Surface-enhanced Raman spectroscopy (SERS) has repeatedly been shown to be capable of single molecule detection in
laboratory controlled environments. However, superior detection of desired compounds in complex situations requires
optimization of factors in addition to sensitivity. For example, SERS sensors are metals with surface roughness in the
nm scale. This metallic roughness scale may not adsorb the analyte of interest but instead cause a catalytic reaction
unless stabilization is designed into the sensor interface. In addition, the SERS sensor needs to be engineered sensitive
only to the desired analyte(s) or a small subset of analytes; detection of every analyte would saturate the sensor and make
data interpretation untenable. Finally, the SERS sensor has to be a preferable adsorption site in passive sampling
applications, whether vapor or liquid. In this paper, EIC Laboratories will discuss modifications to SERS sensors that
increase the likelihood of detection of the analyte of interest. We will then demonstrate data collected for TATP, a
compound that rapidly decomposes and is undetected on standard silver SERS sensors. With the modified SERS sensor,
ROC curves for room temperature TATP vapor detection, detection of TATP in a non equilibrium vapor environment in
30 s, detection of TATP on a sensor exposed to a ventilation duct, and detection of TATP in the presence of fuel
components were all created and will be presented herein.
An effective method to create fear in the populace is to endanger the water supply. Homeland Security places significant
importance on ensuring drinking water integrity. Beyond terrorism, accidental supply contamination from a spill or
chemical residual increases is a concern. A prominent class of toxic industrial chemicals (TICs) is pesticides, which are
prevalent in agricultural use and can be very toxic in minute concentrations. Detection of TICs or warfare agents must
be aggressive; the contaminant needs to be rapidly detected and identified to enable isolation and remediation of the
contaminated water while continuing a clean water supply for the population. Awaiting laboratory analysis is
unacceptable as delay in identification and remediation increases the likelihood of infection. Therefore, a portable or online
water quality sensor is required that can produce rapid results. In this presentation, Surface-Enhanced Raman
Spectroscopy (SERS) is discussed as a viable fieldable sensor that can be immersed directly into the water supply and
can provide results in <5 minutes from the time the instrument is turned on until analysis is complete. The ability of
SERS to detect several chemical warfare agent degradation products, simulants and toxic industrial chemicals in distilled
water, tap water and untreated water will be shown. In addition, results for chemical warfare agent degradation products
and simulants will be presented. Receiver operator characteristic (ROC) curves will also be presented.
Despite the recent interest in organically grown foods, most agricultural crops use multiple pesticides to optimize yield.
There are many persons whose health may be affected by the spraying; there is the active applicator and the passive
neighbors. In between these extremes are the farm workers who pick the crops anywhere from days to weeks after
application. How much pesticide residue are these workers exposed to during a workday and how much is transferred
back to the residence? Despite the low vapor pressures, what is the true concentration of pesticides surrounding a person
when pesticides adsorbed to particulate matter are included? What is the relationship between the concentration around
an individual and the amount adsorbed/ingested? To answer these questions on a statistically significant scale in actual
field conditions, a portable, fast, inexpensive measurement device is required. We present herein results obtained using
Surface-Enhanced Raman Spectroscopy (SERS) that demonstrate the capability to detect < 100 organophosphate,
organochlorine and carbamate-based pesticides in the vapor phase as well as the ability of SERS sensors to detect a
particular analyte in a synthetic urine matrix. We will also present data collected from CDC quantified urine samples
and will present results obtained in a field test wherein SERS sensors wore worn as dosimeters in the field and real-time
vapor sampling of the farm workers barracks was performed. The issue of potential interferences will also be discussed.
One approach to CBRNE detection is analytical monitoring with portable spectroscopy systems. Such a technique needs
to work in adverse environments, be amenable to use by field operators, and, given the sensitive nature of the target
materials, should have an extremely rapid response time with no false negatives. This research demonstrates that
surface-enhanced Raman scattering (SERS) is capable of detecting ppb levels of CBRNE materials with high sensitivity
and no false positives. We present reproducible and selective detection using novel SERS structures that exhibit an
inherently uniform surface morphology, leading to rapid, reproducible manufacturing. Our work includes receiver-operator
characteristic (ROC) curves for the detection of both conventional and improvised nitro explosives at low
signal-to-noise ratios. We also present the detection of added CBRNE materials including chemical and biological
agents as well as nuclear enriching materials. Our expertise extends to instrumentation of portable, robust Raman
spectrographs that can be packaged with our sensors for a versatile security tool with applications extending from points
of entry to points of production, from people to objects and freight.
