AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Bioaerosols Composed of Bacteria or Proteins: A Model of Their Fluorescence and Its Variations with Size and Water Content
STEVEN HILL, David Doughty, Chatt Williamson, Yong-Le Pan, Joshua Santarpia, US Army Research Lab
Abstract Number: 498 Working Group: Bioaerosols
Abstract We use a mathematical model of fluorescent bioaerosols composed of bacteria and/or proteins to investigate the size-dependence of the total fluorescence from these and its variation with water content. The model applies to particles which have negligible reabsorption of fluorescence within the particle. The specific particles modeled here are composed of ovalbumin and of a generic Bacillus. The particles need not be spherical, and in some cases need not be homogeneous. The results shown are of spherical homogeneous particles excited at 266 nm. Light absorbing and fluorescing molecules included in the model are amino acids, nucleic acids, and coenzymes. Emission from tryptophan is emphasized. We investigate power law (Ad$^y) approximations to for the fluorescence cross section (C$_F), where d is diameter, and A and y are parameters adjusted to fit the data, and examine how y varies with d and composition, including the fraction as water. The particle’s fluorescence efficiency (Q$_F = C$_F / geometric-cross-section) can be written for homogeneous particles as Q$_(abs)R$_F, where Q$_(abs) is the absorption efficiency of the particle in its specific orientation, and RF, the fraction of the absorbed light emitted as fluorescence, is independent of size and shape. When Q$_F is plotted vs. m$_id or m$_i(m$_r – 1)d, where m = m$_r + i m$_i is the complex refractive index, the plots for different fractions of water in the particle tend to overlap, a feature that can help in extracting mi from a set of measured values.