Showing papers in "Sensors and Actuators B-chemical in 2017"

Gold nanoparticles as efficient sensors in colorimetric detection of toxic metal ions: A review

Abstract: Rapid and high precision detection of toxic metal ions is one of the chief requirements today to combat environment pollution. Gold nanoparticles play a key role in this by assisting the development of smart sensors and detection agents. Their high surface to volume ratio and unique optical property facilitates the development of high sensitive analytical GNP based bio-sensing tools. Recently, a major research thrust area has been the design and development of smartly fabricated GNPs as probes for selective detection of toxic contaminates and metal pollutants. In this review we focus on the use of GNPs and its functionalization for colorimetric detection of metal ions. Colorimetric detection enables cost effective and simple monitoring of toxic ions accompanied with the advantages of on-site applicability, avoids complex instrumentation, ease of analysis and usage. We also discuss the promising prospects and future potentiality of GNPs to serve as next generation multi-functional sensing tools and “lab-on-chip” detection agents.

Tunable photoluminescence of water-soluble AgInZnS–graphene oxide (GO) nanocomposites and their application in-vivo bioimaging

Abstract: Water-soluble quantum dots (QDs) with biocompatibility and photostability show a potential application in biomedical optical imaging. Herein, we reported biocompatible, photostable and eco-friendly AgInZnS–graphene oxide (AIZS–GO) nanocomposites with tunable emissions by transferring hydrophobic AIZS QDs on water-soluble GO via a mini-emulsion method. The as-prepared hydrophilic AIZS–GO nanocomposites still exhibited bright and stable photoluminescence (PL) even after phase-transfer by using GO, moreover, their PL emission could be well tuned widely in the range of 530 nm–680 nm by controlling the composition of Zn. In addition, AIZS–GO nanocomposites could be used for imaging of SK-BR-3 breast cancer cells via intratumoral administration. MTT assay result proved that these nanocomposites demonstrated comparable low cytotoxicity due to the absence of highly toxic cadmium. The in vivo imaging experiments of mice indicated that the prepared red emitted AIZS–GO nanocomposites could be used for the cancer cell and organ of mice labeling, which shows potential applications in bioimaging and related fields such as phototherapy and imaging.

Green synthesis of carbon dots from rose-heart radish and application for Fe3+ detection and cell imaging

Abstract: Herein, a simple, green, and low-cost way was developed in the synthesis of fluorescent carbon dots (CDs) with well-distributed size, using one-pot hydrothermal treatment of rose-heart radish. The as-prepared carbon dots exhibit exceptional advantages including high fluorescent quantum yield (13.6%), excellent biocompatibility, low-toxicity, and satisfactory chemical stability. More strikingly, as-synthesized N-CDs generate strong response to Fe 3+ ions and gives rise to the fluorescence quenching. This phenomenon was used to develop a fluorescent method for facile detection of Fe 3+ with a linear range from 0.02 to 40 μM and a detection limit of 0.13 μM (S/N = 3), and further extended to measure environmental water samples with satisfactory recoveries. Eventually, the low toxicity and strongly fluorescent carbon dots were applied for cell imaging and the quenched fluorescence by adding Fe 3+ , demonstrating their potential towards diverse applications.

Metal oxide composites in conductometric gas sensors: Achievements and challenges

Abstract: The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composite using in conductometric gas sensors and can restrict application of nanocomposites in these devices. Technology features of composite synthesis and device fabrication, which should be taken into account while designing and fabricating sensors based on metal oxide composites, are considered. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed.

Sensitivity enhancement by using few-layer black phosphorus-graphene/TMDCs heterostructure in surface plasmon resonance biochemical sensor

Abstract: The heterostructure of two-dimensional (2D) materials are promising and useful in the field of surface plasmon resonance (SPR) biochemical sensors. To enhance the sensitivity, we design a novel SPR biochemical sensor by using heterostructures of few-layer black phosphorus (BP) and graphene/transition metal dichalcogenides (TMDCs). The SPR biochemical sensor based on the different heterostructures of BP and graphene/TMDCs are analyzed, and the highest sensitivity with 279°/RIU for the heterostructure of BP and bilayer WSe2 is obtained. Moreover, the proposed biochemical sensor can be used to detect the analyte with different refractive index. The most prominent advantage of the proposed structure is its high sensitivity. The maximum sensitivity of our proposed SPR biochemical sensor is about 2.4 times of the conventional biochemical sensor. We believe that this biochemical sensor could find potential applications in chemical examination, medical diagnosis and biological detection.

