Showing papers in "Sensors and Actuators B-chemical in 2007"

Metal oxide-based gas sensor research: How to?

Abstract: The paper critically reviews the state of the art in the field of experimental techniques possible to be applied to the study of conductometric gas sensors based on semiconducting metal oxides. The used assessment criteria are subordinated to the proposed R&D approach, which focuses on the study, and subsequent modelling, of sensors’ performance in realistic operation conditions by means of a combination of phenomenological and spectroscopic techniques. With this viewpoint, the paper presents both the to-date achievements and shortcomings of different experimental techniques, describes – by using selected examples – how the proposed approach can be used and proposes a set of objectives for the near future.

Chemical sensors based on nanostructured materials

Abstract: This article provides a comprehensive review of current research activities that concentrate on chemical sensors based on nanotubes, nanorods, nanobelts, and nanowires. We devote the most attention on the experimental principle, design of sensing devices, sensing mechanism, and some important conclusions. We elaborate on development of chemical sensors based on nanostructured materials in the following four sections: (1) nanotube sensors; (2) nanorod sensors; (3) nanobelt sensors; (4) nanowire sensors. We conclude this review with personal perspectives on the directions towards which future research on nanostructured sensors might be directed.

A review of fiber-optic biosensors

Abstract: Fiber-optic biosensors (FOBS) are optical fiber-derived devices which use optical field to measure biological species such as cells, proteins, and DNA. Because of their efficiency, accuracy, low cost, and convenience, FOBS are promising alternatives to traditional immunological methods for biomolecule measurements. Tapered fiber-optic biosensors (TFOBS) are a type of FOBS which rely on special geometries to expose the evanescent field to interact with samples. In order to amplify sensitivity and selectivity, TFOBS are often used with various optical transduction mechanisms such as changes in refractive index, absorption, fluorescence, and Surface Plasmon Resonance. In this review, the basic principles of TFOBS are summarized. Various common geometries for evanescent sensing and the influence of geometric parameters on optical principles are reviewed. Finally, a detailed account of the studies done to date for biomolecules detection using TFOBS will be provided. © 2007 Elsevier B.V. All rights reserved.

Recent advancements in surface plasmon resonance immunosensors for detection of small molecules of biomedical, food and environmental interest

Abstract: Interest in the development of surface plasmon resonance (SPR) based immunosensors for detection and monitoring of low-molecular-weight analytes of biomedical, food and environmental fields has been rapidly increasing over the last 10 years. By combining the advantages of the specific antigen–antibody immunoreaction and the high sensitivity and reliability of SPR signal transduction, SPR immunoassays offer exceptional performance capabilities with respect to sensitivity, specificity, speed and multianalyte detection in complex analytical matrices. Advancements in the technology of antibody production and the signal transduction provide a promising scope for SPR immunosensors to lead in the next generation biosensors. This review highlights the current state-of-the-art in SPR immunosensors and outlines briefly the important issues with regard to the development of SPR immmunosensors, such as preparation of the biomolecules, sensor fabrication, non-specific adsorption, surface regeneration and detection principles. Particular emphasis is given to the indirect competitive immunoassay principle which is compatible and highly promising for detection of small analytes with enhanced sensitivity. In addition, recent advancements and trends in the application of SPR immunosensors in biomedical, environmental and food-related analyses are discussed.

Hydrophilization and hydrophobic recovery of PDMS by oxygen plasma and chemical treatment—An SEM investigation

Abstract: Rapid prototyping of polydimethylsiloxane (PDMS) is frequently used to build microfluidic devices. PDMS is inherently hydrophobic; however, the surface can be temporarily rendered hydrophilic by exposing the surface to oxygen plasma. Hydrophilic microchannels are sometimes advantageous over hydrophobic microchannels due to increased cell adhesion or increase in electro osmotic flow (EOF) leading to ease of liquid filling in microchannels. However, the hydrophilic surface is unstable and that low molecular weight (LMW) chains diffuse from the bulk of the PDMS and cover up the thermodynamically unstable surface. This is one reason for the hydrophilic unstability of PDMS. Present study shows that not only chemistry of the creation of silanol groups on the surface, but also morphology of the film surface nanostructuring of PDMS plays an important role in hydrophilization of PDMS. Present paper tries to understand the mechanism of hydrophobic recovery taking into consideration physical and chemical parameters using SEM characterization.

