Showing papers in "Sensors and Actuators B-chemical in 2020"

Evolution of breath analysis based on humidity and gas sensors: Potential and challenges

Abstract: Breath analysis is an attractive strategy that holds tremendous potential to achieve non-implantable physical health management enabled by flexible humidity sensors for breathing behaviors (e.g., continuity, frequency) related to disease monitoring and chemiresistive gas sensors related early disease diagnosis. Compared to other techniques for breath component detection, non-invasive breathing diagnostics based on chemical sensors can offer several advantages like miniaturization, low power consumption, simple structure and cost-saving, which is helpful to enhance the portability of practical tests. Although extensive research has been carried out over the past two decades to improve sensing performances of breath gas sensors, many problems need to be further addressed when it comes to clinical disease diagnosis. Developing integrated gas sensor arrays have become one of the efficient solutions to improve detection accuracy. To get rid of external power supply, various novel sensors combining with self-powered technology are designed to exhibit a desirable development prospect in breath analysis. Thus, this review aims to summarize the latest research advances on wearable humidity-enabled breathing behaviors monitoring and typical biomarker gases-based disease screening, and also provides the prospects of future development from individual sensors to integrated devices and self-powered health monitoring systems.

CoOOH nanosheets-coated g-C3N4/CuInS2 nanohybrids for photoelectrochemical biosensor of carcinoembryonic antigen coupling hybridization chain reaction with etching reaction

Abstract: A signal-on photoelectrochemical (PEC) biosensor was successfully established for the sensitive monitoring of carcinoembryonic antigen (CEA) by using copper indium disulfide-sensitized graphitic-like carbon nitride (g-C3N4/CuInS2) as the photosensitive material and cobalt oxyhydroxide (CoOOH) as the light-blocking material, coupling target-triggered hybridization chain reaction (HCR) with hydrolysate-induced dissolution/etching of CoOOH nanosheets. Initially, a sandwiched reaction occurred between capture aptamer-conjugated magnetic bead and trigger aptamer in the presence of CEA. Then, the carried trigger aptamer initiated HCR between two hairpin sequences to produce long double-helix strand for capturing alkaline phosphatase. The generated ascorbic acid reduced/etched CoOOH nanosheets into divalent cobalt ions, which decreased the amount and thickness of CoOOH and exposed the underlying g-C3N4/CuInS2, thus leading to a distinct increase in the photocurrent. Under optimum conditions, PEC sensor showed high sensitivity toward CEA with a dynamic range of 0.02−40 ng mL−1 and a detection limit of 5.2 pg mL−1. Also, it possessed favorable selectivity, high stability as well as good precision. The accuracy of PEC approach was well consistent with commercial CEA ELISA kit. These exceptional analytical performances of PEC biosensor indicated that it might have a broad application prospect in the diagnosis of CEA.

Oxygen vacancy defects engineering on Ce-doped α-Fe2O3 gas sensor for reducing gases

Abstract: Surface oxygen vacancy defects (OV) are regarded to be beneficial to the gas sensing behavior by significantly improving the carrier density and providing more oxygen adsorption sites. In this work, Ce-doped α-Fe2O3 composites with abundant OV defects were synthesized using an oil bath method assisted with annealing treatment. Morphological characterization results indicate that the lamellar architecture of α-Fe2O3 is transformed to nanospheres composed of massive nanoparticles with small sizes (7–9 nm) after introducing Ce elements. Gas sensing results show that the FeCe10 (Fe/Ce = 10:1) sensors exhibit enhanced acetone sensing response of 26.3–100 ppm gas at the operating temperature of 220 °C toward that of pure α-Fe2O3. Most importantly, X-ray photoelectron spectroscopy and electron spin resonance spectroscopy results confirm that the sensing responses of Ce-doped α-Fe2O3 sensors are directly related to the OV defects, that is, the larger the quantity of the OV defects, the higher the sensing response. The unpaired electrons trapped in OV defects can provide more active sites for adsorption of oxygen and acetone molecules, resulting in a thicker depletion layer and a higher potential barrier. Our work highlights the decisive role of OV defects in gas sensors, which can also provide a rational approach to boost the sensing performance.

Size-controllable Fe-N/C single-atom nanozyme with exceptional oxidase-like activity for sensitive detection of alkaline phosphatase

Abstract: Nanozymes become currently a frontier of chemical research. However, exploiting a novel nanozyme with high activity, good stability and reproducibility is challenging. Here, size-controllable Fe-N/C nanozymes containing exclusive single Fe atoms coordinated Fe-Nx sites were succesfully prepared through a facile pyrolysis of size controllable Fe-Zn ZIFs precursors. The Fe-N/C nanozymes exhibit exceptional high oxidase-mimicking activity able to catalyze oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) by dissolved oxygen to generate blue product. Their catalytic activities can be regulated by modulating the molar ratios of methanol to metal salts (e.g., Fe and Zn) through which the size controllable Fe-Zn ZIFs precursors are obtained. Upon introduction of ascorbic acid (AA) into Fe-N/C/TMB system, complete inhibition of TMB oxidation was observed, resulting in significant decline in absorbance with a clear color change. In the presence of alkaline phosphatase (ALP), ascorbic acid 2-phosphate (AAP) is hydrolyzed to produce AA. When coupled with AAP, a novel colorimetric biosensor platform was fabricated for ALP activity screening in the range of 0.05 U/L-100 U/L (four orders of magnitude) with an ultra-low limit of detection of 0.02 U/L. The work provides a promising strategy to rationally design the transition metal-N/C single-atom nanozyme with high oxidase-like activity.

