We have used a number of methods to grow long aligned single-walled carbon nanotubes. Geometries include individual long tubes, dense parallel arrays, and long freely suspended nanotubes. We have fabricated a variety of devices for applications such as multiprobe resistance measurement and high-current field effect transistors. In addition, we have measured conductance of single-walled semiconducting carbon nanotubes in field-effect transistor geometry and investigated the device response to water and alcoholic vapors. We observe significant changes in FET drain current when the device is exposed to various kinds of different solvent. These responses are reversible and reproducible over many cycles of vapor exposure. Our experiments demonstrate that carbon nanotube FETs are sensitive to a wide range of solvent vapors at concentrations in the ppm range.

In this paper, we report the results of an attempt to disperse MWCNTs in water and determine their biocompatibilities. The length of the MWCNTs was reduced by treating the acidic nanotube suspension with ultrasonic irradiation. Then, the cut nanotubes were size-separated into 670, 550 and 220 nm length by filtration using polycarbonate membrane filters. The neutrophils activity (TNF-α) of size-separated MWCNTs was low and confirmed biocompatible.

We present a method for synthesizing inorganic-thin-layer-coated carbon nanotubes by pulsed laser deposition. Isolated multi-walled carbon nanotubes (MWNTs) were coated with inorganic thin layer in a multishell form. The product showed that various inorganic thin layers were uniformly wrapped around a MWNT, and reflected the shape of the MWNT. The thickness of the coated thin layer was precisely controlled with nanometer accuracy. Moreover, a metal-coated carbon nanotube (CNT) tip for scanning tunneling microscope (STM) has been developed. The observation of a Si(111)-7x7 surface using the metal-coated CNT tip demonstrated stable atomic imaging and potentiality of scanning tunneling spectroscopy (STS) measurement, which can be achieved from the pristine stage. It was demonstrated that the mechanical robustness and flexibility of the tip were maintained by virtue of the thin coated layer.

Carbon nanotubes, which have attracted a significant amount of research attention in recent years, are promising nanoscale materials as building blocks for "bottom-up" assembly of nanoelectronics and nanosensing devices. So far, the fabrication of nanotube devices has often been based on randomly growing or depositing nanotubes, and subsequently finding the ones with desired origin and direction using microscopy techniques. However, it is crucial to be able to assemble such devices in a controllable way, in order to study a large number of them systematically. In this paper, I will present our efforts to tackle this assembly problem by using physics and engineering to control the chemistry of nanotube growth. In particular, we have aligned single-walled carbon nanotubes on oxide surfaces by applying an in situ electric field across microfabricated electrodes during chemical vapor deposition growth. We have then extended this technique to two-dimensional assembly of carbon nanotubes. In particular, we have designed an electrode configuration that would give nanotube crosses in a single growth step. Using this design, we have demonstrated the feasibility of 2D assembly of carbon nanotubes using electric field engineering. These experiments also provide invaluable information about how nanotubes respond to the direction, magnitude, and polarity of external electric fields that may be present during growth. The generality, versatility, and scalability of this assembly technique make it very attractive for controlled growth and assembly of nanoelectronics and nanosensing devices.

Nanoscale electronic devices offer bio-detection schemes that are complementary to optical detection methods. This paper reviews the utilization of field effect transistor devices with carbon nanotubes as conducting channels - the device architectures and detection schemes are reviewed in the paper 5592-34 presented at this meeting- for the detection and monitoring biological processes such as ligand-receptor interactions and enzymatic processes. A complex device with both biological and electronic functionality is also discussed.

he fabrication, electrochemical characterization, and sensing applications of low-site density carbon nanotubes based nanoelectrode arrays (CNT-NEAs) are reported in this work. Spin-coating of an epoxy resin provides a new way to create the electrode passivation layer that effectively reduces the current leakage and eliminates the electrode capacitance by sealing the side-wall of CNTs. The CNT-NEAs fabricated in our work effectively use the open ends of CNTs for electrochemical sensing. The open ends of the CNTs have fast electron transfer rates similar to a graphite edge-plane electrode, while the side-walls present very slow electron transfer rates similar to the graphitic basal plane. Cyclic voltammetry showed the sigmoidal shape curves with low capacitive current and scan-rate-independent limiting current. The successful development of a glucose biosensor based on CNT-NEAs for the selective detection of glucose is also described. Glucose oxidase was covalently immobilized on the CNTs tips via carbodiimide chemistry by forming amide linkages between the amine residues and carboxylic acid groups on the open ends of CNTs. The biosensor effectively performs selective electrochemical detections of glucose in the presence of common interferences.

The study of the ac properties of nano-electronic systems is still in its infancy. In this paper we present an overview of recent work aimed at advancing the understanding of this new field. Specifically, we first discuss the passive RF circuit models of one-dimensional nanostructures as interconnects. Next, we discuss circuit models of the ac performance of active 1d transistor structures, leading to the prediction that THz cutoff frequencies should be possible. We recently demonstrated the operation of nanotube transistors at 2.6 GHz. Third, we discuss the radiation properties of 1d wires, which could form antennas linking the nanoworld to the macroworld. This could completely remove the requirements for lithographically defined contacts to nanotube and nanowire devices, one of the greatest unsolved problems in nanotechnology.

This paper reviews the development of microwave carbon nanotube resonator sensors for gas sensing applications. The carbon nanotube sensor is a passive circuit that does not rely on battery for operation. Our experimental results demonstrate that the microwave carbon nanotube resonator sensor achieve a sensitivity of 8000 and 4000 Hz/ppm at 20 and 100 ppm respectively. This sensor platform has great potential for wireless sensing network applications.

In-situ Raman and fluorescence measurements were used to detect optically trapped single-walled carbon nanotubes (SWNTs). The in-situ fluorescence technique provides strong indirect visual evidence of optical trapping of SWNTs by monitoring the fluorescence quenching from a solution containing a mixture of carbon nanotubes and a fluorescent dye. The second monitoring technique uses in-situ Raman spectroscopy to show that in the presence of the optical trap, both the profile and the intensity of the nanotube Raman spectrum changes compared to when the optical trap is off. The Raman monitoring setup consists of two lasers which independently create the optical trapping path and Raman probing path. In this technique the Raman probe is capable of detecting structural information of the carbon nanotubes in the optical trap; therefore providing direct evidence of the local SWNTs concentration variation and chirality distribution. Both methods were used to verify optical trapping of SWNT and to determine the trapping threshold, trapping volume profile, and information on tube concentration change during optical trapping.

I will review recent advances in DoD nanoscience and technology (NST) at the Air Force Research Laboratory (AFRL) in the areas of nano-materials, nano-electronics, and nano-energetics. NST will profoundly change all critical aspects of maintaining a technologically superior national defense capability. In this talk, I will focus on programmatic priorities for AFRL basic and applied R&D in the seven selected priority areas that comprise the AFRL Strategic Nanotech Plan. The goal of this plan is to focus, prioritize and guide future AF funding in nanotechnology. The selected topics include: tailorable dielectrics, reconfigurable optical response materials, adaptive structural materials, quantum confined optical sensors and sources, nanotechnology for RF, as well as several cross-cutting topics such as self-assembly, interfaces, and modeling and simulation.

