This PDF contains front matter associated with SPIE Proceedings Volume 8024, including Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Surface Plasmon Resonance (SPR) is a powerful label free optical biosensing technology that relies on the measurement of the refractive index or change of mass in close vicinity of the sensor surface. Therefore, there is an experimental limitation in the molecular weight of the molecule that can be detected and consequently small molecules are intrinsically more difficult to detect using SPR. One approach to overcoming this limitation is to first adsorb smaller molecules onto the sensor surface, and to follow this by using their higher molecular weight antibodies counterparts which ensure the specificity (and are easier to detect via SPR due to their higher weight). Although this has been demonstrated with some success, it is not applicable in every case and some biomolecules such as enzyme are still difficult to detect due to their specific reactivity (enzymatic reaction). In this paper, we present a powerful new method that utilises specifically engineered spacers attached on one end to the sensor surface and on the other end to a nanoparticle that behaves as a plasmonic label. These spacers are design to specifically react with the biomolecule to be detected and release the (relatively large) plasmonic label, which in turn results in a measurable SPR shift (which is much larger than the shift that would have been associated with the binding of the relatively small biomolecule). As a proof of concept, this approach was used within a recently developed new form of SPR optical fibre sensor which relies on the measurement of the re-emitted light by surface scattering of the plasmonic wave rather than transmission through the fibre was used to detect an enzyme. Here trypsin (25kDa) was successfully sensed. This molecule is involved in both intestinal and pancreatic diseases.

An optical fiber biosensor featuring miniaturization, electromagnetic interference (EMI)-immunity, and flexibility is presented. The sensor was fabricated by aligning two gold-deposited optical single-mode fiber facets inside V-grooves on a silicon chip to form a Fabry-Perot (FP) cavity. The mirrors on the fiber facets were made of deposited gold (Au) films, which provided a high finesse to produce a highly sensitivity. Microelectromechanical systems (MEMS) fabrication techniques were used to precisely control the profile and angle of the V-grooves on the silicon. The biotin-terminated thiol molecule was firstly immobilized on the gold surface. Subsequently, the molecules of Neutravidin were specifically bound to the biotin-terminated self-assembled monolayers (SAMs). The induced changes of cavity length and refractive index (RI) upon the gold surface lead to an optical path difference (OPD) of the FP cavity, which was detected by demodulating the transmission spectrum phase shift. By taking advantage of MEMS techniques, multiple biosensors can be integrated into one small silicon chip for detecting various biomolecule targets simultaneously.

The Extreme Measurement Communications Center at Oak Ridge National Laboratory (ORNL) explores the deployment of a wireless sensor system with a real-time measurement-based energy efficiency optimization framework in the ORNL campus. With particular focus on the 12-mile long steam distribution network in our campus, we propose an integrated system-level approach to optimize the energy delivery within the steam distribution system. We address the goal of achieving significant energy-saving in steam lines by monitoring and acting on leaking steam valves/traps. Our approach leverages an integrated wireless sensor and real-time monitoring capabilities. We make assessments on the real-time status of the distribution system by mounting acoustic sensors on the steam pipes/traps/valves and observe the state measurements of these sensors. Our assessments are based on analysis of the wireless sensor measurements. We describe Fourier-spectrum based algorithms that interpret acoustic vibration sensor data to characterize flows and classify the steam system status. We are able to present the sensor readings, steam flow, steam trap status and the assessed alerts as an interactive overlay within a web-based Google Earth geographic platform that enables decision makers to take remedial action. We believe our demonstration serves as an instantiation of a platform that extends implementation to include newer modalities to manage water flow, sewage and energy consumption.

We report on the progress of an optical tag designed to indicate the presence of HF. The approach we followed uses a high spatial frequency grating consisting of lines of conductive polymer. The conductive polymer has been designed to be sensitive to HF; changing its conductivity upon exposure. This material change results in a change in the polarization response of the grating which can be read out remotely using optical techniques. The use of a polarization response makes the signal more robust to intensity fluctuations in the background or interrogation system. Additionally, the use of optical interrogation allows for standoff detection in instances where hazardous conditions may be present. A review of the material development work will be presented as well as the device fabrication efforts. Examples of material and device responses will be shown and directions for further investigation discussed.