W18O49/Ti3C2Tx Mxene nanocomposites for highly sensitive acetone gas sensor with low detection limit

Abstract: The development of gas sensor that is capable of detecting ppb-level detection of acetone and possesses high response toward low-concentration acetone remains a great challenge. Herein, we present the construction of the W18O49/Ti3C2Tx composites based on the in situ grown of the 1D W18O49 nanorods (NRs) on the surfaces of the 2D Ti3C2Tx Mxene sheets via a facile solvothermal process. The W18O49/Ti3C2Tx composites exhibit high response to low concentration acetone (11.6 to 20 ppm acetone), ideal selectivity, long-term stability, very low limit of detection of 170 ppb acetone, and fast response and recover rates (5.6/6 s to 170 ppb acetone). Compared to the W18O49 NRs and Ti3C2Tx sheets, the W18O49/Ti3C2Tx composites show significant improvement on the acetone-sensing performance, which can be ascribed to the homogeneous distribution of the W18O49 NRs on the Ti3C2Tx surface, the removal of the fluorine-containing groups from the Ti3C2Tx after the solvothermal process, and the synergistic interfacial interactions between the W18O49 NRs and the Ti3C2Tx sheets. The synthesis of the 1D/2D W18O49/Ti3C2Tx Mxene composites provides a new avenue to develop other promising hybrids for acetone sensing.

Design of highly porous SnO2-CuO nanotubes for enhancing H2S gas sensor performance

Abstract: Highly porous SnO2-CuO hollow nanofiber mats were synthesized by electrospinning combined with thermal processing for high performance H2S gas sensing applications. The porous morphology generated in the one-dimensional (1-D) nanocomposite led to an improvement in surface-to-adsorbate molecule interactions. Our novel concept lies in fabrication of SnO2-CuO with a 1-D highly porous structure by electrospinning coupled with generation of hollow nanostructures drawing on nanofiber-to-nanotube transformation affected by Kirkendall effect during thermal processing. The fibrous structure was synthesized by electrospinning with mixed solution of Sn and Cu precursors, which then underwent heat treatment under various temperature conditions. The hollow structures were generated based on the different diffusion rates between SnO2-CuO and Sn/Cu. The SnO2-CuO nanotubes have low operating temperatures and high H2S sensing performance. The increased surface area for detecting H2S resulted in great enhancement of the response (Ra/Rg = 1395) and a very fast response time of 5.27 s with a stable recovery time to a low concentration of H2S to 5 ppm at 200 °C. The porous SnO2-CuO hollow nanofiber gas sensor proved to be a promising candidate for gas sensor systems due to increased surface area with metal oxide catalyst. The mechanisms involved in enhancement of gas response and extended applications are also discussed.

A chemically modified laser-induced porous graphene based flexible and ultrasensitive electrochemical biosensor for sweat glucose detection

Abstract: Porous laser-induced graphene (LIG) is an attractive and promising carbon material for electrochemical applications because it can immobilize various proteins, such as enzymes, antibodies, and receptors. However, poor inherent electrical properties caused by low surface conductivity is still a critical drawback for various applications. Here, we have proposed a surface modification method for the LIG electrode using acetic acid treatment via facile and practicable dipping technique. This simple acetic acid treatment dramatically increased the ratio of carbon-carbon bonds which effectively increased conductivity and decreased sheet resistance. In other words, acetic acid additionally reduced carbohydrate functional groups. Importantly, these unique properties also facilitated the stable and uniform dispersion of highly catalytic Pt nanoparticles (PtNPs) on LIG by avoiding the concentration of electric field on nanoparticles that can cause aggregation during electrodeposition. Finally, chitosan-glucose oxidase (GOx) composite was successfully immobilized onto the LIG/PtNPs electrode to fabricate a sweat glucose biosensor. The as-prepared LIG/PtNPs electrode exhibited a high sensitivity of 4.622 μA/mM as well as an ultra-low limit of detection (signal to noise ratio is 3) which was less than 300 nM and dynamic linear range up to 2.1 mM. Furthermore, we tested the variation of blood glucose level before and after meal using the amperometric response of the sensor which demonstrates the commercial potential of this unique sweat glucose biosensor.