Green synthesis of carbon dots from Ocimum sanctum for effective fluorescent sensing of Pb2+ ions and live cell imaging

Abstract: A simple, rapid and cost-effective approach is developed to synthesize fluorescent carbon dots (CDs) using the leaves of Ocimum sanctum as a carbon source for the first time. The as-synthesized CDs possess high stability in aqueous solution and exhibit strong fluorescence with quantum yield of 9.3%. We have explored the use of such CDs as a fluorescent sensor for Pb2+ ions detection, which is based on Pb2+ ions induced fluorescence quenching of CDs. More significantly the resultant CDs has excellent selectivity and sensitivity towards Pb2+ ions with a limit of detection (LOD) 0.59 nM and linear detection range of 0.01–1.0 μM. The practical use of synthesized CDs for detection of Pb2+ ions is demonstrated in triple negative breast cancer cells (MDA-MB 468 cells) and real water samples successfully. Moreover, the CDs are also possessing low cytotoxicity to exhibit excellent fluorescent probe for multicolour cellular imaging.

Sensitive and selective NO2 gas sensor based on WO3 nanoplates

Abstract: Gas sensors based on a chemiresistive metal oxide semiconductor are widely used including nitrogen dioxide (NO 2 ) at a moderate temperature. In this work efforts are taken to fabricate NO 2 gas sensor using thin films of tungsten oxide (WO 3 ) grown directly on to a soda-lime glass substrate without assistance of any seed layer by a simple and a facile hydrothermal technique. As per our knowledge, the deposition of nanostructured WO 3 thin films without assistance of any seed layer on the glass substrate was rarely reported. The WO 3 thin film samples were synthesized at various deposition times ranging from 3 h to 7 h and were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV–vis spectroscopy and Brunauer-Emmett-Teller techniques. The surface morphological and structural characterization showed the two dimensional (2D) nanoplate-like structure of as synthesized WO 3 thin films with plate thickness ranging from 90 to 150 nm and had an orthorhombic structure, respectively. Moreover, the 2D nanoplates of WO 3 exhibited a gas response ∼10 for 5 ppm for toxic NO 2 gas at relatively low operating temperature. The new synthesis route and sensing behavior of as synthesized WO 3 nanoplates revealed a promising candidate for the fabrication of the cost effective gas sensors.

Photonic crystal fiber based plasmonic sensors

Abstract: The development of highly-sensitive miniaturized sensors that allow real-time quantification of analytes is highly desirable in medical diagnostics, veterinary testing, food safety, and environmental monitoring. Photonic Crystal Fiber Surface Plasmon Resonance (PCF SPR) has emerged as a highly-sensitive portable sensing technology for testing chemical and biological analytes. PCF SPR sensing combines the advantages of PCF technology and plasmonics to accurately control the evanescent field and light propagation properties in single or multimode configurations. This review discusses fundamentals and fabrication of fiber optic technologies incorporating plasmonic coatings to rationally design, optimize and construct PCF SPR sensors as compared to conventional SPR sensing. PCF SPR sensors with selective metal coatings of fibers, silver nanowires, slotted patterns, and D-shaped structures for internal and external microfluidic flows are reviewed. This review also includes potential applications of PCF SPR sensors, identifies perceived limitations, challenges to scaling up, and provides future directions for their commercial realization.

