Development of a microconductometric biosniffer for detection of trimethylamine

The paper describes the development of a conductometric biosensor for detecting trimethylamine (TMA) which is a good parameter for estimating fish freshness. The biosensor consists of two parts: a microconductometric transducer and a structured enzymatic membrane using a flavin-containing monooxygenase 3 (FMO3) which is known for its sensitivity and selectivity for TMA. The process parameters for the fabrication of the biosniffer and various experimental variables such as pH, time of exposure to glutaraldehyde vapour were investigated with regard to their influence on sensitivity and limit of detection. A low detection limit of 2 μg/mL (ppm) and a linear range up to 40 μg/mL (ppm) were obtained. 90% response was reached in less than 10 min.     

Zinc oxide thin-film chemical sensors in conjunction with neural network pattern recognition for trimethylamine and dimethylamine gases

Transient response curves for exposure to several gases are observed using zinc oxide (ZnO) thin-film gas sensors. It is found that an aluminium-doped ZnO (ZnO:Al) sensor exhibits a high sensitivity and an excellent selectivity for amine gases. In order to discriminate between gas species such as trimethylamine (TMA), dimethylamine (DMA) and other gases pattern recognition analysis using a neural network is carried out using parameters which characterize the transient responses of the sensor for exposure to gases. The recognition probability of the neural network is 90% for TMA and DMA with constant concentration and is 100% for TMA and DMA with different concentrations, except for a concentration of 1 p.p.m.     

Highly sensitive and selective trimethylamine sensor using one-dimensional ZnO-Cr2O3 hetero-nanostructures

Highly selective and sensitive detection of trimethylamine (TMA) was achieved by the decoration of discrete p-type Cr(2)O(3) nanoparticles on n-type ZnO nanowire (NW) networks. Semielliptical Cr(2)O(3) nanoparticles with lateral widths of 3-8 nm were deposited on ZnO NWs by the thermal evaporation of CrCl(2) at 630 °C, while a continuous Cr(2)O(3) shell layer with a thickness of 30-40 nm was uniformly coated on ZnO NWs at 670 °C. The response (R(a)/R(g): R(a), resistance in air; R(g), resistance in gas) to 5 ppm TMA of Cr(2)O(3)-decorated ZnO NWs was 17.8 at 400 °C, which was 2.4 times higher than that to 5 ppm C(2)H(5)OH and 4.3-8.4 times higher than those to 5 ppm p-xylene, NH(3), benzene, C(3)H(8), toluene, CO, and H(2). In contrast, both pristine ZnO and ZnO (core)-Cr(2)O(3) (shell) nanocables (NCs) showed comparable responses to the different gases. The highly selective and sensitive detection of TMA that was achieved by the deposition of semielliptical Cr(2)O(3) nanoparticles on ZnO NW networks was explained by the catalytic effect of Cr(2)O(3) and the extension of the electron depletion layer via the formation of p-n junctions.     

一维氧化锌的水热合成及其气敏性能的研究

Zn(NO₃)₂为原料,CTAB为形貌控制剂, 采用水热合成技术制备了一维氧化锌粉体. 采用X射线衍射(XRD)、透射电镜(TEM)、扫描电镜(SEM)等测试技术对产物的相组成和微观形态进行了表征和分析, 结果表明一维氧化锌属于六方晶系, 分散性好, 纯度高, 直径～200nm, 长度～5μm. 用该粉体制成烧结型旁热式气敏元件, 测试其气敏性能. 结果表明, 在170℃左右对10ppm的三甲胺、甲醇等还原性气体有很好的响应. 文中对一维材料的气敏机理也进行了讨论.     

