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- Front Matter: Volume 8024
- Biosensors
- Advanced Sensing Technologies
- Spectrographic Trace Detection
- Environmental Sensing
- Gas Sensing
- Poster Session
Front Matter: Volume 8024
Front Matter: Volume 8024
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This PDF contains front matter associated with SPIE Proceedings Volume 8024, including Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.
Biosensors
Enzyme detection by surface plasmon resonance using specially engineered spacers and plasmonic labelling
Show abstract
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 biosensor using MEMS-based V-grooves
Show abstract
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.
Advanced Sensing Technologies
Steam distribution and energy delivery optimization using wireless sensors
Show abstract
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.
Development of an optically interrogated chemical tag
Show abstract
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.
Infrared surface waves on semiconductor and conducting polymer
Show abstract
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.
Simultaneous ultrahigh harmonic detection wavelength modulation spectroscopy for resolving congested spectra
Show abstract
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.
Spectrographic Trace Detection
671-nm microsystem diode laser based on portable Raman sensor device for in-situ identification of meat spoilage
Show abstract
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.
High sensitivity calixarene SERS substrates for the continuous in-situ detection of PAHs in seawater
Show abstract
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.
Remote mid-infrared sensing using chirped laser dispersion spectroscopy
Show abstract
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.
Long range trace detection by radar REMPI
Arthur Dogariu,
Celine Stein,
Alexander Glaser,
et al.
Show abstract
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
Remote air lasing for trace detection
Arthur Dogariu,
James B. Michael,
Richard B. Miles
Show abstract
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.
Environmental Sensing
Nanopillars array for surface enhanced Raman scattering
Show abstract
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.
Battery-operated planar-geometry microplasma on a postage-stamp size chip: some fundamentals
S. Weagant,
V. Karanassios
Show abstract
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.
GaN-nanowire/ TiO2-nanocluster hybrid sensors for detection of Benzene and related aromatic compounds
Show abstract
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.
Gas Sensing
Characteristics of CO sensors made by polar and nonpolar ZnO nanowires gated AlGaN/GaN high electron mobility transistor
Show abstract
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.
High sensitivity detection of NO2 employing off-axis integrated cavity output spectroscopy coupled with multiple line integrated spectroscopy
Gottipaty N. Rao,
Andreas Karpf
Show abstract
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.
A low-volume microstructured optical fiber hydrogen peroxide sensor
Show abstract
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.
Tin oxide nanowire sensors for highly sensitive detection of the toxic gas H2S
Show abstract
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.
Standoff identification and quantification of flare emissions using infrared hyperspectral imaging
Show abstract
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.
Trace gas detection and monitoring with the Digital Array Gas-correlation Radiometer (DAGR)
Show abstract
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.
Poster Session
The effects of two noises from passive FTIR (Fourier transform infrared) spectroscopy system on the detection probability of stand-off hazardous compounds with passive Fourier transform infrared spectroscopy system using Michelson interferometer
Show abstract
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.
Strong room-temperature chemiresistive effect of TiO2 nanowires to nitro-aromatic compounds
Show abstract
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.
Gas cloud infrared image enhancement based on anisotropic diffusion
Show abstract
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.
Monitoring organic volatiles and flammable gases with a holographic sensor
J. L. Martínez-Hurtado,
C. A. B. Davidson,
C. R. Lowe
Show abstract
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.
Compact USB-powered mobile ELISA-based pathogen detection: design and implementation challenges
Show abstract
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.