This PDF file contains the front matter associated with SPIE Proceedings Volume 6769, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The contribution presents the results obtained in the last years by applying an established aerosol based production technology for metal oxide nanoparticles mainly used in catalysis and filler materials, the so called flame spray pyrolysis (FSP), to gas sensor fabrication. The final achievement of this technology is a fast and clean single step process to fabricate fully functionalized multilayer sensors. This is a substantial progress as it merges the two fundamental processes of producing the sensing material and fabricating the sensing element.

The understanding of the gas sensing mechanism at a fundamental level implies the knowledge of the state of preadsorbed surface species. Some question marks on the commonly accepted ideas were raised by the recorded higher sensitivity of sensors to CO in nitrogen and by the fact that the combustion of CO was observed in air and in humid nitrogen. These facts question the monopoly of oxygen ions as the reaction partners for CO and they were the driving force for thereby presented investigations. DRIFT Spectroscopy and resistance measurements have been simultaneously applied to discriminate between the species that are actively taking part in the sensing processes and spectators. The comparison between the different sensors has been focused on verifying whether the observed phenomena are general or whether they depend on the technology. It was observed that for SnO₂ sensors, the reaction of oxygen, with water results in the formation of terminal hydroxyls and the release of an electron to the conduction band. It indicates that water compete with reducing gases for the oxygen ions. This phenomenon was independent of the technology and thus it could be SnO₂ characteristic. It was shown that CO reacts preferentially with ionosorbed oxygen at the surface of tin dioxide. In the case of lack of oxygen different scenarios are possibly dependent on hydration state of the surface.

Semiconductor nanowires such as zinc oxide nanowires are projected to be the next generation materials for nanoscale sensors and actuators. They also serve as ideal systems for studying material behavior at the small scale. In this paper, we report experimental results on the mechanical properties of zinc oxide nanowires. We have designed a MEMS (microelectromechanical systems) test-bed for mechanical characterization of nanowires and use a microscale version of pick-and-place as a generic specimen preparation and manipulation technique. We performed experiments on zinc oxide nanowires inside a scanning electron microscope (SEM) and estimated the Young's modulus to be approximately 21 GPa and the fracture strain to vary from 5 % to 15 %. We attribute the difference in mechanical properties of the nanowires from bulk properties to several factors such as lower number of defects, charge redistribution at the atomic scale and surface effects.

A new way of developing optical nanosensors is presented. Organic nanofibers serve as key elements in these new types of devices, which exploit both the smallness and brightness of the nanoaggregates to make new compact and sensitive optical nanosensors. On the basis of bottom up technology, we functionalize individual molecules, which are then intrinsically sensitive to specific agents. These molecules are used as building blocks for controlled growth of larger nanoscaled aggregates. The aggregates in turn can be used as sensing elements on the meso-scale in the size range from hundred nanometers to a few hundred microns. The organic nanofibers thereby might become a versatile tool within nanosensor technology, allowing sensing on the basis of individual molecules over small aggregates to large assemblies. First experiments of Bovine Serum Albumin (BSA) coupling to para-hexaphenyl (p-6P) nanofibers are presented, which could lead towards a new type of protein sensors. Besides large versatility and sensitivity, the nanofibers benefit from the fact that they can be integrated in devices, either in liquids by the use of microfluidic cavities or all in parallel.

Porous silicon is an excellent material for biosensing because of its large surface area and ability to filter out large contaminant species. In order to characterize the sensitivity of porous silicon based biosensors for biomolecules of different sizes, a mesoporous silicon waveguide with average pore diameter of 20 nm is used to detect single strand DNA oligos with different numbers of base pairs at different concentrations. Experimental results indicate that 16-mer DNA is detected most sensitively with the mesoporous silicon waveguide.

Wide bandgap semiconductor nanowires are attractive for a variety of sensing purposes because of their excellent stability, large surface area, pizeo-electric nature and ability to be integrated with on-chip wireless communication systems. In this brief review, we will discuss progress in these nanowires for gas sensing.

We present the scaling of percolation resistivity in nanotube films as a function of nanotube and device parameters both experimentally and using simulations. We first characterize the resistivity of these films down to 200 nm lateral dimensions by fabricating standard four-point-probe structures. We find that the film resistivity starts to increase at device widths below 20 microns, and exhibits an inverse power law dependence on width below a critical width of 2 microns. We then use quasi-3D Monte Carlo simulations to model and fit these experimental results. In addition to fitting the experimental data, we also study the effect of four parameters, namely nanotube density, length, alignment, and measurement direction on resistivity and its scaling with device width. We explain these simulation results by simple physical and geometrical arguments. Nanoscale study of percolation transport mechanisms in nanotube films is essential for understanding and characterizing their performance in nanosensing device applications.

