For airborne threats or hazards, the development of point detection capability for materials that are inherently aerosols is principally an issue concerned with determining aerosol composition. The utility of receiver operating characteristic (ROC) curves to clarify tradeoffs between the probability of detection, and probability of false positive classification will be discussed, as well as the application of confusion matrix description of data feature separation. Examples will be taken from ongoing optical imaging and spectroscopy efforts to illustrate the connection between parameters such as discrimination, sensitivity, and response time made on an individual sample basis, to potential overall system performance.

Developing equipment and instrumentation for use by first responders and HAZMAT professionals in a Homeland Defense role requires an understanding of the real needs of those responders. These needs are driven by the manner in which the incident response takes place and how the response actions occur over time. This paper describes a chemical terrorist incident, the response functions and related timelines, and the detection and identification needs during each phase. From this information, developers will be able to better understand requirements related to sensitivity, specificity, response time, weight, ruggedness, ease of use, and other design parameters.

IR spectroscopy is a broadly applicable technique for the identification of covalent materials. Recent advances in instrumentation have made Fourier Transform infrared (FT-IR) spectroscopy available for field characterization of suspect materials. Presently, this instrumentation is broadly deployed and used for the identification of potential chemical hazards. This discussion concerns work towards expanding the analytical utility of field-based FT-IR spectrometry in the characterization of biological threats. Two classes of materials were studied: biologically produced chemical toxins which were non-peptide in nature and peptide toxin. The IR spectroscopic identification of aflatoxin-B1, trichothecene T2 mycotoxin, and strychnine was evaluated using the approach of spectral searching against large libraries of materials. For pure components, the IR method discriminated the above toxins at better than the 99% confidence level. The ability to identify non-peptide toxins in mixtures was also evaluated using a "spectral stripping" search approach. For the mixtures evaluated, this method was able to identify the mixture components from ca. 32K spectral library entries. Castor bean extract containing ricin was used as a representative peptide toxin. Due to similarity in protein spectra, a SIMCA pattern recognition methodology was evaluated for classifying peptide toxins. In addition to castor bean extract the method was validated using bovine serum albumin and myoglobin as simulants. The SIMCA approach was successful in correctly classifying these samples at the 95% confidence level.

Highly active and stable substrates for surface-enhanced Raman scattering (SERS) can be fabricated by using colloidal crystals to template gold nanoparticles into structured porous films. The structure-dependent performance of these SERS substrates was systematically characterized with cyanide in continuous flow millifluidic chambers. A matrix of experiments was designed to isolate the SERS contributions arising from nano- and microscale porosity, long range ordering of the micropores, and the thickness of the nanoparticle layer. The SERS results were compared to the substrate structure observed by scanning electron microscopy (SEM) and optical microscopy to correlate substrate structure to SERS performance. The Raman peak intensity was consistently highest for nanoporous substrates with three-dimensionally ordered micropores, and decreases if the micropores are not ordered, or not templated. Removing the nanoscale porosity by fusion of the nanoparticles (without removing the large micropores) leads to drastic plunge in substrate performance. The peak intensity does not strongly correlate to the thickness of the nanoparticle films. Receiver operating characteristic (ROC) curve analysis for cyanide in water revealed a limit of detection (LOD) of ca. 150 ppb based on a 5% probability of false alarm. The results make possible the efficient controlled fabrication of stable, reproducible and highly active substrates for SERS-based chemical sensors with continuous sampling.

The United States and its allies have been increasingly challenged by terrorism, and since the September 11, 2001 attacks and the war in Afghanistan and Iraq, homeland security has become a national priority. The simplicity in manufacturing chemical warfare agents, the relatively low cost, and previous deployment raises public concern that they may also be used by terrorists or rogue nations. We have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect extremely low concentrations (e.g. part-per-billion) of chemical agents, as might be found in poisoned water. Since trace quantities of nerve agents can be hydrolyzed in the presence of water, we have expanded our studies to include such degradation products. Our SERS-active medium consists of silver or gold nanoparticles incorporated into a sol-gel matrix, which is immobilized in a glass capillary. The choice of sol-gel precursor allows controlling hydrophobicity, while the porous silica network offers a unique environment for stabilizing the SERS-active metals. Here we present the use of these metal-doped sol-gels to selectively enhance the Raman signal of the hydrolyzed products of the G-series nerve agents.

As the war on terrorism in Afghanistan and Iraq continue, future attacks both abroad and in the U.S.A. are expected. In an effort to aid civilian and military personnel, we have been investigating the potential of using a surface-enhanced Raman spectroscopy (SERS) sampling device to detect Bacillus anthracis spores in nasal swab samples. Such a device would be extremely beneficial to medical responders and management in assessing the extent of a bioterrorist attack and making detect-to-treat decisions. The disposable sample device consists of a glass capillary filled with a silver-doped sol-gel that is capable of extracting dipicolinic acid (DPA), a chemical signature of Bacilli, and generating SERS spectra. The sampling device and preliminary measurements of DPA extracted from spores and nasal mucus will be presented.