Quantitative detection of formaldehyde and ammonia gas via metal oxide-modified graphene-based sensor array combining with neural network model

Abstract: This paper reports metal oxide (MOx)-decorated graphene-based sensor array combining with back-propagation (BP) neural network toward the detection of indoor air pollutant exposure. Tin dioxide (SnO 2 ) nanospheres and copper oxide (CuO) nanoflowers-decorated graphene were used as candidates for formaldehyde and ammonia gas sensing, respectively. The as-synthesized sensing materials were characterized in terms of their nanostructural, morphological and compositional features by SEM, Raman spectra, and XRD. The sensor array was fabricated via one-step hydrothermal route and layer-by-layer (LbL) self-assembly technique on the substrate with interdigital microelectrodes. The sensing properties of MOx/graphene composite toward the mixture gas of ammonia and formaldehyde, such as dynamic response, sensitivity, response/recovery time, and stability, were investigated at room temperature. And furthermore, this work successfully achieved the recognition and quantitative prediction of components in the gas mixture of formaldehyde and ammonia through the combination of MOx/graphene-based sensor array and neural network-based signal processing technologies.

Facile green synthesis of nitrogen-doped carbon dots using Chionanthus retusus fruit extract and investigation of their suitability for metal ion sensing and biological applications ☆

Abstract: Nitrogen-doped carbon dots (N-CDs) were synthesized from Chionanthus retusus (C. retusus) fruit extract using a simple hydrothermal-carbonization method. Their ability to sense metal ions, and their biological activity in terms of cell viability and bioimaging applications were evaluated. The resulting N-CDs were characterized by various physicochemical techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy. The optical properties were characterized by ultraviolet visible (UV-vis) fluorescence spectroscopy techniques. The average size of the N-CDs was approximately 5 ± 2 nm with an interlayer distance of 0.21 nm, as calculated from the HRTEM images. The presence of phytoconstituent functionalities and the percentages of components in the N–CDs were confirmed by XPS studies, and a nitrogen content of 5.3% was detected. The N–CDs demonstrated highly durable fluorescence properties and low cytotoxicity with a quantum yield of 9%. The synthesized N–CDs were then used as probes for the detection of metal ions. The N–CDs exhibited high sensitivity and selectivity towards Fe3+, with a linear relationship between 0 and 2 μM and a detection limit of 70 μM. The synthesized N–CDs are anticipated to have diverse biomedical applications, particularly for bioimaging, given their high fluorescence, excellent water solubility, good cell permeability, and negligible cytotoxicity. Finally, the potential of N–CDs as biological probes was investigated using fungal (Candida albicans and Cryptococcus neoformans) strains via fluorescent microscopy. We found that N–CDs were suitable candidates for differential staining applications in yeast cells with good cell permeability, localization with negligible cytotoxicity. Hence, N–CDs may find dual utility as probes for the detection of cellular pools of metal ions (Fe3+) and also for early detection of opportunistic yeast infections in biological samples.

Field calibration of a cluster of low-cost commercially available sensors for air quality monitoring. Part B: NO, CO and CO2

Abstract: In this work the performances of several field calibration methods for low-cost sensors, including linear/multi linear regression and supervised learning techniques, are compared. A cluster of either metal oxide or electrochemical sensors for nitrogen monoxide and carbon monoxide together with miniaturized infra-red carbon dioxide sensors was operated. Calibration was carried out during the two first weeks of evaluation against reference measurements. The accuracy of each regression method was evaluated on a five months field experiment at a semi-rural site using different indicators and techniques: orthogonal regression, target diagram, measurement uncertainty and drifts over time of sensor predictions. In addition to the analyses for ozone and nitrogen oxide already published in Part A [1], this work assessed if carbon monoxide sensors can reach the Data Quality Objective (DQOs) of 25% of uncertainty set in the European Air Quality Directive for indicative methods. As for ozone and nitrogen oxide, it was found for NO, CO and CO 2 that the best agreement between sensors and reference measurements was observed for supervised learning techniques compared to linear and multilinear regression.

Formaldehyde detection: SnO2 microspheres for formaldehyde gas sensor with high sensitivity, fast response/recovery and good selectivity

Abstract: Tin oxide microspheres were successfully obtained through a facile hydrothermal method without any polymer templates or surfactant. The as-synthesized SnO 2 microspheres are composed of large amount of small spheres with average diameters of about 250 nm, and every small sphere consists of numerous primary nanocrystallites with average sizes of about 8 nm. The resultant product was used as sensing material for gas sensor to detect the formaldehyde (HCHO) gas. The gas response, response and recovery time, selectivity and stability were carefully studied. It was found that the response value of the sensor to 100 ppm HCHO was 38.3 at the operating temperature of 200 °C. The gas sensor based on SnO 2 microspheres has excellent gas response, good response-recovery properties, linear dependence, repeatability and selectivity, making it to be a promising candidate for practical detectors for HCHO.

