Single wall carbon nanotubes (SWNT)-nafion bilayer composites have a significant mechanical response (photoactuation) upon exposure to near infrared or visible light. The composites are formed as cantilevers of a thick nafion film (tens to hundreds of microns) coated with a thin SWNT film (one to ten microns). This configuration leads to a bending response upon light exposure. The wavelength dependence of the magnitude of the photoactuation corresponds to the absorption spectrum of semiconducting SWNTs. The thickness of each film in the bilayer affects both the magnitude of the bending and the rate of the response. The mechanism of the photoresponse is proposed to be a result of the photocarriers migrating to the interface, attracting hydrated hydrogen ions from the nafion acid groups, which then induces swelling of the nafion substrate.

Single walled carbon nanotube (SWNT), a potential component of nano-biosensor systems, has been successfully demonstrated as a nanoscale platform of biochips which efficiently accommodate biomolecules, such as proteins and peptides. Highly pure SWNTs directly grown in high yield on a SiO₂/Si substrate (SWNT film) by chemical vapor deposition (CVD) process have shown that biomolecules are immobilized as their shapes are well retained. Furthermore, SWNT film substrates have embodied a BSA-free chip system by utilizing non-covalent functionalization of SWNT surfaces with 1,1'-carbonyldiimidazole(CDI)-Tween20. Using SWNT films, high specific/nonspecific discrimination ratio has been obtained from biotin-Streptavdin and Protein A (SpA)-Immunoglobulin G (IgG) pairs as well as from small peptide-protein interactions of 3×FLAG-antiFLAG pair. Systematic studies comparing with the state-of-art protein chip have confirmed that the performance of SWNT protein chip is superior in terms of high specific binding efficiency as well as low background signal due to the efficient prevention of nonspecific bindings.

We present experimental evidence that iron ions implanted into silicon/silicon dioxide substrates form nanoscale islands during subsequent annealing, which act as catalyst for nanotube chemical vapor deposition (CVD) growth. We have implanted Fe+ ions into thermally grown SiO₂ layers on silicon substrates with an energy of 60 keV and a dose of 10¹⁵ cm^-2. Using this implanted catalyst, we have then grown carbon nanotubes by CVD at 900°C with methane as the precursor gas. We have characterized the catalyst islands and the grown carbon nanotubes by Atomic Force Microscopy (AFM) and Raman spectroscopy. The diameters of carbon nanotubes we have grown from ion implanted catalyst in this work are much smaller than those reported previously. The presence of small diameter nanotubes implies single-walled nanotube (SWNT) growth. The height distribution of the catalyst islands correlates very well with the diameter distribution of nanotubes. This is consistent with previous work which has found evidence that nanotube diameter depends strongly on the size of the catalyst particles. Since ion-implantation can be easily masked by lithography, this technique of nucleating nanotube growth opens up the possibility of controlling the origin of nanotubes at the nanometer scale over high aspect ratio topography. This technique also has the advantage that it can easily be integrated with silicon processing, and scaled to larger substrates.

A review is given of how resonance Raman spectroscopy (RRS) and photoluminescence (PL) can be used to reveal unique information about nanostructures, 1nm in diameter, thus providing new techniques for probing the electronic and vibrational properties of nanostructures with particular regard to nanosensing applications. Special attention is given to recent advances made in this field and to perspectives about future research directions.

A new procedure was used for the preparation of stable silver colloids by reduction of silver nitrate with (N (2 hydroxyethyl) piperazine N'-2 ethanesulfonic acid (HEPES). The nanoparticle size and the surface charge could be tuned by changing the initial pH of a HEPES solution. Rhodamine 6G and NaSCN were used respectively as model cationic and anionic analytes to study the effect of surface charge of the silver colloids on detection sensitivity. The silver colloids exhibit SERS activity comparable to those obtained by the popular Lee-Meisel approach. The combination of the high SERS sensitivity and the ability to control the nature of surface charge renders HEPES-reduced polyampholytic silver colloids a potentially powerful platform for sensing and detection of both cations and anions in aqueous solutions.

Silver nanoshells, nanospheres and metal coated dielectric nanowires have been directly compared for their surface enhanced Raman (SERS) activity. SERS was measured from trace deposits of Rhodamine 6G (Rh6G). It was found that the SERS enhancement is largest for samples that are 3D in nature compared to 2D arrays. Furthermore Ag coated dielectric nanowires had the strongest SERS. These results demonstrate the importance of electric field hot spots and molecular orientation in the SERS process.