Conductors with infrared plasma frequencies are potentially useful hosts of surface electromagnetic waves with sub-wavelength mode confinement for sensing applications. Such materials include semimetals, semiconductors, and conducting polymers. In this paper we present experimental and theoretical investigations of surface waves on doped silicon and the conducting polymer polyaniline (PANI). Resonant absorption features were measured in reflection from lamellar gratings made from doped silicon for various p-polarized CO₂ laser wavelengths. The angular reflectance spectra for doped silicon was calculated and compared with the experiments using experimental complex permittivities determined from infrared (IR) ellipsometry data. Polyaniline films were prepared, optical constants determined, and resonance spectra calculated also. A specific goal is to identify a conductor having tight mode confinement, sharp reflectivity resonances, and capability to be functionalized for biosensor applications.

Wavelength modulation spectroscopy (WMS) with simultaneous detection at high harmonics (up to and including N = 11) is reported for the first time. A Vertical Cavity Surface Emitting Laser (VCSEL) is used to probe atmospheric oxygen using a multi-pass optical cell. The laser frequency is modulated at a low modulation index while synchronous detection is performed simultaneously at all harmonics up to the 11th. These higher harmonic signals allow for better resolution of congested spectra. Experimental results are used to detect and resolve absorption features in the A-band region of oxygen. The high harmonic signals are used to distinguish between stronger rotational-vibrational absorption lines in oxygen and weaker absorption lines formed by low-density isotopic oxygen. This detection method also allows for the resolution of overlap between these weaker isotopic spectra. Higher harmonic signals resolve additional structure, which does not appear at direct absorption measurements, or even in lower harmonic signals (N < 3). Since harmonic signal power decreases rapidly with detection order (N), the technique employed clearly shows that the commonly used signal-to-noise power ratio, while important, is not the only criterion for a good measurement. We examine the effects of optical pathlength saturation for these weak isotopic lines by measuring the effect of an optically thick path (at fixed density) on the signal.

Based on a miniaturized optical bench with attached 671 nm microsystem diode laser we present a portable Raman system for the rapid in-situ characterization of meat spoilage. It consists of a handheld sensor head (dimensions: 210 x 240 x 60 mm³) for Raman signal excitation and collection including the Raman optical bench, a laser driver, and a battery pack. The backscattered Raman radiation from the sample is analyzed by means of a custom-designed miniature spectrometer (dimensions: 200 x 190 x 70 mm³) with a resolution of 8 cm^-1 which is fiber-optically coupled to the sensor head. A netbook is used to control the detector and for data recording. Selected cuts from pork (musculus longissimus dorsi and ham) stored refrigerated at 5 °C were investigated in timedependent measurement series up to three weeks to assess the suitability of the system for the rapid detection of meat spoilage. Using a laser power of 100 mW at the sample meat spectra can be obtained with typical integration times of 5 - 10 seconds. The complex spectra were analyzed by the multivariate statistical tool PCA (principal components analysis) to determine the spectral changes occurring during the storage period. Additionally, the Raman data were correlated with reference analyses performed in parallel. In that way, a distinction between fresh and spoiled meat can be found in the time slot of 7 - 8 days after slaughter. The applicability of the system for the rapid spoilage detection of meat and other food products will be discussed.

In-situ monitoring of pollutant chemicals in sea-water is of worldwide interest. For that purpose, fast response sensors based on Raman spectroscopy are suitable for a rapid identification and quantification of these substances. Surface-enhanced Raman scattering (SERS) was applied to achieve the high sensitivity necessary for trace detection. In the project SENSEnet, funded by the European Commission, a SERS sensor based on calixarene-functionalized silver nanoparticles embedded in a sol-gel matrix was developed and adapted for the in-situ detection of polycyclic aromatic hydrocarbons (PAHs). The laboratory set-up contains a microsystem Raman diode laser with two slightly different emission wavelengths (670.8 nm and 671.3 nm) suitable also for shifted excitation Raman difference spectroscopy (SERDS). The output power at each of both wavelengths is up to 200 mW. For the detection of the SERS spectra integration times of typically 1 - 10 seconds were chosen. The SERS substrate is located inside a flow-through cell which provides continuous flow conditions of the analyte. The spectra were recorded using a laboratory spectrograph with a back-illuminated deep depletion CCD-detector. We present scanning electron microscope images of the developed calixarene-functionalized Ag colloid based SERS substrates as well as results for the SERS adsorption properties of major PAHs (pyrene, fluoranthene, and anthracene) in artificial sea-water and their limits of detection (e. g. 0.1 nM for pyrene). The suitability of the presented device as an in-situ SERS sensor for application on a mooring or buoy will be discussed.

