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Many CBRNE threat materials are optimally implemented as aerosols. However, aerosol threats present unique challenges for sensor development, test and evaluation since particles may disburse in a turbulent atmosphere differently from tracer gases. This presentation addresses the need for tracer aerosol particles with known size distributions to be released with agent target simulant aerosols to provide ground truth for sensor test and evaluation. A novel approach for achieving uniquely identifiable individual aerosol particles is described based on utilization of quantum dots (QDs) and/or other luminescent nanocrystals (NCs), to create a multiplexed spectral barcode in tracer aerosol particles. QDs are small, typically nanometer scale, compared to micron-sized polymer beads as host aerosol particles. They also possess desirable optical properties of narrow, efficient emission bands, and are typically long-lived compared to organic dye molecules that photodegrade in sunlight. Multiple QD subpopulations, each with a narrow emission band at a distinct peak wavelength, can be encapsulated in a polymer microbead, conferring a superposition emission profile having multiple narrow peaks. The relative intensities of the emission peaks can be controlled by adjusting the number of QDs in each subpopulation. This spectral emission profile effectively becomes an individual particle barcode. Multiple polymer bead samples can be prepared each with different emission pattern (barcode). These samples can be mixed with target materials to be simultaneously released as aerosols to provide test ground truth for the simulant. Proof-of-principle experiments assessing the feasibility for using combinations of embedded NC populations in micron-sized droplets, as well as potential challenges to practical implementation will be discussed.
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