AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Individually Identifiable Aerosol Particles Using Luminescent Nanocrystals
Michael H. Stewart, Kimihiro Susumu, Jozsef Czege, Cathy S. Scotto, Alan Huston, JAY D. EVERSOLE, Naval Research Laboratory
Abstract Number: 629 Working Group: Aerosol Physics
Abstract Commercial polymer beads with narrow size distributions available in a wide range of mean diameters from 10’s of nm to 10’s of µm have become de facto particle standards with pervasive use throughout the aerosol research community. Moreover, a wide range of organic molecule dyes can also be selected to impart tailored emission profiles to these beads. This combination of diameter and excitation/emission profile selection provides capabilities for many aerosol applications, such as tracking in complex gas flows using either fluorescent imaging or fluorescent particle counting. However, for environmental applications, ambiguity remains at the individual particle level regarding whether any given particle belongs to ambient aerosol background, or a released tracer aerosol.
Here, we describe initial work to produce and characterize particles that use luminescent nanocrystals (NC’s) instead of organic dyes for imparting photo-emissive properties to micron-sized particles. NC’s offer significant advantages over dye molecules including: (a) narrower emission profiles (no long tails to the red), and (b) chemical and photo stability, since nanocrystals do not photo-bleach (unlike dyes). Consequently, embedding multiple separate populations of NC’s, each with a distinct, non-overlapping emission profile, into a micron-sized bead sample will create a complex spectral superposition “bar-code” that can serve as an identifying optical mark on each individual bead in that sample. Such complex emission profiles cannot be emulated in natural processes. While traditional NC’s (quantum dots) have previously demonstrated emission “bar code” identification for larger beads (>20 µm) [1], so far, this has not been achieved in beads small enough for aerosol use. Traditional quantum dots may also present an issue as hazardous materials for environmental releases. Our effort focuses on more recent, and more benign, NC materials, as well as new upconverting NC’s [2] which can provide an additional dimension for creating unique identification signatures.
[1] For example: Yuanjin Zhao, et.al., J. Am. Chem. Soc., 2011, 133 (23), pp 8790–8793, DOI: 10.1021/ja200729w. [2] Noah J. J. Johnson, et. al., J. Am. Chem. Soc. 2017, 139, 8, 3275-3282 DOI: 10.1021/jacs.7b00223.