We have systematically designed, fabricated, and tested chalcogenide-glass waveguides. Among all the characterization techniques, we have found that the prism-coupling method is the most effective and accurate for determining all the parameters describing the performance of the slab waveguides. Furthermore, we have also achieved the end-fire coupling in these waveguides to study the characteristics of the transmitted beams. These waveguides can be optimized eventually for the biosensor applications.

The distribution of Bacillus anthracis spores through the US postal system in the autumn of 2001, initiated a secondary form of terror, the mailing of hoax materials. In the past three years nearly 20,000 letters containing harmless powders have been mailed, creating additional anxiety. Thus, there is a need for analyzers that can not only identify anthrax-causing spores to save lives, but also identify hoax materials to eliminate time-consuming and costly shutdowns. Recently, we established that Raman spectroscopy has the ability to identify both Bacilli endospores and hoax materials. Here we present Raman spectra of several Bacilli spores along with the dipicolinate salts, to further define the abilities of this technology to not only identify hoax materials, but also identify spores at the genus and species level.

A two-wavelength excitation bioaerosol sensor has been developed and characterized for classifying various types of aerosols, including biological organisms and non-biological interferents. Single aerosols, smaller than 10 μm, are interrogated with 266 nm and 355 nm laser pulses separated in time by 400 ns. Fluorescence signals excited by these pulses are detected in three broad spectral bands centered at 350 nm, 450 nm and 550 nm. The results indicate that bacterial spores, vegetative bacterial cells and proteins can be differentiated based on the two wavelength excitation approach.

As part of an effort to develop a portable probe for real-time detection of chemical agents using Raman spectroscopy, the kinetics of adsorption of selected volatile organic molecules on high surface area silica supports was studied using Raman spectroscopy with 785-nm excitation. Two aspects of this work are described. First, the affinity of organic molecules in a flowing gas stream to ultraporous mineralized wood substrates was shown to be very high under a variety of representative conditions, suggesting that a sensor based on in-situ Raman measurement of adsorption rates may be feasible. Moreover, the mechanism of adsorption was found to vary for different molecules thereby promoting a high degree of chemical specificity. Second, the possibility of using Surface-Enhanced Raman Spectroscopy (SERS) to enhance Raman signals and thereby improve the sensitivity of an in-situ Raman probe even further was demonstrated. Detection limits were estimated based on the current state of development of the approach.

Recent developments in the characterization of particle dispersions have demonstrated that complementary information on the joint particle property distribution (size-shape-chemical composition) of micron and sub-micron particles is available from multiwavelength spectrophotometric measurements. The UV-VIS transmission spectra of the microorganism suspensions reported herein were recorded using a Hewlett-Packard 8453 diode array spectrometer with an acceptance angle smaller than 2 degrees. To eliminate concentration and particle number effects, the transmission spectra were normalized with the average optical density between 230-900 nm. Experimental results demonstrate that microorganisms at various states of growth give rise to spectral differences that can be used for their identification and classification and that this technology can be used for the characterization of the joint particle property distribution for a large variety of continuous, on-line, and in-situ particle characterization applications. An interpretation model has been developed for the quantitative interpretation of spectral patterns resulting from transmission measurements of microorganism suspensions. The interpretation model is based on light scattering theory and spectral deconvolution techniques and yields the quantitative information necessary to define the probability of the detection and identification of microorganisms. A data base of 54 pathogens has been created and demonstrates that the technology can be used in the field for real-time in-situ monitoring applications.

The ability of a Kromoscope to discriminate between chemical warfare agent simulants and toxic industrial chemicals is evaluated. The Kromoscope response to the simulants DMMP and DIMP is compared to a pesticide (diazanon) and cyclopentanol. The response of a mid-infrared Kromoscope to the nerve agents VX and GB and the stimulant DF are calculated.

Fluorescence represents one of the most attractive approaches for chemical sensing due to the abundant light produced by most fluorophores, resulting in excellent detection sensitivity. However, the broad and overlapping emission spectra of target and background species have made it difficult to perform species identification in a field instrument because of the need to perform spectral decomposition and analysis. This paper describes a new chemical sensing strategy based on differential fluorescence measurements from molecularly imprinted polymers, which eliminates the need to perform any spectral analysis. Species identification is accomplished by measuring the differential light output from a pair of polymers-one imprinted to a target species and the other identical, but not imprinted. The imprinted polymer selectively concentrates the target molecule and controls the energy (wavelength) of the emitted fluorescence signal and the differential output eliminates common mode signals associated with non-specific background interference. Because no spectral analysis is required, the sensors can be made extremely small and require very little power. Preliminary performance parameters from a prototype sensor are presented and discussed.

