Showing papers in "Sensors and Actuators B-chemical in 2014"
TL;DR: In this article, high performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O3 were reviewed.
Abstract: High-performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 were reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concentration through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. p-Type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors.
1,642 citations
TL;DR: In this paper, the dominant electronic and chemical mechanisms that influence the performance of metal-oxide-based resistive-type gas sensors are discussed, including p-n and n-n potential barrier manipulation, n-p-n response type inversions, spillover effects, synergistic catalytic behavior, and microstructure enhancement.
Abstract: Metal oxide-based resistive-type gas sensors are solid-state devices which are widely used in a number of applications from health and safety to energy efficiency and emission control. Nanomaterials such as nanowires, nanorods, and nanoparticles have dominated the research focus in this field due to their large number of surface sites facilitating surface reactions. Previous studies have shown that incorporating two or more metal oxides to form a heterojunction interface can have drastic effects on gas sensor performance, especially the selectivity. Recently, these effects have been amplified by designing heterojunctions on the nano-scale. These designs have evolved from mixed commercial powders and bi-layer films to finely-tuned core–shell and hierarchical brush-like nanocomposites. This review details the various morphological classes currently available for nanostructured metal-oxide based heterojunctions and then presents the dominant electronic and chemical mechanisms that influence the performance of these materials as resistive-type gas sensors. Mechanisms explored include p–n and n–n potential barrier manipulation, n–p–n response type inversions, spill-over effects, synergistic catalytic behavior, and microstructure enhancement. Tables are presented summarizing these works specifically for SnO2, ZnO, TiO2, In2O3, Fe2O3, MoO3, Co3O4, and CdO-based nanocomposites. Recent developments are highlighted and likely future trends are explored.
1,392 citations
TL;DR: A detailed review of the key underpinning science for such systems and of recent progress in the development of a number of LSPR-based biosensors which use gold nanorods as the active element is provided in this paper.
Abstract: Noble metal nanoparticle-based localized surface plasmon resonance (LSPR) is an advanced and powerful label-free biosensing technique which is well-known for its high sensitivity to the surrounding refractive index change in the local environment caused by the biomolecular interactions around the sensing area. The characteristics of the LSPR effect in such sensors are highly dependent on the size, shape and nature of the material properties of the metallic nanoparticles considered. Among the various types of metallic nanoparticles used in studies employing the LSPR technique, the use of gold nanorods (GNRs) has attracted particular attention for the development of sensitive LSPR biosensors, this arising from the unique and intriguing optical properties of the material. This paper provides a detailed review of the key underpinning science for such systems and of recent progress in the development of a number of LSPR-based biosensors which use GNR as the active element, including an overview of the sensing principle, the synthesis of GNRs, the fabrication of a number of biosensors, techniques for surface modification of GNRs and finally their performance in several biosensing applications. The review ends with a consideration of key advances in GNR-based LSPR sensing and prospects for future research and advances for the development of the GNR-based LSPR biosensors.
576 citations
TL;DR: In this article, a chemically reduced graphene oxide (RGO)/poly(diallylimethyammonium chloride) (PDDA) nanocomposite film sensor with high-performance humidity properties was reported.
Abstract: Chemically reduced graphene oxide (RGO)/poly(diallylimethyammonium chloride) (PDDA) nanocomposite film sensor with high-performance humidity properties was reported in this paper. The film sensor was fabricated on flexible polyimide substrate with interdigital microelectrodes structure. By the layer-by-layer nano self-assembly approach, graphene oxide and PDDA were exploited to form hierarchical nanostructure, and then was partially reduced via solution-based chemically reduction for obtaining both conductivity and chemically active defect sites. The effect of hydrobromic acid treatment on the conductivity properties of PDDA/GO film was examined, further verifying the advantage of hydrobromic acid reduction. The humidity sensing properties of the presented nanocomposite film sensor, such as repeatability, hysteresis, stability, response–recovery characteristics, were investigated by exposing to the wide relative humidity range of 11–97% at room temperature. As a result, the sensor exhibited not only excellent sensing behavior to humidity, but also fast response–recovery time and good repeatability, highlighting the unique advantages of layer-by-layer nano self-assembly for film sensors fabrication. As last, the possible humidity sensing mechanism of the proposed sensor was discussed in detail.
