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A novel technique is here presented, based on inverse opal metal oxide structures for the production of high quality macro and meso-porous structures for gas sensing. Taking advantage of a sol-gel templated approach, different mixed semiconducting oxides with high surface area, commonly used in chemical sensing application, were synthesized. In this work we report the comparison between SnO2 and SnO2:Zn. As witnessed by Scanning and Transmission Electron Microscopy (SEM and TEM) analyses and by Powder x-ray Diffraction (PXRD), highly ordered meso-porous structures were formed with oxide crystalline size never exceeding 20 nm. The filled templates, in form of thick films, were bound to allumina substrate with Pt interdigitated contacts and Pt heater, through in situ calcination,in order to perform standard electrical characterization. Pollutant gases like CO and NO2 and methanol, as interfering gas, were used for the targeted electrical gas tests. All samples showed low detection limits towards both reducing and oxidizing species in low temperature measurements. Moreover, the addiction of high molar percentages of Zn(II) affected the behaviour of electrical response improving the selectivity of the proposed system.
WO3 layers have been synthesized by thermal evaporation at high temperature in order to induce the crystallization of stable films. Phase stability has been proved by annealing treatments carried out at different temperatures. Annealing effects on gas sensing performances have been explained in terms of crystallinity degree and grain coarsening phenomena.
In this work we present data on investigation of the current-voltage and capacitance characteristics of Au/PS Schottky type structures in the presence of different hydrogen-containing solutions (glucose, ethanol, methanol, boric acid, sodium tetraborate pentahydrate, sodium borohydride, benzine, KOH). Generation of the open-circuit voltage and short-circuit current density and capacitance up to 0.55 V, 25 mA/cm2 and 1μF respectively on placing of Au/PS structures in these solutions was discovered. This effect is mainly caused by hydrogen component of solutions. The possible mechanism generation of voltage and capacitance in metal/PS sensors hydrogen-containing solutions is suggested. The advantage of metal/PS Schottky type sensors consists in working without applying external electricity.
Nanostructured tungsten oxide synthesized from SiO2 templates (SBA-15 and KIT-6) has been used for NO2 gas sensing. Chromium has been added as catalytic additive to WO3 in order to enhance sensor response. Several techniques have been used for identifying both additive location in the tungsten oxide matrix and its oxidation state. Raman spectroscopy confirmed the presence of terminal chromium-oxygen bonds at the material surface. Besides, X-ray photoelectron spectroscopy showed chromium peaks attributable to Cr(III) species. Electrical behavior of pure WO3 has found to be highly dependent on the nanostructure type, i. e. 2D SBA-15 and 3D KIT-6 replicas. Chromium addition diminishes response time and improves sensor response at low NO2 concentrations. Electrical differences due to WO3 nanostructure disappears as a result of additive introduction in the material.
Carbon nanotubes and nanofibers are intriguing materials for medical applications due to their unique mechanical, electrical, and surface properties which have been shown to enhance neural cell functions compared to other central nervous system implants such as silicon. The objective of this study was to determine if stem cells can be combined with carbon nanofibers in the treatment of stroke damaged neural tissue in rats. Preliminary results demonstrate the ability of stem cells to differentiate into neurons when injected with carbon nanofibers into stroke damaged neural tissue. Moreover, little scar tissue formation was observed. Although preliminary, such results indicate promise for the use of carbon nanofibers as novel stem cell delivery vehicles for neural damage.
This work shows the possibilities of using the silicon-based microchannel array (Si-MCA) as a 3D-solid support of DNA probes and studying of application of optical methods for DNA hybridization direct analysis. It was obtained that amount of immobilized oligodeoxyribonucleotides on the Si-MCA surface is enhanced with lighting of Si-MCA microchannel. The sample of 160 μm thickness succeeded in immobilizing oligonucleotides 40 times as much as the standard glass slides having the same external surface. The application of Si-MCA as a carrier of DNA allows doing direct analysis of nucleic acids in infrared region by the FTIR method that essentially simplifies creation of a biosensor based on the Si-MCA. It is indicated that using of the Si-MCA as a diffraction grating in visible and UV spectra allows simplifying the spectral analysis of biochemical reaction. It was success confidently to distinguish the mediums differing on the refractive index by dn=0.006.
WO3 nanofibers have been produced by a simple method as electrospinnig. This is a process by which polymer nanofibers (with submicron scale diameters) can be formed when a droplet of viscoelastic polymer solution is subjected to high voltage electrostatic field. Polymer PMMA and WCl6 solution mixtures were used as precursors. The nanofiber were characterized morphologically and chemically by XPS, SEM, and XRD measurements and it was found the formation of mixed WOx/PMMA nanowires at room temperature that evolve after annealing at 300°C towards pure WO3 nanofibers as evidenced by XPS measurements. After the characterization the nanofibers have been deposited on the sensor devices to check their gas sensing properties. They show a semiconductor-like behaviour when they are heated and wide variation of the electrical resistance when they are exposure to NO2 gas.