A new spectroscopic technique for remote molecular detection is presented. Chirped Laser Dispersion Spectroscopy (CLaDS) uses a two-color dynamic interferometric heterodyne detection to measure optical dispersion caused by molecular transitions. The dispersion sensing is based on measurement of instantaneous frequency of an optical heterodyne beatnote which provides high immunity to optical power fluctuations. Thus CLaDS is well suited to long distance remote sensing and open-path monitoring. In this work we present CLaDS experimental setup for remote sensing of nitric oxide using 5.2 μm quantum cascade laser. System performance as well as advantages and limitations are discussed.

We demonstrate the feasibility of using microwave scattering from free electrons generated by resonantly enhanced multi-photon ionization (REMPI) for trace species detection. The laser is tuned to ionize only the selected molecular trace species in ambient air. We achieve detection of parts-per-billion of NO in atmospheric pressure nitrogen, in dry air and in laboratory air with 50% humidity. In addition, we performed at-range measurements in order to prove the feasibility of using the Radar REMPI detection technique in a remote configuration. We obtained reliable backscattered microwave signal 1m away while focusing a laser from 10m distance from the target. We have extended the use of the Radar REMPI detection scheme to more complicated molecular systems by pre-dissociating the molecule into smaller fragments which can be detected with high specificity. We demonstrate the detection of SF₆ by laser dissociation of the SF₆ molecule, and measuring the Radar REMPI signals obtained from the SF₂ product. The SF₂ is produced by the UV REMPI laser pulse itself, and a scattered microwave signal is detected from the SF₂ molecule. Significant enhancement is achieved using a pre-ionizing pulse from a Nd YAG laser shortly before the measurement. The short time between fragmentation and detection allows transient fragments and fragments in vibrational nonequilibrium to be detected. This approach may allow for the identification of complex molecules by remotely detecting even short lived molecular constituents or fragments which are produced either during or just shortly before the Radar REMPI measurement

We demonstrate coherent light propagating backwards from a remotely generated high gain air laser. A short ultraviolet laser pulse tuned to a two-photon atomic oxygen electronic resonance at 226 nm simultaneously dissociates the oxygen molecules in air and excites the resulting atomic oxygen fragments. Due to the focal depth of the pumping laser, a millimeter long region of high gain is created in air for the atomic oxygen stimulated emission at 845nm. We demonstrate that the gain in excess of 60 cm^-1 is responsible for both forward and backwards emission of a strong, collimated, coherent laser beam. We present evidence for coherent emission and characterize the backscattered laser beam while varying the pumping conditions. The optical gain and directional emission allows for six orders of magnitude enhancement for the backscattered emission when compared with the fluorescence emission collected into the same solid angle. . This opens new opportunities for the remote detection capabilities of trace species, and provides much greater range for the detection of optical molecular and atomic features from a distant target.

We present a new class of surface-enhanced Raman scattering (SERS) substrates based on lithographically-defined two-dimensional rectangular array of nanopillars. Two types of nanopillars within this class are discussed: vertical pillars and tapered pillars. For the vertical pillars, the gap between each pair of nanopillars is small enough (< 50 nm) such that highly confined plasmonic cavity resonances are supported between the pillars when light is incident upon them, and the anti-nodes of these resonances act as three-dimensional hotspots for SERS. For the tapered pillars, SERS enhancement arises from the nanofocusing effect due to the sharp tip on top. SERS experiments were carried out on these substrates using various concentrations of 1,2 bis-(4-pyridyl)-ethylene (BPE), benzenethiol (BT) monolayer and toluene vapor. The results show that SERS enhancement factor of over 0.5 x 10⁹ can be achieved, and BPE can be detected down to femto-molar concentration level. The results also show promising potential for the use of these substrates in environmental monitoring of gases and vapors such as volatile organic compounds.

