Wayne W. Smith

Chemical agent detection by surface-enhanced Raman spectroscopy

In the past decade, the Unites States and its allies have been challenged by a different kind of warfare, exemplified by the terrorist attacks of September 11, 2001. Although suicide bombings are the most often used form of terror, military personnel must consider a wide range of attack scenarios. Among these is the intentional poisoning of water supplies to obstruct military operations in Afghanistan and Iraq. To counter such attacks, the military is developing portable analyzers that can identify and quantify potential chemical agents in water supplies at microgram per liter concentrations within 10 minutes. To aid this effort we have been investigating the value of a surface-enhanced Raman spectroscopy based portable analyzer. In particular we have been developing silver-doped sol-gels to generate SER spectra of chemical agents and their hydrolysis products. Here we present SER spectra of several chemical agents measured in a generic tap water. Repeat measurements were performed to establish statistical error associated with SERS obtained using the sol-gel coated vials.

pH dependence of methyl phosphonic acid, dipicolinic acid, and cyanide by surface-enhanced Raman spectroscopy

U.S. and Coalition forces fighting terrorism in Afghanistan and Iraq must consider a wide range of attack scenarios in addition to car bombings. Among these is the intentional poisoning of water supplies to obstruct military operations. To counter such attacks, the military is developing portable analyzers that can identify and quantify potential chemical agents in water supplies at microgram per liter concentrations within 10 minutes. To aid this effort we have been investigating the value of a surface-enhanced Raman spectroscopy based portable analyzer. In particular we have been developing silver-doped sol-gels to generate SER spectra of chemical agents and their hydrolysis products. Here we present SER spectra of methyl phosphonic acid and cyanide as a function of pH, an important factor affecting quantitation measurements, which to our knowledge has not been examined. In addition, dipicolinic acid, a chemical signature associated with anthrax-causing spores, is also presented.

Differentiating bacterial spores from hoax materials by Raman spectroscopy

The bioterrorism of October 2001 caused by the distribution of anthrax through the U.S. postal system was compounded by the significant delay associated with positive identification of the Bacillus anthracis spores and the unknown extent of their distribution along the eastern seaboard. In the ensuing two years, literally thousands of hoaxes, letters containing harmless powders, have been mailed creating additional anxiety. Thus, there is a need for instruments and/or methods that can not only identify anthrax-causing spores to save lives, but also identify hoax materials to eliminate costly shutdowns. Here we present Raman spectra of Bacillus cereus spores, an anthrax surrogate, as well as of 30 common substances that might be used as hoax materials. We also examine the choice of laser excitation, 785 nm or 1064 nm, and its impact on the ability to measure visible particles in 5 minutes or less, and to provide a complete answer to the question of suspicious material identity.

Detection of bioagent signatures: a comparison of electrolytic and metal-doped sol-gel surface-enhanced Raman media

Since September 11, 2001, the threat of terrorist attack and biological warfare within U.S. borders has become a sobering reality. In an effort to aid military personnel and the public at large, we have been investigating the utility of surface-enhanced Raman spectroscopy (SERS) to provide rapid identification of chemical agents directly, and biological agents through their chemical signatures. This approach is based on the ability of Raman spectroscopy to identify molecular structure through the abundant vibration information provided in spectra and the ability of SERS to detect extremely low concentrations (e.g. part-per-billion) through the enhancement of Raman scattering by six orders of magnitude or more. Toward the goal of developing a portable analyzer, we have been studying the ability of two SER media to obtain continuous (i.e., reversible) and quantitative (i.e., reproducible) measurements. Here we compare measurements of nucleic acid bases, adenosine monophosphate, and ribonucleic acid extracted from Escherichia coli, Bacillus subtilis and Staphylococcus aureus obtained by electrolytic SERS and metal-doped sol-gel SERS. The capabilities of these SER media are summarized in terms of rapid detection of B. anthracis and dipicolinic acid.

