The importance of elucidating the direct and indirect effects of aerosol radiative forcing is now recognized as a significant component of our global climate forecasting models that must be better understood and quantified. Of particular interest is that of aerosol forcing through the so-called "direct" effect of aerosol absorption and scattering. This forcing can be of a magnitude comparable to those induced by anthropogenically-released greenhouse gases, yet can be either the opposite sign [negative (cooling)] or same sign [positive (warming)]. However, despite focused work on this issue, significant discrepancies on aerosol absorption still exist between measurements inferred from remote sensing and those obtained by in situ techniques. This is due, in large part, to the simple fact that the scattering channel dominates aerosol extinction, and thereby, makes measurement of the absorption difficult. An alternative method to measuring aerosol absorption will be presented: measurement of the thermal dissipation of the spectrally absorbed energy through interferometry. The use of this coherent optical detection technique is particularly well suited to measuring the refractive index change that accompanies this energy transfer process. [1,2] This technique was even demonstrated towards measuring aerosol absorption in the mid-1980s [3]. Attractive features of this technique for measuring aerosol absorption include its insensitivity to aerosol scattering, its ability to conduct the measurement in situ, its inherent high sensitivity, and near real-time response. A discussion on the theoretical basis for this technique along with some preliminary data will be presented. Potential applications of this instrument to environmental security problems will also be discussed.

Airborne material particles in the 5μm size range have been collected, resuspended and analyzed by the TAOS (two-dimensional angular optical scattering) technique. The corresponding patterns of light intensity scattered by single particles have been automatically classified by an algorithm based on "spectrum enhancement", multivariate statistics and supervised optimization. The enhanced spectrum has resulted from some non-linear operations on fractional spatial derivatives of the pattern. It has yielded morphological descriptors of the pattern. A multiobjective optimization algorithm has included principal components analysis and has maximized pairwise discrimination between classes. The classifier has been trained by TAOS patterns from 10μm polystyrene spheres (P) and background aerosol particles (B). Then it has been applied to recognize patterns from airborne debris (A) sampled on a car racing track. Training with at least 10 patterns per class has discriminated P and B from A at confidence levels ≥90%. Training by samples of smaller sizes (e.g., 5P and 12B patterns) has obviously yielded lower confidence levels (65% in B-A discrimination).

This paper reports a novel method for measuring the effective refractive index (RI) of single living cell with a small integrated chip. This microchip is able to determine the RI of living cell in real time without extra requirements of fluorescence labeling and chemical treatments, offering low cost and high accuracy meanwhile. It might provide an efficient approach for diseases or cancer diagnosis. The measurement system integrates laser diode, microlenses, and microfluidic channels onto a monolithic chip. In the experiments, two standard polystyrene beads with nominal RIs are employed to calibrate the system and five types of cancerous cells are subsequently measured. The results indicate that the RI of the tested cells ranges from 1.392 to 1.401, which is larger than typical value 1.35-1.37 for normal cells.

Biological warfare agents (BWAs) pose significant threats to both military forces and civilian populations. The increased concern about bioterrorism has promoted the development of rapid, sensitive, and reliable detection systems to provide an early warning for detecting the release of BWAs. We have developed a high-density DNA array to detect BWAs in real environmental samples with fast response times and high sensitivity. An optical fiber bundle containing approximately 50,000 individual 3.1 μm diameter fibers was chemically etched to yield an array of microwells and used as the substrate for the array. 50-mer single-stranded DNA probes designed to be specific for target BWAs were covalently attached to 3.1-μm microspheres, and the microspheres were distributed into the microwells to form a randomized high-density DNA array. We demonstrated the applicability of this DNA array for the identification of Bacillus thuringiensis kurstaki, a BWA simulant, in real samples. PCR was used to amplify the sequences, introduce fluorescent labels into the target molecules, and provide a second level of specificity. After hybridization of test solutions to the array, analysis was performed by evaluating the specific responses of individual probes on the array.