A battery-operated, atmospheric-pressure, micro-diameter (and nano-volume) microplasma on a hybrid, quartz-polymer (e.g., Teflon®) chip with area the size of a small postage stamp is described. Rapid prototyping of the microplasma device; some fundamental aspects (e.g., excitation temperatures), and characterization of background spectral emission using a portable, fiber-optic, CCD-based spectrometer are discussed in some detail.

Nanowire-nanocluster hybrid chemical sensors were realized by functionalizing gallium nitride (GaN) nanowires with titanium dioxide (TiO₂) nanoclusters for selectively sensing Benzene and other related aromatic compounds. Hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN nanowires followed by the deposition of TiO₂ nanoclusters using RF magnetron sputtering. The sensor fabrication process employed all standard micro-fabrication techniques. A change of current was observed for these hybrid sensors when exposed to aromatic compounds such as Benzene, Toluene, Ethylbenzene, Xylene, and Chlorobenzene mixed with air. However, these sensors did not show any sensitivity when exposed to Methanol, Ethanol, Isopropanol, Chloroform, Acetone, and 1, 3-Hexadiene. These sensors were capable of sensing the aromatic compounds only under ultraviolet excitation. The sensitivity range for the above mentioned aromatic compounds varied from 1% down to 50 parts per billion (ppb) at room-temperature. By combining the enhanced catalytic properties of the TiO₂ nanoclusters with the sensitive transduction capability of the nanowires, an ultra-sensitive and highly selective chemical sensing architecture is demonstrated. We have proposed a mechanism that could qualitatively explain the observed sensing behavior.

AlGaN/GaN high electron mobility transistors (HEMTs) with polar and nonpolar ZnO nanowires modified gate exhibit significant changes in channel conductance upon expose to different concentration of carbon monoxide (CO) at room temperature. The ZnO nanowires, grown by chemical vapor deposition (CVD), with perfect crystal quality will attach CO molecule and release electrons, which will lead to a change of surface charge in the gate region of the HEMTs, inducing a higher positive charge on the AlGaN surface, and increasing the piezoinduced charge density in the HEMTs channel. These electrons create an image positive charge on the gate region for the required neutrality, thus increasing the drain current of the HEMTs. The HEMTs source-drain current was highly dependent on the CO concentration. The limit of detection achieved was 400 ppm and 3200ppm in the open cavity with continuous gas flow using a 50x50μm² gate sensing area for polar and nonpolar ZnO nanowire gated HEMTs sensor.

We report on the development of a new sensor for NO₂ with ultrahigh sensitivity of detection. This has been accomplished by combining off-axis integrated cavity output spectroscopy (OA-ICOS) (which can provide large path lengths of the order of several km in a small volume cell) with multiple line integrated absorption spectroscopy (MLIAS) (where we integrate the absorption spectra over a large number of rotational-vibrational transitions of the molecular species to further improve the sensitivity). Employing an external cavity tunable quantum cascade laser operating in the 1601 - 1670 cm^-1 range and a high-finesse optical cavity, the absorption spectra of NO₂ over 100 transitions in the R-band have been recorded. From the observed linear relationship between the integrated absorption vs. concentration of NO₂, we report an effective sensitivity of detection of 10 ppt for NO₂. To the best of our knowledge, this is among the most sensitive levels of detection of NO₂ to date. A sensitive sensor for the detection of NO₂ will be helpful to monitor the ambient air quality, combustion emissions from the automobiles, power plants, aircraft and for the detection of nitrate based explosives (which are commonly used in improvised explosives (IEDs)). Additionally such a sensor would be valuable for the study of complex chemical reactions that undergo in the atmosphere resulting in the formation of photochemical smog, tropospheric ozone and acid rain.