We present a new approach for growing Si nanowires directly from a silicon substrate, without the use of a metal catalyst, silicon vapor or CVD gasses. The growth can be performed in a furnace type configuration at moderate temperatures or in localized regions by resistive heating. Since the silicon wires grow directly from the silicon substrate, they do not need to be manipulated nor aligned for subsequent applications. Wires in the 20-50 nm diameter range with lengths over 80 μm can be grown by this technique. We have studied the effects of various growth parameters, including temperature, substrate orientation, initial sample cleaning and carrier gasses. Results indicate that most important parameters in the growth of the nanowires are the surface cleaning, the temperature and the type of carrier gas used. A model is proposed, which involves an oxide catalyst for the process, with the growth of the nanowires enabled by a significantly enhanced silicon surface diffusion process, due to adsorption of hydrogen gas on the substrate surface. These nanowires can be grown locally by resistive heating, and thus they are ideal candidates for direct growth on a MEMS cantilever sensor, where the Si nanowire growth can be performed in such a way that the rest of the structure remains at low temperature, reducing the chance of high temperature damage of already processed regions. The wires, once formed on the MEMS device, can be used as adsorption sites for an NRL sorptive polymer, which is currently being used for nerve gas detection. The addition of the nanowires enhances the surface area significantly and thereby it is expected to improve the detection capability of the MEMS structure.

Enormous manufacturing cost and technical complexity of continued shrinking of electronic devices through the conventional transformative "top-down" approach have motivated efforts worldwide to explore simpler alternatives. New nano-scale assembly technology, such as catalyzed or self-assembled growth of nanowires and quantum dots, may enormously benefit integrated circuit fabrication technique methods. In the recent past, semiconductor nanowire devices have exhibited many novel electronic, optical and chemical properties. Despite a significant progress in nanowire synthesis and many promising single device demonstrations, nanowire applications have been hindered by our incapability to incorporate them within ICs. Several research groups have demonstrated an approach of serially connecting metal electrodes to individual nanowires using costly and slow e-beam lithography and made considerable investigations of the nanowire devices. However, none of those are massively parallel and manufacturable interfacing techniques that are crucial for reproducible fabrication of dense, low-cost nanodevices. In this paper, we present a novel bridging techniques that can connect a large number of highly directional metal-catalyzed nanowire devices between two pre-fabricated electrodes. Two opposing vertical and electrically isolated semiconductor surfaces are fabricated using coarse optical lithography along with wet and dry etching. Lateral nanowires are then grown from one surface and epitaxially connected to the other, forming mechanically robust "nano-bridges". By forming the structure on a silicon-on-insulator (SOI) substrate, the needed electrical isolation is achieved. The bridges are found to be mechanically robust and can resist significant force and chemical attacks. The technique, for the first time, can help access individual nanowire devices without using a nanoprobe or expensive lithography techniques. Using this novel bridging technique, novel nano-electronic and photonic devices can be designed and integrated with conventional circuits. The results will open doors to unprecedented device-density in integrated circuits, eventually making the nanowire based devices a commercial reality.

We present the synthesis of two novel morphologies for carbon tubular structures: Nanopipettes and Micropipes. The synthesis procedures for both these structures are both unique and different from each other and the conventional methods used for carbon nanotubes. Carbon nanopipettes, open at both ends, are made up of a central nanotube (~10-20 nm) surrounded by helical sheets of graphite. Thus nanopipettes have an outer conical structure, with a base size of about a micron, that narrows down to about 10-20 nm at the tip. Due to their unique morphology, the outer walls of the nanopipettes continuously expose edge planes of graphite, giving a very stable and reversible electrochemical response for detecting neurological compounds such as dopamine. The synthesis of carbon nanopipettes is based on high temperature nucleation and growth of carbon nanotubes under conditions of hydrogen etching during growth. Carbon micropipes, on the other hand, are tubular structures whose internal diameters range from a few nanometers to a few microns with a constant wall thickness of 10-20 nm. In addition to tuning the internal diameters, the conical angles of these structures could also be changed during synthesis. Due to their larger inner diameters and thin walls, both the straight and conical micro-tubular structures are suitable for microfluidic devices such as throttle valves, micro-reactors, and distribution channels. The synthesis of carbon micro-tubular structures is based on the wetting behavior of gallium with carbon during growth. The contact angle between gallium and the carbon wall determines the conical angle of the structure. By varying the contact angle, one can alter the conical angles from 400 to -150, and synthesize straight tubes using different N₂/O₂ dosing compositions. An 'n-step' dosing sequence at various stages of growth resulted in 'n-staged' morphologies for carbon micro-tubular structures such as funnels, tube-on-cone, Y-junctions and dumbbells.

Controlling fabrication of mono-dispersed and well-aligned arrays of one-dimensional (1D) nanostructures, nanowires or nanotubes, will benefit a lot for the investigation of their physical properties and their potential use in nanolasers, chemical and biological sensors, and nanoelectrode arrays for solar energy conversion and catalysis. In our previous works, we have fabricated a broad range of semiconductor nanowire arrays by electrochemical synthesis in template. In this present, we design a well-controlled process to fabricate uniform nanotube arrays through a multi-step template replication and electrodeposition approach. The resulting nanotubes with uniform wall thickness and diameters along the entire tubes are highly ordered and mono-dispersed. Moreover, we develop a supercritical drying route to avoid the clustering or collapse of the nanowire arrays caused by capillary force during the removing of the template. By this strategy, we have obtained large-scale, non-collapse, well-aligned nanowire arrays on conductive substrates. Final, the uses of these nanowire arrays for future nanodevices are discussed.

Single-crystalline tin dioxide (SnO₂) nanobelts have been assembled with microfabricated suspended heaters as low-power, sensitive gas sensors. With less than 4 mW power consumption of the micro-heater, the nanobelt can be heated up to 500°C. The electrical conductance of the heated nanobelt was found to be highly stable and sensitive to toxic and inflammable gas species including dimethyl methyl phosphonate (DMMP), nitrogen dioxide (NO₂), and ethanol. The experiment is a step towards the large scale integration of nanomaterials with microsystems, and such integration via a directed assembly approach can potentially enable the fabrication of low-power, sensitive, and selective integrated nanosensor systems.

A series of inorganic nanorods, nanowires, nanoribbons, and nanoscrolls have been synthesized in large-area arrays vertically aligned on metallic surfaces. The simple syntheses of the nanowire films are accomplished in situ by gas-solid and liquid-solid reactions under mild conditions. For the preparation of endohedral metallofullerene films, solution casting and electrochemical techniques are employed. The structural, optical, and electrical properties of the nanostructures have been characterized, which provide interesting prospects of these film materials in various applications. Potential uses of these films as passive and/or active components in dye-sensitized solar cells and gas sensors have been demonstrated in a number of preliminary experiments.