Perovskite oxides for semiconductor-based gas sensors

Abstract: The oxygen partial pressure dependence of the point defect concentration, and thus conductivity, in oxide semiconductors allows for their use in high-temperature gas sensors. In addition to responding to oxygen partial pressure, the resistance of oxide semiconductors can be affected by other gases, such as carbon monoxide, hydrocarbons and ethanol, which creates opportunities for developing new sensors, but also leads to interference problems. The most common oxide used in such sensors is tin oxide, although other simple oxides, and some mixed oxides, are also used. The focus of this paper is on the use of perovskite oxides in semiconductor-based gas sensors. The perovskite structure, with two differently-sized cations, is amenable to a variety of dopant additions. This flexibility allows for control of the transport and catalytic properties, which are important for improving sensor performance.

Nanopillar ZnO gas sensor for hydrogen and ethanol

Abstract: Aligned zinc oxide nanorods were synthesized directly via a two-step solution approach on an Al2O3 tube, and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The zinc oxide nanorods prepared were uniform with diameters of 10–30 nm and lengths about 1.4 μm. The response Sr (= Ra/Rg) of the aligned zinc oxide nanorod sensor reached 18.29 and 10.41 to 100 ppm ethanol and hydrogen, respectively, which was a two-fold increase compared with that reported in literature, demonstrating the potential for developing stable and sensitive gas sensors.

Laterally grown ZnO nanowire ethanol gas sensors

Abstract: We report the growth of ZnO nanowires on ZnO:Ga/glass templates and the fabrication of laterally grown ZnO nanowire ethanol sensors. It was found that growth direction of the nanowires depends strongly on growth parameters. It was also found that resistivity of the fabricated sensor decreased upon ethanol gas injection. By introducing 1500 ppm ethanol gas, it was found that the device response were around 20%, 35%, 58% and 61% when the gas sensor was operated at 180 °C, 230 °C, 260 °C and 300 °C, respectively. It was also found that the device response at 300 °C were around 18%, 26%, 43%, 55% and 61% when the concentration of injected ethanol gas was 50 ppm, 100 ppm, 500 ppm, 1000 ppm and 1500 ppm, respectively.

Ultrahigh resolution long range surface plasmon-based sensor

Abstract: An ultra-high sensitive surface plasmon resonance (SPR) sensor based on excitation of a long range surface plasmon was developed. Compared to previous reports, the sensor employs more advanced photonic components like superluminescent diode source and polarization-maintaining fibers, which allowed for dramatic decrease of the sensor detection limit. The attained refractive index detection limit of 2.5 × 10−8 is so far the highest value reported for any SPR-based sensor.

Fabrication and gas sensitivity of polyaniline–titanium dioxide nanocomposite thin film

Abstract: A polyaniline–titanium dioxide (PANI/TiO2) nanocomposite was prepared by an in-situ chemical oxidation polymerization approach in the presence of colloidal TiO2 at room temperature, and the PANI/TiO2 nanocomposite thin film was formed on a silicon substrate covered with interdigital electrodes to fabricate a gas sensor via the self-assembly method. The gas-responses of the PANI/TiO2 thin film to NH3 and CO toxic gases were examined. The results showed that the response, reproducibility and stability of the PANI/TiO2 thin film to NH3 were superior to CO gas. Compared with NH3 and CO gases, humidity had less effect on the resistance of the PANI/TiO2 thin film. It was also found that the difference between pure PANI and PANI/TiO2 thin films was not only in gas-sensing property but also in surface morphology.