Cu-Ag bimetallic nanoparticles on reduced graphene oxide nanosheets as peroxidase mimic for glucose and ascorbic acid detection

Abstract: Bimetallic nanoparticles (NPs) in several instances have resulted in improved catalytic properties when compared to the monometallic analogues. This paper reports on a wet-chemistry approach for the synthesis of reduced graphene oxide (rGO) nanosheets decorated with bimetallic Cu-Ag NPs. The nanocomposite possesses the advantages of combining rGO and metallic NPs and exhibits excellent intrinsic peroxidase like activity, which can be used to catalyse the reaction of peroxidase substrates such as 3,3′,5,5′-tetramethylbenzidine (TMB) in presence of hydrogen peroxide (H 2 O 2 ). A combination of the peroxidase-like activity of the Cu-Ag/rGO nanostructures with glucose oxidase (GluO x ), allowed the construction of a sensitive and a selective colorimetric assay for glucose detection in blood serum with a detection limit of 3.8 μM. The monometallic analogues displayed a detection limit of 7.9 μM (Ag/rGO) and 9.7 μM (Cu/rGO). In addition, the Cu-Ag/rGO nanostructures were also successfully applied for sensing ascorbic acid with a detection limit of 3.6 μM.

WS2 nanoflakes based selective ammonia sensors at room temperature

Abstract: A selective room-temperature ammonia sensor using WS 2 nanoflakes as the sensing materials was successfully developed in this work. The two-dimensional WS 2 sharing the same structure with MoS 2 , has a typical graphene-like 2D microstructure. The WS 2 nanoflakes based sensor shows a good sensitivity and an excellent selectivity to ammonia at room temperature. The sensor showed an increased resistance when exposed to ammonia from 1 ppm to 10 ppm indicating a p-type response. The response and recovery time of the sensor to 5 ppm ammonia are ∼120 s and ∼150 s, respectively. The developed ammonia sensor shows excellent selectivity to formaldehyde, ethanol, benzene and acetone at room temperature. The response of the sensor increased as the humidity increase up to 73% possibly due to the sulfides ions-assisted hydroxylation of the co-adsorbed water and the oxidation of the solvated ammonia with adsorbed oxygen ions on the surface of the WS 2 nanoflakes.

Flexible room temperature ammonia sensor based on polyaniline

Abstract: Here we present, a useful ammonia (NH3) gas sensor based on polyaniline (PANI) film as an active sensing layer. The PANI films were successfully deposited on a polyethylene terephthalate (PET) flexible substrate by a simple in-situ polymerization technique. Ammonia (NH3) gas-sensing properties of the films prepared at optimum conditions were examined at room temperature in the range of 5–1000 ppm. The room temperature functioning of the sensor is critical, which facilitates low-power operation and also enhances the life time of a sensor. The observed variation in resistance of PANI film corresponding to 1000 ppm and 200 ppm of NH3 exposure, is approximately 520 and 110 times of that observed for ∼5 ppm of NH3. Furthermore, good reproducibility and long-term stability were also observed over a concentration range from 5 to 1000 ppm. Moreover the sensor is mechanically robust and can be bent sharply without damage, demonstrating excellent mechanical stability and exhibiting no lack in performance even after several bending cycles. These results indicate that the PANI films on flexible substrates are promising for portable on-site detection.