Parallel arrays of self-assembled rare earth disilicides (erbium and dysprosium) nanowires were grown on Si(001) substrates with nanowire width between 3-10 nm and used as a template for fabricating noble metal (platinum and gold) nanostructure arrays. Submonolayer coverage of platinum and gold were deposited on the nanowire/Si(001) surface post rare earth disilicide growth. Scanning tunneling microscopy and reactive ion etching showed that platinum and gold preferentially deposited on the nanowire surface versus the Si surface. Reactive ion etching of erbium disilicide nanowires with and without platinum on the surface demonstrated that platinum acted as a more resistant etch mask than erbium disilicide. By varying the platinum coverage on the surface we demonstrate the ability to select arrays of nanowire or nanocrystal arrays as a function of platinum coverage.

Inorganic nanowires are expected to play a central role in the re-engineering of products with applications in composites, thin films, nanodispersions, energy conversion devices, sensors, nanoelectronic devices and optics. The synthesis of materials at the nanoscale might also help in the discovery of new phases with interesting properties. However, the synthesis strategies for inorganic nanowires is quite limited and have not reached the level of maturity needed for either bulk manufacturing or for controlling nanowire characteristics such as sub 10 nm diameters and different growth directions. In this regard, we report several synthesis strategies that potentially offer in-situ control over the resulting nanowire characteristics such as size, growth direction and an ability to form two-dimensional networks. The techniques described here could be scaled up easily for bulk production of various nanostructures. Our preliminary results suggest that the nanowires form stable dispersions in both organic and aqueous solvents compared to nanoparticles of the same material.

This article introduces a process for the growth of oxide nanorod arrays that combines sol preparation and template-based electrophoretic deposition. First, fundamentals and practical approaches in sol-gel processing for synthesis of inorganic or inorganic/organic hybrid materials are briefly described. Secondly, electrophoresis in colloidal dispersions and electrophoretic deposition technique are discussed. Particular attention is devoted to the electrophoretic deposition for the growth of oxide nanorod arrays from sols. Lastly, techniques similar to or derived from sol electrophoretic deposition for the growth of single crystalline oxide nanorod arrays are presented with vanadium pentoxide as a model system. Further examples are shown that the sol electrophoretic deposition is an effective method for the formation of conformal coating of thin films of oxides on metal nanorods to produce metal-oxide core-shell nanocable arrays. Relations between processing conditions, growth parameters, morphologies, microstructures, and properties of nanorod arrays are discussed.

We report a fabrication technique that is potentially capable of producing arrays of individually addressable nanowire sensors with controlled dimensions, positions, alignments, and chemical compositions. The concept has been demonstrated with electrodeposition of palladium wires with 75 nm to 350 nm widths. We have also fabricated single and double conducting polymer nanowires (polyaniline and polypyrrole) with 100nm and 200nm widths using electrochemical direct growth. Using single Pd nanowires, we have also demonstrated hydrogen sensing. It is envisioned that these are the first steps towards nanowire sensor arrays capable of simultaneously detecting multiple chemical species.

We demonstrate detection of NO₂ down to ppb levels using transistors based on both single and multiple In₂O₃ nanowires operating at room temperature. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors. A comparison between the single and multiple nanowire sensors reveals that the latter have numerous advantages in terms of great reliability, high sensitivity and simplicity in fabrication. Furthermore, selective detection of NO₂ can be readily achieved with multiple-nanowire sensors even with other common chemicals such as NH₃, O₂, CO and H₂ around.

Highly sensitive, sequence-specific and label-free DNA sensors were demonstrated by monitoring the electronic conductance of silicon nanowires with chemically bonded single stranded (ss) DNA or peptide nucleic acid (PNA) probe molecules. For a 12-mer oligonucleotide, tens of pM of target ss-DNA in solution was recognized when the complementary DNA oligonucleotide probe was attached to the SiNW surfaces. In contrast, ss-DNA samples of 1000x concentration with single base mismatch only produce a weak signal due to nonspecific binding.

A nanosensor technology has been developed using nanostructures, such as single walled carbon nanotubes (SWNTs) and metal oxides nanowires or nanobelts, on a pair of interdigitated electrodes (IDE) processed with a siliconbased microfabrication and micromachining technique. The IDE fingers were fabricated using thin film metallization techniques. Both in-situ growth of nanostructure materials and casting of the nanostructure dispersions were used to make chemical sensing devices. These sensors have been exposed to hazardous gases and vapors, such as acetone, benzene, chlorine, and ammonia in the concentration range of ppm to ppb at room temperature. The electronic molecular sensing in our sensor platform can be understood by electron modulation between the nanostructure engineered device and gas molecules. As a result of the electron modulation, the conductance of nanodevice will change. Due to the large surface area, low surface energy barrier and high thermal and mechanical stability, nanostructured chemical sensors potentially can offer higher sensitivity, lower power consumption and better robustness than the state-of-the-art systems, which make them more attractive for defense and space applications. Combined with MEMS technology, light weight and compact size sensors can be made in wafer scale with low cost.

We have studied ways to control density as well as spacing among functional groups. In particular, we observed that use of aziridine for the surface hyperbranching polymerization yielded extremely high surface density of primary amine that is useful for the immobilization of molecules of biological relevance such as oligo DNA. Also, an employment of dendrons of appropriate molecular architecture provided mesospacing among the reactive functional groups. The spacings was expected to guarantee the freedom of the biological macromolecules so that their properties are close to that in solution in spite of the confinement in the two dimensional world. We demonstrated that this was the case for oligonucleotide microarrays.

A procedure is developed to modify silicon surface by organic monolayer films with designed micrometer patterns of different chemical functionalities, which is based on the photolithography and photoactivated reaction of alkenes with Si-H on the hydrogen-terminated silicon surface. Subsequent chemical modification of the micro-pattern can be devised. As an illustration, DNA probe arrays are formed with the spatial resolution limited only by the current photolithography technology. The hybridization of the patterned probes with complementary targets is demonstrated through fluorescence detection. This method is applicable to high throughput biochips.

This contribution summarizes some of our efforts in designing, assembling and functionally characterizing supramolecular interfacial architectures for bio-affinity studies and for biosensor development. All the surface interaction studies will be based on the recently introduced novel sensor platforms involving surface plasmon fluorescence spectroscopy (SPFS) and -microscopy (SPFM). Emphasis will be put on documenting the distance-dependence of fluorescence intensity at the metal-dielectric interface and utilizing this principle to optimize the conformation/orientation of the interfacial supra-molecular sensor coatings. This is exemplified by a number of examples, including a layer-by-layer assembly system, antibody-antigen interactions, oligonucleotide-oligonucleotide, and oligonucleotide-PCR amplicon hybridization. For practical sensing purposes, a three-dimensionally extended surface coating is then employed to overcome the fluorescence quenching problem on a planar matrix. A commercial dextran layer is shown to be an optimized matrix for SPFS, with an example of a protein-binding study.

