Correction: Comparative study on formic acid sensing properties of flame-made Zn2SnO4 nanoparticles and its parent metal oxides.

Correction for 'Comparative study on formic acid sensing properties of flame-made Zn2SnO4 nanoparticles and its parent metal oxides' by Matawee Punginsang et al., Phys. Chem. Chem. Phys., 2023, 25, 15407-15421, https://doi.org/10.1039/D3CP00845B.

Comparative study on formic acid sensing properties of flame-made Zn2SnO4 nanoparticles and its parent metal oxides.

In this work, the formic acid (CH2O2)-sensing properties of flame-made inverse spinel Zn2SnO4 nanostructures were systematically studied by comparing with its parent oxides, namely ZnO and SnO2. All nanoparticles were synthesized via single nozzle flame spray pyrolysis (FSP) in one step and verified by electron microscopy, X-ray analysis, and nitrogen adsorption to exhibit high phase purity and high specific surface area. From gas-sensing measurements, the flame-made Zn2SnO4 sensor displayed the highest response of 1829 towards 1000 ppm CH2O2 at the optimal working temperature of 300 °C compared with ZnO and SnO2. In addition, the Zn2SnO4 sensor presented a moderately low humidity sensitivity and high formic acid selectivity against several volatile organic acids, volatile organic compounds, and environmental gases. The enhanced CH2O2-sensing of Zn2SnO4 was attributed to very fine FSP-derived nanoparticles with a high surface area and unique crystal structure, which could induce the creation of a large number of oxygen vacancies useful for CH2O2 sensing. Moreover, the CH2O2-sensing mechanism with an atomic model was proposed to describe the surface reaction of the inverse spinel Zn2SnO4 structure to CH2O2 adsorption in comparison with that of the parent oxides. The results suggest that Zn2SnO4 nanoparticles derived from the FSP process could be a promising alternative material for CH2O2 sensing.

A discrete dielectrophoresis device for the separation of malaria-infected cells.

Malaria is a serious disease caused by Plasmodium parasites that infect red blood cells (RBCs). This paper presents the continuous separation of malaria-infected RBCs (iRBCs) from normal blood cells. The proposed method employed the discrete dielectrophoresis (DEP) in a microfluidic device with interdigitated electrodes. Our aim is to treat a sample having high concentration of cells to realize high throughput and to prevent the clogging of the microchannel with the use of the discrete DEP. The discrete DEP force for deflecting cells in the device was controlled by adjusting the magnitude, frequency, and duty cycle of the applied voltage. The effectiveness of the proposed method was demonstrated by separating the malaria-infected cells in samples having a cell concentration of 106 cells/µl. From experimental results, we determined the enrichment that is needed to enhance the detection in the case of low parasitemia. The enrichment of the infected cells at the device output was 3000 times as high as that of the input containing 1 infected cell to 106 normal cells. Therefore, the proposed method is highly effective and can significantly facilitate the detection of the infected cells for the identification of Malaria patients.

Study on the discrete dielectrophoresis for particle-cell separation.

This paper presents the application of the discrete dielectrophoretic force to separate polystyrene particles from red blood cells. The separation process employs a simple microfluidic device that is composed of interdigitated electrodes and a microchannel. The discrete dielectrophoretic force is generated by adjusting the duty cycle of the applied voltage. The electrodes make a tilt angle with the microchannel to change the moving direction of the red blood cells. By adjusting the voltage magnitude and duty cycle, we investigate the deflection of red blood cells and the variation of cell velocity along electrode edge under positive dielectrophoresis. The experiments with polystyrene particles show that the enrichment of the particles is greater than 150 times. The maximum separation efficiency is 97% for particle-to-cell number ratio equal to 1:2000 in the sample having high cell concentration. Using the appropriate applied voltage magnitude and duty cycle, the discrete dielectrophoretic force can prevent the clogging of microchannel while successfully separating the particles from the cells with high enrichment and efficiency. The proposed principle can be readily applied to dielectrophoresis-based devices for biomedical sample preparation or diagnosis such as the separation of rare or infected cells from a blood sample.

Chemophysical acetylene-sensing mechanisms of Sb2O3/NaWO4-doped WO3 heterointerfaces.