One-step synthesis of self-doped carbon dots with highly photoluminescence as multifunctional biosensors for detection of iron ions and pH

Abstract: The nitrogen doped carbon dots (C-dots) with highly photoluminescence (PL) are synthesized using m-aminobenzoic acid (MAC) as the only precursor by a simple, one-step hydrothermal method. The NH2 groups of MAC have been used as nitrogen source to dope C-dots. The synthesized nitrogen doped (N-doped) C-dots present an unexpectedly large quantum yield of 30.7% and possess an essentially crystalline nature and desirable functional groups. More important, the C-dots can serve as multifunctional fluorescence nanosensors to detect pH and Fe3+. The fluorescent intensity of the C-dots increases dramatically as pH increases from 2 to 10. The fluorescent paper with C-dots coated for visual detection of pH by naked eyes has been successfully prepared. Moreover, the C-dots are employed for assaying Fe3+ based on direct interactions between Fe3+ and COOH and NH2 groups of C-dots. Under the optimal condition, a linear relationship between the decreased fluorescence intensity of C-dots and the concentration of Fe3+ is established in the range from 0 to 1.6 μM. The detection limit is as low as 0.05 μM, suggesting a promising assay for Fe3+. The results reported here provide a new approach for the design of N-doped multifunctional florescent sensor.

Fabrication of nanostructured ZnO thin films based NO2 gas sensor via SILAR technique

Abstract: Zinc oxide (ZnO) thin films have been widely used as an effective gas sensor element. In the present study, nanostructured thin films of ZnO were prepared by using the simplistic and economical successive ion layer adsorption and reaction (SILAR) technique. The effects of SILAR cycles on the structural, optical, surface morphological and electrical properties of nanostructured ZnO thin films were investigated. Characterization techniques such as XRD, UV-vis, PL, FESEM, and Hall measurement were utilized to study the physical and chemical properties of the synthesized films. XRD confirms the formation of hexagonal phase structural ZnO thin films. FE-SEM analysis reveals the formation of well-dispersed ZnO nanoparticles having sizes of ∼18–40 nm. The SILAR cycles play a key role in the synthesis of nanostructured ZnO thin films and it is found that, with increasing SILAR cycles, the grain size continues increasing. Optical studies confirm the presence of oxygen vacancies in synthesized ZnO thin films. Finally, the ZnO thin films were exposed to NO 2 gas with a concentration of 100 ppb–200 ppm and the resulting resistance transient was recorded. The nanostructured ZnO thin films synthesized at 30 SILAR cycles displays an enhancement of gas sensing performance and exhibit significantly higher responses (∼5% per ppm). Moreover, our ZnO thin-film-based gas sensor is sensitive to very low concentrations of dangerous NO 2 (100 ppb). The sensitive gas sensor used to trace level NO 2 detection, synthesized via simple SILAR route proves the novelty of our work. The present report provides a new direction in fabricating nanostructured ZnO thin films for low-cost and efficient gas sensing applications.

Recent progress in the development of fluorescent probes for the detection of hypochlorous acid

Abstract: As one of the reactive oxygen species, hypochlorous acid (HOCl) may be associated with various diseases. To understand the roles of HOCl in living organism, fluorescent probes for imaging HOCl in living systems have been developed fast in recent years owing to their high selectivity, excellent sensitivity and spectral resolution. In this review, we summarized and highlighted the recent advances in the development and application of HOCl fluorescent probes. This review is focused on the detection mechanisms of probes for HOCl. According to the various recognition groups, we divided the HOCl fluorescence probes into five parts and discussed detection mechanisms, respectively.

Room temperature hydrogen gas sensor based on palladium decorated tin oxide/molybdenum disulfide ternary hybrid via hydrothermal route

Abstract: This paper demonstrates a hydrogen gas sensor based on palladium-tin oxide- molybdenum disulfide (Pd-SnO 2 /MoS 2 ) ternary hybrid via hydrothermal route. The morphologies, microstructures and compositional characteristics of the Pd-SnO 2 /MoS 2 nanocomposite were sufficiently examined by X-ray diffraction (XRD), Raman spectroscopy (RS), nitrogen sorption analysis, energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The gas-sensing performances of the Pd-SnO 2 /MoS 2 sensor were investigated by exposed to different concentrations of hydrogen gas from 30 ppm to 5000 ppm at room temperature. The experimental results showed that the hydrogen gas sensor has a quite sensitive response, swift response-recovery time, good repeatability and selectivity toward hydrogen gas. Furthermore, the effect of Pd loading in the hybrid on the hydrogen gas sensing was investigated. The sensing mechanism of the Pd-SnO 2 /MoS 2 sensor was attributed to the synergistic effect of the ternary nanostructures and the modulation of potential barrier with electron transfer. This work indicates that the as-prepared Pd-SnO 2 /MoS 2 composite is a candidate for detecting hydrogen gas in various applications at room temperature.