Quenched-fluorescence oxygen sensing allows non-chemical, reversible, real-time monitoring of molecular oxygen and rates of oxygen consumption in biological samples. Using this approach we have developed Respirometric Screening Technology (RST); a platform which facilitates the convenient analysis of cellular oxygen uptake. This in turn allows the investigation of compounds and processes which affect respiratory activity. The RST platform employs soluble phosphorescent oxygen-sensitive probes, which may be assessed in standard microtitter plates on a fluorescence plate reader. New formats of RST assays and time-resolved fluorescence detection instrumentation developed by Luxcel provide improvements in assay sensitivity, miniaturization and overall performance. RST has a diverse range of applications in drug discovery area including high throughput analysis of mitochondrial function; studies of mechanisms of toxicity and apoptosis; cell and animal based screening of compound libraries and environmental samples; and, sterility testing. RST has been successfully validated with a range of practical targets and adopted by several leading pharmaceutical companies.

A promising new fiber optic sensor is under development that combines fiber Bragg gratings coated with polymer materials for sensitive and rapid detection and identification of chemical and/or biological agents. Volumetric expansion of the polymer coating transfers characteristic strain to the Bragg grating, modifying directly its grating period rather than sensing through a change of effective guide index of refraction. The optical interrogation of the sensor element utilizes a sensitive transmission spectroscopy technique with a balanced receiver that minimizes polarization and laser intensity noise problems. A compact, rugged, all-solid-state laser at 1550 nm is being adapted for rapid tuning between discrete preset locked wavelengths. To accompany use of this laser at these few discrete wavelengths, a sampled (superstructure) fiber Bragg grating is being designed using coupled mode theory. Hence, the need for a continuously tunable laser, often with moving mechanical optical elements, and its attendant reference etalon will be avoided entirely. This process exploits a novel vernier effect between the discrete laser wavelengths and the sampled grating responses to create 'signatures' for an artificial neural network. Therefore, the total spectral response pattern of strain can constitute a unique fingerprint used to identify and quantify chemical agents or biomarkers. The sensor is intended for applications requiring multi-functionality, sensitivity, speed, mobility and remote operability in vibrational, electromagnetic, and explosive environments.

A novel fiber optic prototype sensor based on Raman spectroscopy for qualitative and quantitative monitoring of various chemicals in the sample was developed. The sensor employs a high power 670nm laser diode as an excitation light source and a specially designed fiber optic Raman probe with launching and collecting fibers. Raman signal was collected by six optical fibers; filtered, and then fed to the spectrometer through another optical fiber bundle. The uniqueness of the sensor lies in its compact and stable design configuration, that includes carefully aligned optical components, viz. laser diode, filter holder, and miniature spectrometer. Developed sensor is immune to ambient light fluctuation and offers a cost effective solution for probing several species in harsh environment. Various issues like system fabrication, optimization, functional stability, signal/noise ratio, repeatibility etc are well addressed and presented in this paper.

There is an increasing demand for sensors that includes military, homeland security, industrial process, civil structures, transportation and biomedical over wide range of applications. As a result, biophotonic and fiber optic sensing systems can play a key role in meeting many of these needs. Specifically, fiber optic sensors have the potential to measure physical parameters such as movement (strain), acceleration, rotation, pressure, temperature and flow. Biophotonic technology expands the sensing concepts to include the detection of chemical and biological agents (toxins) as well as monitor biological processes.

A UV (266 nm) laser-induced fluorescence (LIF) system with high sensitivity has been used to record fluorescent spectra (300 nm - 700 nm) of various water samples, such as distilled, tap and river water. Large fluorescence peaks corresponding to the fluorescence of Dissolved Organic Compounds (DOCs) were observed in river samples. Significant differences in spectra between different brands of drinking and distilled bottled water were also observed. The LIF system is currently used to measure the trace species in water processed by Reverse Osmosis Water Purification Unit (ROWPU). Initial spectra of the input and output water are presented.