419 citations
TL;DR: In this article, a gas sensor was fabricated using SnO2-rGO nanocomposites as sensing materials and investigated for detection of NO2 at low operating temperature (50°C).
Abstract: SnO2 nanoparticles-reduced graphene oxide (SnO2-rGO) nanocomposites have been successfully prepared by a facile method via hydrothermal treatment of aqueous dispersion of GO in the presence of Sn salts. The combined characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate the successful formation of SnO2-rGO nanocomposites. To demonstrate the product on sensing application, gas sensors are fabricated using SnO2-rGO nanocomposites as sensing materials and investigated for detection of NO2 at low operating temperature (50 °C). It is found that SnO2-rGO nanocomposites exhibit high response of 3.31 at 5 ppm NO2, which is much higher than that of rGO (1.13), and rapid response, good selectivity and reproducibility. Furthermore, the reason for enhancing sensing performance by addition of SnO2 nanoparticles has also been discussed.
416 citations
TL;DR: In this article, the interaction of Schiff bases with different metal ions has been studied over UV-vis absorption spectra and photofluorescent spectra, and the results indicated that Schiff base L 1 and L 2 exhibited turn-on fluorescent behavior with Al 3+ ions in methanol, which could be directly detected by the naked-eye under the UV-lamp.
Abstract: Thiazole Schiff bases 2-(4-phenyl-1,3-thiazol-2-yliminomethyl)phenol (L 1 ) and 1-(4-phenyl-1,3-thiazol-2-yliminomethyl)naphthalen-2-ol (L 2 ) have synthesized and characterized. The interaction of Schiff bases with different metal ions has been studied over UV–vis absorption spectra and photofluorescent spectra. The results are indicated that Schiff base L 1 and L 2 exhibited turn-on fluorescent behavior with Al 3+ ions in methanol, which could be directly detected by the naked-eye under the UV-lamp. The limits of detection were calculated for L 1 and L 2 since 1.0 × 10 −6 and 7.5 × 10 −7 by the titration method. Both sensors exhibited excellent fluorescent behavior in 5.0–13.5 pH range. The fluorescent behavior of legends-aluminum complex solution goes to turn-off in the presence of Ni 2+ and EDTA.
409 citations
TL;DR: In this paper, a facile electrochemical method was applied to prepare electrochemically reduced graphene oxide (ERGO), and the morphology and structure of ERGO were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectrography and Xray diffraction (XRD).
Abstract: A facile electrochemical method was applied to prepare electrochemically reduced graphene oxide (ERGO). The morphology and structure of ERGO were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and X-ray diffraction (XRD). Compared with the bare glassy carbon electrode (GCE), ERGO modified GCE (ERGO/GCE) exhibits much higher electrocatalytic activities toward the oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with increasing of peak currents and decreasing of oxidation overpotentials. Differential pulse voltammetry results show that DA, AA and UA could be detected selectively and sensitively at ERGO/GCE with peak-to-peak separation of 240 mV and 130 mV for AA–DA and DA–UA, respectively. The linear ranges for AA, UA and DA are 500–2000 μM, 0.5–60 μM and 0.5–60 μM, respectively. Meanwhile, due to the negligible response to physiological level of AA (0.1 mM), ERGO/GCE could be used for the determination of DA in biological sample with high sensitivity and good selectivity. In addition, the presented method was successfully applied for the simultaneous determination of DA, AA and UA in urine sample with reliable recovery. This work provides a simple and green route to construct graphene-based electrochemical sensor, which is promising for the simultaneous determination of DA, AA and UA.
392 citations
TL;DR: A facile Au nanoplates and reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) was fabricated via a simple electrochemical method, denoted as Au/RGO/GCE.
Abstract: A facile Au nanoplates and reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) was fabricated via a simple electrochemical method, denoted as Au/RGO/GCE. The Au/RGO/GCE electrode was used for the simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The modified electrodes fabricated by different methods presented different morphologies and performances for determination of AA, DA, and UA. Three well-defined voltammetric peaks along with remarkable increasing electrooxidation currents were obtained on the Au/RGO/GCE with needle-like Au nanoplates in differential pulse voltammetry (DPV) measurements. It was found that there are linear relationships between the peak currents and the concentrations in the range of 2.4 × 10 −4 to 1.5 × 10 −3 M (AA), 6.8 × 10 −6 to 4.1 × 10 −5 M (DA), and 8.8 × 10 −6 to 5.3 × 10 −5 M (UA), and the limits of simultaneous determination (based on S/N = 3) are 5.1 × 10 −5 M, 1.4 × 10 −6 M, and 1.8 × 10 −6 M for AA, DA and UA, respectively. Additionally, the Au/RGO/GCE electrode presented well anti-interference ability, stability and reproducibility.