In this paper, an optical biosensor based on the localized surface plasmon resonance (LSPR) of Ag nanostructured films is proposed and demonstrated. The Ag nanostructured films, which are fabricated by the reduction of AgOx thin films, exhibit a strong LSPR at wavelengths around 370 nm in an air environment. The reflectance spectra of the Ag nanostructured film represent that the shift in the LSPR wavelength follows a linear dependence on the refractive index of the surrounding medium. By varying the concentration of streptavidin solution, we demonstrate that the Ag nanostructured films functionalized with thiol and biotin molecules can sensitively detect a binding event between biotin and streptavidin molecules.
An optical-based humidity sensor with a sub-second response time was fabricated from a nanostructured titanium dioxide thin film. A refractive index profile designed to yield a narrow-bandpass optical interference filter was obtained through nanoscale porosity variations produced by glancing angle deposition (GLAD). Under varying humidity conditions the transmittance spectrum of the filter shifts due to effective index changes of the porous structure resulting from adsorption/desorption of water vapor. In the following we will show that this device is highly sensitive, exhibits minimal hysteresis, and is extremely fast. The adsorption and desorption response times were measured to be 270 ms and 160 ms, respectively.
Highly dispersive and size controlled Pd and Pt nanoclusters have been synthesized by gas condensation and Arc plasma source. The morphology, crystallographic structures, electronic structure and the temperature dependence of chemical states of nanocluster were investigated by using TEM, AFM, EXAFS and XPS, respectively. The results show that non-passivized Pd nanoclusters with the size of 1.5~ 5.7nm are consisted with pure Pd core covered by highly oxidized PdO2 thin layer. The dioxide state PdO2 layers start to converting to Pd at 120°C and vanishing at 180°C in a reduction atmosphere.
The electrical properties of chemical sensors constructed from mats of bare GaN nanowires and GaN nanowires decorated with gold nanoparticles are presented. The sensors were tested in vacuum and at atmospheric pressures of Ar, N2 and methane. The current-voltage (I-V) curves of the sensor constructed with bare GaN nanowires were Ohmic and the device was insensitive to all gases tested. The I-V curves of the sensor constructed from GaN decorated with Au nanoparticles were non-linear and exhibited a drop in conductivity of five orders of magnitude relative to bare GaN nanowire sensors. The Au nanoparticle decorated nanowires also exhibited electrical responses that were chemically selective. The sensor exhibited a nominal response to Ar and a slightly greater response to N2 relative to vacuum. A suppression of the conductivity of the Au-GaN device of 50% was observed upon exposure to methane. Both the drop in conductivity of the Au-GaN nanowire-based sensor, relative to bare GaN nanowires, and the response to methane are explained in terms of the formation of a depletion layer and an increase in the depletion layer width due to physisorption induced surface potentials.
The process of encapsulating antibodies in sol-gel was used for sensing various hormones, specifically cortisol, insulin, and C-peptide. A sol-gel optical biosensor for cortisol has been developed for monitoring of crew health on-orbit during space missions. Our studies involving silica sol-gel materials with competitive immunoassays demonstrated linear calibration for cortisol in the range of 2-60 μg/dL, which covers the physiological range of cortisol blood concentration for an adult (2-28 μg/dL). The method of standard additions was used to analyze human serum samples sent to us from a NASA laboratory. Our sol-gel immunosensor values were typically within 20% of the values obtained by NASA-JSC using traditional immuno-binding techniques, with some values having less than a 5% error. Initial results are presented for sensing the hormones insulin and C-peptide.
A novel co-precipitation route for preparing pure nanograined (Ti, Sn, Nb)O2 solid solution has been accomplished. The solid solution containing the three elements has been synthesized with the molar ratios for Sn:Ti:Nb 100:42:5. Electron microscopy and X-ray diffraction have been adopted to observe the morphology, the crystalline structure and the mean grain radius. Calcining at 550, 650, 850 or 1050 °C for 2h, showed rutile-like single-phase.
The prepared powders have been deposited to produce gas sensors in form of thick films through screen-printing technology. SEM micrographs of both powders and films showed regularly-shaped particles with grain dimensions at nanometric level, the nanostructure being maintained up to 1050°C. The sensors have been tested with different reducing gases showing large responses to hydrogen and good selectivity.
The possibility of a label-free electrical detection of charged macromolecules using semiconductor field-effect sensors offers a new approach for the development of DNA chips with fast and direct electrical readout. A deep understanding of the adsorption and interaction of charged biomolecules onto charged surfaces is of great interest also for the fundamental understanding of many key physiological processes. In the present work, two types of field-effect sensors, namely a capacitive EIS (electrolyte-insulator-semiconductor) structure and an ISFET (ion-sensitive field-effect transistor) have been utilised for monitoring layer-by-layer adsorption of polyelectrolytes as well as for the DNA immobilisation and hybridisation detection.
