OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Biotechnology OBJECTIVE: Develop a micro-Raman aerosol detector that meets the size, weight, power, and cost (SWaP-C) requirements for UAV-delivery and is capable of semi-continuously collecting and analyzing particles from the ambient atmosphere using hyperspectral Raman spectroscopy. The system may use additional spectroscopic or light scattering techniques to achieve an adequate measurement rate and should be able to store raw data and provide processed data for integration into data fusion systems. DESCRIPTION: Micro-Raman spectroscopy is considered an attractive method for early warning of chemical and biological threats because of its broad applicability including detection of aerosols, explosives, and pharmaceuticals adaptability, and lack of sample preparation [1]. Unfortunately, the adoption of automated micro-Raman spectroscopy is limited by several challenges that hinder its utility. For example, luminescence is known to overwhelm signals from biological or mineral particles; spectra from heterogeneous, or mixed composition, particles can be difficult to interpret; high laser intensity can alter the spectra of particles; and long analyses (seconds) for smaller particles (< 10 m) has slowed the speed of identification. Moreover, a hyperspectral approach e.g., line-scanning [2] or fiber-array [3] is needed to obtain spectra from adequate numbers of particles. Recent technological advancements make early warning applications of Raman spectroscopy more attainable. These include decreases in laser size, weight, and power for Raman spectroscopy systems; the availability of compact energy efficient deep-UV lasers [4]; and the use of Raman and fluorescence from deep-UV excitation to aid in identification [5] Other developments such as the use of shifted-excitation Raman difference spectroscopy [6] time-resolved spectroscopy [7] also enhance Raman signals relative to background. A early version of this technology is the REBS (Battelle, Dayton, OH), which uses electrostatic precipitation coupled to a line-scanning hyperspectral Raman system, though compact, UAV-use requires even greater reduction in SWaP-C [2]. It is feasible to envisage the development of a small, lightweight hyperspectral micro-Raman aerosol detector-airborne (HRAD-A). The HRAD-A should be able to measure Raman spectra of individual aerosol particles as small as 500 nm (e.g., polystyrene latex spheres) and analyze over 150 one- m size particles sampled at an atmospherically relevant concentration in 15 minutes (e.g., ammonium nitrate, bacillus spores, paracetamol). The HRAD-A should provide greater situational awareness and capability of force protection by providing information on a wide range of harmful airborne particles [8], including chemical or biological agents and particles affecting visibility and/or communications. The US Army Training and Doctrine Command (TRADOC) Force Operating Capabilities calls for robotic platforms that provide environmental risk assessment from an established baseline [9], and can allow for remote CBRN reconnaissance [10, 11]. These elements should be able to be integrated with battlefield information management and data fusion systems to provide actionable information [9]. The HRAD-A should be designed to be a portable, low SWaP-C sensor capable of being distributed throughout an area of operations to achieve an increased situational understanding and provide CBRN and environmental background surveillance data as needed. For example, a sensor might be placed in an austere location by a UAV and then run off a solar panel for remote surveillance. Additionally, a system with open-source hardware and software that can be integrated into data-fusion systems ensures future compatibility as part of the multi-domain operations battlespace. Further, if the system is modular i.e., the optical path can be switched it can enable integration with future systems. PHASE I: Design the HRAD-A to sample and analyze ambient aerosol particles leveraging hyperspectral Raman spectroscopy from multiple particles at a time. Use of other techniques to aid in discrimination, such as fluorescence (excited by the same laser for the Raman), is encouraged. Particles of interest include such as polystyrene latex spheres (0.5 m), 1 m bacterial/mold spores, chemical simulants, ammonium nitrate, and pharmaceuticals. Minimum specification of the design includes operating from DC 8-16V, a size of < 3L, weight of < 10kg, and sufficient power for 4 hours of operation. The aerosol system should be able to run continuously for several days connected to mains power without human intervention. The deliverables for Phase I will include: the design for the HRAD-A including specific concept details; a description of why the HRAD-A is likely to perform as desired; proof of concept results, if obtained; how this concept can be prototyped; and criteria Phase II validation. PHASE II: In Phase II a prototype will be fabricated and validated. Deliverables will include a prototype capable of collecting aerosol particles measuring Raman spectra from polystyrene latex spheres as small as 500nm, collecting and measuring Raman spectra from 150 particles in 15 minutes, and demonstration of semi-continuous sampling in the ambient outdoor environment, in accordance with the validation success criteria developed in Phase I. PHASE III: In Phase III a low-SWaP-C HRAD-A will be provided for long-term surveillance for ambient aerosol hazards and for measuring particles which affect visibility and communications. The desired HRAD-A could also be used (on a UAV/UGV) to investigate areas for potential hazards, e.g., chem/bio agents. Commercialization of the technologies will also be pursued. The ability of the optical pathway to be used for other purposes also has significant utility. Employed in a handheld manner, Raman spectroscopy can be used to non-destructively determine the composition of materials inside plastic bags and some plastic and glass containers. REFERENCES: 1. Silge, A., et al., Trends in pharmaceutical analysis and quality control by modern Raman spectroscopic techniques. TrAC Trends in Analytical Chemistry, 2022. 153: p. 116623. 2. Doughty, D.C. and S.C. Hill, Automated aerosol Raman spectrometer for semi-continuous sampling of atmospheric aerosol. Journal of Quantitative Spectroscopy and Radiative Transfer, 2017. 188: p. 103 117. 3. Frosch, T., et al., Fiber-Array-Based Raman Hyperspectral Imaging for Simultaneous, Chemically-Selective Monitoring of Particle Size and Shape of Active Ingredients in Analgesic Tablets. Molecules, 2019. 24(23): p. 4381. 4. Feng, K., et al., Simple and compact high-power continuous-wave deep ultraviolet source at 261nm based on diode-pumped intra-cavity frequency doubled Pr:LiYF4 green laser. Optics Express, 2023. 31(12): p. 18799-18806. 5. Bhartia, R., et al., Perseverance's Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Investigation. Space Sci. Rev., 2021. 217(58): p. 1-115). 6. Lorenz, B., et al., Comparison of conventional and shifted excitation Raman difference spectroscopy for bacterial identification. Journal of Raman Spectroscopy, 2022. 53(7): p. 1285-1292. 7. Fau, A., et al., Time-resolved Raman and luminescence spectroscopy of synthetic REE-doped hydroxylapatites and natural apatites. American Mineralogist, 2022. 107(7): p. 1341-1352. 8. Pope III, C.A., et al., Lung Cancer, Cardiopulmonary Mortality, and Long-term Exposure to Fine Particulate Air Pollution. JAMA, 2002. 287(9): p. 1132-1141. 9. TRADOC, TP 525-66: Force Operating Capabilities. 2008. 10. Army, U., Field Manual 3.0: Operations. 2023. 11. CJCS, JP 3-11: Operations in Chemical, Biological, Radiological, and Nuclear Environment. 2018. KEYWORDS: Raman, detection, chem-bio, atmosphere, UAV