This work presents the development of new methodologies centering on surfaces with immunologically induced affinities for biomaterials in aqueous systems. The immunologically active surfaces concentrate the biomaterials at the interface and therefore eliminate the need for preconcentration steps. This results in a highly sensitive and rapid immunoassay technique. The very strong localized of surface enhanced Raman scattering (SERS) that occurs at noble metal surfaces is combined with the unparalleled selectivity of immunoassays. Localization of the SERS signal eliminates the problem of washing and allows assays to be performed without treatment steps associated with removing excess agents. Previous work with small illicit drug molecules and large microorganisms clearly demonstrates trace detection of species in aqueous environments is possible. This paper discusses further work to detect Bacillus globigii by couping surface enhanced Raman scattering with immunoassays (SERIA) using citrate reduced silver nanoparticles. The spores of B. globigii are used to simulate the behavior of another bacterium that forms spores-the potential biological warfare agent, Bacillus anthracis, the causative agent of anthrax.

Terahertz Time domain spectroscopy (THz-TDS) can provide the optical response of a medium in both amplitude and phase. We show that such capability can enable a detail analysis of optical properties of biological sample. Such study is important for standoff detection of presence of biological sample, where a detail analysis is difficult if not possible due to a complicated system involved and multiple effects involved. We proposed a transfer function study of the response of such system.

We have recently extended our studies of the infrared signatures of Bacillus bacterial spores from the mid-infrared to the far-infrared (sometimes called the terahertz, THz) spectral domain. The ultimate goal is to use such signatures to distinguish different strains of spores from unknowns as well as from one another. Five different strains of Bacillus were prepared by culturing the spores, washing repeatedly in sterile water and drying them onto windows that are simultaneously transparent in both the mid- and far-infrared. The strains include B. globigii BG-01, B. thuringiensis subsp kurstaki ATCC 35866, B. subtilis ATCC 49760, B. subtilis ATCC 6051, and B. atrophaeus ATCC 49337. Using different combinations of hardware in the Fourier transform infrared (FTIR) spectrometer, essentially continuous spectral coverage was obtained from ~8 to 6,000 cm^-1. Preliminary results indicate that any THz signatures are at least 25 times weaker (based on p-p noise) than the strongest mid-IR amide I bands near 1657 cm^-1.

Raman spectroscopy is just one of the diverse set of detection techniques which, under the CB Rapid Agent Aerosol Detection (RAAD) program, are being evaluated for their ability to detect and identify biological materials. In order to compare and contrast different techniques, a Common Sample Set composed of threat simulants, interferents and growth media was provided to all RAAD participants. The samples were investigated using both normal Raman and surface-enhanced Raman spectroscopy. This paper focuses on near-infrared Raman data from the Common Sample Set bacterial simulants. Results are also given from a principal component analysis performed on these samples. These measurements provide and initial assessment of the detection and discrimination capability of Raman spectroscopy as applied to biological materials. Despite the challenges facing this detection method, Raman spectroscopy is emerging as a rapid and information-rich method of investigating biological threats.

Light-guiding fused silica capillary tubing has promising applications in the field of chemical sensors. Light propagation in these waveguides occurs within the fused silica capillary wall as opposed to liquid core waveguides where light traverses the solution-filled inner core. The electric field of light within the capillary wall extends slightly into the capillary inner diameter as an evanescent wave. An evaluation of the optical absorbance characteristics of these novel capillaries was performed by coupling the light source from a spectrophotometer into a capillary waveguide flow cell. A series of four thiacyanine dyes in methanol solution provided distinct absorbance peaks throughout the visible spectrum (400-800 nm). Evanescent absorbance values show a linear dependence upon capillary length up to ~10 m (with 150 mm inner diameter). Evanescent absorbance measurements were nonlinear with solution concentration for all capillary lengths and may be attributed to adsorption of the ionic dye on the capillary fused silica inner surface. The waveguide effective pathlength ratio (EPLR) was determined by comparing evanescent absorbance values to conventional measurements in a 0.1 mm pathlength cuvette. The EPL is on the order of 10^-5-10^-6 m per meter of capillary tubing and also shows wavelength dependence. The evanescent field penetration depth ratios from experiment were dp ratio (424 nm) = 0.60 ± 0.07, dp ratio (557 nm) = 0.78 ± 0.10, and dp ratio (652 nm) = 0.73 ± 0.07 when normalized to dp ratio (758 nm) and compare reasonably with predicted values of 0.56, 0.73, 0.86, and 1.00 respectively. Absorbance sensitivity was investigated with 50, 150, and 250 mm inner diameter capillaries (360 mm outer diameter) that have theoretical inner reflection ratios of 1, 1.7, and 6.9 respectively. Experimentally measured ratios were 1, 2.0 ± 0.9, and 6.5 ± 1.2.

Vapor analytes of methanol and ammonia are quantitatively generated separately and as mixtures in the presence of water vapor. Generation of these analytes relies on the vapor liquid equilibria properties of associated aqueous solutions for delivering targeted vapor amounts into an equilibrium vapor cell. Gravimetric solution preparation and maintaining a constant solution temperature permits control of the analyte amount that is delivered to the optical equilibrium vapor cell. A laboratory Fourier transform infrared spectrometer examines the fixed path length optical cell contents. This examination furnishes vapor-phase infrared absorbances for analyte mixtures in the Beer's Law concentration range. Literature vapor liquid equilibrium data and infrared absorbance measurements show that the methanol/ammonia binary compontents of the ternary aqueous solutions of this study exhibit ideal solution behavior.