A label-free, microfluidics and interdigitated array microelectrode-based impedance biosensor in combination with nanoparticles immunoseparation for detection of Escherichia coli O157:H7 in food samples

Abstract: A microfluidic flow cell with embedded gold interdigitated array microelectrode (IDAM) was developed and integrated with magnetic nanoparticle-antibody conjugates (MNAC) into an impedance biosensor to rapidly detect pathogenic bacteria in ground beef samples. The flow cell consisting of a detection microchamber and inlet and outlet microchannels was fabricated by bonding an IDAM chip to a poly(dimethylsiloxane) (PDMS) microchannel. The detection microchamber with a dimension of 6 mm × 0.5 mm × 0.02 mm and a volume of 60 nL was used to collect bacterial cells in the active layer above the microelectrode for sensitive impedance change. MNAC were prepared by conjugating streptavidin-coated magnetic nanoparticles with biotin-labeled polyclonal goat anti-E. coli antibodies and were used in the separation and concentration of target bacteria. The cells of E. coli O157:H7 inoculated in a food sample were first captured by the MNAC, separated, and concentrated by applying a magnetic field, washed, and then suspended in mannitol solution and finally injected through the microfluidic flow cell for impedance measurement. This impedance biosensor was able to detect as low as 1.6 × 102 and 1.2 × 103 cells of E. coli O157:H7 cells present in pure culture and ground beef sample, respectively. The total detection time from sampling to measurement was 35 min. Equivalent circuit analysis indicated that the bulk medium resistance, double layer capacitance, and dielectric capacitance were responsible for the impedance change due to the presence of E. coli O157:H7 cells on the surface of IDAM. Sample pre-enrichment, secondary antibodies on the microelectrode surface, and redox probes were not required in this impedance biosensor.

Determination of paracetamol based on electropolymerized-molecularly imprinted polypyrrole modified pencil graphite electrode

Abstract: Preparation of a molecularly imprinted polymer (MIP) film and its recognition property for paracetamol are investigated. The polypyrrole (PPy) film was prepared by the cyclic voltammetric deposition of pyrrole (Py) in the presence of a supporting electrolyte (LiClO4) with and without a template molecule (paracetamol) through on a pencil graphite electrode (PGE). The performance of the imprinted and non-imprinted (NIP) films was evaluated by differential pulse voltammetry (DPV). Several important parameters controlling the performance of the PPy was investigated and optimized. The molecularly imprinted film exhibited a high selectivity and sensitivity toward paracetamol. The calibration curve for the DPV peak current observed for paracetamol oxidation versus paracetamol concentration at MIP electrode shows two linear regions. The first region demonstrates linearity over a concentration range of 5 μM to 0.50 mM with a correlation coefficient of 0.996. The slope of the second linear region was smaller than the first region's slope with a wide concentration range of 1.25–4.5 mM (R2 = 0.990). The detection limit (3σ) of paracetamol is 7.9 × 10−7 M (S/N = 3). Molecularly imprinted polypyrrole modified pencil graphite electrode showed a stable and reproducible response without any influence of interferents commonly existing in pharmaceutical samples.

A review of DNA functionalized/grafted carbon nanotubes and their characterization

Abstract: The functionalized carbon nanotubes (CNTs) are believed to be very promising in the fields such as preparation of functional and composite materials and biological technologies. Immobilization of nanotubes with specific recognition biosystems indeed provides ideal miniaturized biosensor. A prerequisite for the search in this area is the development of chemical methods to immobilize biomolecules onto carbon nanotubes in a reliable manner. The DNA-based biomolecular recognition principle has been applied to CNTs to constant nanotube electronic devices as well as CNT–DNA electrochemical sensors. The sp2 hybridization and the outstanding electronic properties of the nanotubes coupled with their specific recognition properties of the immobilized system indeed make CNTs, an ideal biosensor. DNA immobilization has been paid great attention and considered as a fundamental methodology for the construction of DNA biosensors. Successful integration of CNTs in electronic devices and sensors requires controlled deposition at well-defined locations and appropriate electrical contacts to metal leads. Different methods for achieving this goal are directional growth of the tubes, alignment by mechanical forces, alignment by electric and magnetic fields, patterned- and self-assembly. Also the concept of using DNA to direct the assembly of nanotubes into nanoscale devices is attracting attention because of its potential to assemble a multicomponent system in one step by using different base sequence for each component. Thus, DNA functionalization of CNTs holds interesting prospects in various fields including solubilization in aqueous media, nucleic acid sensing, gene-therapy and controlled deposition on conducting or semiconducting substrates. This review highlights the functionalization/grafting of DNA onto single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) with or without self-assembly which can be employed in fabricating biosensors for selective recognition of DNA. The review also addresses various characterization techniques that have been employed by various researchers to give the readers an insight into the planning of experiments and subsequent interpretation.