Using surface enhanced Raman spectroscopy (SERS), we have observed bio-molecules at extremely low concentration, adsorbed on self-organized semiconductor quantum dots, grown by molecular beam epitaxy. Quantum dots have found application in the field of biosensors, and the performance of these devices depends critically on the properties of the surface features. It is therefore of interest to explore useful and versatile spectroscopic sensing technique such as SERS to determine these properties. The SERS technique employs rough substrates with structures in the nanometer range to enhance Raman signals from adsorbed species. This spectroscopy has a number of important advantages: sensitivity, selectivity and non-destructive detection. In addition to this, SERS enables the determination of detailed information about adsorbed species such as molecular structure and orientation, while greatly increasing the Raman cross section and suppressing fluorescence. We show that the Raman signal observed from various biologically important molecules can be enhanced by up to six orders of magnitude by means of surface enhancement caused by adhesion to self-organized CdSe/CdZnSeMg quantum dots grown by molecular beam epitaxy.

The growth of monoclinic Ga₂O₃ nanowires, nano-ribbons and nano-sheets has been investigated. Results indicate that high quality single crystal nanowires can be grown at 900°C using an Au catalyst, while single crystal nano-ribbons and nano-sheets require no metal catalyst for growth. Since bulk Ga₂O₃ is a promising material for high temperature sensing, Ga₂O₃ nanowires and nano-ribbons may prove to enhance the sensing capability due to the high surface area. We have investigated the nature of defects in this material using Electron Spin Resonance, in as grown material, as well as under annealing in a reducing gas (H₂) at various high temperatures. Results indicate the presence of an oxygen deficiency in the material, resulting in a conduction electron signal that becomes enhanced with annealing. An alternate use of these nanowires for sensing applications will also be presented, involving Surface Enhanced Raman Spectroscopy.

Both ac and dc conductivities of nominally pure nanocrystalline ZnO ceramics with grain size of ~ 40 nm were measured as a function of oxygen partial pressure and temperature, and compared with coarsened microcrystalline samples (grain size of ~ 5 μm). Nanocrystalline ceramics showed intrinsic bulk properties which turned into extrinsic behavior on coarsening. This is attributed to extreme impurity segregation into grain boundary core in nanocrystalline ceramics owing to the markedly enhanced interface-to-volume ratio. Nonetheless the blocking effect (Schottky barriers) of the grain boundaries in the nanocrystalline sample was negligible compared to that in the coarsened material due to the extreme dilution of the interfacial traps. Investigations on dopant behavior in ZnO nanowire bridges based on high temperature electrical measurements are currently under progress.

We report complementary detection of prostate-specific antigen (PSA) using n-type In₂O₃ nanowires and p-type carbon nanotubes. Our innovation involves developing an approach to covalently attach antibodies to In₂O₃ NW surfaces via the onsite surface synthesis of phosphoric acid-succinylimide ester. Electronic measurements under dry conditions revealed complementary response for In₂O₃ NW and SWNT devices after the binding of PSA. Real time detection in solution has also been demonstrated for PSA down to 5 ng/mL, a benchmark concentration significant for clinical diagnosis of prostate cancer, which is the most frequently diagnosed cancer.

Zinc oxide nanowires are configured as n-channel field effect transistors. These transistors are implemented as highly sensitive chemical sensors for detection of various gases such as O₂, NO₂, NH₃, and CO at room temperature. They show oxidizing sensing property to oxygen and nitrogen dioxide. Nanowires' ammonia sensing behavior is observed to switch from oxidizing to reducing when temperature increased from 300 to 500 K. This effect is attributed to the temperature dependent chemical potential shift. Carbon monoxide is found to increase the nanowire conductance in the presence of oxygen. Due to a Debye screening length comparable to the nanowire diameter, the electric field applied over the back gate significantly affects the sensitivity as it modulates the carrier concentration. A strong negative field is utilized to refresh the sensors by an electro-desorption mechanism. In addition, different chemisorbed species could be distinguished from the "refresh" threshold voltage and the temporal response of the conductance. These results demonstrate a refreshable field effect sensor with a potential gas identification function.