3D-Printed graphene/polylactic acid electrode for bioanalysis: Biosensing of glucose and simultaneous determination of uric acid and nitrite in biological fluids

Abstract: Additive manufacturing, also known as 3D-printing, is receiving great interest by chemists due to the easy design of novel materials, fast prototyping and reducing waste, which enables large-scale fabrication of electrochemical devices. Herein we demonstrate the development of (bio)sensors for the analysis of biological fluids using 3D-printing. Fused deposition modelling was used to fabricate (bio)sensing platforms from commercially-available filaments made of polylactic acid containing graphene (G-PLA). An enzymatic glucose biosensor fabricated on the G-PLA surface was developed and applied for glucose sensing in blood plasma using chronoamperometry. Oxygenated groups from the polymeric matrix provides suitable condition to enzyme immobilization by crosslinking with glutaraldehyde. The biosensor presented a limit of detection (LOD) of 15 μmol L−1, inter-day and intra-day precision lower than 5 %, and adequate recovery values (90–105 %) for the analysis of plasma. We also show that the surface treatment of the 3D-printed sensor (mechanical polishing followed solvent immersion) provides improved electrochemical properties for the direct detection of nitrite and uric acid. Differential-pulse voltammetry and multiple-pulse amperometry under flow conditions were evaluated and compared for the determination of both species in saliva and urine. Highlights are presented for the amperometric detection within a linear range from 0.5–250 μmol L−1 for both analytes, LODs of 0.02 and 0.03 μmol L−1 for uric acid and nitrite, respectively, and high precision (RSD

Metal-Organic frameworks-derived bamboo-like CuO/In2O3 Heterostructure for high-performance H2S gas sensor with Low operating temperature

Abstract: Hydrogen sulfide (H2S) sensors with excellent response and selectivity are in great demand to monitor its concentration changes in the real environment, especially at an ultra-trace level. This work presents a metal-organic framework (MOF)-derived metal oxide prepared via the solvothermal method and the developed sensors based on such materials exhibits enhanced gas-sensing performance. The bamboo-like CuO/In2O3 derived from Cu2+-impregnated CPP-3 were investigated through structural analyses, and it confirms that the n-type In2O3 and p-type CuO were successfully combined and heterojunctions were formed at CuO/In2O3 interfaces. The gas-sensing properties of CuO/In2O3 towards H2S were evaluated, and the sensor based on CuO/In2O3 with 3.5 wt% of Cu to CPP-3(In) is found to exhibit excellent H2S response (Rair/Rgas = 229.3–5 ppm), which are 8.5 times higher than that of with pristine In2O3. It also discloses low detection limits (200 ppb), low operating temperature (70 °C) and superior selectivity against other interfering gases. The gas sensing mechanism is thoroughly discussed and CuO/In2O3 could be considered as a novel and promising material for the practical application to selectively detect H2S at low operating temperature.

Ultrasensitive flexible NH3 gas sensor based on polyaniline/SrGe4O9 nanocomposite with ppt-level detection ability at room temperature

Abstract: Detection limit as an important parameter of gas sensors, much effort has been devoted to developing high-performance gas sensors with low detection limit. However, the development of gas sensors with ppt-level detection limit still faces enormous challenges. In this work, a flexible and ultra-highly sensitive ammonia (NH3) sensor based on polyaniline/SrGe4O9 nanocomposites (PSN) was successfully fabricated via a facile in situ chemical oxidation polymerization method. When exposed to 0.2–10 ppm NH3 at 25 °C in 60% relative humidity (RH), the PSN sensor showed larger sensitivity (20.59% ppm−1) than that of PANI sensor (9.82% ppm−1). The response of the PSN sensor (16%) was two-fold higher than that of the PANI one (8%) to 0.2 ppm NH3 at room temperature. Meanwhile, the response time of the PSN sensor (24 s) was reduced to up to a third of that of the PANI sensor (64 s) for 800 ppb NH3. Additionally, the flexible PSN sensor exhibited good reproducibility, satisfactory long-term stability, excellent selectivity and outstanding flexibility to NH3 at room temperature. Significantly, the PSN sensor presented the ultra-low detection limit of 250 ppt toward NH3. Such outstanding gas-sensing properties were attributed to the unique hierarchical architecture with abundant mesoporous and the formation of p-n heterojunction at the interface between p-type PANI and n-type SrGe4O9. This research provides new strategies for developing high-performance NH3 sensors with supersensitive and ultra-low detection limit.

Ultra-sensitive molecularly imprinted electrochemical sensor for patulin detection based on a novel assembling strategy using Au@Cu-MOF/N-GQDs

Abstract: This study introduces an innovative procedure for the development of a molecularly imprinted electrochemical sensor for ultra-sensitive and selective detection of patulin. Firstly, the surface of a glassy carbon electrode (GCE) was decorated by nitrogen doped graphene quantum dots (N-GQDs) and AuNPs-functionalized Cu-metal organic framework (Au@Cu-MOF) and then a layer of molecularly imprinted polymer (MIP) was grown on Au@Cu-MOF/N-GQDs/GCE by electropolymerization. Electrochemical techniques were used to characterize and study the electrochemical behavior of the MIP/Au@Cu-MOF/N-GQDs/GCE, which exhibited a stable reference peak of Au@Cu-MOF at −0.11 V after elution of patulin molecules. This peak current density decreased with rebinding of patulin molecules therefore it was considered as indicator signal. The designed MIP sensor presented a wide linear range from 0.001 to 70.0 ng mL−1, and a low detection limit (0.0007 ng mL−1). This newly developed method based on the synergistic effects of N-GQDs and Au@Cu-MOF combined with MIP technique offered outstanding selectivity, sensitivity, stability, and reproducibility. The good accuracy (recovery%, 97.6–99.4) and high precision (RSD%, 1.23–4.61) of this sensing system for analysis of apple juices proved the high potential of it for rapid and low cost determination of patulin compared to chromatographic methods.