Carbon-coated nickel magnetic nanoparticles modified electrodes as a sensor for determination of acetaminophen

Abstract: A novel type of carbon-coated nickel magnetic nanoparticles modified glass carbon electrodes (C–Ni/GCE) was fabricated and the electrochemical properties of N-acetyl-p-aminophenol (acetaminophen or paracetamol, ACOP) were studied on the C–Ni/GCE. Carbon-coated nickel magnetic nanoparticles showed an excellent electrocatalytic activity for the oxidation of ACOP and accelerated electron transfer between the electrode and ACOP. The anodic peaks of ACOP, dopamine (DA) and ascorbic acid (AA) can be well separated on the C–Ni/GCE. Differential pulse voltammetry (DPV) was used for their simultaneous determination. The linear calibration curves of ACOP, DA and AA were obtained in the range of 7.8 × 10−6 to 1.1 × 10−4 mol L−1, 4.0 × 10−6 to 1.8 × 10−4 mol L−1 and 1.4 × 10−4 to 1.3 × 10−3 mol L−1, respectively. The C–Ni/GCE showed good sensitivity, selectivity and stability, and has been applied to the determination of ACOP in effervescent dosage samples.

Electrocatalytic oxidation of hydrazine and hydroxylamine at gold nanoparticle—polypyrrole nanowire modified glassy carbon electrode

Abstract: A novel electrochemical sensor was fabricated by electrodeposition of gold nanoparticle on pre-synthesized polypyrrole (PPy) nanowire, forming an Au/PPy composite matrix on glassy carbon electrode (Au/PPy/GCE). Field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (XRD) techniques were used for characterization of the composite. As an electrochemical sensor, the Au/PPy/GCE exhibited strongly catalytic activity toward the oxidation of hydrazine and hydroxylamine. The kinetic parameters such as the electron transfer coefficient (α) and charge transfer rate constant (k) for the oxidation of hydrazine and hydroxylamine were determined utilizing cyclic voltammetry (CV). The diffusion coefficient (D) of both two species was also estimated using chronoamperometry. Furthermore, the linear range, current sensitivity and detection limit for hydrazine and hydroxylamine were evaluated by differential pulse voltammetry (DPV). The detection limit of hydrazine and hydroxylamine was 0.20 and 0.21 μM (s/n = 3), respectively. In addition, the sensor showed excellent sensitivity, selectivity, reproducibility and stability properties.

A self-heating gas sensor with integrated NiO thin-film for formaldehyde detection

Abstract: This study develops a MEMS-based formaldehyde gas sensor based on a suspended silicon nitride microstructure with an integrated micro Pt heater, a thin-film NiO sensing layer and Pt interdigitated electrodes (IDEs) to measure the resistance changes of the NiO layer in the presence of formaldehyde. A specific orientation of the NiO layer is observed as the substrate temperature in the sputtering process is increased. The increase in substrate temperature assists in the formation of a NiO layer with the correct stoichiometric ratio (1:1). When formaldehyde is present in the atmosphere, oxidation occurs near the heated NiO sensing layer. This oxidization causes a change in the electrical conductivity of the NiO film, and hence changes the measured resistance between the interdigitated electrodes. The formaldehyde concentration is then determined from the change in the measured resistance. The application of a voltage to the Pt heaters causes the temperature of the micro-hotplate to increase, which in turn enhances the sensitivity of the sensor. The current experimental results show that the sub-micrometer grain sizes of the sputtered oxide thin film yield a high degree of sensitivity (0.33 Ω ppm−1), a low hysteresis value (0.7 ppm), a detection capability of less than 0.8 ppm, a quick response time (13.2 s), a quick recovery time (40.0 s) and a high selectivity over a wide range of formaldehyde concentrations in the presence of interfering species, such as acetone, ethanol and methanol. The novel micro formaldehyde gas sensor developed in this study is ideal for applications aimed at preventing and controlling sick building syndrome (SBS).