375 citations
TL;DR: In this article, a NO2 gas sensor was constructed using reduced graphene oxide-ZnO nanoparticles hybrid as sensing materials, which exhibits higher sensitivity, shorter response time and recovery time than those of the sensor based on rGO.
Abstract: NO2 gas sensor has been constructed using reduced graphene oxide-ZnO nanoparticles (ZnO-rGO) hybrids as sensing materials. Most importantly, the sensor exhibits higher sensitivity, shorter response time and recovery time than those of the sensor based on rGO, indicating that the sensing performances for NO2 sensing operating at room temperature have been enhanced by introduction of ZnO nanoparticles into rGO matrix.
318 citations
TL;DR: Al-doped ZnO (AZO) nanoparticles have been prepared using a modified sol-gel technique as discussed by the authors, and as-prepared AZO nanoparticles were annealed at 400°C, and their morphologies and microstructural characteristics were investigated using transmission electron microscopy (TEM) and x-ray powder diffraction (XRD).
Abstract: Al-doped ZnO (AZO) nanoparticles have been prepared using a modified sol–gel technique The as-prepared AZO nanoparticles were annealed at 400 °C, and their morphologies and microstructural characteristics were investigated using transmission electron microscopy (TEM) and x-ray powder diffraction (XRD) analyses Crystallites with an average size of approximately 60–70 nm and ZnO as a primary phase were observed in all samples In addition, smaller nanoparticles (less than 5 nm) with an Al-rich structure covering the surface of larger ZnO crystallites were also noted on the Al-doped samples Chemoresistive devices consisting of a thick layer of AZO nanoparticles on interdigitated alumina substrates have been fabricated, and their electrical and sensing characteristics for carbon monoxide were investigated Al-doping provided a remarkable decrease in the electrical resistance of the sensing layer at the working temperature of the sensors (250–300 °C) The sensors based on Al-doped ZnO exhibited a higher response than the pure ZnO sample, allowing the detection of CO at sub-ppm concentrations in air The enhancement in sensing properties was discussed in terms of the characterization and electrical data
304 citations
TL;DR: In this article, the quenching of as-prepared GQDs fluorescence by Cu(II) in water has been studied for the detection of Cu2+ ions.
Abstract: Graphene quantum dots (GQDs) have been attractive due to their optical properties with the change of the size. The stable blue fluorescent GQDs are prepared via the hydrothermal method using reoxidized graphene oxide. Based on the quenching of as-prepared GQDs fluorescence by Cu(II) in water, a facile and direct fluorescence sensor for the detection of Cu2+ ions has been studied. It exhibits an extraordinarily high sensitivity and selectivity to Cu2+ ions compared to other metal ions in aqueous solution. The fluorescence intensity is inversely proportional to the concentration of Cu2+ ions, and the calibration curve displays linear regions over the range of 0-15 μM, with a detection limit of 0.226 μM. These results indicate that GQDs, as a fluorescent sensing platform, could meet the selective requirements for biomedical and environmental application and be sensitive enough to detect Cu2+ ions in environmental water samples, even in drinking water, which has a limit of 20 μM defined by the U.S. Environmental Protection Agency. The possible mechanism of Cu(II)-induced fluorescence quenching of GQDs was also discussed. The fluorescence lifetime experimental result demonstrates that the quenching mechanism appears to be predominantly of the static (rather than dynamic) type.
TL;DR: In this article, a high quantum yield carbon quantum dots (CQDs) are successfully synthesized via a simple, low cost, and green hydrothermal method using bamboo leaves as carbon source for the first time.
Abstract: High quantum yield carbon quantum dots (CQDs) are successfully synthesized via a simple, low cost, and green hydrothermal method using bamboo leaves as carbon source for the first time. Branched polyethylenimine (BPEI)-capped CQDs (BPEI-CQDs) are prepared by coating the CQDs with BPEI via electrostatic adsorption. The BPEI-CQDs are then employed as fluorescent probes for sensitive and selective Cu 2+ detection. Experimental results show that the synthesized CQDs have average size of 3.6 nm in diameter with narrow size distribution. The biomass-based CQDs offer high quantum yield of 7.1%. The BPEI-CQDs-based sensing system renders a simple, reliable and sensitive Cu 2+ detection with limit of detection (LOD) as low as 115 nM and a dynamic range from 0.333 to 66.6 μM. In addition, the BPEI-CQDs are successfully used to detect Cu 2+ in river water, demonstrating its good selectivity and great potential for analysis of environmental water samples.