The ability to measure the concentration of hydrogen peroxide (H₂O₂) in solution is critical for quality assessment and control in many disparate applications, including wine, aviation fuels and IVF. The objective of this research is to develop a rapid test for the hydrogen peroxide content that can be performed on very low volume samples (i.e. sub-μL) that is relatively independent of other products within the sample. For H₂O₂ detection we use suspended core optical fibers to achieve a high evanescent field interaction with the fluid of interest, without the constraint of limited interaction length that is generally inherent with nanowire structures. By filling the holes of the fiber with an analyte/fluorophore solution we seek to create a quick and effective sensor that should enable detection of desired species within liquid media. By choosing a fluorophore that reacts with our target species to produce an increase in fluorescence, we can correlate observed fluorescence intensity with the concentration of the target molecule.

We have realized gas sensor devices, which are based on a single SnO₂-nanowire or a multiple SnO₂-nanowire network as gas sensing components and are very sensitive to the toxic gas H₂S. The nanowires are fabricated in a two-step atmospheric pressure synthesis process directly on the Si-chip by spray pyrolysis and subsequent annealing. Exposure of the single SnO₂-nanowire sensor H₂S with a concentration of only 1.4 ppm decreases the resistance by ~ 30%, while the multiple SnO₂-nanowire network sensor exhibits a resistance decrease by ~ 90%. The nanowire sensors have extraordinary sensitivity with resolution limit in the ppb range and are able to measure concentrations well below the threshold limit value of 10 ppm. Due to their high performance the nanowire based sensors are basically suited for the realization of smart gas sensing devices for personal safety issues as well as industrial applications.

There is growing interest in measuring gaseous emissions to understand their environmental impact. It is thus desired to identify and quantify such emissions, ideally from standoff distances. AFIT and Telops have performed several field experiments, using the Telops Hyper-Cam infrared hyperspectral imager to perform identification and quantification of gaseous emissions from various pollution sources. Recent experiments have focused on turbulent gaseous emissions from sources of great interest from the environmental protection community, such as emergency flares. It is important to understand the flare emissions under varying operating conditions. This paper presents the first results of flare emission measurements with the Hyper-Cam.

We present the first results from a Digital Array Gas-correlation Radiometer (DAGR) prototype sensor, and discuss applications in remote sensing of trace gases. The sensor concept is based on traditional and reliable Gas Filter Correlation Radiometry (GFCR), but overcomes the limitations in solar backscatter applications. The DAGR sensor design can be scaled to the size of a digital camera and is ideal for downlooking detection of gases in the boundary layer, where solar backscatter measurements are needed to overcome the lack of thermal contrast in the IR. Ground-based portable DAGR sensors can monitor carbon sequestration sites or industrial facilities. Aircraft or UAV deployment can quickly survey large areas and are particularly well suited for gas leak detection or carbon monitoring. From space-based platforms, Doppler modulation can be exploited to produce an extremely fine spectral resolution with effective resolving power exceeding 100,000. Such space-based DAGR observations could provide near-global sensing of climatically important species such as such as CO₂, CO, CH₄, O₃ and N₂O. Planetary science applications include detection and mapping of biomarkers in the Martian atmosphere.

An Fourier Transform Infra-Red(FTIR) spectrometry has played an significant role in a variety of fields in recent years. In particular, FTIR spectrometer technology has been adopted in passive remote sensing system to predict detection probabilities of stand-off hazardous compounds. There are three steps to detect hazardous compounds. Firstly, MODerate spectral resolution atmospheric TRANsmittance(MODTRAN) algorithm is used to calculate spectral radiances of background and atmosphere affected by hazardous compounds. It transfers a difference of spectral radiance between background and hazardous compounds existing region to FTIR spectroscopy system. Secondly, FTIR spectrometry system collects an interferogram which represents spectral radiances respective to given time intervals (reciprocal of wavenumber) and sends it to signal processing part. Lastly, the signal processing part performs Fourier Transformation on the interferogram and identifies the spectral radiance with reference data from gas library by using Spectral Angle Mapper(SAM) algorithm which results in visualizing the hazardous gases. However, there are some noises which affect the interferogram and the spectrum in practice. Specifically, there are two main noises which have critical effects on the interferogram and the spectrum by reducing its Signal to Noise Ratio(SNR) such as detector noise, jitter of moving mirror and optics misalignment. In this paper, a theory of the effects of the detector noise and the jitter of moving mirror on the interferogram and its demonstration through simulation are presented.