Smartphone-based portable electrochemical biosensing system for detection of circulating microRNA-21 in saliva as a proof-of-concept

Abstract: Circulating microRNAs (miRNAs) are effective cancer biomarkers that are highly stable in body fluids enabling noninvasive detection. Portable, low-cost and efficient biosensing systems is crucial for early on-site diagnosis, especially in resource-limited settings. Present work deals with the development of a smartphone-based biosensing system for electrochemical detection of circulating microRNA-21 (miR-21) biomarker in saliva as a proof-of-concept. The smartphone-based biosensing system composed of a disposable screen-printed biosensor modified with reduced graphene oxide/gold (rGO/Au) composite, a circuit board for detection and a Bluetooth-enabled smartphone equipped with specially designed Android application. The hybridization between miR-21 target and ssDNA probe on the rGO/Au-modified electrode resulted in the decrease in peak current with increase in miR-21 target concentration. The smartphone-based biosensing system showed comparable performance with commercial electrochemical workstation, for miR-21 detection in the concentration range of 1 × 10−4 M to 1 × 10-12 M with correlation coefficient (r2) of 0.99. In addition to good selectivity in discriminating mismatched and non-target sequences, the biosensing system also showed acceptable recovery rate ranging from 96.2%–107.2 % in spiked artificial saliva. The smartphone-based biosensing system is envisioned to be able to realize rapid and highly sensitive detection of circulating miRNA biomarker in body fluid for point-of-care testing in remote areas.

High-performance acetone gas sensor based on Ru-doped SnO2 nanofibers

Abstract: We report the Ru doping effect on the gas-sensing properties of SnO2 nanofibers for acetone detection in this paper. For this purpose, pure and 1, 2, 3 mol% Ru-doped SnO2 nanofibers were prepared through electrospinning technique combined with calcination treatment. The fibrous microstructure of these nanofibers were maintained and the grain size of the SnO2 nanoparticals were decreased from 9.2 nm (pure) to 5.1 nm (3% Ru-doped) after Ru doping. In order to confirm that Ru doping is an effective way to improve the gas sensing properties of the SnO2-based gas sensor, the gas sensing properties of the sensors based on pure and Ru doped SnO2 nanofibers were investigated systematically. The results showed that the response to 100 ppm acetone of 2 mol% Ru-doped SnO2 nanofibers was 118.8, which was 12 times higher than that of pure SnO2 nanofibers. In the end, the role of Ru in the gas sensing mechanism of SnO2 nanofibers was analyzed according to the results of the X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoelectron spectroscopy (UPS).

Smart colorimetric sensing films with high mechanical strength and hydrophobic properties for visual monitoring of shrimp and pork freshness

Abstract: During recent years the use of smart colorimetric packaging films for monitoring food freshness has received widespread attention. However, their poor mechanical strength and hydrophilic properties are the major problems hindering the large-scale application. Here, we employed biodegradable cellulose and naphthoquinone dyes extracted from Arnebia euchroma (AENDs) to fabricate a novel colorimetric sensing film with high tensile strength of 227 MPa and hydrophobic properties (water contact angle of 112.2°) for real-time monitoring of the freshness of shrimp and pork. In addition, the effectiveness of the sensing film in detecting the freshness of shrimp and pork under 20 °C, 4 °C and-20 °C conditions was confirmed by measuring the total volatile basic nitrogen (TVBN) and total viable count (TVC). Visual observation confirmed that the sensing film clearly changed from rose-red to purple, then to bluish violet providing a good indication of spoilage, which correlated well with TVBN and TVC content in shrimp and pork measures by standard lab procedures. The colorimetric sensing film developed here would be promising in fabricating high mechanical strength and hydrophobic properties smart labels for visual monitoring the freshness of shrimp and pork.

Toward agricultural ammonia volatilization monitoring: A flexible polyaniline/Ti3C2Tx hybrid sensitive films based gas sensor

Abstract: The monitoring of ammonia (NH3) produced in agricultural fields is of great importance due to its huge threat to ecological environment and human health, yet routine monitoring technologies rely on manual completion and complex agricultural environment brings great challenges to the application feasibility of gas sensors. Herein, a flexible chemiresistive gas sensor based on polyaniline (PANI)/Ti3C2Tx hybrid sensitive films is developed toward agricultural NH3 volatilization monitoring. The hybrid film was deposited on the flexible polyimide substrate by an in-situ self-assembly method. The sensor shows high sensitivity, low detection limit, excellent repeatability, high selectivity and good air stability, which could be attributed to the gas-sensing enhancement effects of PANI/Ti3C2Tx Schottky junction and improved protonation degree of PANI in the hybrids. Especially, the sensor exhibits excellent NH3-sensing properties to 20–80 % relative humidity (RH) environments at a temperature range of 10–40 ℃, making it promising for practical agricultural applications. Furthermore, the application feasibility of the sensor to ammonia volatilization monitoring is verified through agricultural simulation experiments. This work provides a fast and accurate gas sensor methodology toward unattended agricultural application, which is an important supplement to the existing technical methods and may greatly pushes forward the development of modernized intelligent agriculture.