TL;DR: In this paper, a high performance gas sensor based on Au-functionalized ZnO nanorods was fabricated, where Au nanoparticles were successfully immobilized onto the surface of ZnOs to serve as a sensitizer by a facile solution reduction process.
Abstract: One-dimensional (1D) semiconductor nanostructure has been widely used for gas sensor devices. In this work, a high performance gas sensor based on Au-functionalized ZnO nanorods was fabricated. Au nanoparticles were successfully immobilized onto the surface of ZnO nanorods to serve as a sensitizer by a facile solution reduction process. The hybrid Au/ZnO nanorods have been systematically characterized by XRD, SEM, EDS, TEM and optical absorption spectrum. Gas sensing tests reveal that the Au/ZnO sensor has remarkably enhanced performance compared to pure ZnO. It could detect ethanol gas in a wide concentration range with very high response, fast response–recovery time, good selectivity and stable repeatability. The possible sensing mechanism is discussed. The superior sensing features indicate the present Au/ZnO nanorods are promising for gas sensors.
TL;DR: A simple and easily synthesized fluorescent and colorimetric chemosensor based on juloidine-imidazole moieties as a binding and signaling unit, has been synthesized in a one-step procedure as mentioned in this paper.
Abstract: A simple and easily synthesized fluorescent and colorimetric chemosensor 1 , based on juloidine-imidazole moieties as a binding and signaling unit, has been synthesized in a one-step procedure. Receptor 1 showed immediate responses toward Zn 2+ and Al 3+ ions through selective fluorescence enhancement in buffer-acetonitrile and dimethylformamide (DMF) solution, respectively. Moreover, receptor 1 sensed the two states (Fe(II) and Fe(III)) of iron by “naked eye” with a different color. Upon the addition of Fe 2+ and Fe 3+ into each solution of 1 , the color of the solutions instantly changed from colorless to orange for Fe 2+ and to purple for Fe 3+ . Thus, this sensor provides a novel approach for selectively recognizing the biologically important three elements in the human body simultaneously, for Zn 2+ and Al 3+ by emission spectra and Fe 2+ and Fe 3+ by the naked eye.
TL;DR: Two new sensors were prepared and characterized as novel fluorescent probes for detecting mercury ions in pure aqueous solution with a broad pH and it suggested that both CD-1 and CD-2 exhibited high sensitivity and selectivity toward mercury ions.
Abstract: Based on two kinds of hetero atom doping carbon dots (CD-1, CD-2) with brilliant fluorescent quantum yield and other fluorescence properties, two new sensors were prepared and characterized as novel fluorescent probes for detecting mercury ions in pure aqueous solution with a broad pH. Mercury ions can be captured by the carboxyl groups of these two kinds of carbon dots to form nonfluorescent complexes, resulting in a strong quenching. It suggested that both CD-1 and CD-2 exhibited high sensitivity and selectivity toward mercury ions: the linear ranges of CD-1 and CD-2 were estimated to be 1–12 μM and 1–15 μM while the limit of detection (LOD) was calculated to be 226 nM and 845 nM, respectively. Furthermore, these two kinds of CDs were applied to intracellular sensing and imaging of mercury ions as a consequence of the fluorescence properties and the established low cytotoxicity.
TL;DR: A smartphone application algorithm with inter-phone repeatability was developed to quantify commercial colorimetric urine tests with high accuracy and reproducibility in measuring pH, protein, and glucose.
Abstract: A smartphone application algorithm with inter-phone repeatability was developed for both Android and iOS operating systems. The app transformed the smartphone into a reader to quantify commercial colorimetric urine tests with high accuracy and reproducibility in measuring pH, protein, and glucose. The results showed linear responses in the ranges of 5.0–9.0, 0–100 mg/dL and 0–300 mg/dL, respectively.
TL;DR: Graphene/Zinc oxide (ZnO) nanocomposite was prepared by in situ reduction of zinc acetate and graphene oxide (GO) during refluxing as mentioned in this paper.