Nano-engineered devices with potential for trace level detection of chemical or biological species are investigated. The sensor system is a ChemFET device based on micro- and nano-scale silicon wires. The sensor response to changes in pH reveals a significantly higher sensitivity of nano-scale devices compared to micro-scale devices. By immobilizing DNA probe molecules on the silicon wire surface, the ChemFET devices are rendered specific to this DNA sequence. Differential measurements minimize the effects of non-specific binding. At a concentration of C_DNA=10μM, two different single stranded 24-base DNA oligonucleotides have been clearly distinguished in the sensor response. DNA hybridization on the silicon wire surface is further corroborated by fluorescence spectroscopy and analysis of characteristic time constants in the sensors response.

Carbon nanotube and semiconductor nanowires could potentially usher in a new era in chemical detection for environmental, biomedical, and security applications by providing highly sensitive detection at very low cost. For wireless sensor networks and implantable biomedical sensing devices, system power consumption is a critical factor in determining volume, operating lifetime, and circuit performance. We describe several key circuit challenges related to interfacing variable resistance nanosensors to digital integrated circuits through analog-to-digital data conversion. These challenges include drift in nanosensor baseline resistance due to fabrication variances and incomplete chemical desorption, various sensor and circuit noise sources, and integrated sensor and circuit area and power tradeoffs. We describe and evaluate the potential of several circuit techniques to address these issues, including self-test, self-calibration, and noise cancellation. Simulations indicate that +/- 40% variations in fabricated baseline resistance can be reduced to +/- 2% with a 25% increase in sensing area using a configurable sensor design. Based on these results, we explore potential A/D converter architectures for their use as low power nanosensor interfaces. Finally, we discuss resolution limits to miniaturization of nanosensor interface circuits.

A microdroplet can act as a high quality factor optical cavity that supports Morphology Dependent Resonances(MDRs). Enhanced radiative energy transfer through these optical resonances can also be utilized as a transduction mechanism for chemical and biological sensing. Enhancement in radiative energy transfer is observed when a donor/acceptor pair is present in the resonant medium of a microcavity. Here, we demonstrate avidin-biotin binding and its detection through a FRET pair as a potential application for ultra-sensitive detection for fluoroimmunoassays. The binding interaction between the biotinylated donor molecules and streptavidin-acceptor conjugate was used to observe the energy transfer between the dye pairs. The radial modes of MDRs extend to approximately 0.6 r₀ inside the droplet. As a result, the fluorescent emission around the center is not coupled to the optical resonances losing sensitivity. To address this problem, we prepared water-in-oil emulsions of avidin and biotin containing solutions. The water phase contains the streptavidin-Alexa Fluor 610 and the oil phase contains biotinylated fluorescent bead. Streptavidin-biotin binding reaction occurs at the water-oil interface. The water phase accumulates at the droplet air interface due to higher specific density enhancing the resonance coupling. Water and oil phase are index-matched to avoid scattering problems. As a result, a large portion of the avidin-biotin complex was localized at the pendant droplet and air interface. Strong coupling of acceptor emission into optical resonances shows that the energy transfer is efficiently mediated through these resonances.

We demonstrate an integrated fluorescence sensor chip consisting of an InGaN-GaN light emitting diode for fluorescence excitation, a bonded silicon junction photodiode for fluorescence detection, and a thin film filter for pump rejection and fluorescence selectivity. Evanescent field excitation at the LED surface is used to lessen the background due to stray pump light. The device is robust, and amenable to wafer-scale fabrication. Initial results with CdSe/ZnS quantum dot fluorophores yield a surface-bound sensitivity of 10 femtomoles, from which we predict a bulk fluid sensitivity of ~ 10 nanomolar for typical antibody-antigen assays.

We present an InAs/GaAs quantum dot long wave infrared photodetector based on nonlinear photocurrent generation process. A dark current suppression factor of over 10⁴ is obtained at 180K. Photocurrent generation process was simulated and compared with conventional linear absorption photocurrent generation. A photodetectivity of nearly 10¹⁰cmHz^1/2/W were obtained at 180K. This kind long wave infrared photodetector is promising in working at air-cooled temperature.