Gas Sensitive Porous Silver-Rutile High-Temperature Schottky Diode on Thermally Oxidized Titanium

The fabrication of porous silver-${rm TiO}_{2}$ gas sensitive Schottky diodes by utilizing thermally grown oxide layer on titanium substrates is described. The junction was formed by the partial sintering of silver particles on the oxidized metal substrate. The connection between titanium metal and its native oxide is ohmic and the substrate performs as a stable back-contact to the oxide semiconductor. For the characterization of the device, electrical contacts were made by connecting silver wires to the titanium substrate and the silver aggregate. Operating at elevated temperatures, the device behaved as a Schottky diode of high junction energy barrier in clean air, while in highly reducing atmospheres the barrier height dropped to zero and the junction was characterized as an ohmic contact. This reversible transition afforded a broad dynamic range and high sensitivity for chemical detection: Operating at 300 $~^{circ}$C, the reverse current of the diode increased by six orders of magnitude in response to the presence of 1 w-% 1-butanol vapor in the surrounding air, and a single diode was able to detect hydrogen in the 50 ppm to 8% concentration range. The observed electronic features of the device were described through a model constructed based on the work function of silver varying from 4.3 to $sim$6.5 eV with oxygen adsorption.      

Immobilization of a catalytic DNA molecular beacon on Au for Pb(II) detection

A Pb(II)-specific DNAzyme fluorescent sensor has been modified with a thiol moiety in order to immobilize it on a Au surface. Self-assembly of the DNAzyme is accomplished by first adsorbing the single-thiolated enzyme strand (HS-17E-Dy) followed by adsorption of mercaptohexanol, which serves to displace any Au-N interactions and ensure that DNA is bound only through the S-headgroup. The preformed self-assembled monolayer is then hybridized with the complementary fluorophore-containing substrate strand (17DS-Fl). Upon reaction with Pb(II), the substrate strand is cleaved, releasing a fluorescent fragment for detection. Fluorescence intensity may be correlated with original Pb(II) concentration, and a linear calibration was obtained over nearly four decades: 10 microM > or = [Pb(II)] > or = 1 nM. The immobilized DNAzyme is a robust system; it may be regenerated after cleavage, allowing multiple sensing cycles. In addition, drying of fully assembled DNAzyme before reaction with Pb(II) does not significantly affect analytical performance. These results demonstrate that, in comparison with solution-based schemes, immobilization of the DNAzyme sensor onto a Au surface lowers the detection limit (from 10 to 1 nM), maintains activity and specificity, and allows sensor regeneration and long-term storage. Realization of Pb(II) detection through an immobilized DNAzyme is the first important step toward creation of a stand-alone, portable Pb(II) detection device such as those immobilizing DNAzyme recognition motifs in the nanofluidic pores of a microfluidic-nanofluidic hybrid multilayer device.     

Effect of rf power on the structural properties of indium tin oxide thin film prepared for application in hydrogen gas sensor

Indium tin oxide films were grown on glass substrate by rf magnetron sputtering at 648 K. Influence of rf power on structural properties of the ITO films was studied. XRD measurements showed (222) preferred orientation under the optimized deposition conditions. The surface morphology of ITO films analyzed by scanning electron microscope appears to be uniform over the entire surface area, the film exhibited dense layers with fine grains. Finally, ITO sensor device was fabricated and the sensing properties of the device towards hydrogen gas were investigated. The variation in sensitivity of the ITO sensor with operating temperature and with concentration of hydrogen gas was studied. The maximum response was found to be 1.6 at 400 K, for 1,000 ppm of hydrogen gas, and the response of the sensor was found to decrease with increase in concentration of H₂ gas.     