Halloysite nanotubes: Natural, environmental-friendly and low-cost nanomaterials for high-performance humidity sensor

Abstract: Benefiting from the development of nanomaterials synthesis technology, the performance of many electronic devices, including humidity sensors, has been improved greatly. However, the synthesis of nanomaterials usually involves complex processes, expensive raw materials and even toxic reagents. Herein, the natural nanomaterials of halloysite nanotubes (HNTs) are deliberately selected for the fabrication of high-performance humidity sensor. Characterization results show that the HNTs have good hydrophilicity, hollow tubular nanostructure and large specific surface area, which contribute to humidity sensing performance of the humidity sensor. Further, the humidity sensor based on HNTs is fabricated and its humidity sensing properties are tested at the room temperature (25 °C). The results show that the impedance variation of the HNTs humidity sensor is five orders of magnitude within the humidity range from 0% to 91.5% relative humidity (RH) at the optimum working frequency (100 Hz), and its response time is only about 0.7 s. Notably, the HNTs humidity sensor exhibits wide humidity detection range of 0–91.5% RH, very low RH (7.2%) response characteristic and good linear responses at 0–28.8% and 28.8–91.5% RH. This work provides a simple, low-cost and environmental-friendly strategy for fabricating high-performance humidity sensor by exploring the natural nanomaterials like HNTs.

MIPs for commercial application in low-cost sensors and assays - An overview of the current status quo

Abstract: Molecularly imprinted polymers (MIPs) have emerged over the past few decades as interesting synthetic alternatives due to their long-term chemical and physical stability and low-cost synthesis procedure. They have been integrated into many sensing platforms and assay formats for the detection of various targets, ranging from small molecules to macromolecular entities such as pathogens and whole cells. Despite the advantages MIPs have over natural receptors in terms of commercialization, the striking success stories of biosensor applications such as the glucose meter or the self-test for pregnancy have not been matched by MIP-based sensor or detection kits yet. In this review, we zoom in on the commercial potential of MIP technology and aim to summarize the latest developments in their commercialization and integration into sensors and assays with high commercial potential. We will also analyze which bottlenecks are inflicting with commercialization and how recent advances in commercial MIP synthesis could overcome these obstacles in order for MIPs to truly achieve their commercial potential in the near future.

Structural hybridization of bimetallic zeolitic imidazolate framework (ZIF) nanosheets and carbon nanofibers for efficiently sensing α-synuclein oligomers

Abstract: A high-efficiency sensing system for α-synuclein (α-Syn) oligomers was designed based on a novel one dimensional (1D)/2D structural nanohybrid (denoted as CoMnZIF@CNF) of CoMn-based zeolitic imidazolate framework nanosheets (CoMnZIF NSs) vertically grown around carbon nanofibers (CNFs). CNFs were prepared by calcining electrospun polyacrylonitrile under Ar/H2 atmosphere and used as the template for CoMnZIF synthesis, which can remarkably enlarge the electrochemical signal of the CoMnZIF@CNF nanohybrid. The series of CoMnZIF@CNF nanohybrids were modulated by changing the ratios of precursors Co(NO3)2 and Mn(NO3)2 (i.e. 3:1, 1:1, and 1:3), leading to optimized sensing performances of α-Syn oligomers. Owing to the hierarchical nanostructure, good biocompatibility, and strong bioaffinity, the α-Syn oligomer aptamer can be strongly anchored over the CoMnZIF@CNF nanohybrid. Although the three CoMnZIF@CNF nanohybrids show comparable electrochemical activity, the CoMnZIF@CNF(1–3)-based aptasensor exhibits the superior sensing performance to other CoMnZIF@CNF nanohybrids and reported MOFs, giving a low detection limit of 0.87 fg mL−1 (45.7 fM) within the concentration of α-Syn oligomers rangefrom 1 fg mL−1 (52.6 fM) to 0.2 ng mL−1 (0.1 nM). The aptasensor based on CoMnZIF@CNF also has excellent selectivity, stability, reproducibility, and usability for the detection of α-Syn oligomersin human serum. The efficient strategy of structural hybridization can be used in designing different aptasensors and further extend the application range of ZIFs materials.

Visible-light activated room temperature NO2 sensing of SnS2 nanosheets based chemiresistive sensors

Abstract: The visible-light activated gas sensor has been successfully fabricated for detecting NO2 by using two dimensional (2D) structured SnS2 nanosheet as the chemiresistive sensing material. Under the light illumination, the SnS2 nanosheet based chemiresistive gas sensor exhibits a high response and excellent selectivity to NO2 at room temperature. Influences of light wavelength, light intensity, operating temperatures and humidity on the sensing characteristics are investigated in details. It suggests that photo-energy activation can effectively activate the SnS2 sensor and the green light is the most effective to achieve superior sensing property of the SnS2 sensor at room temperature in terms of the excellent sensitivity and a better response/recovery speeds. The sensor also demonstrated an excellent selectivity to NO2 over several possible interferants such as SO2, CO2, NH3, acetone, methanol, ethanol and formaldehyde, and a good stability for about six months activated by the green light. The sensing mechanism is intimately related to the extra photo-generated electrons which subsequently attract more NO2 at its 2D surface. A simple Langmuir - Hinshelwood dynamics model is proposed to explain the effect of the visible light irradiation on the absorption/desorption speed of gas molecules.