Extracellular enzymes, lignin peroxidase (LiP) and manganese peroxidase (MnP) from white rot fungus Phanerochaete chrysosoporium, have been shown to degrade various harmful organic compounds ranging from chlorinated compounds to polycyclic aromatic hydrocarbons (PAH) to polymeric dyes. The problems in using immobilized enzymes for biocatalysis/bioremediation are their loss of activity and long-term stability. To address these issues, adsorption by layer-by-layer assembly (LbL) using polyelectrolytes, entrapment using gelatin, and chmisorption using coupling reagents have been investigated. In order to increase surface area for catalysis, porous silicon, formed by electrochemical etching of silicon, has been considered. The efficacy of these extremely stable nanoassemblies towards degradation of model organic compounds-veratryl alcohol (VA and 2,6-dimethoxyphenol (DMP)-in aqueous and in a mixture of aqueous/acetone has already been demonstrated. In parallel, we are pursuing development of sensors using these immobilized enzymes. Experiments carried out in solution show that NO can reversibly bind Ferri-LiP to produce a diamagnetic complex with a distinct change in its optical spectrum. NO can be photolyzed off to produce the spectrum of native paramagnetic ferri-species. Preliminary data on the detection of NO by LiP, based on surface plasmon resonance (SPR) using fiber optic probe, are presented.

Self-assembly, the spontaneous organization of parts into ordered arrays and structures, is an omnipresent process in nature. Our group explores the use of self-assembly as an engineering concept to construct functional devices across the size scale. In this paper we present two examples of self-assembly. In the first example, we show how self-assembled monolayers of anthryl phosphonic acid can be used to form a nano-scale charge conduction channel. The molecular monolayer forms on a silicon dioxide surface and is placed between two metal electrodes. We have synthesized the molecules, verified the formation of the monolayer with X-ray photoemission spectroscopy and atomic force microscopy, and characterized the lateral charge carrier transport properties of the molecules. This molecular monolayer provides a facile way for integration of a nano-scale electronic device with conventional circuitry. In the second example, we demonstrate how microfabricated components can self-assemble into an electrical network. We have developed a microfabrication process for parallel production of 100 mm hexagonal silicon parts each carrying a portion of an electrical network. We functionalize the parts either with a low-melting point alloy or with a polymer and allow for their self-assembly into an ordered lattice at an air-water interface due to capillary forces.

Scanning probe microscopy has been applied in many studies to manipulate atoms or molecules. In particular, force spectroscopy using an atomic force microscope (AFM) is a powerful tool to elucidate intermolecular or intramolecular interactions and provide mechanical information. If enzymes could retain their activity when immobilized on probes, not only could enzyme-substrate interactions be investigated but also the probes could be used for precise biomolecular manipulation at the nano-scale. In our study, a method based on "Enzymatic Nanolithography" was successfully performed in a buffered solution using Staphylococcal serine V8 protease and AFM. To estimate the fabricating activity of the protease immobilized on the AFM tip to peptides immobilized on a substrate, we designed and synthesized peptides that showed enzymatic action specific to the protease. When the protease digested the reporter peptide a quencher residue was released from the main flame of the peptide and resulted in fluorescence. In the designed 9 mer peptides, TAMRA functioned as a good quencher for FAM. After contact of the protease-immobilized tip to the reporter peptide layer, a fluorescent area was observed by microscopic imaging.

Oligonucleotide probe arrays were in-situ synthesized on the H₂/N₂ plasma modified poly(terafluoroethylene) (PTFE) surface via micro-fluidic channels connected with an automated synthesizer. A contact angle measurement of water droplets was used to ascertain the hydrophilicity of the surface. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of polar amino groups on the surface. Ultra-violet (UV) spectrum analysis indicated that the surface showed a coupling efficiency higher than 98% for in situ synthesis of oligonucleotides arrays. The probe array specificity was discriminated by hybridizing with fluorescent target sequencyes. Oligonucleotide probe arrays on modified PTFE surface showed high stability and durability after repetitive denaturing and hybridizing. The results implied the plasma modified PTFE surface was extremely stable, performed well in DNA hybridization assays and could service as a good substrate for high-density oligonucleotide array synthesis.

Biocompatible semiconductor quantum dot (QD) probes with extended plasma circulating times have been developed for cancer imaging in living animals. The structural design involves encapsulating luminescent QDs with a triblock copolymer, and linking this amphiphilic polymer to multiple poly(ethylene glycol) (PEG) molecules. In vitro histology and in vivo imaging studies indicate that the QD probes can be delivered to tumor sites by enhanced permeation and retention. Using both systemic injection of long-circulating QD probes and subcutaneous injection of QD-tagged microbeads, we have achieved sensitive and multicolor fluorescence imaging of cancer cells under in vivo conditions. These results raise new possibilities for ultrasensitive and multiplexed imaging of molecular targets in vivo.

We demonstrate the use of a photochromic dye to achieve fluorescence resonance energy transfer (FRET) modulation between a QD donor and the dye acceptor brought in close proximity in a selfassembled QD-protein-dye conjugate. The E. coli maltose binding protein (MBP) appended on its C-terminal with an oligohistidine attachment domain, immobilized onto CdSe-ZnS core-shell QDs was labeled with a sulfo-N-hydroxysuccinimide activated photochromic BIPS molecule (1',3-dihydro-1'-(2-carboxyethyl)-3,3-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indoline]). Two different dye-to-MBP-protein ratios of 1:1 and 5:1 were used. The ability of MBP-BIPS to modulate QD photoluminescence was tested by switching BIPS from the colorless spiropyran (SP) to the colored merocyanine (MC) using irradiation with white light (>500 nm) or with UV light (~365 nm), respectively. QDs surrounded by ~20 MBP-BIPS with a dye to protein ratio of 1 showed ~25% loss in their photoemission with consecutive repeated switches, while QDs surrounded by ~20 MBP-BIPS with BIPS to MBP ratio of 5 produced a substantially more pronounced rate of FRET where the QD emission was quenched by ~60%. This result suggests the possibility of using QD-protein conjugates to assemble reversible FRET nanoassemblies where the QD emission can be controlled by changing the properties of the acceptors dyes bound to the protein.

Metal nanoshells are a novel type of composite nanoparticle consisting of a dielectric core covered by a thin metallic shell which is typically gold. Nanoshells possess highly favorable optical and chemical properties for biomedical imaging and therapeutic applications. By varying the relative the dimensions of the core and the shell, the optical resonance of these nanoparticles can be precisely and systematically varied over a broad wavelength region ranging from the near-UV to the mid-infrared. This range includes the near-infrared (NIR) region where tissue transmissivity peaks. In addition, nanoshells offer other advantages over conventional organic dye imaging agents, including improved optical properties and reduced susceptibility to chemical/thermal denaturation. Furthermore, the same conjugation protocols used to bind biomolecules to gold colloid are easily modified for nanoshells. We first review the synthesis of gold nanoshells and illustrate how the core/shell ratio and overall size of a nanoshell influences its scattering and absorption properties. We then describe several examples of nanoshell-based diagnostic and therapeutic approaches including the development of nanoshell bioconjugates for molecular imaging, the use of scattering nanoshells as contrast agents for optical coherence tomography (OCT), and the use of absorbing nanoshells in NIR thermal therapy of tumors.