Surface-enhanced Raman scattering (SERS) is emerging as a versatile and powerful technique for the detection of various defense related hazardous materials. This work illustrates the level of sensitivity and reproducibility achieved using SERS substrates with structural features engineered at the nanometer scale. Nanostructured substrates show significant sensitivity toward a number of different analytes. Pinacolyl methyl phosphonic acid (PMPA), a nerve-agent degradation product, was detected in less than 30 seconds at 1ppb. Para-nitroaniline, an explosives simulant, was detected in the same amount of time at 10 ppm. Multiple tests showed signal reproduction of PMPA at 100 ppb below a 7% standard deviation. The substrates are small and lightweight. In addition, a portable SERS spectrometer, equipped with a fiber coupling for excitation and detection, can act as the sensor body. On a previous occasion, electrochemically roughened SERS substrates were loaded into this portable spectrometer and deployed in the field for the successful blind detection of buried, defused, landmines. Such a system accommodates multiple substrate technologies, allowing sensing in the vapor and liquid phase as well as via solids extraction, and is compatible with nanoscale substrates.
Surface-enhanced Raman spectroscopy (SERS) is a spectroscopic technique that enables trace detection of analytes of relevance using fieldable equipment. SERS uses the enhanced Raman signals observed when an analyte adsorbs to a roughened metal substrate, generally gold, silver, or copper. Coupled to a microscope, single molecule detection has been demonstrated. With a fieldable instrument, enhancements of 108 compared to unenhanced Raman spectroscopy are expected, allowing trace detection in the field. Proper development of the metal substrate will optimize the sensitivity and selectivity towards the analytes of interest. In this presentation, we will discuss applications under development at EIC Laboratories that are of importance to Homeland Defense. We will review the capabilities of SERS to detect buried explosives, explosives associated with nuclear weaponry and chemicals involved in the nuclear enrichment process. We will discuss the detection of chemical and biological warfare agents in the water supply in research performed under the Joint Service Agent Water Monitor. We will demonstrate the current detection limits, the reproducibility of the signal, and results collected using actual chemical warfare agents, and show how the results can be extended to vapor detection. We will also discuss the current state-of-the art for fieldable instrumentation. The emphasis on portability and speed will be stressed; SERS acquisitions are restricted to 30 s or less.
Resonance Raman spectroscopy is an enhanced Raman technique that can be used to selectively identify a particular analyte in complex matrices. Resonance Raman requires the excitation laser to overlap with an absorption band of the analyte of interest. Since analytes have diverse absorption spectra, dilute concentrations may be detected when resonantly enhanced. A significant portion of interesting molecules absorb only in the UV; unfortunately current UV Raman instrumentation for scientifically desirable spectral resolution is large and costly. In the area of Homeland Defense, explosives, nerve agents, amino acid residues (for toxin analysis) and nucleic acids (for DNA detection and identification of bacteria) are all enhanced using UV laser sources. EIC Laboratories has developed a more user-friendly UVRRS spectrograph that is based upon the use of an echelle grating. The spectrograph has a footprint of 7" x 11" and is capable of providing 4 cm-1 resolution over a fairly wide spectral range. The spectrograph design and spectra from analytes of particular relevance will be presented.
Protection of the drinking water supply from a terrorist attack is of critical importance. Since the water supply is vast, contamination prevention is difficult. Therefore, rapid detection of contaminants, whether a military chemical/biological threat, a hazardous chemical spill, naturally occurring toxins, or bacterial build-up is a priority. The development of rapid environmentally portable and stable monitors that allow continuous monitoring of the water supply is ideal. EIC Laboratories has been developing Surface-Enhanced Raman Spectroscopy (SERS) to detect chemical agents, toxic industrial chemicals (TICs), viruses, cyanotoxins and bacterial agents. SERS is an ideal technique for the Joint Service Agent Water Monitor (JSAWM). SERS uses the enhanced Raman signals observed when an analyte adsorbs to a roughened metal substrate to enable trace detection. Proper development of the metal substrate will optimize the sensitivity and selectivity towards the analytes of interest.
Through its several orders of magnitude signal enhancement over normal Raman, surface-enhanced Raman spectroscopy (SERS) provides an opportunity to extend the benefits of vibrational spectroscopy to trace level detection. SERS in particular holds great potential for biological sensing due to the weak Raman bands of water and the reduction in fluorescence backgrounds from interactions of the analyte with the metal SERS substrate. This work examines the trace level detection of biological molecules and oligomers such as amino acids, peptides, and oligonucleotides as well as the detection of whole cell bacteria. The SERS substrates employed are electrochemically roughened gold. The biological molecules show well-resolved and intense bands that are an effective spectral signature; these bands also persist in corresponding oligomeric compounds. Spectra from whole cell bacteria have been obtained for several species, including gram-positive and gram-negative strains. Viable and nonviable cells have also been examined and significant spectral differences are observed. The results show the potential for using SERS as an analytical tool for the identification of biological molecules and microorganisms with applications in biological agent detection, food and water monitoring, and the search for signs of extraterrestrial life.