The selective detection of C2H5OH using SnO2–ZnO thin film gas sensors prepared by combinatorial solution deposition

Abstract: Sensing materials for selective detection of C2H5OH were designed using combinatorial solution deposition of SnO2–ZnO thin films. The SnO2–ZnO composite sensor prepared by alternate deposition of 10 droplets of SnO2 and ZnO sols (S50Z50 sensor) showed a high response to 200 ppm C2H5OH (S(ethanol) = Ra/Rg = 4.69, Ra: resistance in air, Rg: resistance in gas) at 300 °C, while the gas responses to 100 ppm C3H8, 100 ppm CO, 200 ppm H2, and 5 ppm NO2 ranged from 1.11 to 1.19. The S(ethanol) value of the S50Z50 sensor was twice that to 200 ppm CH3COCH3 (S(acetone)). In contrast, the S(ethanol) and S(acetone) of pure SnO2 and ZnO thin films were similar to each other. The heterostructure between SnO2 and ZnO was suggested as one of the probable reasons for the successful discrimination between C2H5OH and CH3COCH3.

LPG sensing properties of ZnO films prepared by spray pyrolysis method : Effect of molarity of precursor solution

Abstract: Nanocrystalline ZnO films were deposited onto glass substrates by spray pyrolysis of zinc nitrate solutions and used as a liquid petroleum gas (LPG) sensor. The dependence of the LPG sensing properties on the molar concentration of zinc nitrate solutions was investigated. The ZnO films were oriented along (0 0 2) with the hexagonal crystal structure. The grain size and grain density increased with an increase in molar concentration of zinc nitrate solutions. The gas sensing properties for LPG of the ZnO films for LPG with different grain sizes were measured at different temperatures. The maximum sensitivity of 43% at the operation temperature of 673 K was found for the ZnO film prepared by spraying a 0.1 M solution. The ZnO thin films exhibited good sensitivity and rapid response–recovery characteristics to LPG. Further, it has been shown the gas sensitivity of the ZnO gas sensor depends upon its grain size.

Characterization of binding sites in molecularly imprinted polymers

Abstract: In recent years interest has grown in a deeper understanding of the heterogeneity nature of binding sites in molecularly imprinted polymers, purposively designed artificial receptor materials. This article reviews the progress of the understanding of the molecular recognition binding sites beyond the usual description of adsorption isotherms. Analytical and numerical methods used for calculating the adsorption isotherms and the adsorption energy distribution, as a quantitative measure of the imprinted polymer heterogeneity, are included. Advantages and limitations of the different approaches are also discussed.

Inkjet printed chemical sensor array based on polythiophene conductive polymers

Abstract: Multiple regioregular polythiophene polymers with a variety of side chains, end groups and secondary polymer chains were used as active sensing layers in a single chip chemresistor sensor array device A custom inkjet system was used to selectively deposit the polymers onto the array of transduction electrodes The sensor demonstrated sensitivity and selectivity for detection and discrimination of volatile organic compounds (VOCs) The conductivity responses to VOC vapors are dependent on the chemical structure of the polymers For certain VOCs, conductivity increased in some polymers, while it decreased in others Principal component analysis (PCA) of sensor responses was used to discriminate between the tested VOCs These results are correlated to the chemical structures of the different polymers, and qualitative hypothesis of chemical sensing mechanisms are proposed This research demonstrates the potential for using such devices in VOC detection and discrimination sensing applications

The preparation and gas-sensing properties of NiFe2O4 nanocubes and nanorods

Abstract: NiFe2O4 nanorods and nanocubes were prepared by a hydrothermal method without any surfactant for the first time. The length and diameter of the nanorods were about 1 μm and 30 nm, respectively; the side length of the nanocubes was about 60–100 nm. It was found that the sensor based on NiFe2O4 nanorods was relatively sensitive and selective to triethylamine. Especially, the sensitivity to 1 ppm triethylamine attained 7 when operating at 175 °C. On the other hand, the sensor based on NiFe2O4 nanocubes exhibited the opposite behavior; namely, the conductivity of the sensor increased in a reducing gas atmosphere.