The crystal facet-dependent gas sensing properties of ZnO nanosheets: Experimental and computational study

Abstract: Herein, we focused on the effects of exposed crystal planes on the gas sensing property of ZnO. For this purpose, we designed and synthesized two porous ZnO nanosheets with different exposed crystal facets (0001) and (10 1 ¯ 0) by a facile hydrothermal routes. The characterization results show that both the porous nanosheets have a near specific surface area about 7.5 m2/g, thickness about 100 nm, diameter about 5 μm and pore size of tens of nanometers. However, their dominating exposed crystal facets are (0001) and (10 1 ¯ 0), respectively. When employed them as sensing materials in gas sensors, porous ZnO nanosheets with dominating exposed (0001) facet exhibit a superior sensitivity than the (10 1 ¯ 0) one. The enhanced gas response is attributed to a large amount of oxygen vacancy defects and unsaturated dangling bonds existing in the ZnO nanosheets with exposed crystal facet (0001), which is favorable for the adsorption of gas molecular on the sensor surface and result in improvement of the gas response. Finally, the calculation of the chemisorption energy of oxygen on ZnO crystal facets also proves the reactive-facet-enhanced gas sensitivity.

One-step synthesis of uniform nanoparticles of porphyrin functionalized ceria with promising peroxidase mimetics for H2O2 and glucose colorimetric detection

Abstract: Hydrogen peroxide (H 2 O 2 ) is a key molecule in biology. As a byproduct of many enzymatic reactions, H 2 O 2 is also a popular biosensor target. We report the first use of uniform nanoparticles of porphyrin functionalized ceria (Por-Ceria) prepared by a one-step method, as a colorimetric probe in detection for H 2 O 2 . Por-ceria nanoparticles exhibited strong intrinsic peroxidase activity toward a classical peroxidase substrate, 3,3′,5,5′-tetramethylbenzidine (TMB), in the presence of H 2 O 2 . Enhanced peroxidase-like activity of Por-ceria originated from synergistic effect of porphyrin and ceria, thereby explaining the high performance of Por-Ceria as an artificial enzyme mimicking peroxidase. When coupled with glucose oxidase, glucose is detected. A detection limit of 1.9 × 10 −2 mM glucose with a linear range up to 0.15 mM.

Facile synthesis of sulfur-doped graphene quantum dots as fluorescent sensing probes for Ag+ ions detection

Abstract: Sulfur-doped graphene quantum dots (S-GQDs) with bright blue emission have been prepared by a facile one-pot hydrothermal treatment. A specific compound, 1,3,6-trinitropyrene, which has a mother nucleus structure similar with graphene, was chosen as the carbon source and 3-mercaptopropionic acid (MPA) was employed for S-doping and carboxyl groups modification. The synthesized S-GQDs were characterized by atomic force microscopy (AFM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and fluoscence (FL) spectrum. Results indicated that S-GQDs possessed single layer graphene structure with mean size of about 2.5 nm and presented an excitation-independent photoluminescence behavior with maximum excitation/emission wavelength at 360/450 nm, respectively. The sulfur-doping of GODs drastically improved their electronic and chemical properties, which afforded the S-GQDs a sensitive response to Ag + ions. Furthermore, the S-GQDs were successfully explored as a sensing probe for Ag + detection with high sensitivity and selectivity. A wide linear range of 0.1-130.0 μM with a low detection limit of 30 nM was obtained. The facile preparation method and the high performace of the as-prepared S-GQDs present promising potential for their applications in sensing, biological imaging and catalysis.