Graphene oxide-decorated Fe<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> microflowers as a promising anode for lithium and sodium storage

Mixed transition metal oxides (MTMOs) have received intensive attention as promising anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). In this work, we demonstrate a facile one-step water-bath method for the preparation of graphene oxide (GO) decorated Fe₂(MoO₄)₃ (FMO) microflower composite (FMO/GO), in which the FMO is constructed by numerous nanosheets. The resulting FMO/GO exhibits excellent electrochemical performances in both LIBs and SIBs. As the anode material for LIBs, the FMO/GO delivers a high capacity of 1,220 mAh·g^–1 at 200 mA·g^–1 after 50 cycles and a capacity of 685 mAh·g^–1 at a high current density of 10 A·g^–1. As the anode material for SIBs, the FMO/GO shows an initial discharge capacity of 571 mAh·g^–1 at 100 mA·g^–1, maintaining a discharge capacity of 307 mAh·g^–1 after 100 cycles. The promising performance is attributed to the good electrical transport from the intimate contact between FMO and graphene oxide. This work indicates that the FMO/GO composite is a promising anode for high-performance lithium and sodium storage.

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Air-cooled cold trap channel integrated in a microfluidic device for monitoring airborne BTEX with an improved detection limit

We integrated an air-cooled cold trap (CT) channel in a microfluidic device for monitoring airborne benzene, toluene, ethylbenzene, and xylene (BTEX) gases and demonstrated its effect on improving the detection limit of the microfluidic device. The device consists of concentration and detection cells formed of 3 x 1 cm Pyrex plates. We first introduced a sample gas into the concentration cell, and the gas was adsorbed onto an adsorbent in the channel. We then raised the temperature using a thin-film heater and introduced the desorbed gas into the detection cell. To prevent dilution of the gas before detection, we propose an improvement to the concentration cell structure that involves the integration of the CT channel. We examined the CT effect by comparing three types of concentration cell with different channel structures. We found that we could detect a gas concentration about 2 orders of magnitude lower than in our previous work by optimizing the channel structure and integrating a CT channel. As an example of BTEX detection,we obtained a 0.05 ppm detection limit for toluene gas with a sampling time of 30 min.     

Microwave plasma enhanced CVD of aluminum oxide films: OES diagnostics and influence of the RF bias

Aluminum oxide films are obtained in a remote-microwave-plasma-enhanced chemical vapour deposition (RMPECVD) reactor. In this technique, only oxygen gas plasma is generated while trimethylaluminum (TMA) carried by argon is fed near the substrate holder which can be RF biased and deposition occurs at the surface of a silicon wafer. Optical emission spectroscopy (OES) is used in order to gain information on the plasma excitation of various species. The presence of an inert gas (argon) allows an evaluation of the relative densities of reactive species by the actinometry technique. A comparison has been done with and without RF biasing or TMA injection at different microwave powers in the same conditions of Ar and O₂ flow rates. The RF biasing creates an additional plasma near the substrate holder but has a weak influence on the OES signal. The microwave plasma is the major mode in the present experimental set up. Less than 2% of TMA modifies the plasma chemistry by improving the atomic oxygen formation. In addition, the TMA decomposition involves a cooling effect of the electron energy. Although this dual mode configuration of the plasma production induces a slight decrease of the deposition rate, it limits the incorporation of impurities (O, H) in the layer by improving the ion bombardment and etching of the growing layer.     

Fabrication of single- and multilayer MoS2 film-based field-effect transistors for sensing NO at room temperature

Single- and multilayer MoS(2) films are deposited onto Si/SiO(2) using the mechanical exfoliation technique. The films were then used for the fabrication of field-effect transistors (FETs). These FET devices can be used as gas sensors to detect nitrous oxide (NO). Although the single-layer MoS(2) device shows a rapid response after exposure to NO, the current was found to be unstable. The two-, three-, and four-layer MoS(2) devices show both stable and sensitive responses to NO down to a concentration of 0.8 ppm.     