Humidity sensors based on TiO2 nanoparticles/polypyrrole composite thin films

Abstract: Resistive-type humidity sensors were fabricated through in situ photopolymerization of pure polypyrrole (PPy) and TiO 2 nanoparticles/polypyrrole (TiO 2 NPs/PPy) composite thin films on an alumina substrate. The characterizations of the thin films were analysed by scanning electron microscopy (SEM) coupled with an energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR). The electronic properties of PPy and TiO 2 NPs/PPy composite thin films were investigated based on the components AgNO 3 and TiO 2 used as electron acceptor and photoinitiator, respectively. The humidity sensing mechanism of TiO 2 NPs/PPy composite thin films was investigated via the results of activation energy and impedance spectroscopy. The sensor made of TiO 2 NPs/PPy composite thin films, using the added amount of TiO 2 NPs as 0.0012 g showed the highest sensitivity, smaller hysteresis and best linearity. Moreover, other sensing properties, such as effects of applied frequency, ambient temperature, response and recovery time and long-term stability were also investigated.

NO2 gas sensing with polyaniline nanofibers synthesized by a facile aqueous/organic interfacial polymerization

Abstract: A new chemical gas sensor for NO2 detection is reported using polyaniline nanofibers synthesized by an interfacial polymerization method. Upon exposure to different contents of NO2 gas, the emeraldine salt form of polyaniline leads to a large increase in resistance-greater than three orders of magnitude in 100 ppm. In these cases, NO2 acts as a strong oxidant, converting the emeraldine form (half oxidized form) of polyaniline to its higher oxidized state. The structures of the nanofibers (high surface area, porosity and small diameters) enhance diffusion of the molecules and oxidative agent into the nanofibers, resulting into high sensitivity and short response time for NO2 detection.

Development of zirconia-based potentiometric NOx sensors for automotive and energy industries in the early 21st century : What are the prospects for sensors?

Abstract: Since the beginning of new millennium substantial progress in the development of potentiometric zirconia-based NOx sensors for automotive and combustion industries has been made. Among the various zirconia-based sensors, special attention has been paid to the group of devices based on the mixed potential gas-sensing mechanism owing to its attractive performances. These devices with appropriate designs and properly selected material of sensing electrodes (SE) can exhibit high sensitivity and selectivity to nitrogen oxides in oxygen containing humid atmospheres at high temperatures showing promising achievements of being applied for automotive and combustion applications. Search for a new material of SE capable of satisfying requirements of both these industries is on its way. This article aims to overview recent progress in the early 21st century in the development of the zirconia nitrogen oxides sensors based on mixed-potential gas-sensing mechanism with specific attention to the recent development of both oxide materials for SE and sensors’ design. Particular attention is focused on the factors determining high NO2 sensitivity and on the future trends in the development of the zirconia-based nitrogen oxides sensors.

Characterization and gas sensitivity study of polyaniline/SnO2 hybrid material prepared by hydrothermal route

Abstract: A polyaniline (PAni)/SnO2 hybrid material was prepared by a hydrothermal method and characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The XRD pattern suggested that PAni did not modify the crystal structure of SnO2, but SnO2 affected the crystallization of PAni to some extent. The gas sensitivity of the PAni/SnO2 hybrid was also studied to ethanol and acetone at operation temperatures of 30, 60 and 90 °C. It was found that the PAni/SnO2 hybrid material had gas sensitivity only when operated at 60 and 90 °C, and it showed a linear relationship between the responses and the concentrations of ethanol and acetone at 90 °C. The sensing mechanism was also discussed.

