billion (ppb) could be detected with a.c. and d.c. electrical measurements. The sensor worked within a wide range of ozone concentrations, from 80 to 890 ppb, being also selective to ozone compared to CO, NH3 and NO2. The high performance could be attributed to the large surface area to volume ratio inherent in yolk-shell structures. Indeed, ozone molecules adsorbed on the ZnCo2O4 surface create a layer of holes that affect the conductivity, as in a p-type semiconductor. Since this mechanism of detection is generic, ZnCo2O4 microspheres can be further used in other environment monitoring devices.

Journal ArticleDOI
TL;DR: In this paper, the performance of a 2D Ti3C2Tx (MXene), where T: O, OH, F) sheets modified with Pt nanoparticles (PtNPs) was investigated.
Abstract: Electrochemical performance of a 2D Ti3C2Tx (MXene, where T: O, OH, F) sheets modified with Pt nanoparticles (PtNPs) was investigated. The results showed that Ti3C2Tx/PtNP nanocomposite deposited on the surface of GCE showed much better and stable redox behavior in an anodic potential window as compared to the GCE modified with pristine Ti3C2Tx MXene. For example, the H2O2 sensor of Ti3C2Tx/PtNP on GCE offered LOD of 448 nM with a potential at which reduction starts of ∼+250 mV (vs. Ag/AgCl) in comparison to values of 883 μM and ∼−160 mV observed for Ti3C2Tx modified GCE. Moreover, the Ti3C2Tx/PtNP sensor could detect small redox molecules such as ascorbic acid (AA), dopamine (DA), uric acid (UA) and acetaminophen (APAP) at a potential higher than +250 mV with high selectivity and LOD down to nM level. We proved that selectivity of detection of such molecules (AA, DA, UA and APAP) could be modulated to high extent using external membranes.

Journal ArticleDOI
TL;DR: A comprehensive review of the main state-of-the-art applications of micromixers in biomedical systems over the past ten years is presented in this article, where the fundamental fluidic behaviors involved in microfluidic mixing are reviewed.
Abstract: Micromixers are crucial components within micro biomedical systems. This article presents a comprehensive review of the main state-of-the art applications of micromixers in biomedical systems over the past ten years. The article commences by reviewing the fundamental fluidic behaviors involved in microfluidic mixing. The biomedical applications of micromixers are then described in regard to their use particularly for (1) sample concentration, (2) chemical synthesis, (3) chemical reaction, (4) polymerization, (5) extraction and purification, (6) biological analysis, and (7) droplet/emulsion processes and others. The review concludes with a brief statistical analysis of the published literature in the micromixer field and an overview of the relative advantages of passive micromixers compared to active micromixers.

Journal ArticleDOI
TL;DR: In this paper, first-principles calculations have been performed on the adsorption of NO2 and its various interfering gases on the pristine C3N monolayer (p-C3N) and the B-doped C 3N monoline.
Abstract: Searching for suitable materials for NO2 sensing has important scientific significance and application value. First-principles calculations have been performed on the adsorption of NO2 and its various interfering gases on the pristine C3N monolayer (p-C3N) and the B-doped C3N monolayer. The studies on the adsorption stability, geometric structure, charge transfer, and electronic structure indicate that the p-C3N is a promising room-temperature NO2 sensor, with high selectivity and sensitivity, and good reversibility. For the B-doped C3N monolayer, the calculated formation energies suggest that B doping into the C3N lattice is thermodynamically highly favorable. Furthermore, B doping by replacing the N atom in the C3N monolayer should can further improve the sensing selectivity and sensitivity of the C3N monolayer toward NO2. However, it is noted that a large adsorption energy for NO2 indicates that the B-doped C3N monolayer may be reversibly operated above the room temperature. The possible reason for the distinct adsorption behaviors of the various molecules is also provided. Our theoretical studies indicate the great potential of the C3N-based two-dimensional semiconductor as good NO2 gas sensors.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the latest microfluidic designs for spheroid formation and culture, comparing their strategies and efficacy, and evaluate their performance with regard to key parameters, including shear stress, diameter, culture medium delivery and flow rate.
Abstract: A cell spheroid is a three-dimensional (3D) aggregation of cells. Synthetic, in-vitro spheroids provide similar metabolism, proliferation, and species concentration gradients to those found in-vivo. For instance, cancer cell spheroids have been demonstrated to mimic in-vivo tumor microenvironments, and are thus suitable for in-vitro drug screening. The first part of this paper discusses the latest microfluidic designs for spheroid formation and culture, comparing their strategies and efficacy. The most recent microfluidic techniques for spheroid formation utilize emulsion, microwells, U-shaped microstructures, or digital microfluidics. The engineering aspects underpinning spheroid formation in these microfluidic devices are therefore considered. In the second part of this paper, design considerations for microfluidic spheroid formation chips and microfluidic spheroid culture chips (μSFCs and μSCCs) are evaluated with regard to key parameters affecting spheroid formation, including shear stress, spheroid diameter, culture medium delivery and flow rate. This review is intended to benefit the microfluidics community by contributing to improved design and engineering of microfluidic chips capable of forming and/or culturing three-dimensional cell spheroids.