A system designed to address the problem of distribution system monitoring is described here. The developed system employs an array of common analytical instrumentation, such as pH and chlorine monitors, coupled with advanced interpretive algorithms housed in an event monitor to provide detection/identification-response networks that are capable of enhancing system security and quality. A variety of real world venues and testing protocols were used to verify the efficacy of the system. Deployed systems are shown to demonstrate the capability of learning base line in a rapid timeframe while being capable of detecting and characterizing system anomalies related to security and basic water quality operations. Included are data generated from several real world events including caustic overfeeds, rain events, street work and major line breaks among others.

In this paper, progress towards the development of real-time sensing of chemical and biological threats in liquid samples will be presented. This overall goal of this work is to combine the selective, molecular recognition of nucleic acid aptamers with a rapid signal transduction using fluorescence resonance energy transfer (FRET) for a single step identify and detect approach. Of particular interest is the application to whole-cell target recognition of biologicals, such as environmental pathogens (e.g., Campylobacter jejuni), without requiring cell lysis or other complex protocols to access biochemical species internal to the organism. An aptamer staining protocol for whole cell targets is developed and applied to the investigation of aptamers against Campylobacter jejuni cells. A comparison of aptamer binding using this method with and without the primer regions utilized in the aptamer selection process is presented and the primer regions were found to have little impact on binding performance. C. jejuni aptamers exhibited strong binding as evidenced through the fluorescence images acquired and little to no background fluorescence was observed from non-specific binding of the streptavidin-dye conjugate used in the staining method. A thrombin targeted molecular aptamer beacon was also studied and a rapid analysis was demonstrated. A 10 nM sample of thrombin was distinguishable from the fluorescence baseline of the probe alone, when using a 40 nM aptamer probe concentration. The fluorescence intensity was found to increase until saturation of the aptamer probe was achieved. These results show promise for the development of single-step identification of whole-cell targets using an aptamer bioreceptor and fluorescence resonance energy transfer transduction signaling scheme.

The application of the new compact platform of structurally integrated, photoluminescent (bio)chemical sensors, where the photoluminescence (PL) excitation source is an OLED, to the detection of hydrazine and anthrax, is described. The hydrazine sensor is based on the reaction between nonluminescent anthracene-2,3-dicarboxaldehyde and hydrazine or hydrazine sulfate, which generates a luminescent product. The anthrax sensor is based on a Foerster resonance energy transfer (FRET) assay, where the anthrax-secreted lethal factor enzyme cleaves certain labeled peptides at a specific site. The cleaving separates the FRET donor-acceptor pair, resulting in an increase in the PL of the donor, which was previously absorbed by the acceptor.

Surface enhanced Raman spectroscopy (SERS) has widely been used for material composition analysis because it can provide good selectivity and sensitivity without the labeling process required by fluorescence detection. SERS enhancements on the order of 10¹⁴ have been demonstrated, which can enable the detection of a single molecule. However, further enhancement is necessary to increase the sensitivity of SERS systems, and to make single molecule detection and analysis more practical. In this work, we demonstrate a composite system of silver nanoparticles and an optical microsphere resonator to create an even higher average Raman enhancement than SERS alone. The Raman pump is coupled into the microsphere resonator, where it repeatedly circulates around the surface via total internal reflection in the form of whispering gallery modes (WGMs). Microsphere resonators can have Q-factor values higher than 10⁶, which results in a tremendous local field enhancement. The evanescent field of the WGM interacts with the silver nanoparticles and target analytes, which are adsorbed onto the surface of the microsphere. With this composite system, we demonstrate an increase in Raman enhancement of approximately 300. Engineering improvements to this experimental prototype system may increase the enhancement by an order of magnitude. Further improvements that can leverage the microsphere resonator system to promote stimulated Raman scattering (SRS) may result in a dramatic increase in sensitivity. Ultimately, this composite system will increase the sensitivity of SERS sensor systems, and will bring single molecule detection and analysis systems closer to practical implementation.

We have developed a class of aperture coding schemes for Remote Raman Spectrometers (RRS) that remove the traditional trade-off between throughput and spectral resolution. As a result, the size of the remote interrogation region can be driven by operational, rather than optical considerations. In this paper we present the design of our coded-aperture standoff spectroscopy system as well as experimental data collected while making remote measurements.