Abstract: Graphene/zinc oxide (ZnO) nanocomposite was prepared by in situ reduction of zinc acetate ((CH3COO)2Zn·2H2O) and graphene oxide (GO) during refluxing. For the structural, morphological and elemental analysis, the synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX) and Fourier transform infrared spectroscopy (FTIR). Hydrogen sensing properties of synthesized graphene/ZnO nanocomposite have been reported in this paper. For gas sensing properties, thick films of synthesized nanocomposite powder were fabricated on alumina substrate. Sensing results revealed that sensor based on 1.2 wt% graphene/ZnO composite exhibits best sensing response towards 200 ppm of hydrogen gas at an optimum operable temperature of 150 °C among the prepared samples with varying concentrations. Inclusion of graphene into ZnO significantly reduced the optimum operable temperature and increased the sensing response of graphene/ZnO composite towards hydrogen gas. Reported results are based on the change in electrical conductivity of synthesized nanocomposites due to superior electronic conductivity of graphene and the interaction between p-type graphene and n-type zinc oxide.
TL;DR: The use of porous silicon (PSi) as a sensor for detection of various analytes is reviewed in this article, where the authors provide a critical assessment of the development of PSi as a promising material for chemical and biosensing applications.
Abstract: The use of porous silicon (PSi) as a sensor for detection of various analytes is reviewed. The optical or electrical properties of PSi are key sensing parameters that have been used in many chemical and biological sensing applications. PSi is a promising candidate due to ease of fabrication, large surface area, various accessible pore sizes and morphologies, controllable surface modification and its compatibility with conventional silicon processing technology. The adsorption of chemical or biological molecules into the pores modifies the electrical and/or optical properties, allowing convenient and sensitive measurement approach. In this review, we provide a critical assessment of the development of PSi as a promising material for chemical and biosensing applications. Formation procedures of PSi with various pore sizes and morphologies are firstly given. Surface properties and structural characteristics of the material are briefly described. The recent progress on utilization of such porous structures in chemical and biosensing applications is then addressed in the context of surface chemistry effects and nanostructures, measuring approaches, operating concepts and device sensitivity and stability. Finally, concluding remarks with existing challenges that hinder the material for commercial use are highlighted.
TL;DR: In this paper, a carbon dioxide gas sensor from the room-temperature reduction of graphene oxide via hydrogen plasma was developed, where the hydrogen plasma contains radicals and atoms which give dissociation energies for oxygen functional groups, which is capable of reducing the graphene oxide.
Abstract: We report on the development of a carbon dioxide gas sensor from the room-temperature reduction of graphene oxide via hydrogen plasma. The hydrogen plasma contains radicals and atoms which give dissociation energies for oxygen functional groups, which is capable of reducing the graphene oxide. The sample morphology, degree of reduction, chemical bonding and gas sensing capability were systematically studied. The effective removal of oxygen functional groups at the edges and both basal planes while restoring C=C bonds has been observed by AFM, XPS and Raman analysis. The C/O ratio increased from 0.81 to 7.9 and the resistance decreased significantly from 33 kΩ to 1.6 kΩ after the reduction process. The fabricated rGO-F20 sensor shows the highest CO 2 gas sensing response of 71% and 15% at 1500 ppm in N 2 (37% RH) and air environment (68% RH), respectively. In addition, the sensor shows a good repeatability performance with the sensing and recovery time of about 4 min when exposed to 750 and 769 ppm CO 2 concentration. The repeatability performance was measured in air environment at 68% RH without external assisted recovery. This simple, room-temperature reduction process and sensing capability, low cost fabrication process of a graphene sensor could lead to the implementation of a practical indoor air quality monitor.
TL;DR: In this paper, surface plasmon resonance (SPR) based fiber optic gas sensors using nanocomposite film based on poly(methyl methacrylate) [PMMA], reduced graphene oxide (rGO) and PMMA/rGO nanocompositionites having varying amounts of rGO are presented.