Detectors (sensor) having detection capability ranging from visible to near-infrared region are very much required for multi-color image sensor, necessary for next generation bio-medical, bio-chem(ical), and security applications. The capability of using broadband detection in a single sensor would help to receive real-time imaging not detectable using today's CCD or CMOS sensor. We proposed a detector structure as a single sensor element (pixel) having the detection capability ranging from visible to 1.7 μm, wavelengths requiring in bio-chem, biomedical cell detection and security application. This invited paper has two-fold objectives: (a) provide a comprehensive overview of conventional photo detectors array (focal-plan array) and their types, being used in today's imaging, and (b) introduce a development of multi-color detector array (image sensor) which authors pioneered. The features of proposed multi-color detector are simple structure, low-cost, high quantum efficiency, high sensitivity, and high speed. Performance results so far attained will be presented along with its possible applications.

Highly-integrated mixed-mode nanocircuits are required to interface nanosensors with mainstream information systems based on advanced sub-50nm CMOS architectures. Such nanocircuits may serve a number of crucial signal processing tasks such as current sensing, filtering and amplification. Most importantly they are required to have 'adaptive' or programmable features that can deal with the signal integrity concerns and fluctuations in nanosensor characteristics. Yet another requirement for nanocircuits serving to nanosensors is low-power and high-linearity whereby impact to the working ambient is minimized and signal quality is ensured, respectively. In this work we introduce a range of mixedmode nanocircuits built using double-gate (DG) MOSFET technology expected to replace the planar bulk CMOS in sub-50nm regime, i.e. within the next decade.

Among the family of wide band-gap semiconducting metal oxides, tungsten trioxide is the most promising oxide for gas sensing. A metastable open-structured hexagonal phase of WO3 was successfully synthesized using acid precipitation method. The oxide was characterized using SEM, TEM and XRD. The sensing property to reducing ammonia gas was measured. The sensitivity is much higher than that of monoclinic tungsten oxides. The oxide polymorph exhibits a p-n type transition when the temperature goes from 100 °C to 300 °C.

Here we report efforts towards fabrication of DNA based nanosensors, where DNA molecules were immobilized on gold-dot arrays. AFM was used as the main characterization tool. Two major challenges associated with characterizing these nanosensors are: 1) constructing small (<10 nm high) attachment sites on a flat surface to resolve the details of the hybridized DNA lattice and 2) fabricating attachment sites on a surface that allows the lattices to be well separated. We have chosen silicon as the substrate since atomically flat surfaces are readily available. For the formation of the gold-dot arrays, we combined e-beam lithography with metal deposition via an e-beam evaporation. The fabrication process was confirmed by AFM imaging. For DNA attachment we have used DNA functionalized on one end with multi-thiolated dendrimers, an attachment strategy developed in our lab. After exposing the surface to the DNA solution, the DNA was found to be attached to ~5% of the gold dots. To improve the attachment technique, oxygen plasma cleaning and ethanol treatment have been investigated. Finally, a higher yield (65% of total scanned areas) of DNA attachment to the gold dots was achieved.

Typical biological samples are inherently complicated. They may contain a myriad of compounds that are electroactive at the same potential as that used in many electrochemical biosensors. Therefore, a biosensor design feature must be included that either eliminates or blocks the interferents from generating false positive signals. The ability to use an insoluble compound, that of MnO₂, in order to oxidize interferents such as ascorbic acid, acetaminophen and uric acid, was investigated in a prototype sensor system at a bias potential of 0.6 V versus Ag/AgCl. Unlike previous work with these materials, a difference between the ability for the metal oxide to oxidize the interferents was observed. Most effective was the capability of MnO₂ to oxidize uric acid. Alternatively, the MnO₂ had little effect on acetaminophen. The study is both introduced and results are discussed within the context of an implantable glucose sensor.

Lipid bilayer membranes deposited on solid surfaces are called "supported planar bilayers" (SPBs), and expected to be an effective cell-membrane-mimicking model system in vitro. We have investigated the influence of the substrate surface properties on the SPB formation process and on the photo-induced shape transformation of bilayers, by means of atomic force microscopy and fluorescence microscopy. The SPB of dipalmitoleoylphosphatidylcholine was formed on SiO₂/Si(100) surfaces and rutile-TiO₂(100) surface by the vesicle fusion method. On the SiO₂ surface, one or a few adsorbed vesicles can transform to a SPB resulting in a small bilayer patches. The SPB formation rate was accelerated on thermally treated SiO₂ surfaces, which had less hydrophilicity, but the initial SPB formation process did not change. On the TiO₂(100), the surface was completely covered with the adsorbed vesicles prior to the SPB formation, and the planar bilayer was obtained only if the lipid concentration in the suspension was sufficiently high. Photo-induced activation of molecular motion through the fluorescence dye excitation achieved the area-selective SPB formation from the adsorbed vesicular layers with small SPB domains on the TiO₂(100). This photo-activation transformed the SPB shapes threedimensionally on the SiO₂ and TiO₂ surfaces in different way.