The growth of GaN films by alternate source gas supply hot-mesh CVD method

Gallium nitride (GaN) films and Aluminium nitride (AlN) layers were deposited on SiC/Si (111) substrates by an alternating source gas supply or an intermittent supply of a source gas such as ammonia (NH₃), trimethylgallium (TMG) or trimethylaluminum (TMA) in a hot-mesh chemical vapor deposition (CVD) apparatus. The AlN layer was deposited as a buffer layer using NH₃ and TMA on a SiC layer grown by carbonization on Si substrates using propane (C₃H₈). GaN films were grown on an AlN layer by a reaction between NH_x radicals generated on a ruthenium (Ru) coated tungsten (W)-mesh and TMG molecules. An alternating source gas supply or an intermittent supply of one of the source gases during the film growth are expected to be effective for the suppression of gas phase reactions and for the enhancement of precursor migration on the substrate surface. By the intermittent supply of alkylmetal gas only during the growth of the AlN layer, the defect generation in the GaN films was reduced. GaN film growth by intermittent supply on an AlN buffer layer, however, did not lead to the improvement of the film quality.     

Nondestructive Measurement of Fatigue Damage of Thermally Sprayed Al2O3/NiCr Using ESPI Method Under High Temperature

High-temperature fatigue (R = 0) damage and deformation behaviors of SUS304 steel thermally sprayed with an Al₂O₃/NiCr coating were investigated using a servopulse fatigue-testing machine, SEM, and an electronic speckle pattern interferometry (ESPI) method. The relation between crack/delamination and strain variation is discussed. Surface cracks occurred at the outer Al₂O₃ coating but stopped at the inner NiCr coating after one fatigue cycle when the tensile stress was 202 MPa at 873 K. They propagated into the NiCr coating but stopped at the substrate, and local delamination occurred along the NiCr/substrate interface after 1 × 10⁵ cycles test in condition (_max = 202 MPa, T = 873 K). Cracks and delamination largely decreased when _max = 115 MPa or T = 573 K. No influence of cycle frequencies (6.7 or 14 Hz) was detected. The strain value measured by ESPI method was confirmed to be almost the same as that obtained with strain gauges at 293 K. Strain values along cracks measured with the ESPI method were much larger than other areas as a result of crack opening under the tensile load, referred to as the strain concentration zone in this work. Positions of strain concentration zones on strain distribution figures by the ESPI method corresponded well to positions of cracks on sprayed coatings. Moreover, strain values largely decreased where local delamination occurred.     

Vertically integrated human P450 and oxygen sensing film for the assays of P450 metabolic activities

An assaying method of cytochrome P450 (P450 or CYP) monooxygenase activities for toxicological evaluation of drugs and environmental pollutants was developed by immobilizing P450 on an oxygen sensoring layer. Membrane fractions from E. coli expressing human P450 were entrapped in agarose or silica-based gels and immobilized on 96-well microarrays having an oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with Tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp)(3)Cl(2)). P450 activity toward the substrates was monitored through the fluorescence intensity enhancement due to the oxygen consumption by the metabolic reactions. For the metabolism of chlortoluron, a selective herbicide used to control grass weeds, CYP1A1 immobilized in agarose gel showed a higher activity and stability compared with those in silica gels and free suspensions. The luminescence changing rate evaluated by the dynamic transient method (DTM) could be correlated with the substrate concentration. We also compared the metabolic responses of human P450s (CYP1A1,CYP2C8, CYP2E1, CYP3A4) toward various substances. The use of immobilized P450 on an oxygen sensing layer provides a versatile assaying platform owing to the following features. First, the oxygen sensor can detect metabolic reactions of any P450 species, in contrast with assays using fluorogenic substrates. Second, vertical integration of the oxygen sensor and immobilized P450 enhanced the sensitivity because of the effective depletion of oxygen in the vicinity of the oxygen sensing layer. Third, immobilization enables repeated use of P450 by replacing the substrate solutions using a flow cell. Furthermore, the activity of immobilized P450 was retained at least for 3 weeks at 4 °C, suggesting its long-term stability, which is an additional attractive feature.     