In this paper several approaches to fabricate semiconductor magnetic nanocomposite are reported. Several thiol- and amino- silane cross linked molecules were used to couple and embed CdSe and Fe3O4 nanoparticles into silica particles. The resulting nanocomposites were characterized by optical spectroscopies, transmission electron microscopy, electron paramagnetic spectroscopy and fluorescence optical microscopy. The new developed nanocomposite particles posses the advantage of being both magnetic and luminescent. The chemical functionality rich surface of these new nanoparticles could enable their application in bioassays, cell separation and drug delivery.

The use of polystyrene nanoparticles with europium chelate has been demonstrated as fluorescent reporters in an immunoassay for atrazine. The limit of detection with the nanoparticles was similar to that achieved with a conventional ELISA. It was shown that as the particle size decreased the time required for binding decreased and the sensitivity of the assay increased. This suggests that the use of smaller particles would greatly speed up the reaction and simultaneously increase sensitivity. However, the detection system used sets limits to the particle size as well. There is clearly a point where our detection system would not be sensitive enough to detect the emission from small particles. Therefore, a highly sensitive excitation/detection system needs to be developed to fully utilize the kinetic advantage from small particle size.

Biomedical or Biological Micro-Electro-Mechanical- Systems (BioMEMS) have in recent years become increasingly prevalent and have found widespread use in a wide variety of applications such as diagnostics, therapeutics and tissue engineering. This paper reviews the interdisciplinary work performed in our group in recent years to develop micro-integrated devices to characterize biological entities. We present the use of electrical and mechanically based phenomena to perform characterization and various functions needed for integrated biochips. One sub-system takes advantage of the dielectrophoretic effect to sort and concentrate bacterial cells and viruses within a micro-fluidic biochip. Another sub-system measures impedance changes produced by the metabolic activity of bacterial cells to determine their viability. A third sub-system is used to detect the mass of viruses as they bind to micro-mechanical sensors. The last sub-system described has been used to detect the charge on DNA molecules as it translocates through nanopore channels. These devices with an electronic or mechanical signal output can be very useful in producing practical systems for rapid detection and characterization of cells for a wide variety of applications in the food safety and health diagnostics industries. The paper will also briefly discuss future prospects of BioMEMS and its possible impact and on bionanotechnology.

Low dimensional lead salt structure such as quantum-well (QW) structure is proposed for the fabrication of opto-electronic devices. Among [100], [111], and [110] orientations, [110]-orientated QW structure offers the highest gain. Theoretical simulations of [110] QW Pb-salt edge-emitting lasers show a 70-degree temperature increase in continuous-wave (CW) operation compared to the conventional [100]-orientated lasers. With modestly reduced Auger recombination of low dimensional material and with improved heat dissipation for laser structure, CW operation with about 10 mW output powers at room temperature for PbSe QW laser is predicted. PbSe epitaxial layer and PbSe/PbSrSe QW structures were, for the first time, successfully grown on [110]-orientated BaF₂ substrate by molecular-beam-epitaxy (MBE). The linewidth of the rocking curve from high-resolution x-ray diffraction (HRXRD) measurement for PbSe thin film is 60 arcsec, which indicates high crystalline quality. The dislocation density estimated by the rocking curve is 1.18x10⁷ cm^-2. Photoluminescence intensity of [110]-orientated samples was twice as high as that on [111]-orientated BaF₂ substrates from the same MBE run.

Wireless Sensor Nodes are basic building blocks for future ubiquitous networks. These nodes have to be able to gather and transmit information to their neighbors in complete autonomy. This means that with no battery, they rely on scavenging the energy necessary to operate directly from their environment, like conversion of solar or vibration based energy. This stringent requirement drastically limits the power budget of those devices to a level below 100μW. From the architecture prospective, work on reducing the complexity of the transceiver is mandatory, in order to reduce both size and power consumption. The simplest approach relies on the on/off modulation of a GHz range carrier frequency signal in a transmit channel, which is then directly selected and demodulated in the receiving path. For these particular functionalities, i.e. frequency generation and filtering, nano-mechanical resonators present a strong advantage of scalability that helps to integrate them into dense arrays directly on top of CMOS. This avoids package parasitic, allows for MEMS/circuitry co-design, and eventually leads to size shrinkage and power saving.

Building photonic integrated circuits, which overcome the quantum limitation of the uncertainty principle, requires a new paradigm for optical waveguide design that is fundamentally different from the conventional approach. With recent advances in creating nanomaterials, quantum dots made of semiconductor compounds have enabled manipulation of electron and photon interaction in the presence of optical or electrical stimulus. In this paper, we explore the frontier of using quantum dots in new waveguide structures to pave the way for devices whose dimensions are below the diffraction limit of light. These components handle signals in the optical domain, and exploit the high-speed and transparency advantages of light. We first calculate the gain spectrum for pulsed optically-pumped quantum dots and derive the gain coefficient for waveguides. Then, a new model for a quantum dot waveguide is presented and optimum waveguide structure for propagation is determined. The results for two material systems, CdSe and CdTe quantum dots operating in free space, are given throughout. The model may be applied and extended to other compounds and establishes a foundation for quantum dot nano-scale photonic integrated circuits. By utilizing the non-linear properties of quantum dots, the proposed device forms a basis for applications in sensing, computing, and signal processing.

A novel photonic crystal in which the refractive index of the interstitial void region in a colloidal crystal is gradually changed with respect to the specific direction of the crystal was proposed. This was achieved by infiltrating polymers using the interfacial-gel polymerization with high refractive index dopants. Therefore, the resulting colloidal photonic crystal has a gradually varying stop-band at different positions of the crystal when the incident light was normal to the [111] crystallographic axis. This structure could be a kind of tunable photonic crystals based on the positional variations. The optical properties and potentials for other photonic applications will be investigated.

Quantum-dot infrared photodetectors (QDIPs), based on intersubband transitions in nanoscale self-assembled dots, are perceived as a promising technology for mid-infrared-regime sensing since they are based on a mature GaAs technology, are sensitive to normal incidence radiation, exhibit large quantum confined stark effect that can be exploited for hyperspectral imaging, and have lower dark currents than their quantum well counterparts. High detectivity (D* = 1.0E11 cmHz^1/2/W at 9 microns) QDIPs have been recently shown to exhibit broad spectral responses approximately 2-micron FWHM) with a bias-dependent shift in their peak wavelengths. This controllable, bias dependent spectral diversity, in conjunction with signal-processing strategies, allows us to extend the operation of the QDIP sensors to a new modality that enables us to achieve: (1) spectral tunability (single- or multi-color) in the range 2-12 microns in the presence of the QDIP's dark current; and (2) multispectral matched filtering in the same range. The spectral tuning is achieved by forming an optimal weighted sum of multiple photocurrent measurements, taken of the object to be probed, one for each bias in a set of prescribed operational biases. For each desired spectral response, the number and values of the prescribed biases and their associated weights are tailored so that the superposition response is as close as possible, in the mean-square-error sense, to the response of a sensor that is optically tuned to the desired spectrum. The spectral matching is achieved similarly but with a different criterion for selecting the weights and biases. They are selected, in conjunction with orthogonal-subspace-projection principles in hyperspectral classification, to nullify the interfering spectral signatures and maximize the signal-to noise ratio of the output. This, in turn, optimizes the classification of the objects according to their spectral signatures. Experimental results will be presented to demonstrate the QDIP sensor's capabilities in these new modalities. The effect of dark current noise on the spectral-tuning capability is particularly investigated. Examples of narrowband and wideband multispectral photocurrent synthesis as well as matched filtering are presented.