Ultrathin two-dimensional metal-organic framework nanosheets decorated with tetra-pyridyl calix[4]arene: Design, synthesis and application in pesticide detection

Abstract: Chemical pesticides are highly toxic and widely spread as environmental pollutants. New strategies are being developed to selectively and sensitively detect pesticides. Herein, we prepared ultrathin two-dimensional (2D) metal-organic framework (MOF) nanosheets, decorated with tetra-pyridyl calix[4]arene, for determination of pesticide based on host-guest chemistry. The 3D layered MOF {[Cd2(5-NO2-BDC)2L(MeOH)]∙2MeOH}n (MOF-Calix; 5-NO2-H2BDC = 5-nitro-1,3-benzenedicarboxylic acid; L = 25,26,27,28-tetra-[(4-pyridylmethyl)oxy]calix[4]arene) was elaborately constructed, with features of 2D layered structure that are held together by weak π…π interactions. Due to the cup-shaped characteristic of calix[4]arene ligand and easy-to-departure MeOH molecules in the interspaces of the 2D layers in MOF-Calix, the 3D bulk MOF-Calix can be readily exfoliated into ultrathin single (2.20 nm) or double-layer (3.73 nm) of 2D nanosheets by ultrasound method with high efficiency. We take the intrinsic advantages of calix[4]arene and the highly accessible active site of calix[4]arene on the surface of the 2D MOF-Calix nanosheets for selective and sensitive sensing of glyphosate via fluorescence enhancement effect with a detection limit of 2.25 μM. This work demonstrates the simple preparation of a 2D MOF nanosheet as fluorescent sensor for glyphosate detection.

Simultaneous determination of ascorbic acid, dopamine, and uric acid using graphene quantum dots/ionic liquid modified screen-printed carbon electrode

Abstract: In this work, graphene quantum dots (GQDs) and ionic liquid (IL) modified screen-printed carbon electrode (GQDs/IL-SPCE) were introduced for the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). GQDs were synthesized by directly pyrolyzing citric acid and then dropped onto the surface of IL-SPCE, which was prepared by screen-printing the mixture of IL and carbon ink on a portable substrate. UV–vis spectrophotometry, fluorescence spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to characterize the synthesized GQDs and the modified electrodes. The GQDs/IL-SPCE exhibited excellent electrocatalytic activity for the oxidation of AA, DA, and UA in the mixture solution. Moreover, the anodic peak responses of these three analytes were also resolved into three well-defined peaks. Under the optimized conditions, the linear response ranges for AA, DA, and UA were 25–400 μM, 0.2–10 μM, and 0.5–20 μM, respectively, with low detection limits (σ/N = 3) of 6.64 μM, 0.06 μM, and 0.03 μM, respectively. The proposed sensor exhibited high sensitivity, low cost and successfully applied for the simultaneous detection of AA, DA, and UA in pharmaceutical products and biological samples.

Measurement of temperature and relative humidity in exhaled breath

Abstract: Temperature and relative humidity are two of the most important variables in breath analysis. Several studies have investigated the temperature range of exhaled breath, mostly in the context of respiratory disease diagnostics, but none of them inspected the correlation with clinical parameters, nor the effect of different geographic locations. In this study, we have built a tailor-made device for measuring temperature and relative humidity in exhaled breath. With it, we have carried out 340 measurements (265 in Paris/France and 75 in Haifa/Israel) from 31 participants. The results show that the temperature range of exhaled breath is 31.4-35.4 °C for Haifa’s participants and 31.4-34.8 °C for Parisian participants and the range of exhaled breath relative humidity is 65.0-88.6% and 41.9-91.0% for Haifa and Paris participants, respectively. Clinical and environmental effects were also inspected to give more information on the confounding factors. The results presented in this study contribute to the definition of the ranges of temperature and relative humidity of exhaled breath in individuals, in addition to their correlation with clinical and environmental factors such as gender, BMI and age. These factors must be taken into consideration in order to increase the reproducibility and reliability of a wide variety of measurements in this particular field.