Ultra-violet fluorescence remains a corner stone technique for the detection of biological agent aerosols. Historically, these UV based detectors have employed relatively costly and power demanding lasers that have influenced the exploitation of the technology to wider use. Recent advancements from the Defense Advanced Research Project Agency's (DARPA) Solid-state Ultra Violet Optical Sources (SUVOS) program has changed this. The UV light emitting diode (LED) devices based on Gallium Nitride offer a unique opportunity to produce small, low power, and inexpensive detectors. It may, in fact, be possible to extend the SUVOS technology into detectors that are potentially disposable. This report will present ongoing efforts to explore this possibility. It will present candidate UV fluorescence based detector designs along with the biological aerosol responses obtained from these designs.

Laser induced native fluorescence (LINF) is the most sensitive method of detection of biological material including microorganisms, virus', and cellular residues. LINF is also a sensitive method of detection for many non-biological materials as well. The specificity with which these materials can be classified depends on the excitation wavelength and the number and location of observation wavelengths. Higher levels of specificity can be obtained using Raman spectroscopy but a much lower levels of sensitivity. Raman spectroscopy has traditionally been employed in the IR to avoid fluorescence. Fluorescence rarely occurs at wavelength below about 270nm. Therefore, when excitation occurs at a wavelength below 250nm, no fluorescence background occurs within the Raman fingerprint region for biological materials. When excitation occurs within electronic resonance bands of the biological target materials, Raman signal enhancement over one million typically occurs. Raman sensitivity within several hundred times fluorescence are possible in the deep UV where most biological materials have strong absorption. Since the Raman and fluorescence emissions occur at different wavelength, both spectra can be observed simultaneously, thereby providing a sensor with unique sensitivity and specificity capability. We will present data on our integrated, deep ultraviolet, LINF/Raman instruments that are being developed for several applications including life detection on Mars as well as biochemical warfare agents on Earth. We will demonstrate the ability to discriminate organic materials based on LINF alone. Together with UV resonance Raman, higher levels of specificity will be demonstrated. In addition, these instruments are being developed as on-line chemical sensors for industrial and municipal waste streams and product quality applications.

Laser-induced breakdown spectroscopy (LIBS) is an emerging atomic emission spectroscopic technique that offers the prospect highly- selective, sensitive, and of real-time detection and analysis of both natural and man-made materials. Because LIBS is simultaneously sensitive to all chemical elements due to detector response in the 200-980nm range with 0.1 nm spectral resolution, the technique has many attributes that make it an attractive tool for a variety of military, security, and environmental applications.

A compact, low-cost, multi-wavelength NDIR sensor was designed to measure G-type CW agents at ppm-levels. This 4-color sensor can distinguish between the different agents (sarin, soman, tabun) and is more sensitive than a single wavelength sensor. The design of the sensor and test results with simulants R-12 (dichlorodifluoromethane) and sulfur hexafluoride is presented. These test results support a lower detection limit of 3 ppmv for a 1 sec integration time. Modifications of the sensor design which will enable us to achieve <1 ppmv sensitivity are discussed.

Aegis Semiconductor pioneered the use of tunable thin films based on thermo-optic effects in amorphous semiconductors, with original application to fiber optic telecom networks at 1.5 μm. In this paper we describe an extension of this technology to longer wavelengths in the mid-infrared to produce a new family (named Firefly(tm)) of gas and chemical sensors based on narrowband, micro-tunable, mid-infrared emitters. A prototype Firefly(tm) emitter designed for detection of carbon dioxide using the 4.2 μm absorption band has been constructed and demonstrated. The emitter, packaged in a TO5 can, consists of a high speed blackbody membrane, a micro-tunable membrane filter, and a blocking filter. The emitter produces about 1 mW of IR output in a bandwidth of approximately 50 nm and may be wavelength modulated from 4150 to 4300 nm at a frequency of about 10 Hz. A CO₂ sensor is completed simply by adding a detector.

