OBJECTIVE
This topic seeks disruptive technologies applied to the development of physically semi-porous flexible coupons (e.g. paper or polymer with plasmonic nanoparticles) to sample from a range of smooth and rough or abrasive surfaces found in operational environments using Surface Enhanced Raman Spectroscopy (SERS). Ideally, these tickets would be designed with multiple SERS substrates (either mixed or located in specific separate regions of the coupon) to target multiple classes of chemical and biological (CB) hazards (e.g., toxins, fentanyl analogs). Such coupons would greatly expand the capabilities of fielded hand-held Raman spectrometers from bulk detection and identification to detection of trace/residue amounts of hazard and potentially improving the selectivity against impurities co-present in the sample. Coupons would ideally be compatible with any fielded Raman device and with wavelengths of 785nm, 830nm and 1064 nm.
DESCRIPTION
The Department of Defense has fielded several handheld Raman detectors over the past 15 years to support specialized chemical, biological, radiological, and nuclear (CBRN) units across the services and Special Operations forces. These detectors typically contain very large libraries (in the thousands) of solid and liquid chemicals (including toxins, as chemicals of biological origin) that are identifiable with the device. However, these devices typically require a bulk amount of liquid or solid sample (grams or milliliter amounts) and have difficulty in identification of chemicals in mixtures of materials. SERS is a technique that offers the potential to greatly enhance the sensitivity and selectivity of current and future handheld Raman detectors. SERS coupons are typically inexpensive with very low size and weight and require no additional power or sample preparation, making them a highly attractive option for soldiers already heavily physically burdened. However, SERS signals can vary significantly between different substrates and even within the same substrate, making it difficult to establish consistent measurements. Factors including substrate fabrication, material homogeneity, and analyte adsorption all contribute to this variability.
This topic seeks approaches to overcoming these challenges with application to the range of threat chemicals that could be encountered on the battlefield in liquid or solid form. These include but are not limited to nerve agents, blister agents, arsenicals, pharmaceutical based agents, and toxins. Proposals should provide an innovative solution to the specified need. They should address a science-based approach to how promising substrates are identified and patterned on a coupon (either as a patterned mixture of substrates, separate spots of different substrates, or other). Consideration of consistency in substrate materials and patterning should be addressed. Please include science-based analysis of predicted selectivity and sensitivity enhancements spanning representative members of several previously noted classes of compounds. Preliminary data is preferred to supplement modeling, simulation and analysis, and surrogate chemicals may be used in place of highly regulated target chemicals.
PHASE I
Awardees should provide a comprehensive approach to how substrates are selected or designed and fabricated for enhanced selectivity and sensitivity over the bulk amount of relatively high purity chemicals required by hand-held Raman detectors and comparison to current commercially available substrates. They should address how the substrates will be patterned on a flexible coupon both in selection of one or more patterns as well as attaining consistent patterning and reproducibility of the production process. A plan for the demonstration of enhancements in Raman identification of target materials (chemical, biological, toxin, and/or explosives) or reasonable surrogates sampled from various surfaces in various operationally realistic mixtures (e.g. minute amounts of nerve agent surrogate dimethyl methyl phosphonate sampled from military painted metal) must be included.
PHASE II
In Phase II, the performer shall initially obtain or produce substrates and produce patterned prototype coupons. Their performance should be demonstrated to both dilute chemical targets or surrogates delivered directly to the coupon and those same chemicals in operationally relevant mixtures sampled from a surface to understand the enhancement in sensitivity and selectivity for the latter. At a minimum, substrates should be able to show SERS enhancement for 1 m solutions of BPE (1,2-bis(4-pyridyl)ethylene) and 1 mM solutions of 4-Nitrophenol. This demonstration should include sufficient replicates at the lower end of detection to provide statistically useful variability data at the 80% confidence level. Enhancements to patterns and/or the patterning process may be required to reduce variability. Upon finalization of the patterning process, a Bayesian limit-of-detection at the 80% confidence level will be required for each selected target chemical mixture. During Phase II the performer shall deliver no less than 50 substrates for independent analysis at DEVCOM Chemical Biological Center.
PHASE III DUAL USE APPLICATIONS
PHASE III: Phase III will begin the transition into advanced development for fielding across the services, Special Operations forces, and the National Guard Bureau. Typically, government-developed technology finds its way into non-DoD and commercial entities as commercial-off-the shelf products. As a very low size, weight, cost and unpowered enhancement to existing field handheld Raman detectors, it is expected to be rapidly fielded as an enhancement to the existing fielded materiel.
PHASE III DUAL USE APPLICATIONS: If successful, this product would greatly enhance screening of cargo and mail for the detection of toxic chemicals at organizations such as the Department of Homeland Security's Customs and Border Protection and United States Coast Guard, as well as the presence of toxins in food and counterfeit drugs for the Food and Drug Administration. It has great promise to support commercial entities in testing for the presence of toxic substances in foods (e.g. toxins).
REFERENCES
X. Tang et al, Trends in Food Science & Technology Volume 152, October 2024 and references therein.
Emmons, E. D., Guicheteau, J. A., Fountain III, A. W., Tripathi, A. "Effect of Substituents on Surface Equilibria of Thiophenols and Isoquinolines on Gold Substrates Studied Using Surface-Enhanced Raman Spectroscopy". Phys. Chem. Chem. Phys. 2020, 22, 15953-15965.
Guicheteau, J. A., Tripathi, A., Emmons, E. D., Christesen, S. D., Fountain III, A. W. "Reassessing SERS enhancement factors: using thermodynamics to drive substrate design". Faraday Discuss. 2017, 205, 547-560.
Guicheteau, J. A, Farell, M. E., Christesen, S. D., Fountain III, A. W., Pelligrino, P. M., Emmons, E. D., Tripathi, A., Wilcox, P., Emge, D. "Surface-enhanced Raman Scattering (SERS) Evaluation Protocol for Nanometallic ., Surfaces". Appl. Spec. 2013, 67, 4, 396-403.
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