Enhanced NO2 sensing of SnO2/SnS2 heterojunction based sensor

Abstract: SnS2 nanosheets decorated with SnO2 nanocomposites have been successfully prepared by in-situ high-temperature oxidizing pristine SnS2 in air at 300 °C. The formed SnO2/SnS2 heterojunction based chemiresistive gas sensor exhibits an excellent sensitivity and selectivity to different concentrations of NO2 from 1 ppm to 8 ppm at 80 °C. The higher response of the as-fabricated SnO2/SnS2 heterojunction based sensor to NO2 compared with that of the pure SnS2 based one could be attributed to the extra charge transfer between SnO2/SnS2 interfaces.

Electrochemical sensor based on multiwalled carbon nanotube and gold nanoparticle modified electrode for the sensitive detection of bisphenol A

Abstract: A novel electrochemical sensor for bisphenol A comprising a multiwalled carbon nanotube (MWCNT) and gold nanoparticle (AuNP) composite modified glassy carbon electrode has been developed. Differential pulse voltammetric and electrochemical impedance characterisation were carried out. Modified electrode architectures with different MWCNT loadings and different numbers of deposited AuNP layers were tested, as well as the influence of pH. Under the best experimental conditions, the sensor exhibited a linear response to BPA from 0.01 μM to 0.7 μM, with a limit of detection of 4 nM, one of the lowest achieved up until now. The reproducibility, repeatability and stability of the sensor were examined and are superior to those reported in the literature using similar architectures for BPA sensors. Perspectives for an impedimetric sensor at micromolar concentrations were also assessed. Finally, the selectivity with respect to common interferents was demonstrated and practical application of the developed modified electrode for the determination of BPA in waters was successfully carried out.

Three-dimensional paper-based microfluidic chip device for multiplexed fluorescence detection of Cu2+ and Hg2+ ions based on ion imprinting technology

Abstract: In this study, a novel three-dimensional (3D) origami ion imprinted polymers microfluidic paper-based chip device for specific, sensitive and multiplexed detection of Cu2+ and Hg2+ ions has been proposed. In this device, the surface of the paper was activated by grafting with CdTe QDs through amino processing and formation of Cu2+ or Hg2+ IIPs and CdTe QDs complex that led to fluorescence quenching of QDs because the photo luminescent energy of QDs could be delivered to the complex. This method can realize the liquid phase of QDs@IIPs being transferred to the solid glass fiber paper and improve the portability of the device. Moreover, this platform allows to simultaneous detection of Cu2+ and Hg2+ ions with good selectivity and sensitivity. The proposed method reveals that the copper ion imprinted fluorescent sensor demonstrated a good linearity from 0.11 to 58.0 μg/L with the detection limit of 0.035 μg/L and the mercury ion linear range is 0.26–34.0 μg/L with detection limit of 0.056 μg/L. Importantly, this device can provide quantitative information conveniently and show great potential to be further extended to the detection of other metal ions for environmental monitoring and food safety field.

A smartphone based surface plasmon resonance imaging (SPRi) platform for on-site biodetection

Abstract: We demonstrate a surface plasmon resonance imaging platform integrated with a smartphone to be used in the field with high-throughput biodetection. Inexpensive and disposable SPR substrates are produced by metal coating of commercial Blu-ray discs. A compact imaging apparatus is fabricated using a 3D printer which allows taking SPR measurements from more than 20.000 individual pixels. Real-time bulk refractive index change measurements yield noise equivalent refractive index changes as low as 4.12 × 10−5 RIU which is comparable with the detection performance of commercial instruments. As a demonstration of a biological assay, we have shown capture of mouse IgG antibodies by immobilized layer of rabbit anti-mouse (RAM) IgG antibody with nanomolar level limit of detection. Our approach in miniaturization of SPR biosensing in a cost-effective manner could enable realization of portable SPR measurement systems and kits for point-of-care applications.

Simultaneous measurement of refractive index and temperature using a SPR-based fiber optic sensor

Abstract: A surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated. The sensor consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum. One of the dips is generated by the bare gold-coated fiber section whose wavelength resonance is tuned by the refractive index and temperature of the surrounding medium. The other dip that is exclusively used to monitor the temperature variations of the liquid sample, whose central wavelength at 900 nm corresponds to PDMS refractive index at 20 °C, is produced by the polymerized gold-coated fiber section. The high refractive index and temperature sensitivity achieved, 2323.4 nm/RIU and −2.850 nm/°C respectively, the small size, the ease fabrication process, and the bio-compatibility of the proposed device are appealing characteristics that makes it ideal for practical bio-sensing applications.

