Top-down and sensitive indium oxide nanoribbon field effect transistor biosensor chips integrated with on-chip gate electrodes toward point of care applications.

We report a scalable, uniform, and sensitive top-down fabricated indium oxide (In2O3) nanoribbon biosensor platform with integrated on-chip gate electrodes using two photolithographic masks. The purpose of this on-chip gate electrode is to control the operational point of the sensor during biomolecular detection replacing the cumbersome external Ag/AgCl electrode. It exhibits excellent capability in gating transistors in an aqueous condition and high stability during the sensing experiment, which is similar to the Ag/AgCl electrode. Its compactness increases the portability and pushes this platform toward a practical use. To demonstrate its capability for detection of biomolecules, we combine this platform with the electronic enzyme-linked immunosorbent assay (ELISA) technique to amplify the signal and to bypass limitation of the Debye screening effect from high salt concentration of physiological samples. Troponin I, a cardiac marker for diagnosis of acute myocardial infarction (AMI), was selected as the target molecule in this study. The In2O3 nanoribbon device offers a high response of 30% toward 0.1 pg ml-1 troponin I concentration and a lower detection limit than that of the commercial ELISA kit on the market by five orders of magnitude. The total assay time from the sample collection to the data acquisition is about 45 min, which is within the constraint of the emergency care application. With the demonstrated sensitivity, uniformity, scalability, quick turn-around time and ability to be integrated, our In2O3 nanoribbon biosensor platform has high potential toward clinical tests for early diagnosis of AMI.

Printed organo-functionalized graphene for biosensing applications.

Graphene is a highly promising material for biosensors due to its excellent physical and chemical properties which facilitate electron transfer between the active locales of enzymes or other biomaterials and a transducer surface. Printing technology has recently emerged as a low-cost and practical method for fabrication of flexible and disposable electronics devices. The combination of these technologies is promising for the production and commercialization of low cost sensors. In this review, recent developments in organo-functionalized graphene and printed biosensor technologies are comprehensively covered. Firstly, various methods for printing graphene-based fluids on different substrates are discussed. Secondly, different graphene-based ink materials and preparation methods are described. Lastly, biosensing performances of printed or printable graphene-based electrochemical and field effect transistor sensors for some important analytes are elaborated. The reported printed graphene based sensors exhibit promising properties with good reliability suitable for commercial applications. Among most reports, only a few printed graphene-based biosensors including screen-printed oxidase-functionalized graphene biosensor have been demonstrated. The technology is still at early stage but rapidly growing and will earn great attention in the near future due to increasing demand of low-cost and disposable biosensors.

Graphene oxide based fluorescence resonance energy transfer and loop-mediated isothermal amplification for white spot syndrome virus detection.

Graphene oxide (GO) is attractived for biological or medical applications due to its unique electrical, physical, optical and biological properties. In particular, GO can adsorb DNA via π-π stacking or non-covalent interactions, leading to fluorescence quenching phenomenon applicable for bio-molecular detection. In this work, a new method for white spot syndrome virus (WSSV)-DNA detection is developed based on loop-mediated isothermal amplification (LAMP) combined with fluorescence resonance energy transfer (FRET) between GO and fluorescein isothiocyanate-labeled probe (FITC-probe). The fluorescence quenching efficiency of FITC-probe was found to increase with increasing GO concentration and reached 98.7% at a GO concentration of 50 µg/ml. The fluorescence intensity of FITC-probe was recovered after hybridization with WSSV LAMP product with an optimal hybridization time of 10 min and increased accordingly with increasing amount of LAMP products. The detection limit was estimated to be as low as 10 copies of WSSV plasmid DNA or 0.6 fg of the total DNA extracted from shrimp infected with WSSV. In addition, no cross reaction was observed with other common shrimp viral pathogens. Therefore, the GO-FRET-LAMP technique is promising for fast, sensitive and specific detection of DNAs.

Ultrasensitive hydrogen sensor based on Pt-decorated WO3 nanorods prepared by glancing-angle dc magnetron sputtering.

In this work, we report an ultrasensitive hydrogen (H2) sensor based on tungsten trioxide (WO3) nanorods decorated with platinum (Pt) nanoparticles. WO3 nanorods were fabricated by dc magnetron sputtering with a glancing angle deposition (GLAD) technique, and decorations of Pt nanoparticles were performed by normal dc sputtering on WO3 nanorods with varying deposition time from 2.5 to 15 s. Crystal structures, morphologies, and chemical information on Pt-decorated WO3 nanorods were characterized by grazing-incident X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and photoelectron spectroscopy, respectively. The effect of the Pt nanoparticles on the H2-sensing performance of WO3 nanorods was investigated over a low concentration range of 150-3000 ppm of H2 at 150-350 °C working temperatures. The results showed that the H2 response greatly increased with increasing Pt-deposition time up to 10 s but then substantially deteriorated as the deposition time increased further. The optimally decorated Pt-WO3 nanorod sensor exhibited an ultrahigh H2 response from 1530 and 214,000 to 150 and 3000 ppm of H2, respectively, at 200 °C. The outstanding gas-sensing properties may be attributed to the excellent dispersion of fine Pt nanoparticles on WO3 nanorods having a very large effective surface area, leading to highly effective spillover of molecular hydrogen through Pt nanoparticles onto the WO3 nanorod surface.