Standoff detection, identification and quantification of chemicals in the gaseous state are fundamental needs in several fields of applications. Additional required sensor characteristics include high sensitivity, low false alarms and high-speed (ideally real-time) operation, all in a compact and robust package. The thermal infrared portion of the electromagnetic spectrum has been utilized to implement such chemical sensors, either with spectrometers (with none or moderate imaging capability) or with imagers (with moderate spectral capability). Only with the recent emergence of high-speed, large format infrared imaging arrays, has it been possible to design chemical sensors offering uncompromising performance in the spectral, spatial, as well as the temporal domain. Telops has developed a novel instrument that can not only provide an early warning for chemical agents and toxic chemicals, but also one that provides a "Chemical Map" of the field of view and is man portable. To provide to best field imaging spectroscopy instrument, Telops has developed the FIRST, Field-portable Imaging Radiometric Spectrometer Technology, instrument. This instrument is based on a modular design that includes: a high performance infrared FPA and data acquisition electronics, onboard data processing electronics, a high performance Fourier transform modulator, dual integrated radiometric calibration targets, a visible boresight camera. These modules, assembled together in an environmentally robust structure, used in combination with Telops' proven radiometric and spectral calibration algorithms make this instrument a world-class passive standoff detection system for chemical imaging.

Initial results which demonstrate the ability to classify surface enhanced Raman (SERS) spectra of chemical and biological warfare agent simulants are presented. The spectra of 2 endospores (B. subtilis, B. atrophaeus); 2 chemical agent simulants (Dimethyl methylphosphonate (DMMP), Diethyl methylphosphonate (DEMP)); and 2 toxin simulants (Ovalbumin, Horseradish peroxidase) were collected on multiple substrates fabricated from colloidal gold adsorbed onto a silanized quartz surface. The use of principle component analysis (PCA) and Hierarchical Clustering was used as a method of determining the reproducibility of the individual spectra collected from a single substrate. Additionally, the use of partial least squares-discriminate analysis (PLS-DA) and soft independent modeling of class analogies (SIMCA) on a compilation of data from separate substrates, fabricated under identical conditions, demonstrates the feasibility of this technique for the identification of known but previously unclassified spectra.

We have used a high-repetition-rate, pulsed, 266nm microchip laser and a low-repetition-rate, frequency doubled, tunable dye laser (266nm) to study the fluorescence lifetime of the line spectra of terbium doped dipicolinate in distilled water. Our results are related to the detection of endospores in the environment.

In this paper, a two-dimensional (2-D) spectral estimation is presented. The technique is based on impulse responses carried on the rows and columns of a data matrix. The 2-D frequencies that give the spectrum of a protein molecule in the image plane are obtained from the eigenvalues of open-loop matrices derived from the impulse responses. A modal decomposition of one of the open-loop matrices is used to pair the frequencies without effort. The amplitudes associated with the 2-D frequencies are computed from least-squares of the eigenvalues of the open-loop matrices onto the data. Performance of the technique is tested by computer simulation; effectiveness is confirmed, and results are presented for 2-D nuclear magnetic resonance (NMR) data.

The purged gas containment cell is composed of readily available materials. This cell is charged with analyte samples under the conditions of ambient temperature and pressure. The analyte samples are obtained from dilution of commercially available pure material in lecture bottles. This is achieved by injecting pure analyte material into a Tedlar® bags during filling with a known amount of nitrogen diluent. This study demonstrates the utility of the approach using a series of gas samples with concentration-pathlength products spanning the Beer's law range of infrared absorbances. These absorbance values and blackbody radiance levels are within the linearity range of both the active and passive Fourier transform infrared spectrometers that are used in this study. In addition, these conditions are representative of environments that are often encountered in open-air measurements.