Measurement of thermal degradation in epoxy composites by Fourier transform Raman spectroscopy

The ability of Raman spectroscopy to nondestructively evaluate thermal degradation in graphite reinforced epoxy composites was examined. A series of composite samples, exposed to temperatures ranging from 150 to 400 degree(s)C for periods of 2 to 20 minutes, were analyzed by Fourier transform Raman and reflectance IR spectroscopies. The intensity of the Raman and IR polymeric backbone vibration at 1600 cm-1 diminishes with increasing thermal exposures and can be correlated to failure strain and flexural strength measured by four point bending tests, as well as acoustic emission events. These data, along with IR transmission spectra of species evolved from composite pyrolysis, suggest that thermal degradation occurs in three stages: (1) polymeric fragmentation (possibly microcracking), (2) advanced polymer degradation observed as delamination between the four ply layers, and (3) final composite failure with fiber fracture.

Characterization of polymer composites during autoclave manufacturing by Fourier transform Raman spectroscopy

12 The superior engineering properties of fiber reinforced polymer matrix composites, primarily the high strength-to- weight ratio, make them suitable to applications ranging from sporting goods to aircraft components (e.g. helicopter blades). Unfortunately, consistent fabrication of components with desired mechanical properties has proven difficult, and has led to high production costs. This is largely due to the inability to monitor and control polymer cure, loosely defined as the process of polymer chain extension and cross- linking. Even with stringent process control, slight variations in the pre-polymer formulations (e.g. prepreg) can influence reaction rates, reaction mechanisms, and ultimately, product properties. In an effort to optimize the performance of thermoset composite, we have integrated fiber optic probes between the plies of laminates and monitored cure by Raman spectroscopy, with the eventual goal of process control. Here we present real-time measurements of two high performance aerospace companies cured within an industrial autoclave.

Biological agent identification by nucleic acid base-pair analysis using surface-enhanced Raman spectroscopy

Recently, a number of analytical methods have been successfully developed which use nucleic acid sequencing to identify biological warfare agents. However, the effectiveness of these methods, towards the safety and protection of US Armed Forces and their allies are limited by the period required to enumerate the nucleic acid through polymerase chain reactions or culture growth to produce sufficient quantities for analysis. To overcome this limitation, we have been investigating the ability of surface-enhanced Raman spectroscopy to detect nucleic acids with sufficient sensitivity and selectivity to eliminate the need for enumeration. The design of a small volume electrolytic sample cell will be presented along with analysis of the nucleic acid bases and preliminary analysis of model bacteria.

Characterization of polymer composites by fiber optic Fourier transform Raman spectroscopy

The in-use performance of polymer composites is highly dependent on the polymeric structure, which in turn, is highly dependent on the processing conditions. We have been developing a Fourier transform Raman system capable of high temperature measurements within curing devices through the use of fiber optic probes. The goal is to use real-time spectral data to control heat schedules and ultimately, composite properties. This presentation will describe the development of cure models based on reaction mechanisms for an epoxy resin and a polyimide using IR and Raman spectroscopy. It will also describe correlations between molecular structure and mechanical properties obtained by simultaneous Raman and rheology measurements. In addition, new spectral methods to determine cure kinetics will be presented.

Vehicle‐mounted nephelometer for use in desert environments

Vehicles that are required to travel off‐road in arid and semiarid conditions can be exposed to high levels of airborne particles. The airborne material, typically sand, can be detrimental to the performance of air‐breathing engines and other mechanisms. The U. S. Army, for instance, has experienced the influence of airborne desert dust during testing of equipment at Yuma Proving Ground, and during critical operations at other desert locations. To enhance testing of equipment under loading of airborne desert dust, a laser‐based nephelometer has been constructed which provides the real‐time measurement of dust mass per unit volume. The instrument is sensitive and provides a linear response to dust concentration levels from 0.01 to above 25 g/m3. Important is that: (1) the light scattering technique is independent of particle size distribution in the sampling volume; and (2) the instrument is rugged to allow for mounting and operation on vehicles traveling off‐road in the desert environment.

Multiplexed fiber optic collector for FTIR reflectance and radiance spectroscopy

Recently, solar furnaces have been successfully used to harden steel, coat metals, and initiate physical and chemical vapor deposition. Successful development of this technology requires process monitoring of surface temperature, which can be in excess of 2000 degree(s)C. This severely limits the accuracy of standard devices. This paper describes the use of FT-IR spectroscopy to measure spectral reflectance and radiance of solar-heated samples in order to accurately determine their temperature. The system features a fiber optic arrangement, representative of a hemispherical mirror, to collect diffusely reflected radiation. Preliminary results are given.