Abstract: Surface plasmon resonance (SPR) based fibre optic gas sensors using nanocomposite film based on poly(methyl methacrylate) [PMMA], reduced graphene oxide (rGO) and PMMA/rGO nanocomposites having varying amounts of rGO are presented. The sensing probes were prepared by depositing copper film onto unclad portion of the optical fibre followed by coating of PMMA, PMMA/rGO nanocomposite over-layer. The sensing abilities of the probes were tested for gases like ammonia, hydrogen sulphide, chlorine, hydrogen and nitrogen. The SPR rGO and spectra of all the three types of the sensors for different concentrations of gases were determined using wavelength interrogation technique. Experimental results of SPR spectra showed a red shift in the resonance wavelength on increase in the concentration of gases in the chamber. It was found that the probes were more sensitive to ammonia gas. Further, the probe having PMMA/rGO nanocomposite over-layer coating was found to be more sensitive than the other two. For achieving maximum sensitivity, the performance of the probe with different doping concentrations of reduced graphene in the nanocomposite was evaluated. The sensor has the advantages of high sensitivity, wider operating range, reusability and reproducibility of results which make the sensor compatible for practical applications. Further, the probe was fabricated on optical fibre and hence it has additional advantages such as probe miniaturization, low cost, capability of online monitoring and remote sensing and immunity to electromagnetic field interference.
TL;DR: In this article, the synthesis and detailed investigation on ZnO-SnO 2 composite type hydrogen sensor prototype was reported, which was structurally and morphologically characterized by X-ray diffraction technique and scanning electron microscopy, respectively.
Abstract: This work reports the synthesis and detailed investigation on ZnO–SnO 2 composite type hydrogen sensor prototype. The sensor material was structurally and morphologically characterized by X-ray diffraction technique and scanning electron microscopy, respectively. The gas sensing behaviour of the fabricated sensor prototype was investigated for varied concentration of test gases at different temperature. The cross-response of this sensor to other gases, viz. methane and carbon mono-oxide was also investigated, which showed good selectivity, excellent response and reproducibility to hydrogen at 150 °C.
TL;DR: In this paper, a multilayered self-assembled graphene oxide/polyelectrolyte (GO/PDDA) nanocomposite was fabricated on a polyimide substrate using layer-by-layer self-assembly technique.
Abstract: A ultrahigh performance humidity sensor based on graphene oxide (GO)/poly(diallyldimethylammonium chloride) (PDDA) nanocomposite film was reported in this paper. The multilayered film of GO/PDDA was fabricated on a polyimide substrate using layer-by-layer self-assembly technique. The structures of the self-assembled films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The humidity sensing behaviors of the film sensor were investigated at room temperature over a wide range of 11–97% relative humidity. Unprecedented response of up to 265,640% was demonstrated for the presented sensor when exposed to varying relative humidity levels, which is better than that of the best conventional humidity sensor. Furthermore, the presented sensor exhibited ultrafast response and recovery times capable of monitoring human breath. Moreover, the possible humidity sensing mechanism of the proposed sensor was discussed by using complex impedance spectra and bode diagrams. This measurement results observed highlight the layer-by-layer self-assembled graphene oxide/polyelectrolyte film is a candidate material for constructing humidity sensors.
TL;DR: In this paper, a non-enzymatic glucose sensor based on Copper Oxide Nanowires (Copper oxide nanowires) is presented. But the performance of the sensor was not evaluated.
Abstract: Copper oxide nanowires (CuO NWs) were prepared by a facile two-step procedure consisting of wet-chemistry synthesis and subsequent direct calcination. The morphology, surface property, and crystal structure of the as-prepared CuO NWs were characterized by SEM, TEM, and XRD. The CuO NWs were further employed to construct a non-enzymatic glucose sensor with excellent performance toward glucose detection in 50 mM NaOH solution. The as-developed non-enzymatic glucose sensor showed a fast response time (less than 5 s) and a wide dynamic range with excellent sensitivity of 648.2 μA cm −2 mM −1 and 119.9 μA cm −2 mM −1 toward glucose detection at an applied potential of +0.55 V and +0.3 V (vs. Ag/AgCl), respectively. The Langmuir isothermal theory was employed to fit the obtained calibration curves with high correlation coefficient and the mechanisms for the glucose oxidation promoted by CuO NWs were also discussed. The good selectivity of the CuO NWs based non-enzymatic glucose sensor against electroactive compounds such as ascorbic acid, uric acid, and acetaminophen, and other sugars such as fructose and sucrose at their physiological concentrations were also demonstrated. Furthermore, good accuracy and high precision for the quantification of glucose concentration in human serum samples was attested. These good features indicate that CuO NWs have a great potential in the development of sensitive and selective non-enzymatic glucose sensor.