The precise placement of molecular and nanoparticle species at predetermined locations on a substrate surface remains a current challenge. Some barriers are particularly relevant to soft matter such as biomolecules. The advent of DNA Origami, invented by Rothemund, provides partial solutions to some challenges while raising new challenges. In this paper, two particular levels of molecular placement will be discussed, associating large DNA based molecular nanostructures with traditional lithographic nanostructures and the association of molecular scale species with particular locations within large Origami structures. Typical plasmid based DNA Origami nanostructures are approximately 100 nm in diameter. This size scale closely matches that of gold nanoscale structures which are readily produced using ebeam and other lithographic techniques. The strategy for associating large DNA based nanostructures with these lithographic structures employs the placement of thiol terminated DNA molecules within the molecular assembly, positioned to allow tethering of the biomolecular nanostructure to the substrate through gold-thiol bonds. Although a number of soft chemistry mechanisms can be employed to associate DNA molecules with substrates, the use of the origami constructs as substrates suggests that single stranded DNA provides the optimum attachment strategy. A solid state asymmetric PCR process for ssDNA fabrication is therefore described and demonstrated. Structures generated with the three tiered attachment strategy described here are amenable to characterization and assembly verification using AFM and NSOM. While a complete convergence of top down and bottom up approaches cannot be claimed, it is clear that the practice and methods of molecular lithography are rapidly advancing.

Bilayer lipid membranes (BLMs) have been studied extensively due to functional and structural similarities to cell membranes, fostering research to understand ion-channel protein functions, measure bilayer mechanical properties, and identify self-assembly mechanisms. BLMs have traditionally been formed across single pores in substrates such as PTFE (Teflon). The incorporation of ion-channel proteins into the lipid bilayer enables the selective transfer of ions and fluid through the BLM. Processes of this nature have led to the measurement of ion current flowing across the lipid membrane and have been used to develop sensors that signal the presence of a particular reactant (glucose, urea, penicillin), improve drug recognition in cells, and develop materials capable of creating chemical energy from light. Recent research at Virginia Tech has shown that the incorporation of proton transporters in a supported BLM formed across an array of pores can convert chemical energy available in the adenosine triphosphate (ATP) into electricity. Experimental results from this work show that the system-named Biocell-is capable of developing 2µW/cm² of membrane area with 15μl of ATPase. Efforts to increase the power output and conversion efficiency of this process while moving toward a packaged device present a unique engineering problem. The bilayer, as host to the active proton transporters, must therefore be formed evenly across a porous substrate, remain stable and yet fluid-like for protein interaction, and exhibit a large seal resistance. This article presents the ongoing work to characterize the Biocell using impedance analysis. Electrical impedance spectroscopy (EIS) is used to study the effect of adding ATPase proteins to POPS:POPE bilayer lipid membranes and correlate structural changes evident in the impedance data to the energy-conversion capability of various partial and whole Biocell assemblies. The specific membrane resistance of a pure BLM drops from 40-120kΩ•cm² to only a few hundred Ω•cm² upon reconstitution of ATPase proteins. Power characterization indicates that ATP hydrolysis may result in charging of the silver-silver chloride electrodes.

Nanotechnology applications for food safety and biosecurity, especially development of nanoscale sensors for foodborne pathogen measurement are emerging. A novel bio-functional nanosensor for Salmonella detection was developed using hetero-nanorods. The silica nanorods were fabricated by glancing angle deposition method and the gold was sputtered onto the silica nanorods. Alexa488-succinimide dye was immobilized onto the annealed Si nanorods via the attachment between dye ester and primary amine group supplied by the 3-Aminopropyltriethoxysilane. The anti-Salmonella was conjugated to gold via Dithiobis[succinimidylpropionate] self-assembly monolayer. Due to the high aspect ratio nature of the Si nanorods, hundreds or thousands of dye molecules attached to the Si nanorods produced enhanced fluorescence signal. These biologically functionalized nanorods can be used to detect Salmonella with fluorescent microscopic imaging. This new nanoscale biosensor will be able to detect other foodborne pathogenic bacteria for food safety and security applications.

Strained silicon (ε-Si), the fundamental material of integrated circuit, is finding tremendous attention not only because it boosts the speed but also reduces the power consumptions of electronic devices. Carrier mobility in a ε-Si thin layer is enhanced compared to unstrained layers. However, strain distribution in ε-Si layers is inhomogeneous in the nano-scale, which can degrade performance of electronic devices. Raman spectroscopy can be used to study strain fluctuations in silicon because the optical phonons in Raman spectra are strongly influenced by strain. Though silicon are Raman active devices, the Raman efficiency of a nanometer layer of strained silicon is extremely weak and is often eclipsed under the Raman scattering of underlying buffer substrates. Here, we utilized surface enhancement in Raman scattering to overcome weak emission problems and to suppress averaging effect. Thin ε-Si layers were covered with thin silver layer to invoke surface enhanced Raman spectroscopy. This technique is promising but it lacks the spatial resolution in the nano-scale due to diffraction limit from the probing light. In order to achieve nano-scale spectroscopy, point-surface-enhancement was used, rather than a large surface enhancement. We used a silver-coated sharp tip, just like SERS, but only the sample region very close to the tip apex is characterized. This technique, known as the tipenhanced Raman spectroscopy, provides nanometric resolution in our measurement. For further improvement of SNR, we introduce several approaches mainly for the suppression of background signals arising from crystalline bulk materials. The characterization techniques describe above is applicable to other nano-materials.