Sb2O3-loaded NaWO4-doped WO3 nanorods were fabricated with varying Sb contents from 0 to 2 wt% by precipitation/impregnation methods and their p-type acetylene (C2H2) gas-sensing mechanisms were rigorously analyzed. Material characterization by X-ray diffraction, X-ray photoelectron spectroscopy, scanning transmission electron microscopy and nitrogen adsorption indicated the construction of short NaWO4-doped monoclinic WO3 nanorods loaded with very fine Sb2O3 nanoparticles. The sensors were fabricated by powder pasting and spin coating and their gas-sensing characteristics were evaluated towards 0.08-1.77 vol% C2H2 at 200-350 °C in dry air. The gas-sensing properties of the NaWO4-doped WO3 sensor with the optimum Sb content of 1 wt% showed the highest p-type response of ∼250.2 to 1.77 vol% C2H2, which was more than 20 times as high as that of the unloaded one at the best working temperature of 250 °C. Furthermore, the Sb2O3-loaded sensor offered high C2H2 selectivity against CH4, H2, C3H6O, C2H5OH, HCHO, CH3OH, C8H10, C7H8, C2H4 and NO2. Mechanisms responsible for the observed p-type sensing and response enhancement behaviors were proposed based on the NaWO4-doped WO3-Sb2O3 (p-n) heterointerfaces and catalytic spillover effects. Consequently, the Sb2O3-loaded NaWO4-doped WO3 nanorods have potential as alternative p-type gas sensors for selective and sensitive C2H2 detection in various industrial applications.

H2S Gas Sensor Based on Ru-MoO3 Nanoflake Thick Film.

In this study, H2S-sensing characteristics of the spincoated ruthenium loaded molybdenum trioxide nanoflake (Ru-MoO3 NFs) thick films with 0-1.00 wt% Ru concentrations have been studied. The morphologies, cross section and elemental compositions of sensing films were characterized by SEM and EDS line-scan analyses. The influence of Ru concentration on H2S response of the thick film sensor was studied at the operating temperatures ranging from 200 to 350 °C. It was found that 0.5 wt% RuMoO3 film exhibited an enhanced response of ~30 to 10 ppm H2S, which was more than one order of magnitude higher than that of unloaded one. Plausible mechanisms responsible for the enhanced H2S response by sensing films of Ru-MoO3 NFs were discussed on the basis of the catalytic spill-over effects and enhanced specific surface area provided by Ru nanoparticles.

Conversion of Carbon Dioxide into Chemical Vapor Deposited Graphene with Controllable Number of Layers via Hydrogen Plasma Pre-Treatment.

In this work, we report the conversion of carbon dioxide (CO2) gas into graphene on copper foil by using a thermal chemical vapor deposition (CVD) method assisted by hydrogen (H2) plasma pre-treatment. The synthesized graphene has been characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show the controllable number of layers (two to six layers) of high-quality graphene by adjusting H2 plasma pre-treatment powers (100-400 W). The number of layers is reduced with increasing H2 plasma pre-treatment powers due to the direct modification of metal catalyst surfaces. Bilayer graphene can be well grown with H2 plasma pre-treatment powers of 400 W while few-layer graphene has been successfully formed under H2 plasma pre-treatment powers ranging from 100 to 300 W. The formation mechanism is highlighted.

An alternative ready-to-use electrochemical immunosensor for point-of-care COVID-19 diagnosis using graphene screen-printed electrodes coupled with a 3D-printed portable potentiostat.

A severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a cause of worldwide Coronavirus 2019 (COVID-19) disease pandemic. It is thus important to develop ultra-sensitive, rapid and easy-to-use methods for the identification of COVID-19 infected patients. Herein, an alternative electrochemical immunosensor based on poly(pyrrolepropionic acid) (pPPA) modified graphene screen-printed electrode (GSPE) was proposed for rapid COVID-19 detection. The method was based on a competitive enzyme immunoassay process utilizing horseradish peroxidase (HRP)-conjugated SARS-CoV-2 as a reporter binding molecule to compete binding with antibody against the SARS-CoV-2 receptor binding domain (SARS-CoV-2 RBD) protein. This strategy enhanced the current signal via the enzymatic reaction of HRP-conjugated SARS-CoV-2 RBD antibody on the electrode surface. The modification, immobilization, blocking, and detection processes were optimized and evaluated by amperometry. The quantitative analysis of SARS-CoV-2 was conducted based on competitive enzyme immunoassay with amperometric detection using a 3D-printed portable potentiostat for point-of-care COVID-19 diagnosis. The current measurements at -0.2 V yielded a calibration curve with a linear range of 0.01-1500 ng mL-1 (r2 = 0.983), a low detection limit of 2 pg mL-1 and a low quantification limit of 10 pg mL-1. In addition, the analyzed results of practical samples using the developed method were successfully verified with ELISA and RT-PCR. Therefore, the proposed portable electrochemical immunosensor is highly sensitive, rapid, and reliable. Thus, it is an alternative ready-to-use sensor for COVID-19 point-of-care diagnosis.