Nanostructured TiO₂ thin films are found to be highly responsive to trace vapors of common nitro-explosives at room temperature. Thin films of TiO₂ nanowires, made with high yield hydrothermal synthesis, present very reliable sensing characteristics to nitro-aromatic molecules with high sensitivity and fast response at ambient condition. The detection limit of 2, 4-dinitrotoluene (DNT) vapor at room temperature could reach up to 3ppb. The experimental results indicate titania nanowires as a novel chemical sensor to explosive gas have a great commercial potential due to its unique advantages: high sensitivity, rapid response and recovery, small size suitable for intergration with microelectronics and low fabrication cost. Experimental results and a theoretical model are presented.

Leakage of dangerous gases will not only pollute the environment, but also seriously threat public safety. Thermal infrared imaging has been proved to be an efficient method to qualitatively detect the gas leakage. But some problems are remained, especially when monitoring the leakage in a passive way. For example, the signal is weak and the edge of gas cloud in the infrared image is not obvious enough. However, we notice some important characteristics of the gas plume and therefore propose a gas cloud infrared image enhancement method based on anisotropic diffusion. As the gas plume presents a large gas cloud in the image and the gray value is even inside the cloud, strong forward diffusion will be used to reduce the noise and to expand the range of the gas cloud. Frames subtraction and K-means cluttering pop out the gas cloud area. Forward-and-Backward diffusion is to protect background details. Additionally, the best iteration times and the time step parameters are researched. Results show that the gas cloud can be marked correctly and enhanced by black or false color, and so potentially increase the possibility of gas leakage detection.

There is an increasing preoccupation regarding the effects of organic volatiles or explosive gases in human welfare and society. A holographic sensor for gaseous and volatile compounds was produced by diffusion of silver salts in a silicon elastomer (PDMS). The salts were reduced to produce silver particles, which upon ablation with a pulsed laser form fringes of nano-sized silver grains. The fringes are separated by about half of the wavelength of the laser (266nm) producing a photonic effect that can be measured as a colorful reflection. A CCD spectrophotometer was used to detect the reflected wavelength of the hologram illuminated with a white light source. The molecular affinity of PDMS for organic molecules can be expressed as intermolecular forces in terms of the cohesive energy density. This parameter is used to predict with great accuracy the sensor performance. Hydrocarbon gases at different concentrations were tested for 3 sets of temperatures. Alkanes, alkenes and alkynes containing 2 to 4 carbon atoms were detected. The sensor responds in less than 5s to the hydrocarbon gas presence in a range of concentrations from 0% to 100% (v/v). Liquid organic compounds exhibit a slower response; however, the results agree with the prediction imposed by the cohesive energy densities. The capabilities of the sensor make it ideal for applications in indoor environment monitoring or dangerous environments enriched with such organic compounds.

Physical Optics Corporation (POC) presents a novel Mobile ELISA-based Pathogen Detection system that is based on a disposable microfluidic chip for multiple-threat detection and a highly sensitive portable microfluidic fluorescence measurement unit that also controls the flow of samples and reagents through the microfluidic channels of the chip. The fluorescence detection subsystem is composed of a commercial 635-nm diode laser, an avalanche photodiode (APD) that measures fluorescence, and three filtering mirrors that provide more than 100 dB of excitation line suppression in the signal detection channel. Special techniques to suppress the fluorescence and scattering background allow optimizing the dynamic range for a compact package. Concentrations below 100 ng/mL can be reliably identified. The entire instrument is powered using a USB port of a notebook PC and operates as a plug-and-play human-interface device, resulting in a truly peripheral biosensor. The operation of the system is fully automated, with minimal user intervention through the detection process. The resolved challenges of the design and implementation are presented in detail in this publication.