Cytotoxicity assessment of MDA-MB-231 breast cancer cells on screen-printed graphene-carbon paste substrate.

Graphene is a novel carbon-based material widely studied in bio-electrochemical fields because of its high electrical conductivity and excellent electrocatalytic activity. However, its biological applications have been limited due to the lack of understanding of its compatibility with numerous biological entities. In this paper, cytoxicities of MDA-MB-231 breast cancer cells (MDA cells) on carbon paste (CP) and graphene-carbon paste (GCP) substrates are assessed. GCP was prepared by mixing graphene powder into carbon paste with different graphene contents. Cytotoxic effect was evaluated from cell viability, cell adhesion, ROS production and fluorescence staining studies. Cell viability on GCP substrate was found to initially increase as graphene content increases from 0 to 2.5 wt% but then decrease as the content increases further. In addition, the viability decreases with time for all substrates. Similarly, graphene concentration affected the number of adherent cells in the same manner as the cell viability. Likewise, reactive oxygen species (ROS) induced by carbon substrate increased with time and decreased with small graphene inclusion, confirming that low graphene content led to lower cytotoxicity. Moreover, confluence of MDA cells on substrate evaluated using Hoechst 33342 fluorescence staining was also found to be enhanced at low graphene concentration. Therefore, low-content graphene incorporation can effectively improve biocompatibility of carbon-based materials with MDA-MB-231 breast cancer cells, enabling potential applications such as electrochemical electrode for cell study.

CO detection of hydrothermally synthesized Pt-loaded WO3 films.

Unloaded WO3 and 0.25-1.0 wt% Pt-loaded WO3 nanoparticles were synthesized by hydrothermal method using sodium tungstate dihydrate and sodium chloride as precursors in the acidic condition and further by the impregnation method using platinum acetylacetonate. Pt-loaded WO3 films on Al2O3 substrate interdigitated with Au electrodes were prepared by spin-coating technique. The temperature has an obvious influence on the response of sensors to CO gas. In order to determine the optimal operating temperatures, the response of WO3 sensors with different Pt loading concentrations towards 50-2000 ppm of CO in air was tested as a function of operating temperature of 150-350 degrees C. It was found that 1.0 wt% Pt-loaded WO3 sensing film showed the highest response of - 469 at 2000 ppm CO (250 degrees C). Therefore an optimal operating temperature of 250 degrees C was chosen for CO detection.

Enhanced ethanol selectivity of flame-spray-made Au/ZnO thick films.

Sensing characteristics of the spin-coated Au/ZnO nanoparticles thick films with different Au concentrations have been studied for various gases, namely, CO, SO2, ethanol and acetone. The influence on a dynamic range of Au concentration on ethanol response (0.005-0.1 vol.%) of thick film sensor elements was studied at the operating temperatures ranging from 300 to 400 degrees C in the presence of dry air. The optimum Au concentration was found to be 0.5 mol%. 0.5 mol% Au exhibited an optimum ethanol response of 5.0 x 10(2) and a short response time (10 s) for ethanol concentration of 0.1 vol.% at 400 degrees C. Plausible mechanisms explaining the enhanced ethanol selectivity by thick films of Au/ZnO are discussed.

The effect of Mn on flame spray pyrolysis-made ZnO nanoparticles for flammable gases detection.

The application of Mn-loaded ZnO nanoparticles to the design of flammable gas sensors is nowadays one of the most active research fields, due to their high activity, good adsorption characteristics and high selectivity with high response to toxic and combustible gases. It is sensitive to many gases at moderate temperature, such as C2H4, CH4 and C2H2 gases. FSP presents a new technique for 0.25-1.00 mol% Mn-loaded ZnO nanoparticles synthesis which involves only a single step. The crystallite sizes of ZnO spherical and hexagonal particles were found to be ranging from 5 to 15 nm while ZnO nanorods were seen to be 5-15 nm in width and 20-40 nm in length. In addition, very fine Mn nanoparticles were uniformly deposited on the surface of ZnO particles. The highest response for CH4 gas was -240 towards 0.50 mol% Mn-loaded ZnO at 1.0 vol.% concentration of CH4 in dry air at 300 degrees C. The response of 0.50 mol% Mn-loaded ZnO of C2H4 gas was as high as 72 for 1.0 vol.% while the response for C2H2 gas was -13 towards 0.50 mol% Mn-loaded ZnO at 1.0 vol.% concentration of C2H2 in dry air at 300 degrees C.