A novel photonic band-gap (PBG) based nano-sensor is proposed for cell, biomolecule gas, chemical agents, or various industrial gas detections. The sensor consists of waveguide, made from periodically structured dielectrics forming PBG. This sensor is optimized with a fixed wavelength of light and fixed receptor for detecting specific biomolecule or cell. The absorption of cell or biomolecule causes the changes in refractive index, which thereby changes the optical intensity. The concentration of cell or biomolecule agent can be known from the changes in optical output. The proposed sensor can be very high sensitive and can able to detect the fixed cell in very smaller amount or biomolecule gas in several parts per billion. We will present the detailed simulation for various applications for example in clinical diagnostic system to measure the specific cell or DNA, or in spectroscopy for measuring various biomolecule gases in the space. In addition, this proposed sensor is able to detect the contamination of the environment (e.g. viral germs), food (fungus) and agricultural products.

This paper presents key properties and examples of applications of resonant leaky-mode biosensors operating in the subwavelength regime. The main resonance features observed under variation of input wavelength and angle are discussed. The dependence of the resonance lineshape on element design parameters is highlighted. The surface-localized power concentration at resonance is described along with the standing-wave pattern of the leaky modes obtained at normal incidence. An example fabrication process involving holographic patterning, etching, and deposition of high-index material is provided. The fabricated elements resonate well with good agreement between experiment and theory found. As examples of practical applications, experimental results on detection of proteins and bacteria are given. The tag-free resonant sensor technology demonstrated may be feasible for use in fields such as in medical diagnostics, drug development, environmental monitoring, and homeland security.

A mid-infrared sensor is proposed in which an intersubband quantum-dot (QD) detector is integrated with an avalanche photodiode (APD) through a tunnel barrier. In the proposed three-terminal device, the applied biases of the QD and the APD are controlled separately; this feature permits the control of the QD's responsivity and dark current independently of the operational gain of the APD. It is shown theoretically that the proposed device can achieve a higher signal-to-noise ratio (SNR) over the QD detector without the APD component. Indeed, prior studies have revealed that although a heterostructure barrier lowers both the dark current and the photocurrent of the QD detector, the barrier has a greater impact on the dark current. Thus the dark-current-limited SNR is enhanced in the presence of the barrier. However, due to the reduced photocurrent, the SNR may not achieve its potential in the presence of Johnson noise, which may become dominant, for example, at low integration times or when detecting ultra-weak signals. In the proposed device, the APD component provides the necessary photocurrent gain required to elevate the SNR to the dark-current limit. This improvement, however, comes at a slight penalty in the SNR, due to the excess noise introduced by the APD. In this paper, guidelines for the SNR improvement are discussed in terms of the QD's operational bias voltage and the required APD gain. The higher SNR could be used to obtain a higher sensitivity at the same temperature, or to achieve a comparable performance at higher operating temperatures.

Many sensing applications benefit from a wavelength-selective measurement. For integrated sensors it is therefore necessary to realize compact wavelength splitting devices. Here we discuss dispersive devices based on the photonic crystal superprism effect and related spatial dispersion effects in photonic nanostructures. We focus on one-dimensional nanostructures, since these can be realized reliably and cost-effectively as multilayer thin-film stacks. The thin-film stack is designed such that light incident at an angle experiences a wavelength-dependent spatial beam shift at the output surface allowing a wavelength-selective measurement. We introduce different algorithms for designing thin-film stacks with high spatial dispersion and discuss integration approaches. Results are presented showing that it is possible to custom-engineer both the magnitude of the dispersion as well as the dispersion properties with wavelength.

Ion Optics has developed a thin silicon membrane MEMS device that replaces the thermal source, IR filter, IR detector and mechanical chopper in conventional non-dispersive infrared gas sensors. The key enabling technology is a 2-D photonic crystal. The center wavelength and bandwidth of emitted radiation from the photonic crystal depends upon the pattern etched into the surface. Previously we reported designs based on hexagonal arrangements of holes about 2 microns diameter. New results for more intricate designs with deliberate photonic crystal "defects" will be presented. Experimental results will be compared to 3-D electromagnetic models. The 2-D photonic crystal structure consists of an array of air rods produced by self-aligned etching into a thin (100nm) conductor on top of a dielectric membrane. We describe fabrication routes via conventional silicon microlithography and novel approaches including nano-imprinting and transfer molding. We present spectral emission and absorption measurements which relate optical intensity to details of photonic crystal design and fabrication.