Thermal stability of WS2 flakes and gas sensing properties of WS2/WO3 composite to H2, NH3 and NO2

Abstract: We report on the fabrication and on the morphological, structural, chemical and the electrical characterization of WS2 thin films sensors prepared by drop casting a commercial solution of dispersed few-layers WS2 flakes on Si3N4 interdigitated substrates and annealing the films in air at 150 °C, 250 °C and 350 °C. Thermal stability of WS2 in air at different annealing temperatures has been investigated by X-ray photoemission spectroscopy, scanning electron microscopy, X-ray diffraction and by simultaneous thermal analysis techniques. We found that WS2 is not stable in air and partially oxidizes to amorphous WO3 in the annealing temperature range 25 °C–150 °C. The oxidation of WS2 in air at 250 °C and 350 °C yields a composite crystalline WS2/WO3 hierarchical structure characterized by the presence of surface oxygen and sulphur vacancies. The contribution of each phase of the WS2/WO3 composite to the overall chemoresistive gas response utilizing H2 (1–10 ppm), NH3 (1–10 ppm) and NO2 (40 ppb–1 ppm) gases in dry air carrier is presented and discussed. WS2/WO3 composite films show excellent gas sensing properties to reducing (H2, NH3) as respect to oxidizing (NO2) gases at 150 °C operating temperature. In this work we found low detection limits of 1 ppm H2, 1 ppm NH3 and 100 ppm NO2 in dry air carrier, among the smallest so far ever reported for transition metal dichalcogenides. Furthermore, the sensor doesn’t show any cross sensitivity effects to both H2 and NH3 when exposed to water vapor. Outstanding reproducibility responses, by exposing the 150 °C annealed film to dynamic and cumulative gas pulses where obtained utilizing H2 gas.

Ultrasensitive NO2 gas sensing based on rGO/MoS2 nanocomposite film at low temperature

Abstract: In this paper, both reduced graphene oxide (rGO) and rGO/molybdenum disulfide (MoS2) composite films serving as sensing layers were prepared for nitrogen dioxide (NO2) gas detection at low operation temperature, wherein multiple characterization techniques containing TEM, XRD, XPS and Raman were employed. The experimental results showed that rGO/MoS2 composite film possessed a larger exposure area, more sorption sites and a mass of p–n heterojunctions, thereby resulting in a sensing response of 59.8% toward 2 ppm NO2 at 60 °C (optimal operation temperature), which was nearly 200% enhanced in comparison with bare rGO one. Furthermore, we investigated the role of rGO or MoS2 material in the sensing performance as well as the effect of different MoS2 introduction manners. Apart from these, relative humidity was found to pose a small interfering impact on NO2 response, while long-term stability on exposure to 120 ppb NO2 revealed a small response decay after several weeks. Moreover, the composites showed an excellent selectivity toward NO2 gas against other interfering gas species. Through further exploration of ppb-level NO2 detection, the detection limit was calculated to be as low as 5.7 ppb.

A reversible “turn-on” fluorescent sensor for selective detection of Zn2+

Abstract: A novel Schiff-base oxime sensor H2L with the ONON chelating moieties was designed and synthesized based on condensation reaction. Different methods such as elemental analyses, FT-IR, 1H and 13C NMR were fully utilized in characterizing the structure of sensor H2L. The UV–vis spectra of the Zn2+ complex exhibit four clear isosbestic points which may be assigned to the ONON moieties binding to Zn2+. Sensor H2L operates on the CHEF and PET mechanisms, and the tendency of Zn2+ to strongly enhance fluorescence of sensor H2L was explored. Fluorescence measurements show that sensor H2L has excellent fluorescent selectivity for Zn2+ over many other metal ions based on intramolecular charge-transfer, and the results demonstrate that the binding between sensor H2L and Zn2+ is chemically reversible. The crystal structure of the Zn2+ complex has been characterized by X-ray crystallography.