The sensitivity demonstrated for other nitro-aromatic explosives through SERS has been applied to triaminotrinitro-benzene (TATB). Gas phase and solution phase in strong acids and bases, as well as organic solvents SERS spectra have been collected. For each method of TATB sample introduction on electrochemically roughened gold substrates or gold colloids, different bands and sensitivities were observed. These bands likely result from the three possible adsorption sites in the molecule and its reaction with the gold surface. In some cases, the SERS spectra closely overlapped the carbonaceous background and indicate TATB degradation. Although the mechanisms of the reaction of TATB with the surface are not understood, important aspects of optimized TATB SERS detection have been observed. Para-nitroaniline (p-NA) was also studied due to its similarity with TATB and its greater solubility in water.
The threat of chemical warfare agents being released upon civilian and military personnel continues to escalate. One aspect of chemical preparedness is to analyze and protect the portable water supply for the military. Chemical nerve, blister, and choking agents, as well as biological threats must all be analyzed and low limits of detection must be verified. For chemical agents, this generally means detection down to the low ppb levels. Surface-Enhanced Raman Spectroscopy (SERS) is a spectroscopic technique that can detect trace levels of contaminants directly in the aqueous environment. In this paper, results are presented on the use of SERS to detect chemical and biological agent simulants with an end goal of creating a Joint Service Agent Water Monitor. Detection of cyanide, 2-chloroethyl ethyl sulfide, phosphonates, Gram-positive and Gram-negative bacteria using SERS has been performed and is discussed herein. Aspects of transferring laboratory results to an unattended field instrument are also discussed.
We report surface-enhanced Raman scattering (SERS) for vapors of 2,4-dinitrotoluene (2,4-DNT), 1,3-dinitrobenzene, 4-amino-2, 6-dinitrotoluene and trinitrotoluene (TNT) adsorbed onto gold metal foils. Detection of 2,4-DNT down to approximately 1 ppb has been demonstrated. A compact field portable Raman unit with fiber optic SERS attachment has been fabricated and field tested for landmine detection. Preliminary results showed little environmental interference to the SERS measurement and detection of a buried landmine. The results demonstrate that SERS can detect buried landmines and, with further improvements, has the potential to be a man-portable field unit for landmine detection.
Surface-enhanced Raman scattering has been measured for solutions of 2,4-dinitrotoluene (2,4-DNT), trinitrotoluene (TNT), and hexahydro-1,3,5-trinitro-s-triazine (RDX) adsorbed onto metal foils, island films, coated microspheres, and colloids. The wavelength selectivity of the method was also investigated for lasers which potentially may be used in a field instrument. Preliminary room temperature vapor-phase SERS detection of 2,4-DNT adsorbed on gold foil has been achieved. The results demonstrate the potential of SERS as a detector of buried landmines when coupled to compact man- portable Raman instrumentation.
The importance of techniques to sense and monitor the environment are becoming increasingly more important with the intensifying presence of groundwater and soil contaminations. Our research and development effort is aimed at producing a commercial, low cost, field portable instrument for the field screening/in situ monitoring of contamination from organic solvents based on the principle of combining spectroscopic, electrochemical, and fiber optic techniques. Some of the advantages of this technique for monitoring a contamination site are cost, small size of sampling probe, real-time analysis, the capability of sensing in adverse environments, and the ability of using a central detection facility. The technique has an
advantage over current integrating fiber optic chemical sensing methods in that the sensing only takes place when the electrochemical device is turned on. This should enable long-term monitoring of a site to be accomplished with only one probe/instrument system.
Raman spectroscopy is a powerful noninvasive tool for elucidating chemical structure. Like infrared spectroscopy, it has many potential practical applications, such as process monitoring, environmental sensing, clinical analysis, forensic identification, and as a detector for use with analytical instruments. Until recently, however, Raman has been considered mainly in the context of basic research. The present generation of high performance Raman instruments tend to be large, complex and expensive, and thus have been of primary interest only to specialists in the field. This paper will discuss the development of a compact Raman spectrometer system consisting of a diode laser, fiber optics of excitation and collection, and a compact spectrograph with charge coupled device (CCD) detection.