An electronic nose for amine detection based on polymer/SWNT-COOH nanocomposite.

An electronic nose (e-nose) system based on polymer/carboxylic-functionalized single-walled carbon nanotubes (SWNT-COOH) was developed for sensing various volatile amines. The SWNT-COOH dispersed in the matrix of different polymers; namely, polyvinyl chloride (PVC), cumene terminated polystyrene-co-maleic anhydride (cumene-PSMA), poly(styrenecomaleic acid) partial isobutyl/methyl mixed ester (PSE), and polyvinylpyrrolidon (PVP), were deposited on interdigitated gold electrodes to make the gas sensors. The response of these sensors to volatile amines was studied by both static and dynamic flow measurements. It was found that all sensors exhibited behaviors corresponding to Plateau-Bretano-Stevens law (R2 = 0.81 to 0.99) as the response to volatile amines. Real-world application was demonstrated by applying this e-nose to monitor the odor of sun-dried snakeskin gourami that was pre-processed by salting-preservation. This electronic nose can discriminate sun-dried fish odors with different stored days using a simple pattern recognition based on the principal component analysis (PCA).

Flame-made Nb-doped TiO2 ethanol and acetone sensors.

Undoped TiO(2) and TiO(2) nanoparticles doped with 1-5 at.% Nb were successfully produced in a single step by flame spray pyrolysis (FSP). The phase and crystallite size were analyzed by XRD. The BET surface area (SSA(BET)) of the nanoparticles was measured by nitrogen adsorption. The trend of SSA(BET) on the doping samples increased and the BET equivalent particle diameter (d(BET)) (rutile) increased with the higher Nb-doping concentrations while d(BET) (anatase) remained the same. The morphology and accurate size of the primary particles were further investigated by high-resolution transmission electron microscopy (HRTEM). The crystallite sizes of undoped and Nb-doped TiO(2) spherical were in the range of 10-20 nm. The sensing films were prepared by spin coating technique. The mixing sample was spin-coated onto the Al(2)O(3) substrates interdigitated with Au electrodes. The gas sensing of acetone (25-400 ppm) was studied at operating temperatures ranging from 300-400 °C in dry air, while the gas sensing of ethanol (50-1,000 ppm) was studied at operating temperatures ranging from 250-400 °C in dry air.

Highly Sensitive and Selective Sensing of H2S Gas Using Precipitation and Impregnation-Made CuO/SnO2 Thick Films.

In this work, CuO-loaded tetragonal SnO2 nanoparticles (CuO/SnO2 NPs) were synthesized using precipitation/impregnation methods with varying Cu contents of 0-25 wt% and characterized for H2S detection. The material phase, morphology, chemical composition, and specific surface area of NPs were evaluated using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller analysis. From gas-sensing data, the H2S responses of SnO2 NPs were greatly enhanced by CuO loading particularly at the optimal Cu content of 20 wt%. The 20 wt% CuO/SnO2 sensor showed an excellent response of 1.36 × 105 toward 10 ppm H2S and high H2S selectivity against H2, SO2, CH4, and C2H2 at a low optimum working temperature of 200 °C. In addition, the sensor provided fast response and a low detection limit of less than 0.15 ppm. The CuO-SnO2 sensor could therefore be a potential candidate for H2S detection in environmental applications.

Alpha-MnO2 nanofibers/nitrogen and sulfur-co-doped reduced graphene oxide for 4.5 V quasi-solid state supercapacitors using ionic liquid-based polymer electrolyte.

α-MnO2 nanofibers combined with nitrogen and sulfur co-doped reduced graphene oxide (α-MnO2/N&S-rGO) were prepared through simple hydrothermal and ball milling processes. Structural characterization results by X-ray diffraction, X-ray photoemission spectroscopy, electron microscopy and Raman spectroscopy demonstrated that α-MnO2 nanofibers with the average diameter of ~40 nm were well dispersed on N&S-rGO nanoflakes. The synthesized material was incorporated into supercapacitor (SC) electrodes and assembled with the quasi-solid-state electrolyte comprising N,N-Diethyl-N-methyl-N-(2-methoxy-ethyl)ammonium bis (trifluoromethyl-sulfonyl)amide [DEME][TFSA]/polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP) to produce coin-cell SCs. Electrochemical performances of SCs were measured by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. From the electrochemical data, SC using α-MnO2/N&S-rGO exhibited a good specific capacitance of 165F g-1 at 0.25 A g-1 with a wide potential window of 0-4.5 V, corresponding to a high energy density of 110 Wh kg-1 and a power density of 550 W kg-1. In addition, it exhibited good electrochemical stability with a capacitance retention of 75% after 10,000 cycles at 1 A g-1 and a low self-discharge loss. The attained energy-storage performances indicated that the α-MnO2/N&S-rGO composite could be highly promising for high-performance ionic liquid-based quasi solid-state supercapacitors.