A Ratiometric Electrochemical Sensor for Simultaneous Detection of Multiple Heavy Metal Ions Based on Ferrocene-Functionalized Metal-Organic Framework

Abstract: It is a significant and challenging task to simultaneously detection of multiple heavy metal ions with convenience, sensitivity and reliability. Herein, a novel ratiometric electrochemical sensing method was established for the simultaneously detection of three main heavy metal ion pollutants (Cd2+, Pb2+ and Cu2+). The sensing platform was constructed by a composite of ferrocenecarboxylic acid functionalized metal-organic framework (MOF), Fc-NH2-UiO-66, and thermally reduced graphene oxide (trGNO), which was designated as trGNO/Fc-NH2-UiO-66. NH2-UiO-66 has porous structure and large specific surface area, which is beneficial to the adsorption and preconcentration of heavy metal ions. The introduction of trGNO and Fc improves the conductivity and electrochemical activity of the MOF material. Moreover, the signal of Fc can be used as internal reference to develop ratiometric detection, which greatly improves the reproducibility and reliability of electrochemical detection. Based on this ratiometric electrochemical sensing platform, the simultaneous, sensitive and reliable detection of Cd2+, Pb2+ and Cu2+ was realized. This work provides a new sensing platform for simultaneous detection of multiple heavy metal ions and greatly expands the application of UiO-66-type MOFs in electrochemical field.

An electrochemical aptasensor based on gold-modified MoS2/rGO nanocomposite and gold-palladium-modified Fe-MOFs for sensitive detection of lead ions

Abstract: In this work, an electrochemical aptasensor was proposed by using gold-modified molybdenum disulfide/reduced graphene oxide (Au@MoS2/rGO) nanocomposite and gold-palladium (AuPd)-modified MIL-88 (Fe) metal-organic frameworks (AuPd@Fe-MOFs) for sensitive detection of lead ions (Pb2+). The 8–17 DNAzyme consisting of a substrate strand (Apt1) and a catalytic strand (Apt2) was used to construct the aptasensor. Au@MoS2/rGO nanocomposite was applied as the sensing platform to immobilize the mercapto-group-labeled Apt1. Meanwhile, AuPd@Fe-MOFs was employed to label Apt2, which showed excellent catalytic ability toward H2O2. In the presence of Pb2+, the Apt1 of the DNAzyme was catalytically cut off, decreasing the amount of AuPd@Fe-MOFs. The current response was correlated to the Pb2+concentration, thereby achieving Pb2+ detection. Under the optimal experimental conditions, the fabricated aptasensor showed a highly linear response for Pb2+ in the range from 5.0 pmol/L to 2.0 μmol/L, with a detection limit of 0.07 pmol/L. Additionally, the proposed electrochemical aptasensor exhibited excellent selectivity, stability and reproducibility. Moreover, the proposed aptasensor demonstrated good performance in real water sample analysis, making it promising for use in Pb2+ detection in environmental monitoring.

ZnSe quantum dot based ion imprinting technology for fluorescence detecting cadmium and lead ions on a three-dimensional rotary paper-based microfluidic chip

Abstract: In this study, a newly fluorescent ZnSe quantum dots (QDs) with ion imprinting technology was firstly realized on the three-dimensional (3D) rotary paper–based microfluidic chip platform which can be used to realize specific and multiplexed detection of Cadmium ions (Cd2+) and Lead ions (Pb2+). Compared to CdTe quantum dots, ZnSe quantum dots are less toxic and more environmental friendly. In addition, this design improved the portability of the device by transferred the liquid phase of ZnSe QDs@ion imprinted polymers to solid glass fiber paper. Moreover, the 3D rotary microfluidic chip (μPADs) showed great advantages including low cost, simple and fast facile operation, multiplexed detection, and showed good sensitivity and selectivity. Under optimal experiment conditions, our proposed method was enabled to realize specific and multi-channel determination of Cd2+ and Pb2+ ions. The developed sensor of Cd2+ μPADs provided a linear response from 1 to 70 μg/L with a lower detection limit of 0.245 μg/L, and Pb2+ μPADs provided a linear response from 1 to 60 μg/L with a lower detection limit of 0.335 μg/L, respectively. Excitingly, this newly designed 3D rotary μPADs exhibited quantitative information conveniently, which showed the promising application prospects to rapid testing target metal ions in environmental in the future.

MoS2 hybrid heterostructure thin film decorated with CdTe quantum dots for room temperature NO2 gas sensor

Abstract: Molybdenum disulfide (MoS2) is a very promising candidate for room temperature (RT) gas sensing applications. However, the limitation of synthesis techniques, incomplete recovery, and selectivity at RT are prime drawbacks. In this report, MoS2 nanoworms (NWs) thin film and CdTe quantum dots (QDs) decorated MoS2 NWs hybrid heterostructure thin film (CdTe QDs/MoS2 NWs) have been fabricated by scalable sputtering technique on the p-Si substrate and tested for RT NO2 gas sensing applications. The proposed CdTe QDs/MoS2 NWs hybrid heterostructure thin film sensor manifests an excellent sensor response (∼40 %), fast response time = 16 s, complete recovery (recovery time = 114 s) and highly selective towards 10 ppm NO2 at room temperature in comparison to pristine MoS2 NWs thin film sensor (response ∼26 %, response/recovery time ∼23 s/incomplete recovery). This superior gas sensing performance may be attributed to the combined effect of factors such as hybrid heteronanostructure with unique morphology, catalytic activity, synergistic effects, and p-n heterojunctions. The approach employed here may lead to the development of RT operable MoS2-based heterojunction gas sensors.