Journal ArticleDOI
TL;DR: In this paper, a colorimetric sensor with Au/Co3O4-CeOx nanocomposites as peroxidase mimics has been constructed unprecedentedly to detect H2O2.
Abstract: The Au/Co3O4-CeOx nanocomposites (Au/Co3O4-CeOx NCs) have been synthesized successfully by a facile two-step method. It was proved that Au/Co3O4-CeOx NCs exhibited an excellent peroxidase-like activity and could efficiently catalyze the oxidition reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue product. Furthermore, Au/Co3O4-CeOx NCs possessed a much higher affinity to H2O2 and TMB than horseradish peroxidase (HRP). In view of the excellent peroxidase mimetic catalytic activity of Au/Co3O4-CeOx NCs, a novel, sensitive and efficient colorimetric sensor with Au/Co3O4-CeOx NCs as peroxidase mimics has been constructed unprecedentedly to detect H2O2. Under optimal conditions, the colorimetric platform showed a sensitive response to H2O2 in the range of 10–1000 μM with a limit of detection of 5.29 μM. Moreover, fluorescent data proved that the Au/Co3O4-CeOx NCs could effectively catalyze the decomposition of H2O2 into OH radicals. Thus, we believe that Au/Co3O4-CeOx NCs with high peroxidase-like activity can be employed as nanoenzyme for a wide range of promising applications in biotechnology and environment.

Journal ArticleDOI
TL;DR: In this paper, the authors reported on the ultra-high sensitive and selective hydrogen gas sensing using CeO2-SnO2 mixed oxide heterostructure synthesized by a simple hydrothermal method.
Abstract: Detection of toxic and explosive gases in a selective manner and with higher sensitivity in industries and homes remains very challenging. Therefore, herein, we report on the ultra-high sensitive and selective hydrogen gas sensing using CeO2-SnO2 mixed oxide heterostructure synthesized by a simple hydrothermal method. The BET, photoluminescence, X-ray photoelectron spectroscopy and electron paramagnetic resonance analyses demonstrated that the CeO2-SnO2 heterostructure comprehends a high surface area and a large number of defects related to oxygen vacancies. The formation of heterojunction in CeO2-SnO2 nanostructures was confirmed by the non-linear behaviour I–V curve. The gas-sensing characteristics of the CeO2-SnO2 heterostructure showed shorter response and recovery times of approximately 17 and 24 s, respectively, together with high sensitivity (19.23 ppm−1) to 40.00 ppm H2 gas at 300 °C. The improved H2 gas sensing response of 1323 at 60 ppm H2 gas is correlated with the higher surface area, pore diameter, surface defects and CeO2-SnO2 heterojunction emerging at the interfaces between the CeO2 and SnO2 serves as additional reaction sites and as well as exposed facets creating the surface to be extremely reactive for the adsorption of oxygen species. The high H2 gas selectivity observed for the CeO2-SnO2 makes them possible candidates for monitoring H2 gas at low concentrations (ppm levels).