Nano-structures are increasingly finding more applications in modern electronic/photonic devices. However, an accurate prediction of the nano-device performance is complicated by carrier localization and, in certain applications, the presence of an applied magnetic field. Shot noise measurements are suggested as a means to quantify localization. An alternative technique using tunneling time to characterize localization in nano-structures in the presence of random elastic and inelastic scattering is presented. The treatment is extended to include the effect of magnetic fields. The calculations are carried out self-consistently by solving Schroedinger and Poisson's equations for the accurate determination of the developed space charge.

Recent experimental advances have made carbon nanotubes promising material for utilizing as nano-electro-mechanical systems (NEMS). The key feature of CNT-based NEMS is the ability to drastically change electrical conductance due to a mechanical deformation. The deformation effects can be divided into two major groups: bond stretching of sp² coordinated nanotubes and transition from sp² to sp³ coordination. The purpose of this work is to review the change in electrical response of nanotubes to different types of mechanical deformation. The modeling consists of a combination of universal force-field molecular dynamics (UFF), density functional theory (DFT) and Green's function theory. We show that conductance of metallic carbon nanotubes can decrease by 2-3 orders of magnitude, when deformed by an AFM tip, but is insensitive to bending. These results can explain the experiment of Ref. [1]. Such a decrease is chirality dependent, being maximum for zigzag nanotubes. In contrast, twisting and radial deformation result in bandgap openning only in armchair nanotubes. In addition, radial deformation of armchair nanotubes leads to dramatic oscillations of conductance.

The principles behind the chemical field effect sensor are outlined. A block model for the resistance mode of operation is described. Particular attention is paid to the interaction between semiconductor electrostatics, solution electrostatics, and chemical equilibrium at the surface. The site-binding model of the surface potential and the main models of the electrolyte double layer are reviewed. The semiconductor part of the model is generalized to finite channel thickness. Operation is illustrated using pH sensing as an example. The pH sensitivity is analyzed as a function of semiconductor thickness, gate dielectric thickness, ionic strength of the solution, and other factors.

Of the myriad of potential application areas commonly associated with Nanotechnology, sensors based on carbon nanotubes (CNT) and metal-oxide nanoribbons are one of the closest to commercial reality. In the quest for practical sensing devices, molecular modeling continues to provide useful insight and guidance. In this work we review some of our recent molecular modeling investigations on: (1) CNT-based electromechanical sensors; (2) gas-sensing properties of SnO₂ nanowires/ribbons; and (3) CNT-metal contacts, which can significantly affect the performance of CNT-based sensors.

The Non Equilibrium Green's Function (NEGF) method is a powerful technique to compute quantum transport properties of nanoscale electronic devices. It is applicable to a wide range of devices, ranging from nano transistors, molecular switches, nano wires... Accurately simulating such devices often requires a 2D or a full 3D model. This leads to a large computational expense. We review existing methods for the fast computation of the density of charge using the Schrodinger-Poisson equation, and propose a new algorithm which has a significantly lower computational cost and is exact (in the absence of computer roundoff errors). The algorithm is applicable in the presence of various boundary conditions for the source, drain and gate regions, and for devices of arbitrary geometry.

The effect of particle size on the intensity of surface-enhanced Raman scattering (SERS) using labeled gold nanoparticles has been investigated. Two sets of experiments were preformed, both of which employed 632.8-nm laser excitation. The first entailed a sandwich immunoassay in which an antibody coupled to a smooth gold substrate selectively captured free-prostate specific antigen (f-PSA) from buffered aqueous solutions. The presence of captured f-PSA was then detected by the response of Raman-labeled immunogold nanoparticles with nominal diameters of 30, 40, 50, 60, or 80 nm. The resulting SERS responses were correlated to particle densities, which were determined by atomic force microscopy, by calculating the average response per particle after accounting for differences in particle surface area. This analysis showed that the magnitude of the SERS response increased with increasing particle size. The second set of experiments examined the response of individual nanoparticles. These experiments differed in that the labeled nanoparticles were coupled to the smooth gold substrate by an amine-terminated thiolate, yielding a much smaller average separation between the particles and substrate. The results revealed that particles with a diameter of ~70 nm exhibited the largest enhancement. The origin of the difference in the two sets of findings, which is attributed to the distance dependence of the plasmon coupling between the nanoparticles and underlying substrate, is briefly discussed.

Surface enhanced Raman spectroscopy (SERS), an effect discovered in the 1970s and studied systematically in the 1980s, received a significant "second wind" with the report (primarily by Nie and by Kneipp) of enhancements large enough to allow the Raman spectrum of single molecules to be obtained. It is now understood that this occurs as a result of the extremely high electromagnetic fields that can exist at appropriately configured gaps and interstices between nanoparticles and other nanostructures composed of suitable materials (such as silver). With this insight one is now in a position to fabricate structures that will dependably and repeatably produce single-molecule SERS. We describe three such strategies: using molecular linkers to self assemble silver clusters possessing the correct geometry; fabricating nanowire rafts in which the gap between nanowires are "hot"; and structuring the interior of nanopores so as to produce finely-architectured nanostructured arrays.

Adaptive surface-enhanced Raman scattering (SERS) substrates exhibit unique properties which make them well suited for SERS studies of proteins on surfaces. Specifically, adaptive silver films (ASFs) allow nanoscale restructuring of metal particles during protein deposition which yields a three-fold benefit of soft protein adsorption, protein-metal complex stabilization, and increased SERS signal. In this work ASF fabrication and characterization methods are introduced, with special attention paid to characterization methods that provide insight into the adaptive nature of the substrates, such as UV-vis spectrophotometry, field-emission scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. These ASF substrates show SERS enhancement factors in the range of 10⁶ for an area-averaged signal, and have been successfully used for sub-monolayer protein detection. The addition of a thick metal layer in the ASF fabrication structure typically increases the SERS signal by a factor of four or five. Finally, several examples of current SERS protein studies using ASF substrates are provided.

We developed a label-free, highly sensitive, real time, and micrometer-sized optical fiber biosensor without using any attenuated total reflection (ATR) optics. The sensor is based on the localized surface plasmon resonance (LPR) in gold nanoparticles. The gold nanoparitlces show a large absorption band at around 520 nm due to LPR, which is quite sensitive to the environment around the nanoparticles. Thus change of the refractive index of the ambient medium around the nanoparticles or overcoating a thin dielectric layer on the particles results in a red-shift of the absorption band and change of the absorption intensity. This paper reports a novel optical fiber biosensor that is constructed at the endface of the optical fiber. The fiber probe is consisting of gold nanoparticles that plays as a transducer, where ligand is coated. The return light intensity from the fiber probe is changed by the adsorption of the biomolecules that has affinity to the ligand. The sensitivity was evaluated to be 10 pg/mm² (2x10^-5 RIU) with an LED light, which is compatible with the conventional surface plasmon resonance biosensors that use the ATR optics.