Compared to well established liquid based dye lasers, amplifying media based on amorphous organic thin films allow the realisation of versatile, cost effective and compact lasers. Aside from that, the materials involved are organic semiconductors, which in principle allow the fabrication of future electrically driven organic laser diodes. A highly promising, low-loss resonator geometry for these lasers is the distributed feedback (DFB) structure, which is based on a periodic modulation of the refractive index in the waveguide on the nanometer scale. By variation of the grating period Λ one may tune the laser emission within the gain spectrum of the amplifying medium. We will demonstrate organic lasers spanning the entire spectral region from 360-715 nm. Tuning ranges as large as 115 nm (λ = 598-713 nm) in the red spectral region and more than 30 nm (λ = 362-394 nm) in the UV render these novel lasers highly attractive for various spectroscopic applications. As the grating period Λ is typically between 100 nm and 400 nm the DFB resonators are fabricated by e-beam lithography. These gratings may, however, be used as masters to obtain an arbitrary amount of copies by nanoimprint lithography into plastic substrates. Therefore these lasers are very attractive even for single-use applications (e.g. in medicine and biotechnology). Today, the key challenge in the field is the realisation of the first electrically driven organic laser. Key pre-requisites are highly efficient amplifying material systems which allow for low threshold operation and charge transport materials that bring about the stability to sustain the necessary current densities, several orders of magnitude higher than in OLEDs. We will demonstrate diode structures operated electrically under pulsed conditions at current densities up to 760 A/cm² with a product of the current density and the external quantum effciency (J×η_ext) of 1.27 A/cm². Mechanisms deteriorating the quantum efficieny at elevated current densities will be discussed.

Metal films perforated with periodically-spaced subwavelength diameter holes have been shown to transmit light with greater efficiency than predicted by classical models for evanescent propagation. This transmission mechanism is caused either by the coupling of light to surface plasmon polariton modes on the surfaces of the metal film or by diffraction patterns in the lateral evanescent modes of electromagnetic field. Regardless of the root cause, this characteristic performance leads to electric field enhancement at the apertures in the metal, an effect that holds promise for nanoscale optical sensors. In particular, the propagation of these modes is very sensitive to changes in the index of refraction on either surface of the metal. This paper will describe our work on patterned metal films which are interrogated using infrared (IR) radiation. These metal gratings are fabricated using a surface micromachining process, allowing MEMS actuators to be integrated alongside the optically-active surface. The integration of MEMS structures with subwavelength optical structures can be used to create structures whose optical properties are modulated by changes in the position of a MEMS element, resulting in mechanical sensors and tunable optical filters. We will describe structures in which small changes in the separation between the metal film and a dielectric substrate result in large changes in the optical transmission and reflection spectra.

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.

Dye sensitization effect of semiconductors has been investigated to increase the spectral response of photonic devices and photo-electrochemical cells. Numerous techniques, materials and device architecture have been proposed for this class of devices. Some improvements are necessary to enhance the efficiency and stability at the semiconductor/electrolyte interface of dye-based photonic devices. Though physiochemical phenomena have been well understood, use of novel techniques will lead to further development of practical devices. This paper reviews the current understanding of dye sensitization effect at the semiconductor electrolyte interfaces. Possibility to improve the performance of such devices by integration of nanotechnology is also discussed.

Fluorescent properties and low production cost makes lanthanide oxide nanoparticles attractive labels in biochemistry. Nanoparticles with different fluorescent spectra were produced by doping of oxides such as Y₂O₃ and Gd₂O₃ with different lanthanide ions (Eu, Tb, Sm) giving the possibility for multicolor labeling. Protein microarrays have the potential to play a fundamental role in the miniaturization of biosensors, clinical immunological assays, and protein-protein interaction studies. Here we present the application of fluorescent lanthanide oxide nanoparticles as labels in microarray-based immunoassay for phenoxybenzoic acid (PBA), a generic biomarker of human exposure to the highly potent insecticides pyrethroids. A novel polymer-based protocol was developed for biochemical functionalization of the nanoparticles. Microarrays of antibodies were fabricated by microcontact printing in line patterns onto glass substrates and immunoassays were successfully performed using the corresponding functionalized nanoparticles. The applicability of the fluorophore nanoparticles as reporters for detection of antibody-antigen interactions has been demonstrated for phenoxybenzoic acid (PBA)/anti-PBA IgG. The sensitivity of the competitive fluorescent immunoassay for PBA was similar to that of the corresponding ELISA.

