Activation of Single Aerosol Particles into Droplets with Immediate Capture into an Open Channel Microfluidic Device

WENDY FLORES-BRITO, Thomas Brubaker, Shelley Anna, Ryan Sullivan, Carnegie Mellon University

     Abstract Number: 625
     Working Group: Instrumentation and Methods

Abstract
Individual physicochemical analysis of aerosol particles continues to be a challenge since few techniques exist that can preserve an aerosol's individual identity following sampling each particle for further offline analysis. We developed a new method that features direct activation of aerosol particles into aqueous droplets followed by droplet capture into an open channel microfluidic device while potentially maintaining their individual particle–droplet pair identity in an immiscible fluid. As part of the method development, we produced a model using the Stokes and Weber numbers to predict the impaction and coalescence of the single-particle-droplets into a continuous oil phase. The critical controllable variables to optimize droplet-to-oil collection are the droplet diameter and velocity. We collected single-particle-droplets containing fluorescent salt into an immiscible fluid and measured the total fluorescent droplet volume present. The measured and simulated collected fluorescent volume results were directly compared, resulting in an impacted droplet collection efficiency ranging from 41 ± 12% to 140 ± 16%. The upper bound is a worst-case scenario, based on highly conservative approximations, assuming most droplets will not be collected in the immiscible fluid region, thus inflating the impacted droplet collection efficiency. The lower bound is based on approximations from current Weber and Stokes number literature values and is a more realistic representation for the system. Our analysis indicates this new method successfully collects single-particle-droplets into an immiscible fluid while maintaining the individual identity of the particle contained in each droplet. We have started to extend this droplet collection system into a oil that is flowing through the open channel collection region into a serpentine microfluidic channel. This will enable chemical analysis of each particle contained in each droplet such as by optical spectromicroscopy or electrochemical methods. This technique can be applied used in any field that requires knowledge of individual aerosol particle properties (such as virology, aerosol health effects, and the climate sciences) to better understand their abundance, composition, aerosol lifetime, and the distribution and mixing state of individual aerosols in an indoor or outdoor environment.