Journal ArticleDOI
TL;DR: NiO-SnO2 heterojunction microflowers assembled by thin porous nanosheets were successfully synthesized through a facile one-step hydrothermal route as discussed by the authors.
Abstract: NiO-SnO2 heterojunction microflowers assembled by thin porous nanosheets were successfully synthesized through a facile one-step hydrothermal route. The structural and composition information were examined by means of X-ray diffractometer, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller nitrogen adsorption-desorption. The formaldehyde gas sensing properties were systematically investigated between the pure and NiO-SnO2 microflowers. The experiment results showed that NiO-SnO2 microflower sensor displayed the higher response at a lower operating temperature region compared to pure SnO2 microflower sensor. Meanwhile, introducing NiO obviously reduced operating temperature. Especially, the sensor utilizing 5 mol% NiO-SnO2 microflowers showed significantly enhanced sensing performances to formaldehyde including the higher responses, lower operating temperatures, lower detecting limit level, quick response/recovery characteristics, good reproducibility and stability, and superior selectivity. The enhanced sensing properties were probably attributed to the formation of p–n heterojunctions at interface and the catalytic effect of NiO, which significantly enlarges surface depletion region and increases potential barrier. Our studies provide a facile synthesis process, which could be developed to synthesize other semiconductor oxide composites, and provide a potential material for fabricating high performance sensors.

Journal ArticleDOI
TL;DR: This paper intends to review the developments in water quality monitoring technologies for the detection of biological and chemical contaminants in accordance with instrumental limitations and focuses on the most recently developed techniques for water contaminant detection applications.
Abstract: Water monitoring technologies are widely used for contaminants detection in wide variety of water ecology applications such as water treatment plant and water distribution system. A tremendous amount of research has been conducted over the past decades to develop robust and efficient techniques of contaminants detection with minimum operating cost and energy. Recent developments in spectroscopic techniques and biosensor approach have improved the detection sensitivities, quantitatively and qualitatively. The availability of in-situ measurements and multiple detection analyses has expanded the water monitoring applications in various advanced techniques including successful establishment in hand-held sensing devices which improves portability in real-time basis for the detection of contaminant, such as microorganisms, pesticides, heavy metal ions, inorganic and organic components. This paper intends to review the developments in water quality monitoring technologies for the detection of biological and chemical contaminants in accordance with instrumental limitations. Particularly, this review focuses on the most recently developed techniques for water contaminant detection applications. Several recommendations and prospective views on the developments in water quality assessments will also be included.

Journal ArticleDOI
TL;DR: In this paper, a novel and sensitive non-enzymatic glucose sensor was developed based on the modification of Au@Cu2O nanocomposite on the surface of glassy carbon (Au@cu2O/Nafion/GC) electrode.
Abstract: A novel and sensitive non-enzymatic glucose sensor was developed based on the modification of Au@Cu2O nanocomposite on the surface of glassy carbon (Au@Cu2O/Nafion/GC) electrode. Au@Cu2O nanocomposites were prepared using a facile chemical reduction method and its core-shell structure was confirmed by transmission electron microscopy (TEM) and element analyses, in which the diameter of Au nanoparticle (NP) is about 14 nm and the thickness of shell is about 30–50 nm, being composed of Cu2O nanoparticles. Electrochemical properties of Au@Cu2O/Nafion/GC electrode were investigated by cyclic voltammetric techniques and electrochemical impedance spectroscopy (EIS). It was found that the Au@Cu2O/Nafion/GC electrode exhibited enhanced electrocatalytic activity towards glucose oxidation in alkaline medium (pH = 12.6), as compared to those of Cu2O/Nafion/GC and Au/Nafion/GC electrodes. Some influence parameters including pH value and Au@Cu2O content on electrocatalytic activity of the modified electrode have been investigated. Under the optimized conditions, the electrochemical sensor has a linear dependence over glucose concentrations from 0.05 to 2.0 mM with a sensitivity of 715 μA mM−1 Cm−2. Moreover, such a glucose sensor demonstrated good stability, reproducibility and selectivity. Our results suggest that Au@Cu2O core-shell structure could be a promising candidate for the construction of non-enzymatic sensor.

Journal ArticleDOI
TL;DR: The brush-like SnO2@ZnO hierarchical nanostructures (HNSs) were successfully synthesized by using a simple two-step hydrothermal method as discussed by the authors.
Abstract: The novel brush-like (B–) SnO2@ZnO hierarchical nanostructures (HNSs) are successfully synthesized by using a simple two–step hydrothermal method. The SnO2 nanowires (NWs) grow epitaxially on the non–polarized plane of ZnO nanorods (NRs) with a six–fold symmetry. The heterogeneous nucleation–growth processes of SnO2 and ZnO are discussed in detail based on the dissolution–recrystallization mechanism, growth kinetics and Ostwald ripening. The excellent sensing performances of B–SnO2@ZnO HNSs for NO2 gas sensor are developed, including good selectivity, ultrasensitive, fast response, broad detection range and low detection limits. The detection range of the sensor is measured from 5 ppb to 10 ppm, and the detection limit of the sensor is 5 ppb at 150 °C. The response and recovery time which reach 90% of the final signal is less than 60 s, while retaining the low detection limit. The sensing mechanism is also discussed, and the unique structure of B–SnO2@ZnO is the dominating parameter for excellent sensing performances. The improved sensing performance of the HNSs also suggests the possibilities of other 1D materials combination for further sensing applications.