Nanotechnology offers unique approaches to probe and control a variety of biological and medical processes that occur at nanometer length scales, and is expected to have a revolutionary impact on biology¹ and medicine². Nanomedicine is a new paradigm that seeks to exploit the use of nanotechnology in medicine. Among the various approaches within the nanomedicine paradigm, nanoparticles and nanotemplates offer some unique advantages as sensing, diagnostic, delivery, and image enhancement agents^3,4. Several varieties of nanoparticles⁵ are available: polymeric nanoparticles⁶, metal nanoparticles⁷, liposomes⁸, micelles, quantum dots, dendrimers, magnetic nanoparticles⁹, and nanoassemblies^10,11. All of these nanoparticles can play a major role in medicine, and especially in diagnosis and therapy of cancer^12,13,14, cardiovascular diseases, and infectious diseases. To further the application of nanoparticles in disease diagnosis and therapy, it is important that the systems are stable, capable of being functionalized, biocompatible, and directed to specific target sites in the body after systemic administration. In this short review we discuss four areas of research carried out by the Nanomedicine Consortium using nanoparticles and nanotemplates to explore new approaches in nanotechnology for medical diagnosis, imaging and therapy.

An ultra-narrow width silicon field effect transistor (FET) with a suspended gate, integrated with on-chip microfluidic delivery system is described. The device is designed to be used as an FET based sensor for sequencing of DNA, RNA and proteins, by detecting the local charge variations along the chains of these molecules as they are passed between the gate and the channel of the FET in an aqueous solution. A side-gated FET structure is demonstrated with sub-10 nm width, successfully suppressing the electrical leakage currents at the device edges. Side-gated FET structure allows electrostatic confinement of the electrons in the channel for increased spatial resolution.

The electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy = 2,2'-bipyridine and its derivatives) complexes has attracted interest from chem- and bio-analytical researchers. Particularly, by labeling bio-molecules with Ru(bpy)₃²⁺ derivatives, highly competitive ECL immunoassay and DNA probing have been employed in clinical and research laboratories and are now becoming standard methods. In the well-established commercial systems designed for bench-top applications, paramagnetic microbeads are used for capturing the analytes and separating the excess of labeled biomolecules from the flow cell. The large surface area of the beads provides a high capacity and efficiency for analyte capturing. However, the use of microbeads prevents the instrument from being miniaturized. Furthermore, only a tiny portion of species is enabled to generate luminescence because of the inaccessibility of the majority of the labels to the electrode surface. We propose to develop a handheld device with disposable chips based on the ECL signal modality. Central to this instrumentation is the fabrication of a nanostructured electrode with spatially selective bioimmobilization. The electrode surface is structured to reach the maximum capturing ability and, at the same time, maintain the effective electroactive region and the accessibility for the ruthenium label to be excited electrochemically. In this presentation, we present a manufacturable approach to the fabrication of such disposable nanostructured electrodes for ECL-based handheld devices.

Dense and transparent cadmium tungstate (CWO) scintillation films have been first synthesized by sol-gel processing and their optical properties have been studied. Different precursors (tungsten oxychloride and tungstic acid), solvents (alcohol based and aqueous based) and thermal annealing processing conditions were investigated to achieve stable sols and resultant dense nanocrystalline CWO films. XRD showed CWO was the only detectable crystalline phase in the film derived by tungstic acid based sol and fast sintering at 500°C for 20 min, while the slow sintered films derived both from tungstic acid and tungsten oxychloride at 500°C for 1 hour with a heating ramp of 8°C/min resulted in porous films containing some extra tungsten oxide phases besides CWO. The fast sintered CWO film was uniform, fully dense, crack-free and of 0.5 μm in thickness. Optical transparency and photoluminescence of CWO films were characterized, and the results showed that high density and low porosity of CWO film by fast sintering led to higher transmittance and photoluminescence output. By controlling synthesis and sintering methods the nanocrystalline grains in CWO films can be of 15~52 nm in diameter. The relationships between sol-gel processing, precursor and solvent chemistry, nanostructures, densification and optical properties were discussed.