Although oxide/semiconductor junctions have long been studied in the areas of microelectronics, new phenomena and interests arise from time to time. In particular, in the realm of nanotechnology where materials are shrunk at a length scale of nanometers, the role of heterojunctions in controlling the overall characteristics of the system will become more and more important. In here, we have developed a technique to modify the light emission and charge transport properties of oxide/ZnO system at different dimensionalities. Providing an oxidic overlayer (AlOx) is present on ZnO, a focused electron beam can be used to locally modify optical and electrical properties of ZnO. Under electron bombardment, we find the emission profile of ZnO gradually changes from green-yellow emitting into ultra-violet emitting while the conductivity decreases by more than two orders of magnitude at the same time. Well-defined sub-micron patterns with tunable optical and electrical properties can be fabricated on 2-D ZnO films and 1-D nanoribbons by carefully controlling the dose and energy density of the electron beam. Since ZnO is a versatile material, we believe our studies will shed light on the further use of ZnO in frontier technologies such as gas sensing, display technology, catalysis, spintronics, etc.
Metal oxide nanoparticles within the protein ferritin can act as an energy storage source in nano-bio batteries containing ferrous ferritin and a reconstituted ferritin cage containing different inorganic elements, such as Co, Mn, Ni, and Pt. These components were introduced as two ferritin half-cells with different redox potentials existing between the ferrous ferritin and the reconstituted ferritin. The reduction of ferritin was analyzed in a solution containing 3-[N-morpholino] propanesulfonic acid buffer and oxidized methyl viologen using cyclic voltammetry. The reduction and oxidation peaks of the methyl viologen occurred at potentials of −300 and −100 mV, respectively, and the reduction and the oxidation peaks of the released Fe occurred at potentials of −300 and −100 mV, respectively. The reduction of ferritin was influenced by the pH of the ferritin solution.
An acoustic Love wave immunosensor dedicated to detect biological species such as bacteria, viruses or toxins is described in this paper. We present and analyze results of antibody grafting on the Love wave device using GPTS as coupling agent between SiO2 sensor surface and the sensitive biomembrane layer composed of antibodies. Goat anti-mouse (GAM) antibodies at concentrations from 2μg/ml to 50 μg/ml were introduced on the sensor brass cell. The saturation of the sensor surface by antibodies appears at a concentration of 20 μg/ml. The detection threshold of this primary antibody is around 2 μg/ml, and the lowest concentration allowing antigen detection is around 5 μg/ml.
As our nation's population ages, there will be a substantial demand for surgical services. The best predictor of postoperative outcome is the presence of perioperative ischemia, which is caused by vulnerable coronary plaque rupture. It is not know what makes plaques rupture, but inflammation has been proposed as a unifying etiology. The physiologic perioperative state is one of intense, acute inflammation and thrombosis. This is characterised by the presence of protien- Human Serum C-Reactive Protein( hsCRP) and Myeloperoxidase(MPO). There is a gap in detection capability between gold standard in proteomics detection –Enzyme Linked Immunosorbent Assay (ELISA) assay methods and electrical biosensors.
ELISA based protein biomarker detection in too slow to be applicable in early patient bedside treatment. Electrical biosensors on the other hand may overcome this limitation with their improved sensitivity, specificity and rapid detection. In this application we demonstrate the development of nanomembrane based electrical protein “nano monitor”. This technique overcomes the limitations current “state-of- the- art” methods such as:
• Specificity in detection of multiple markers that characterizes the disease pathogenesis from a single marker to multiple markers.
• Speed of detection from a turnaround time of 12/24 hours to a few minutes.
• Sensitivity of detection from milligram/ml to nanogram/ml.
We report the change to the band structure of two types of carbon nanotubes due to the presence of an isolated, non-conducting, uniformly charged shell held at a fixed distance above their surfaces. We find that, depending on the chirality of the nanotube, the strain on the lattice causes the dispersion relationships to change. This change can result in a modification of the band structure which can induce a metal-semiconductor transition. We consider these effects as a possible mechanism for heavy-metal ion sensing by functionalized carbon-nanotubes.
The presence of toluene and xylene is sensed via surface stress induced deflection of microcantilevers functionalized with self-assembled monolayers (SAMs). Monolayers are formed on gold coated cantilevers using alkanethiols, mercaptanols, and aromatic thiols. These coatings create a variety of chemical functionalities at the cantilever surface, which impact the interactions between target molecules and the cantilever. The differential responses of the cantilevers are investigated as a means to selectively detect aromatic vapors at parts per thousands (ppth) levels.