TL;DR: In this paper, Pd catalysts were used inside and/or outside of WO 3 nanofibers to improve toluene response and superior cross-sensitivity against H 2 S molecules.
Abstract: In this work, we report a remarkably improved toluene response and superior cross-sensitivity against H 2 S molecules by combining Pd catalysts and highly porous WO 3 nanofibers (NFs). We functionalized Pd catalysts inside and/or outside of WO 3 NFs synthesized by electrospinning, which is a facile and versatile process for producing webs of metal oxide NFs. Pd-embedded WO 3 NFs were obtained by the electrospinning of a Pd and W composite precursor/poly(methyl methacrylate) (PMMA) solution followed by calcination at 700 °C. Pd nanoparticles (NPs) (6–10 nm) synthesized by a polyol method were decorated on the WO 3 NFs (Pd-NPs/WO 3 NFs) by the attachment of the Pd NPs on as-prepared WO 3 NFs. The gas sensing characteristics of pure WO 3 , Pd-embedded WO 3 , Pd-NPs/WO 3 , and Pd-NPs/Pd-embedded WO 3 NFs were tested using H 2 S and toluene gases in a highly humid atmosphere (RH 90%), which is similar to human exhaled breath. The results showed that the Pd-NPs/Pd-embedded WO 3 NFs whose inner and outer layers were decorated by Pd catalysts, exhibited a high toluene response ( R air / R gas = 5.5 at 1 ppm) and remarkable selectivity against H 2 S ( R air / R gas = 1.36 at 1 ppm) at 350 °C, whereas pristine WO 3 NFs showed superior H 2 S response ( R air / R gas = 11.1 at 1 ppm) along with a negligible response toward toluene ( R air / R gas = 1.27 at 1 ppm). The highly porous WO 3 NFs decorated with Pd catalysts, exhibited potential feasibility, i.e., a low limit of detection (LOD) of 20 ppb ( R air / R gas = 1.32) at 350 °C, for application in VOCs sensors, particularly for diagnoses of lung cancer.
TL;DR: In this article, a highly sensitive and selective nanostructured triethylamine (TEA) gas sensor has been fabricated successfully by designing PN heterojunction consisting of ZnO nanosheets and NiO nanoparticles.
Abstract: Chemiresistive gas sensors with high sensitivity, selectivity and reliable fabrication potency for specific gas have been now expected for many applications A highly sensitive and selective nanostructured triethylamine (TEA) gas sensor has been fabricated successfully by designing PN heterojunction consisting of ZnO nanosheets and NiO nanoparticles The ZnO nanosheets directly grew on Al2O3 ceramic tubes by introducing a seed layer with a simple and cost-effective hydrothermal method By employing pulsed laser deposition (PLD) method, the construction of NiO/ZnO PN heterojunction is highly controllable and reproducible In comparison with ZnO nanosheet, the NiO/ZnO nanoparticle/nanosheet heterojunction exhibits much better sensing property to TEA gas The depletion layer formed at the PN junction interface in NiO/ZnO sensor can greatly increase the resistance in air and decrease the resistance in TEA gas Due to the general working principle and controllable growth strategy, this study provides a way for design and fabrication of the chemiresistive gas sensors with high performance
TL;DR: In this paper, a liquid-based organic solvent-assisted grinding and sonication method was adopted for the formation of two dimensional (2D) moderately hydrated α-MoO 3 nanoflake suspensions, with a flake thickness in the order of ∼ 1.4nm.
Abstract: A liquid-based organic solvent-assisted grinding and sonication method was adopted for the formation of two dimensional (2D) moderately hydrated α -MoO 3 nanoflake suspensions, with a flake thickness in the order of ∼1.4 nm. This thickness is equal to the largest unit cell parameter of α -MoO 3 . The implemented method had the advantage of simplicity and resulted in a high yield of nanoflakes that were highly crystalline across the planes. This method can be incorporated into 2D semiconducting material-enabled devices. Conductometric transduction templates based on drop-casted thin films of these 2D α -MoO 3 flakes were developed for H 2 gas sensing. The sensors showed large responses to H 2 gas with response and recovery time in the order of seconds. The impressive operation of these devices was attributed to the 2D flake-like structure of the thin films.