Effect of anodization voltage on electron field emission from carbon nanotubes in anodized alumina template.

In this work, electron field emission from AAO-CNT structure is studied as a function of anodizing voltage. It is found that the turn-on electric field of AAO-CNTs reduces from 5 V/microm to 4 V/microm as anodization voltage increase from 20 to 30 V. On the other hand, CNTs the turn-on electric field of AAO-CNTs increases from 4 V/microm to 6 V/microm as anodization voltage increase from 30 to 40 V. Thus, anodization voltage of 30 V provides an optimal AAO-CNTs structure for electron field emission. The emission data have been analyzed based on the Fowler Nordhiem (F-N) model. AAO template prepared with 30 V anodization voltage is found to yield CNT nanoarray with optimum alignment and spacing that increase field enhancement factor by the lowering of field screening effect without significant lowering of CNTs density.

Fast cholesterol detection using flow injection microfluidic device with functionalized carbon nanotubes based electrochemical sensor.

This work reports a new cholesterol detection scheme using functionalized carbon nanotube (CNT) electrode in a polydimethylsiloxane/glass based flow injection microfluidic chip. CNTs working, silver reference and platinum counter electrode layers were fabricated on the chip by sputtering and low temperature chemical vapor deposition methods. Cholesterol oxidase prepared in polyvinyl alcohol solution was immobilized on CNTs by in-channel flow technique. Cholesterol analysis based on flow injection chronoamperometric measurement was performed in 150-µm-wide and 150-µm-deep microchannels. Fast and sensitive real-time detection was achieved with high throughput of more than 60 samples per hour and small sample volume of 15 µl. The cholesterol sensor had a linear detection range between 50 and 400 mg/dl. In addition, low cross-sensitivities toward glucose, ascorbic acid, acetaminophen and uric acid were confirmed. The proposed system is promising for clinical diagnostics of cholesterol with high speed real-time detection capability, very low sample consumption, high sensitivity, low interference and good stability.

Fabrication and characterization of carbon doped molybdenum oxide nanostructures.

Molybdenum oxide (MoOx) nanostructure has gained considerable attention because of its low-cost fabrication by low-temperature evaporation/condensation technique and its promising properties for applications in the field of catalysts and chemical sensors. However, MoOx has some inferior properties including very high electrical resistivity and instability at elevated temperature. These properties may be improved by means of foreign atom addition into its nanostructure. In this work, we develop a simple mean for doping of MoOx nanostructures by introduction of gas source dopant during evaporation. Carbon doped MoOx nanostructures have been synthesized by MoOx powder evaporation in Argon/Acetylene mixture with varying process parameters. Depending on growth conditions, various nanostructures including, nanorod, nanoplate, nanodots, can be formed with different dimensions and doping concentrations. Structural characterization by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) indicate that the MoOx based nanostructures are highly crystalline and carbon dopant is successfully incorporated in the structure with controllable concentration. Electrical characterization shows that the electrical conductivity of molybdenum oxide nanostructures can be increased by several orders of magnitude with carbon incorporation.

The effect of carbon nanotube dispersion on CO gas sensing characteristics of polyaniline gas sensor.

Polyaniline is one of the most promising conducting polymers for gas sensing applications due to its relatively high stability and n or p type doping capability. However, the conventionally doped polyaniline still exhibits relatively high resistivity, which causes difficulty in gas sensing measurement. In this work, the effect of carbon nanotube (CNT) dispersion on CO gas sensing characteristics of polyaniline gas sensor is studied. The carbon nanotube was synthesized by Chemical Vapor Deposition (CVD) using acetylene and argon gases at 600 degrees C. The Maleic acid doped Emeradine based polyaniline was synthesized by chemical polymerization of aniline. CNT was then added and dispersed in the solution by ultrasonication and deposited on to interdigitated AI electrode by solvent casting. The sensors were tested for CO sensing at room temperature with CO concentrations in the range of 100-1000 ppm. It was found that the gas sensing characteristics of polyaniline based gas sensor were considerably improved with the inclusion of CNT in polyaniline. The sensitivity was increased and response/recovery times were reduced by more than the factor of 2. The results, therefore, suggest that the inclusion of CNT in MA-doped polyaniline is a promising method for achieving a conductive polymer gas sensor with good sensitivity, fast response, low-concentration detection and room-operating-temperature capability.