The comparative effect of two different annealing temperatures and times on the sensitivity and long-term stability of WO/sub 3/ thin films for detecting NO/sub 2/

We have deposited 150-nm-thick WO/sub 3/ films on Si/sub 3/N/sub 4//Si substrates provided with platinum interdigital electrodes and annealed in static air at 300/spl deg/C and 500/spl deg/C temperatures for 24 h and 200 h. The morphology, crystalline phase, and chemical composition of the films have been characterized using AFM, grazing incidence XRD and high resolution XPS techniques. The sensor resistance response curve has been obtained in the 0.2 -4 ppm NO/sub 2/ gas concentration range in humid air (50% relative humidity), varying the operating temperature between 25 and 250/spl deg/C. By plotting both sensor resistance and gas concentration logarithmically, the response is linear over the investigated dynamic range. Sensor sensitivities, here defined as the ratio of sensor resistance in gas to that in air (i.e., S=R/sub Gas//R/sub Air/), have been compared at a given NO/sub 2/ gas concentration (0.2 ppm). The long-term stability properties have been evaluated by recording film sensitivity for 1 yr under standardized test conditions. Increasing the annealing temperature from 300 to 500/spl deg/C causes the sensitivities to decrease. The 300/24h film is shown to be the most sensitive at S=233, but with poor long-term stability properties. The 300/200h film with S=32 is stable over the examined period. The 500/24 and the 500/200 films are shown to be less sensitive with S=16 and S=14, respectively. The longer the annealing time and the higher the temperature, the poorer the sensitivity, but with positive effects upon the long-term stability of the electrical response. The influence of the annealing conditions on sensitivity and long-term stability has been correlated with the concentration of surface defects, like reduced WO/sub 3/ phase (i.e., W/sup 4+/), which resulted in a strong effect on the sensors' response.     

Synthesis of ZnO comb-like nanostructures for high sensitivity $$\hbox {H}_{2}$$S gas sensor fabrication at room temperature

Zinc oxide (ZnO) comb-like nanostructures were successfully synthesized on the silicon substrate without a catalyst via chemical vapour deposition. The morphology and crystal structure of the product were characterized by scanning electron microscope and X-ray diffractometer. In this research, a simple gas sensor was fabricated based on the principle of change in resistivity due to oxygen vacancies, which makes its surface chemically and electrically active. The fabricated ZnO nanostructures proved to be quite sensitive to low concentration of \(\hbox {H}_{2}\hbox {S}\) gas at room temperature. The sensitivity and response time were measured as a function of gas concentrations. Small response time (48–22 s) and long recovery time (540 s) were found at \(\hbox {H}_{2}\hbox {S}\) gas concentrations of 0.1–4 ppm, respectively. ZnO comb-like structures are considered as the most suitable materials for gas sensor fabrication due to their high sensing properties. These nanostructures growth and \(\hbox {H}_{2}\hbox {S}\) gas sensing mechanism were also discussed.     

Use of a surface-acoustic-wave (SAW) device to measure gas flow

The use of a surface-acoustic-wave (SAW) device to measure the rate of gas flow is described. The device is a delay-line stabilized SAW oscillator heated to a suitable temperature above the ambient. Flow of gas carries heat away by convection. This lowers the substrate temperature, thereby causing change in oscillator frequency. The frequency of a 68-MHz oscillator fabricated on Y-Z LiNbO₃ substrate increases by more than 160 kHz for variation in flow rate from 0 to 1000 cm³/min     

Development of a fully integrated analysis system for ions based on ion-selective optodes and centrifugal microfluidics