We investigate the optical properties of arrays of closely spaced metal nanoparticles in view of their potential to guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. Finite-difference time-domain simulations of short arrays of noble metal nanospheres show that electromagnetic pulses at optical frequencies can propagate along the arrays due to near-field interactions between plasmon-polariton modes of adjacent nanoparticles. Near-field microscopy enables the study of energy transport in these plasmon waveguides and shows experimental evidence for energy propagation over a distance of 0.5 μm for plasmon waveguides consisting of spheroidal silver particles fabricated using electron beam lithography.

We have used device structures based on the well-established technology for producing high electron mobility transistors to modulate the amplitude and the phase of broadband terahertz pulses. The application of an external gate voltage allowed us to deplete the two-dimensional electron gas, which in turn increased the transmission of the device to THz radiation. In differential transmission experiments at room-temperature we achieved a typical amplitude change of 2-3 % for THz pulses passing through the device. In this paper we present the results of a detailed investigation of the device behavior including I-V characteristics and capacitance measurements that reflect the depletion of the two-dimensional electron gas. In a first demonstration experiment we were also able to use the modulator for audio signal transmission over a THz communication channel. To do this we modified a standard THz time-domain spectrometer to transmit signals up to 25 kHz imprinted onto a 75 MHz train of broadband THz pulses with frequencies between 100 GHz and 3 THz.

We report on the development of an apertureless scanning near-field optical microscope for characterization of dielectric properties of nano-structures at terahertz frequencies. A spatial resolution of ≈ 150 nm is achieved, which corresponds to a sub-wavelength factor of ≈1/1000. The imaging mechanism is due to a resonant coupling between light field and the tip-surface system. This allows for image contrasts which exceed those can be expected from Mie scattering by orders of magnitude. Terahertz images of organic and inorganic structures show that the apertureless terahertz microscopy gives insight into the dielectric properties on submicron scale.

Electro-optic (EO) polymers are promising materials to be used as THz emitters and sensors due to their high nonlinear coefficients and good phase-matching conditions. We demonstrate efficient THz generation from an 80 μm thick EO polymer emitter which is equivalent to that of a 1000 μm thick ZnTe standard. Also, this kind of EO polymer allows a generation up to 20 THz with ultra-short laser pulses. We have observed resonance-enhanced THz generation in another kind of EO polymer composite near its absorption maximum. Due to a sharp resonance of the EO coefficient near the absorption maximum of the material, the amplitude of THz field generated from a 3.1 μm thick film of this composite is 15% larger than that from a 1000 μm thick ZnTe standard. The estimated EO coefficient of this composite at 800 nm is over 1200 pm/V.

Nanostructured materials enable the development of miniature sensing devices that are compact, low-cost, low-energy-consumption, and easily integrated into field-deployable units. Recently we have successfully developed electrochemical sensors based on functionalized nanostructured materials for the characterization of metal ions. Specifically, glycinyl-urea self-assembled monolayer on nanoporous silica (Gly-UR SAMMS) has been incorporated in carbon paste electrodes for the detection of toxic metals such as lead, copper, and mercury based on adsorptive stripping voltammetry, while acetamide phosphonic acid self-assembled monolayer on nanoporous silica (Ac-Phos SAMMS) has been used for the detection of uranium. Both electrochemical sensors yield reproducible measurements with excellent detection limits (at ppb level), are selective for target species, does not require the use of mercury film and chelating agents, and require little or no regeneration of electrode materials. The rigid, open, paralleled pore structure combined with suitable interfacial chemistry of SAMMS also results in fast responses of the electrochemical sensors.

Lab-on-a-Chip (LOC) and μ-TAS (micro-total analytical system) are based on miniaturized integrated platforms that have the potential to revolutionize chemical, biological, and biochemical synthesis and analysis. Here, we demonstrated a process of fabricating a mosaic DNA chip and a corresponding detection method by time-resolved fluorescence (TRF) labeling. We synthesized oligonucleotide sequences in situ on glass slides directly, and then sliced them up into small pieces and patched up the pieces with different sequences to generate a mosaic DNA chip. With multiple BCPDA (BCPDA, abbreviated from 4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid) labeling method based on biotin-avidin amplification, we established a TRF detection format on the mosaic DNA chip. The detection method allows discriminatory signals for perfect match, one-base mismatch, two-base mismatch and three-base mismatch by TRF labeled hybridization, whereby Europium (III, Eu³⁺) was captured and released on the principle of complexation and dissociation interaction between BCPDA and Eu³⁺ solution when the BCPDA-tagged avidin and biotin-ended oligonucleotide sequence linked. The fluorescence spectra and related lifetimes were determined. Also, we compared the TRF detection mode with the conventional fluorescence one. These results showed the former is more reliable and stable than the latter, especially for the mosaic DNA chip. Likewise, by applying TRF probing (or labeling) to specific bio-systems, the discovery is of fundamental interest and has significant implications to time-resolved-fluorescence based detection on biosensor.

A dendron having nine carboxylic acid groups at the end of the branches and a protected amine at the apex was allowed to form a molecular layer on the aminosilylated surface through multipoint ionic attraction. It was found that a compact and smooth monolayer was obtained at appropriate condition. The film quality was maintained successfully after deprotecting CBZ group with trimethylsilyl iodide. The surface density of the primary amine after the deprotection was measured with fluorometry, and 0.1-0.2 amine group per 1 nm² was observed. This implies that the spacing between the amine functional groups is 24-34 Å in hexagonal close packing (hcp) model. In addition, DNA microarrays were fabricated successfully on the dendron-modified surface.

In the gas phase, electron beam irradiation of a furoxan molecule results in the production of two NO molecules and concomitant generation of a triple bond. In this study, we examined whether the selective cleavage of furoxan occurs on the surface of silicon wafers. A furoxan-substituted imine layer was prepared by the reaction of aminosilylated silicon wafers with 4-furoxancarbaldehyde. Formation of the imine layer was confirmed by UV-vis spectroscopy, contact angle goniometry, ellipsometry, and XPS. XPS spectroscopic monitoring of the electron beam (400 eV) induced reaction of the modified silicon wafers showed that two of the furoxan ring nitrogen atoms were lost. To determine if a carbon-carbon triple bond had been generated in the surface product of this reaction, FT-IR spectroscopy and NEXAFS (Near Edge X-ray Absorption Fine Structure) were performed. A weak absorption at 2203 cm^-1 was observed in the FT-IR spectrum, reflecting the presence of a triple bond. The carbon K-edge NEXAFS spectrum contained a π*(C≡C) peak at 286.5 eV. Based on these results, we conclude that electron beam irradiation of the furoxan, incorporated on a silicon wafer surface, results in the release of nitrogen oxide and the formation of a triple bond containing product.