On-chip microfluidic biosensor for bacterial detection and identification

Abstract: In this paper, we have developed a simple and rapid method for the detection and identification of bacteria using a microfluidic lab-chip. The microfluidic chip utilizes impedance-based measurement to (1) detect cells and (2) identify them when used in conjunction with immobilized monoclonal antibodies. Bacteria in suspension passing through the microfluidic chamber are recognized by antibodies and selectively immobilized on the functionalized glass surface, thereby increasing the measured impedance within the chamber. Continuous perfusion of bacteria suspension through the derivatized chamber not only identifies specific bacteria but also enhances the chamber's detection sensitivity by accumulating bacteria on the chamber wall over time; this approach would be useful for detecting low concentrations of bacteria. To demonstrate this approach, we showed that the prototype sensor could detect 9 × 105 CFU mL−1 E. coli (BL21(DE3)) in the solution by consecutive perfusions. The chip sensitivity with immobilized bacteria is governed by height of sensing chamber, and ∼104 CFU mL−1 of E. coli could easily be detected when a shallower chamber (2 μm high) was used. The selectivity of the sensor was tested using a suspension of two bacterial strains, E. coli and M. catarrhalis. The sensor chip is simple to use, requires minuscule samples, and eliminates extensive cell culture processes. Development of more advanced lab-chips with multiple chambers containing different antibodies that allow simultaneous detection of different bacteria strains will be a natural extension of this work.

High response and stability in CO and humidity measures using a single SnO2 nanowire

Abstract: Single SnO 2 metal oxide nanowires are used at the nanoscale level as individual monocrystal for the electrical transduction of the gas interaction with these sensing materials. Electrical contact characteristics and resistance variations under different gas ambient are analyzed from two- and four-probes measurements of individual nanowires. These data have allowed the estimation of their resistivities and contact resistances. At the gas sensor working conditions, AC impedance spectroscopy technique has extensively been applied to analyze the interaction with the gas molecules and study the influence of the nanowire diameter size on the electrical transduction processes. CO and humidity behaviors are reported for single SnO 2 nanowires with CO detection threshold smaller than 5 ppm and measurement instability lower than 4%.

Simultaneous determination of dopamine and serotonin on gold nanocluster/overoxidized-polypyrrole composite modified glassy carbon electrode

Abstract: A promising electrochemical biosensor was developed by electrodeposition of gold nanoclusters on insulating overoxidized-polypyrrole (PPyox) film modified glassy carbon electrode (GCE). The nano-Au/PPyox composite-coated GCE was used to determine dopamine (DA) and serotonin (5-HT), exhibiting stable and sensitive current responses toward DA and 5-HT oxidation. The sensor was also quite effective to simultaneously determine these species in a mixture and resolved the overlapping anodic peaks of 5-HT, DA and ascorbic acid (AA, 1000-fold) into three well-defined voltammetric peaks in differential pulse voltammetry (DPV) at 0.37, 0.20 and 0.01 V (versus SCE), respectively. The linear response was obtained in the range of 7.0 × 10−9 to 2.2 × 10−6 M with a detection limit of 1.0 × 10−9 M for 5-HT, and in the range of 7.5 × 10−8 to 2.0 × 10−5 M with a detection limit of 1.5 × 10−8 M for DA (s/n = 3), respectively. The oxidation of 5-HT and DA were controlled by the adsorption surface process, as well as the competitive adsorption between 5-HT and DA were investigated at the nano-Au/PPyox/GCE. The designed sensor had been successfully applied for the determination of 5-HT and DA in human blood serum and obtained satisfactory results.

Synthesis and characterization of semiconducting nanowires for gas sensing

Abstract: Quasi one-dimensional nanostructures of semiconducting metal oxides are promising for the development of nano-devices. Tin, indium, and zinc oxides were produced in form of single-crystalline nanowires through condensation from vapor phase. Such a growth occurs in controlled thermodynamical condition and size reduction effects on the electrical and optical response to gases have been exploited. Preparation, microstructural, and electrical characterization of nanowires are presented and the peculiarities of these innovative structures are highlighted.

ZnFe2O4 tubes : Synthesis and application to gas sensors with high sensitivity and low-energy consumption

Abstract: ZnFe2O4 tubes with mesoscale dimensions were synthesized by pyrolysis of polyvinyl alcohol (PVA)-mediated xerogel using porous alumina as a template. The product formation was analyzed by X-ray powder diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TG–DTA), scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). This synthetic method yielded open-ended ZnFe2O4 tubes with a typical length of several micrometers, an outer diameter of about 200 nm, and an average thin wall of 20 nm composed of small nanocrystals. Application of the ZnFe2O4 tubes as gas sensor materials displayed low-energy consumption and high sensitivity to organics such as ethanol and acetone, due to the unique interconnected channel structure and small crystal size of the tubes, showing their potential application in sensor areas.