Wearable electrochemical biosensor based on molecularly imprinted Ag nanowires for noninvasive monitoring lactate in human sweat

Abstract: We proposed a wearable electrochemical biosensor based on Ag Nanowires (AgNWs) and molecularly imprinted polymers (MIPs) prepared on the screen-printed electrode for the noninvasive monitoring of lactate in the human sweat. The MIPs were prepared by electropolymerization of 3-aminophenulboronic acid (3-APBA) with imprinted lactate molecule on the AgNWs-coated working electrode. The MIPs-AgNWs biosensor revealed high sensitivity and specificity for the detection of lactate from 10−6 M to 0.1 M, with the detection limit of 0.22 μM. Furthermore, the sensors presented high stability and reproducibility with sensitivity recovery of 99.8% ± 1.7% during 7 months storage in a dark plastic box at room temperature. In addition, the flexible electrodes also showed stable electrochemical response after been bended and twisted for 200 times, respectively. Such MIPs-AgNWs biosensor was attached on volunteers’ skin for the noninvasive monitoring of the perspiration lactate in vivo. The wearable electrochemical biosensor provides feasibility in near future for the evaluation of human sweat in the military, sports and biomedical fields.

Hierarchical porous MXene/amino carbon nanotubes-based molecular imprinting sensor for highly sensitive and selective sensing of fisetin

Abstract: In this work, a highly selective and sensitive electrochemical sensor based on hierarchical porous MXene/amino carbon nanotubes (MXene/NH2-CNTs) composite and molecularly imprinted polymer (MIP) was developed for fisetin detection. The porous MXene/NH2-CNTs films were fabricated by self-assembly of negatively charged Ti3C2Tx MXene flakes and positively charged NH2-CNTs. The utilization of conductive NH2-CNTs as interlayer spacers efficiently inhibited the aggregation of MXene flakes and formed a well-defined porous structure, as a result of increasing the effective surface area, an enhancement of the electrical conductivity and electrocatalytic activity was observed. This sensor takes advantages of molecularly imprinted technique and MXene/NH2-CNTs nanomaterials to achieve high selectivity and high sensitivity for the determination of fisetin. The factors that affect sensor response were studied and optimized. The as-prepared molecular imprinting sensor, under the optimized conditions, presented a good linear relationship with the fisetin concentration ranging from 0.003 μmol L−1 to 20.0 μmol L−1 with a limit of detection (LOD) of 1.0 nmol L−1. Besides, with favorable stability and selectivity, this newly developed sensor was utilized for the detection of fisetin in actual samples with satisfactory results.

Development of a low-cost e-nose to assess aroma profiles: An artificial intelligence application to assess beer quality

Abstract: The assessment of aromas in beer is critical to assess its quality since it could be used as an indicator of contamination or faults, which will directly influence consumers’ acceptability. Traditional techniques to evaluate aromas are time-consuming, require special training, costly equipment, and trained personnel. Therefore, this study aimed to develop a portable, low-cost electronic nose (e-nose) coupled with machine learning modeling to predict aromas in beer. Nine different gas sensors were used i) ethanol, ii) methane, iii) carbon monoxide, iv) hydrogen, v) ammonia/alcohol/benzene, vi) hydrogen sulfide, vii) ammonia, viii) benzene/alcohol/ammonia and ix) carbon dioxide. Output data were assessed for significant differences using ANOVA and least significant differences as post hoc test (α = 0.05). Two artificial neural network (ANN) models were also developed to predict i) the peak area of 17 different volatile aromatic compounds (Model 1) obtained from gas chromatography–mass spectroscopy (GC–MS) and ii) the intensity of ten sensory descriptors acquired from a sensory session with 12 trained panelists. Results from the ANOVA showed that there were significant differences between the samples used, which showed that the e-nose was able to discriminate samples. The resulting ANN models were highly accurate with correlation coefficients of R = 0.97 (Model 1) and R = 0.93 (Model 2). The combined method using the developed e-nose and the ANN models could be used by the industry as a low-cost, rapid, reliable and effective technique for beer quality assessment within the production line. This may also be calibrated for its use in other foods and beverages.

Carbon monoxide gas sensing properties of metal-organic frameworks-derived tin dioxide nanoparticles/molybdenum diselenide nanoflowers

Abstract: A novel metal-organic frameworks-derived tin dioxide nanoparticles/molybdenum diselenide nanoflowers (SnO2/MoSe2) nanocomposite was designed by a facile hydrothermal method. Various characterization techniques demonstrated the successful preparation of the SnO2/MoSe2 nanostructures. The SnO2/MoSe2 composite with SnO2 and MoSe2 mass ratio of 4:1 exhibited a high response towards CO gas sensing at room temperature. The systematical gas sensing tests showed that the SnO2/MoSe2 composite at room temperature exhibited fast gas response/recovery speed, excellent repeatability, and anti-humidity interference for CO detection. It also showed an outstanding selectivity to CO against various potential interfering gases such as SO2, H2S, CH4, H2 and CO2. Further studies indicated that the SnO2/MoSe2 nanocomposite improved CO gas performance due to the n-n heterojunction formed at the interface between SnO2 nanoparticles and MoSe2 nanoflowers.