Diffractive optical elements are designed and demonstrated as elemental units in photonic gas sensors. Diffraction gratings are written on specially designed photosensitive polymers using photolithographic techniques, as well as on multilayer metal/metal oxide thin film structures. Photonic sensors are implemented using grating structures as the elemental units for the detection of the external agent. These gratings are designed from such materials that show response to the external agent and the sensitivity is increased through the design of the grating. The principle of operation is based on the grating's diffraction efficiency variations due to index of refraction alterations and/or geometrical changes of the grating structure (e.g., groove depth, groove spacing) to external factors. The advantageous characteristics of the presented integrated sensor are the fully reversible behavior at ambient operating conditions, without the need for additional heating or light exposure. Applications of these sensitive photonic sensors so far include water vapor, hydrocarbons, and alcohol detection. The optical designs are based on diffraction efficiency measurements, and incorporate a monochromatic optical source and simple optoelectronic detection components. The photonic sensor integration is based on bulk optics approach.

We present the application of ellipsometry to the phase measurement of surface plasmon resonance (SPR) in biomolecular detection. In this configuration, the phase measurement gives a large enhancement of detection sensitivity in comparison to traditional SPR techniques. In this work, the experimental setup for SPR ellipsometry is based on both custom-built rotating analyzer ellipsometer and an imaging ellipsometer which are equipped with a SPR-cell and a flow system, respectively. We investigate the adequate thickness of the gold layer used for SPR cell and the resolution of the phase detection using two ellipsometric methods under the SPR condition. The rotating analyzer method yields higher sensitivity sufficient to detect changes in the effective thickness of biomolecular layers of less than 1 pm. In comparison to conventional SPR the simultaneous measurement of ellipsometric parameters, Δ and ψ, yields more information which is useful for quantitative analysis based on fitting theoretical solutions to experimental results.

We present imaging ellipsometry technique for kinetic measurement of bimolecular interactions with high sensitivity. When combined with surface plasmon resonance (SPR) effects, the ellipsometry becomes powerful technique for analyzing adsorption and desorption of biomolecules on gold layer based sensor chip surfaces. Because ellipsometric measurement gives ellipsometric parameters, namely Δ, that is very sensitive to surface layer changes. The SPR combined ellipsometry is realized by Kretschmann configuration SPR cell comprising with about 30-nm-thick gold film deposited on top of glass slides, SF10 glass prism, and flow injection system. We used nulling type of imagining ellipsometer to acquire two dimensional ellipsometric parameters with spatial resolution down to one micrometer. We present results of kinetic measurements of biotin-streptavidin interactions for custom-built sensor chip.

Molecular sieve zeolites are capable of selectively adsorbing molecular species into their nanoporous structures. Using whitelight interferometry, the changes in optical thickness of b-oriented MFI zeolite thin films have been measured as a function of organic vapor partial pressure in the surrounding environment. The adsorption induced optical thickness changes of the oriented MFI zeolite films were found to be reversible and monotonically dependent on the organic concentration level. The quantitative results of this study are useful for designing optical fiber-based chemical sensors for in-situ detections.

We explore the effect of a newly discovered mechanism on the detection of infrared radiation using Apertureless Near Field Scanning Optical Microscopy (ANSOM). The passage of the ANSOM tip over a sample surface is modelled as a dipole moving over a halfspace. A boundary induced excitation is shown to occur, related to the retarded radiation reaction force of the dipole close to the surface. This excitation modifies the spontaneous emission characteristics of the dipole as it alters the near field. We suggest that this physical effect can cause emission at detectable levels in the infrared region thereby altering the expected signal in a typical ANSOM setup.

An information theoretic approach to maximizing the efficacy of optical sensing devices is presented. The principles used and the results obtained are applicable on a wide range of scales, including those in nano photonics sensing and detection. A key factor which is investigated is the aspect of extraction of the maximum amount of information in any given environment. The method used, which is based on information principles developed by Shannon, augments the many conventional approaches to optimizing performance of sensors. The fundamental issue of how many bits of information can be extracted by a sensor is addressed. The radiation pattern from a radiating or receiving sensor-array provides a spatial probability density function, which carries all the information about the system. Various such arrays are treated and the significance of the structure of the radiation pattern is examined. The technique is extended to the well-known concept of the lineshape profile of radiative atomic and molecular transitions, which is a probability density function in the frequency domain. Extensions of this work have applications in nanotechnology.