TL;DR: In this paper, the synthesis of polyaniline nanofibers in the presence of varying amounts of zinc oxide has been reported, in which the homogeneous PANI nanofiber were prepared through template approach, and the ZnO nanoparticles were used as template.
Abstract: A novel route for the synthesis of polyaniline nanofibers in the presence of varying amounts of zinc oxide has been reported in this paper. The homogeneous PANI nanofibers were prepared through template approach, in which the ZnO nanoparticles were used as template. Structural, optical and morphological analysis of synthesized nanofibers was carried out using X-ray diffraction, UV–vis, IR spectroscopy and FESEM techniques. The thick films of the synthesized polyaniline powder were deposited on alumina substrate and their sensing response to ammonia gas was investigated. Optimum sensing response was achieved with PANI nanofibers synthesized in the presence of 30 wt% ZnO powder. The sensing response of fabricated sensor was proportional to the ammonia gas concentration and exhibited excellent selectivity toward ammonia gas.
TL;DR: In this article, the facile electrochemical fabrication of NiO nanoparticles (NPs)/Pt NPs/electrochemically reduced graphene oxide (NiO/Pt/ERGO) ternary composite modified electrode was reported.
Abstract: We report the facile electrochemical fabrication of NiO nanoparticles (NPs)/Pt NPs/electrochemically reduced graphene oxide (NiO/Pt/ERGO) ternary composite modified electrode. The NiO/Pt/ERGO film was characterized by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDS), atomic force microscopy (AFM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) measurements reveal that NiO/Pt/ERGO can directly catalyze the oxidation of glucose and display enhanced current responses. This nonenzymatic sensor shows an excellent sensitivity of 668.2 μA mM−1 cm−2 (476 mM−1 cm−2), a linear range of 0.05–5.66 mM (R = 0.9996), a fast response time (2.5 s), and a low detection limit (S/N ratio = 3) of 0.2 μM in alkaline medium. The nonenzymatic glucose sensor also exhibits superior stability and good anti-interference properties. The electrochemical detection results demonstrate that NiO/Pt/ERGO/GCE is a good candidate for glucose quantification.
TL;DR: In this paper, a bimetallic PdCu nanoparticle (NP) decorated three-dimensional graphene hydrogel (PdCu/GE) was developed by a simple one-step hydrothermal method.
Abstract: A bimetallic PdCu nanoparticle (NP) decorated three-dimensional graphene hydrogel (PdCu/GE) was developed by a simple one-step hydrothermal method The PdCu/GE hybrids exhibited an interconnected microporous framework with PdCu NPs dispersed and encapsulated within the GE layers The PdCu/GE hybrids showed significant electrocatalytic activity toward glucose oxidation due to the synergistic effect of PdCu NPs and GE sheets in the alkaline solution containing chloride ions, presenting a substantial increase in the oxidation current and decrease in the onset potential of oxidation compared to the monometallic modified GE hybrids At an applied potential of −04 V, the PdCu/GE modified electrode with optimized bimetallic ratio presented quick respond to glucose oxidation with a wide linear range up to 18 mM and a reproducible sensitivity of 48 μA (mg mM) −1 in the presence of chloride ions Furthermore, the PdCu/GE modified electrode exhibited high selectivity to glucose and resistance against poisoning by commonly interfering species such as dopamine, ascorbic acid, uric acid, acetamidophenol and some monosaccharides The PdCu/GE hybrid hydrogels with 3D micropores were therefore promising for the future development of non-enzymatic amperometric glucose sensors with improved electrochemical performances
TL;DR: In this paper, a fluorescence resonance energy transfer (FRET) system between amino-functionalized carbon dots (C-dots) and gold nanoparticles (AuNPs) was constructed.
Abstract: In this paper, we constructed a fluorescence resonance energy transfer (FRET) system between amino-functionalized carbon dots (C-dots) and gold nanoparticles (AuNPs). In this system, C-dots were treated as energy donors, while AuNPs were treated as energy acceptors. We optimized some important factors including incubation time, AuNPs concentration and media pH, which would affect the efficiency of the FRET system. Under the optimized experimental conditions, melamine could be detected based on fluorescence intensity of C-dots. We could get a linear relationship between 50 nM and 500 nM and the detection limit was 36 nM. The proposed method was applied to the determination of melamine in milk samples with satisfactory results. Compared with previous reports, the proposed method manifested great advantages including high sensitivity, short analysis time, low cost and ease of operation.