Design of low cost gas sensor based on SrTiO3 and BaTiO3 films.

We have prepared SrTiO3/BaTiO3 multilayer film on alumina substrates by a sol-gel technique and investigated their response for sensing ethanol vapor. The surface morphology of the films were characterized by atomic force microscope (AFM) showing that the grain size of the films increase up to 40 nm as the annealing temperature increased to 1000 degrees C. The ethanol sensors based on SrTiO3/BaTiO3 thin films were fabricated by applying interdigitated gold electrodes by sputtering technique. The ethanol sensing characteristics of SrTiO3/BaTiO3 thin films were quantified by the change in resistance of the sensors when they were exposed to ethanol. The optimum operating tempearature of these sensors was found to be 350 degrees C. In addition, the film annealed at 1000 degrees C exhibited p-type gas sensing behavior with the best sensitivity of 30-100 for low ethanol concentration in the range of 100-1000 ppm.

Flame-spray-made undoped zinc oxide films for gas sensing applications.

Using zinc naphthenate dissolved in xylene as a precursor undoped ZnO nanopowders were synthesized by the flame spray pyrolysis technique. The average diameter and length of ZnO spherical and hexagonal particles were in the range of 5 to 20 nm, while ZnO nanorods were found to be 5-20 nm wide and 20-40 nm long, under 5/5 (precursor/oxygen) flame conditions. The gas sensitivity of the undoped ZnO nanopowders towards 50 ppm of NO(2), C(2)H(5)OH and SO(2) were found to be 33, 7 and 3, respectively. The sensors showed a great selectivity towards NO(2) at high working temperature (at 300 °C), while small resistance variations were observed for C(2)H(5)OH and SO(2), respectively.

Multi-walled carbon nanotube-doped tungsten oxide thin films for hydrogen gas sensing.

In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO(3)) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO(3) thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO(3) hydrogen sensor prepared by the E-beam method.

Synergistic Effects of PdOx-CuOx Loadings on Methyl Mercaptan Sensing of Porous WO3 Microspheres Prepared by Ultrasonic Spray Pyrolysis.

In this work, PdOx-CuOx co-loaded porous WO3 microspheres were synthesized with varying loading levels by ultrasonic spray pyrolysis (USP) using polymethyl methacrylate (PMMA) microspheres as a vehicle template. The as-prepared sensing materials and their fabricated sensor properties were characterized by X-ray analysis, nitrogen adsorption, and electron microscopy. The gas-sensing properties were studied toward methyl mercaptan (CH3SH), hydrogen sulfide (H2S), dimethyl sulfide (CH3SCH3), nitric oxide (NO), nitrogen dioxide (NO2), methane (CH4), ethanol (C2H5OH), and acetone (C3H6O) at 0.5 ppm under atmospheric conditions with different operating temperatures ranging from 100 to 400 °C. The results showed that the CH3SH response of USP-made WO3 microspheres was collaboratively enhanced by the creation of pores in the microsphere and co-loading of CuOx and PdOx at low operating temperatures (≤200 °C). More importantly, the CH3SH selectivity against H2S was significantly improved and high selectivity against CH3SCH3, NO, NO2, CH4, C2H5OH, and CH3COCH3 were upheld by the incorporation of PdOx to CuOx-loaded WO3 sensors. Therefore, the co-loading of PdOx-CuOx on porous WO3 structures could be promising strategies to achieve highly selective and sensitive CH3SH sensors, which would be practically useful for specific applications including biomedical and periodontal diagnoses.

Electronic tongue and cyclic voltammetric sensors based on carbon nanotube/polylactic composites fabricated by fused deposition modelling 3D printing.

In this work, 3D printed electrodes fabricated by blending Polylactic acid (PLA) with carbon nanotube (CNT), CNT/copper (Cu), CNT/zinc oxide (ZnO) composites were applied as cyclic voltammetric sensors for electronic tongue analysis. Porous rectangular rod-shape electrodes were fabricated by fused-deposition-modelling 3D printing of the CNT-based composites produced by a solution blending method. The physical and chemical properties of 3D printed electrodes were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, four-point-probe electrical tests and thermoelectric measurements. The characterization results confirmed uniform distributions of CNTs, Cu particles and ZnO nanorods in the composites and high electrical conductivity of interconnected CNT networks. The additions of Cu and ZnO nanostructures slightly modified the electrical conductivity but significantly changed thermoelectric properties of the material. Cyclic voltammetric (CV) data demonstrated satisfactory stability of the composite materials under corrosive CV conditions. In addition, Cu and ZnO additives provided distinct electrochemical behaviors towards K4Fe(CN)6, H2O2 and nicotinamide adenine dinucleotide. Principal component analysis of CV features could effectively distinguish the three chemicals with various concentrations, illustrating the possibility to apply 3D printed CNT/PLA-based electrodes for electronic tongue applications.