The biosensors, consisting of immobilized antibodies which were for specific recognition to target molecules and electrodes which were able to convert the binding event between antigen and antibody to a detectable signal, were developed for rapid detection of organophosphate (OPs) pesticides. Anti-OPs antibodies were immobilized onto indium-tin-oxide (ITO) coated interdigitated microsensor electrodes (IMEs). The Faradaic impedance spectra, presented as Nyquist plots (Z' vs Z'') and Bode diagrams, (impedance vs frequency) were recorded in the frequency range from 1Hz to 100 kHz respectively. A linear relationship between the electron-transfer resistance and concentrations of OPs pesticide was found ranging from 0.1 ppm to 100 ppm. The regression equations were Y = 658 X +1861, with the correlation coefficient of 0.977. The biosensing procedure was simple and rapid, and could be completed within 1 h.

The degradation product of cephradine(CEP), a broad spectrum antibiotic, with NaOH was studied in solution by Cyclic Voltammetry and Differential Pulse Voltammetry at a three electrode system (Gold working electrode, Hg/HgCl reference electrode and Platinum counter electrode). Our experiment was based on that the R-SH in degradation product could cause a deoxidization peak at gold working electrode. The response was optimized with respect to accumulation time, ionic strength, drug concentration, reproducibility and other variables. We found that the degradation product of CEP in Na₂HPO₄-NaH₂PO₄ buffer could cause a sensitive deoxidization peak at -0.68V. A linear dependence of peak currents on the concentration was observed in the range of 10^-7 - 10^-6 mol/L, with a detection limit of 0.5*10^-7mol/L. This method can achieve satisfactory results in the application of detecting human-made CEP.

The fruit impedance is related to fruit internal quality. Differences in impedance of various quality of apples were measured by use of solartron 1294 impedance interface and solartron 1260 impedance analyzer instrument, four brass-wire probes electrodes, personal computer and the software of bioimpedance measurement of fruits. Apples as examples were experimented at frequency range (1 Hz ~ 1M Hz), and the relation between their impedance parameters and their quality was studied. The results of experiment indicate that the increasing of the frequency could constantly lead to the decreasing of the impedance. When the frequency was increased from 1Hz to 1MHz, the two points impedance of apples' surface decreased 12-15 times. The impedance of good quality apples was nearly constant at both low and high frequency. When detected the rot apples, the impedance was similar to the good apples' at high frequency, and different at low frequency. It was 60-100 ohm lower than normal for the rot apple detection of various rot area. At 1Hz frequency, the impedance measured of 10cm2 rot area was 397ohm, which was about 200ohm lower than normal. The conclusion is it feasible that the bioimpedance can be adopted to distinguishing the internal quality of fruit.

RNA sequences derived from infectious hematopoeitic necrosis virus (IHNV) could be detected using a combination of surface-associated molecular padlock DNA probes (MPP) and rolling circle amplification (RCA) in microcapillary tubes. DNA oligonucleotides with base sequences identical to RNA obtained from IHNV were recognized by MPP. Circularized MPP were then captured on the inner surface of glass microcapillary tubes by immobilized DNA oligonucleotide primers. Extension of the immobilized primers by isothermal RCA gave rise to DNA concatamers, which were in turn bound by the fluorescent reporter SYBR Green II nucleic acid stain, and measured by microfluorimetry. Surface-associated molecular padlock technology, combined with isothermal RCA, exhibited high selectivity and sensitivity without thermal cycling. This technology is applicable to direct RNA and DNA detection, permitting detection of a variety of viral or bacterial pathogens.

The overall goal of the research was to develop a water quality monitoring system that simultaneously concentrates micron-size particles and bacterial cells in the nodal planes of a standing ultrasonic wave field and monitors the level of contamination using light transmission measurements. Ultrasonic concentration is an attractive method for in-line, continuous sensing since it has no moving parts and is not limited by a physical barrier, e.g., a filter, which may get plugged over time. The degree of concentration was evaluated over a range of initial particle concentration. Results showed that particle banding occurred within seconds of sonication - allowing for real-time analysis - and the degree of concentration increased with decreasing initial concentration of particles in the suspension. Concentration factors of 5 to 10 were achievable. Results from this study can be used in the design and fabrication of sensitive water quality monitoring systems that would permit real-time water quality analysis.