This report characterizes the whispering-gallery mode (WGM) resonators with the design of waveguide and microdisk coupling microstructure. In order to understand and optimize the design, studies over a broad range of resonator configuration parameters including the microdisk size, the gap separating the microdisk and waveguide, and the waveguide width are numerically conducted. The finite element method is used for solving the Maxwell's equations which govern the propagation of electromagnetic (EM) field and the radiation energy transport in the micro/nano-structured WGM systems. The EM field and the radiation energy distributions in the WGM resonator are obtained and compared between the on-resonance and off-resonance cases. A very brilliant ring with strong EM field and high radiation intensity is found inward the peripheral surface of the microdisk under the first-order resonance. While under the second-order resonance, there are two bright rings; and the outer ring inward the peripheral surface is thin and weaker than the internal ring. The microdisk size affects significantly the resonant frequencies and their intervals. The gap also has a slight effect on the resonant frequencies. The effect of waveguide width on the resonant frequencies is negligible. However, the gap as well as the waveguide width does obviously influence the qualify factor and the finesse of the resonant modes.

This paper reports on the investigations of C₆₀ fullerenes films as an optical fiber coating material. The C₆₀ films were coated on the glass substrates and optical fibers by thermal evaporation of commercial C₆₀ powders at a filament temperature of 400°C in a vacuum. The structure and optical properties of these films were investigated. We found that the uniform films could be coated on fibers with a satisfactory adhesion and mechanical properties. In order to improve the properties such as density and surface morphology, we have annealed the coated films in low temperature range (<200°C). Optical transmittance and spectra were recorded and scratch tests were conducted for the coated films. It was found that the densification and reduction of surface roughness occurred when coated C60 films were annealed near by 100°C.

In this experiment, the optical characteristics of porous silicon microcavities (PSM) are studied using spectroscopy analysis. Porous silicon microcavities were fabricated by the anodization of boron doped P-type (111) single crystal wafers in hydrofluoric acid/ethanol (HF/EtOH) electrolytes. The samples were prepared at room temperature under different fabrication conditions in order to obtain different physical parameters such as porosity (p), thickness (d), and pore geometry. The current density was varied from 25mA/cm² to 100mA/cm² and the HF/EtOH concentration was varied from 1:1 to 1:4. The transmission spectra of the prepared samples were investigated over the range of 800 nm to 2400 nm with a period of 2 seconds. The fabricated PSM structures were investigated using SEM and their physical properties were analyzed as a function of the fabrication parameters. The transmission spectra of the prepared samples were compared to the transmission spectra of the reference bulk silicon wafer. We observed that the refractive index of the (PSM) was lower than that of bulk silicon, and it decreased with increasing porosity (p). Based on the experimental spectra of the PSM structure, we report a spectral density function relating the physical properties of the surface and the effective dielectric function.

Porous polypropylene (PP) membranes were modified by the plasma treatment in order to graft amino functional group (-NH₂) onto the membrane surface. Oligonucleotides were in situ synthesized on the aminated polypropylene support. Gold nanoparticle labeled DNAs were bybridized to the synthesized oligonucleotide array. The membranes were exposed to the Silver Enhance Solution for singla amplification. The Hybridization signals of amino plasma-grafted polypropylene membranes were stronger than the commercial polyacrylamide modified polyproplylene membranes that load 0.07 μmol/cm² free primary amino functions. Complementary and mismatched sequences were clearly distinguished. The diameter of nanogold particles and the concentration of thiol DNA modified gold nanoparticles were investigated to improve the hybridization signals. Bigger nanoparticle diameter, as well as higher concentration of thiol DNA modified gold nanoparticles lead to stronger hybridization signals.

We report the preparation, properties and biocompatibility of multi-walled carbon nanotube (MWCNT) disk. Sintered Multi-walled carbon nanotube disk was fabricated by spark plasma sintering the MWCNT and phenol resin mixture by using the Spark Plasma System (SPS) under 1273 K and 80 MPa in vacuum. As the concentration of phenol resin in the sintered MWCNT disk increases, the bending strength and Young’s modulus increased. However, the inflammatory response was observed in the tissue exposed to the surface of the sintered MWCNT disk. This was believed due to the residual phenol resin in the disk. The result indicates that the disk has to be annealed at higher temperatures under inert gas atmosphere to perfectly convert phenol resin to graphitic materials.

Magnetic nanoparticles are considered for biomedical applications, such as the medium in magnetic resonance imaging, hyperthermia, drug delivery, and for the purification or classification of DNA or virus. The performance of magnetic nanoparticles in biomedical application such as hyperthermia depends very much on the magnetic properties, size and size distribution. We briefly described the basic idea behind their use in drug delivery, magnetic separation and hyperthermia and discussed the prerequisite properties magnetic particles for biomedical applications. Finally reported the synthesis and classification scheme to prepare magnetite (Fe₃O₄) nanoparticles with narrow size distribution for magnetic fluid hyperthermia.

Thin film multi-layered chalcogenide glass waveguide structures have been fabricated for evanescent wave sensing of bio toxins and other applications. Thin films of Ge containing chalcogenides have been deposited onto Si substrates, with a-GeSe₂ as the cladding layer and a-GeSbSe as the core layer to form the slab waveguide. Channel waveguides have been written in the slab waveguides by appropriate light the through a mask. The photo-induced structural changes in the core layer selectively enhance refractive index at the portions of interest and thus confining the light to the channels. The waveguides have been characterized and tested for the guiding of light.

Physical vapor deposition can be used to synthesize sculptured thin films with high surface areas. Highly directional vapor deposition onto a tilted, rotating substrate has been shown to produce nanostructured materials with controlled columnar features, including zig-zag, cusp, chevron, and helical geometries. Nanoporous coatings such as these are desirable for optical sensing applications due to their accessible high surface area, but few techniques are available to quantify the surface area of thin films. Electron beam and thermal evaporation techniques are used to synthesize highly porous thin films from silicon dioxide and a germanium antimony selenide chalcogenide glass in order to explore their potential for optical applications in both the visible and infrared spectral ranges. Characterization has been performed using nitrogen adsorption isotherms obtained with a quartz crystal microbalance. It is shown that surface area can be increased up to 375 times that of a flat film by deposition at oblique angles. A nitrogen adsorption technique is introduced as a means to examine the porosity of sculptured thin films at a nanoscale.

We developed a numerical model for the fluorescence output efficiency of a molecularly imprinted polymer (MIP) waveguide sensing system. A polyurethane waveguide imprinted with a polycyclic aromatic hydrocarbon (PAH) molecule was fabricated using micromolding in capillaries. The coupling of light into a 5 mm long MIP segment was verified by comparing the output transmission signals of a deuterium lamp from the MIP waveguide collected by an optical fiber with the background lamp signals collected by the same optical fiber. It was found that polyurethane MIP was an effective waveguide but absorbed much shorter wavelengths, especially in the UV region, thereby the transmission of light appeared orange/red in color. The high background absorption of polyurethane in the spectrometric regions of interest was found to be a critical problem for sensor sensitivity. Our numerical model shows that the fluorescence output is only 2x10^-6 of the input excitation for 25 mM anthracene for a 5 mm polyurethane waveguide. A 10 fold decrease of background absorption will increase the fluorescence output 250 times.