H(2) Sensing Response of Flame-Spray-Made Ru/SnO(2) Thick Films Fabricated from Spin-Coated Nanoparticles.

High specific surface area (SSA(BET): 141.6 m(2)/g) SnO(2) nanoparticles doped with 0.2-3 wt% Ru were successfully produced in a single step by flame spray pyrolysis (FSP). The phase and crystallite size were analyzed by XRD. The specific surface area (SSA(BET)) of the nanoparticles was measured by nitrogen adsorption (BET analysis). As the Ru concentration increased, the SSA(BET) was found to linearly decrease, while the average BET-equivalent particle diameter (d(BET)) increased. FSP yielded small Ru particles attached to the surface of the supporting SnO(2) nanoparticles, indicating a high SSA(BET). The morphology and accurate size of the primary particles were further investigated by TEM. The crystallite sizes of the spherical, hexagonal, and rectangular SnO(2) particles were in the range of 3-10 nm. SnO(2) nanorods were found to range from 3-5 nm in width and 5-20 nm in length. Sensing films were prepared by the spin coating technique. The gas sensing of H(2) (500-10,000 ppm) was studied at the operating temperatures ranging from 200-350 °C in presence of dry air. After the sensing tests, the morphology and the cross-section of sensing film were analyzed by SEM and EDS analyses. The 0.2%Ru-dispersed on SnO(2) sensing film showed the highest sensitivity and a very fast response time (6 s) compared to a pure SnO(2) sensing film, with a highest H(2) concentration of 1 vol% at 350 °C and a low H(2) detection limit of 500 ppm at 200 °C.

Sensing Characteristics of Flame-Spray-Made Pt/ZnO Thick Films as H(2) Gas Sensor.

Hydrogen sensing of thick films of nanoparticles of pristine, 0.2, 1.0 and 2.0 atomic percentage of Pt concentration doped ZnO were investigated. ZnO nanoparticles doped with 0.2-2.0 at.% Pt were successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate as precursors dissolved in xylene. The particle properties were analyzed by XRD, BET, SEM and TEM. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spheroidal and hexagonal particles were found to be ranging from 5 to 20 nm while ZnO nanorods were seen to be 5-20 nm wide and 20-40 nm long. ZnO nanoparticles paste composed of ethyl cellulose and terpineol as binder and solvent respectively was coated on Al(2)O(3) substrate interdigitated with gold electrodes to form thin films by spin coating technique. The thin film morphology was analyzed by SEM technique. The gas sensing properties toward hydrogen (H(2)) was found that the 0.2 at.% Pt/ZnO sensing film showed an optimum H(2) sensitivity of ∼164 at hydrogen concentration in air of 1 volume% at 300 °C and a low hydrogen detection limit of 50 ppm at 300 °C operating temperature.

High sensitivity electrochemical cholesterol sensor utilizing a vertically aligned carbon nanotube electrode with electropolymerized enzyme immobilization.

In this report, a new cholesterol sensor is developed based on a vertically aligned CNT electrode with two-step electrochemical polymerized enzyme immobilization. Vertically aligned CNTs are selectively grown on a 1 mm(2) window of gold coated SiO(2)/Si substrate by thermal chemical vapor deposition (CVD) with gravity effect and water-assisted etching. CNTs are then simultaneously functionalized and enzyme immobilized by electrochemical polymerization of polyaniline and cholesterol enzymes. Subsequently, ineffective enzymes are removed and new enzymes are electrochemically recharged. Scanning electron microscopic characterization indicates polymer-enzyme nanoparticle coating on CNT surface. Cyclic voltammogram (CV) measurements in cholesterol solution show the oxidation and reduction peaks centered around 450 and -220 mV, respectively. An approximately linear relationship between the cholesterol concentration and the response current could be observed in the concentration range of 50-300 mg/dl with a sensitivity of approximately 0.22 µA/mg·dl(-1), which is considerably higher compared to previously reported CNT bioprobe. In addition, good specificity toward glucose, uric acid acetaminophen and ascorbic acid have been obtained. Moreover, sensors have satisfactory stability, repeatability and life time. Therefore, the electropolymerized CNT bioprobe is promising for cholesterol detection in normal cholesterol concentration in human blood.