Journal ArticleDOI
TL;DR: In this article, a modified polymer-network gel method was used for room temperature light-assisted NO2 gas detection, where a ZnO-Ag nanoparticle was utilized for detecting NO2 in photocatalytic applications.
Abstract: Noble metal-metal oxide nanohybrids play an ever-increasing role in photocatalytic applications. Here, a ZnO-Ag nanoparticle prepared by a modified polymer-network gel method was utilized for room temperature light-assisted NO2 gas detection. Since a heterojunction forms between the two materials and surface oxygen vacancies increase, the sensitivities of the sensors to NO2 gas (0.5–5 ppm) under various light (λ = 365–520 nm) illumination conditions are enhanced in comparison with those of pure ZnO sensor. Surface plasmon resonance (SPR) was found to result in the excellent visible-light performance of this ZnO-Ag nanostructure. More importantly, by tuning the working wavelength using different LED light sources, we can obtain an optimized sensitivity. When blue-green LED (470 nm, 75 mW/cm2) is used, the 3 mol% Ag-loaded ZnO sensor shows the highest sensitivity as well as superior stability and selectivity. The effect of humidity on the sensor performance is also discussed in detail.

Journal ArticleDOI
TL;DR: In this article, a "turn-on" fluorescence sensor based on graphene quantum dots and gold nanoparticles was developed for detection of Pb 2+ using an extremely broad detection range from 50 nM to 4 nM with a detection limit of 16.7 nM.
Abstract: Heavy metal, such as Pb 2+ , detection technologies are quite important in environment monitoring and human health protection. However, most existing technologies are often time consuming, expensive with sophisticated equipment, and requirement of complicated sample pre-treatment, which limit the useful range of real-time application. Here, we report the development of a “turn-on” fluorescence sensor for Pb 2+ detection based on graphene quantum dots and gold nanoparticles. We achieved an extremely broad detection range of Pb 2+ from 50 nM to 4 μM, with a detection limit of 16.7 nM. This sensing system is highly sensitive and selective for determination of Pb 2+ . The proposed strategy is expected to provide considerable implication for other heavy metal, antigen, or DNAs by modifying sensing molecules, and fast examination in chemical and biological applications.

Journal ArticleDOI
TL;DR: In this article, a new sensing method for simultaneous measurement of seawater temperature and salinity by C-type micro-structured fiber was proposed, which can be used for double parameter measurement.
Abstract: A new sensing method for simultaneous measurement of seawater temperature and salinity by C-type micro-structured fiber was proposed. The C-type fiber structure formed by removing the outer wall of one pore from a six holes micro-structured fiber, which would bring in birefringence and broke original pattern of degeneracy. By optimizing the parameters of this fiber structure, X polarization and Y polarization of fundamental mode were separate. Therefore, it could be used for double parameter measurement. Besides, gold film coated on the surface of structure to enhance sensing sensitivity by Surface Plasmon Resonance (SPR) principle. In this study, finite element analysis method was used to analyze the spectral transmission characteristics of C-type micro-structured optical fiber. The surface of wedge-shaped defect was contacted with seawater directly to feel salinity; meanwhile, thermo-optic material filled into pores to detect the temperature of seawater. Through model analysis, it was proved that the proposed filling structure could produce two SPR loss valleys, which had different responses to temperature and salinity. Under optimized structure, maximum salinity sensitivity of 1.402 nm/‰ was obtained for X-polarization and maximum temperature sensitivity of −7.609 nm/ °C was obtained for Y polarization, which demonstrated that the designed scheme could not only solve the cross sensitivity problem of two parameters but also achieve high sensitivity. In addition, C-type micro-structured fiber is non-cascade integrated, strong stability, and flexibility in design, which has great potential for sensing applications.