A fully integrated, miniaturized analysis system for ions based on a centrifugal microfluidics platform and ion-selective optode membranes is described. The microfluidic architecture is composed of channels, five solution reservoirs, a measuring chamber, and a waste reservoir manufactured onto a disk-shaped substrate of poly(methyl methacrylate). Ion-selective optode membranes, composed of plasticized poly(vinyl chloride) impregnated with an ionophore, a proton chromoionophore, and a lipophilic anionic additive, were cast, with a spin-on device, onto a support layer and then immobilized on the disk. Fluid propulsion is achieved by the centrifugal force that results from spinning the disk, while a system of valves is built onto the disk to control flow. These valves operate based on fluid properties and fluid/substrate interactions and are controlled by the angular frequency of rotation. With this system, we have been able to deliver calibrant solutions, washing buffers, or "test" solutions to the measuring chamber where the optode membrane is located. An analysis system based on a potassium-selective optode has been characterized. Results indicate that optodes immobilized on the platform demonstrate theoretical responses in an absorbance mode of measurement. Samples of unknown concentration can be quantified to within 3% error by fitting the response function for a given optode membrane using an acid (for measuring the signal for a fully protonated chromoionophore), a base (for fully deprotonated chromoionophore), and two standard solutions. Further, the ability to measure ion concentrations by employing one standard solution in conjunction with acid and base and with two standards alone were studied to delineate whether the current architecture could be simplified. Finally, the efficacy of incorporating washing steps into the calibration protocol was investigated.     

Investigation on the cross sensitivity of NO2 sensors based on In2O3 thin films prepared by sol-gel and vacuum thermal evaporation

In₂O₃ thin films have been prepared from commercially available pure In₂O₃ powders by high vacuum thermal evaporation (HVTE) and from indium iso-propoxide solutions by sol-gel techniques (SG). The films have been deposited on sapphire substrates provided with platinum interdigital sputtered electrodes. The as-deposited HVTE and SG films have been annealed at 500°C for 24 and 1 h, respectively. The film morphology, crystalline phase and chemical composition have been characterised by SEM, glancing angle XRD and XPS techniques. After annealing at 500°C the films’ microstructure turns from amorphous to crystalline with the development of highly crystalline cubic In₂O_3−x (JCPDS card 6-0416). XPS characterisation has revealed the formation of stoichiometric In₂O₃ (HVTE) and nearly stoichiometric In₂O_3−x (SG) after annealing. SEM characterisation has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO₂ gas (0.7–7 ppm concentration range), at 250°C working temperature. At this temperature and 0.7 ppm NO₂ the calculated sensitivities (S=R_g/R_a) yield S=10 and S=7 for SG and HVTE, respectively. No cross sensitivity have been found by exposing the In₂O₃ films to CO and CH₄. Negligible H₂O cross has resulted in the 40–80% relative humidity range, as well as to 1 ppm Cl₂ and 10 ppm NO. Only 1000 ppm C₂H₅OH has resulted to have a significant cross to the NO₂ response.     

The biodegradation pathway of triethylamine and its biodegradation by immobilized Arthrobacter protophormiae cells

A bacterial strain named R4 was isolated from a wastewater treatment pool containing triethylamine (TEA) as the sole source of carbon and nitrogen. Strain R4 was identified as Arthrobacter protophormiae based on 16S rRNA gene sequence analysis and morphological and physiological properties. The optimal pH, temperature and concentration of NaCl for TEA degradation by strain R4 were 7.0, 30°C and 0.5%, respectively. Strain R4 could completely degrade 100 mg l(-1) TEA to ammonia in 32 h, and could also effectively degrade diethylamine (DEA) and ethylamine (EA) to ammonia. The degradation of TEA was strongly inhibited by some metal ions (Cu(2+), Mn(2+), Zn(2+), Co(2+), Ni(2+) and Ag(+)) (1.0mM). Addition of either SO(4)(2-) or NH(4)(+) reduced the degradation efficiency of TEA by strain R4 to a certain extent. The inhibition became significant when the concentration of SO(4)(2-) and NH(4)(+) reached to 11 mM and 30 mM, respectively. Cell-free extracts prepared from cells grown in TEA exhibited TEA monooxygenase, DEA monooxygenase and EA monooxygenase activity. Here, we propose the metabolic pathway of TEA degradation in strain R4. The efficiency of TEA removal by immobilized cells of strain R4 was found to be equivalent to that of free cells. In addition, the immobilized cells could be reused without reduction in their ability to degrade TEA.