Capturing Single Aerosol Particle-Droplets into a Microfluidic Device for Surface-Enhanced Raman Spectroscopic Analysis

WENDY FLORES-BRITO, Shelley Anna, Coty Jen, Ryan Sullivan, Carnegie Mellon University

     Abstract Number: 519
     Working Group: Instrumentation and Methods

Abstract
Individual physicochemical analysis of individual aerosol particles continues to be a challenge since few techniques that can preserve an aerosol's individual identity while transferring the particle for further offline analysis exist. Here, we build upon a method developed in our group that features direct activation of aerosol particles into droplets by water condensation followed by droplet capture into an open channel microfluidic device while potentially maintaining their individual particle–droplet pair identity in an immiscible fluid. We compare the use of a different growth column (Sequential Spot Sampler) from the original method (Cloud Condensation Nuclei Counter), which should prevent condensation-produced droplets from entering the microfluidic device and provide an increased homogeneity in size droplet production using a smaller temperature gradient. The condensational growth column technique used by the spot sampler also allows for a wider range of applications such as the study of volatile particles and collection of viable bioaerosol. To evaluate the experimental method, we collected single-particle-droplets containing fluorescent salt into the open channel of the microfluidic device with oil flowing through it. The success of different surfactants at preventing droplet coalescence following oil capture was evaluated. The droplet capture efficiency was evaluated as a function of microdroplet size using fluorescence microscopy. Additionally, we present our initial work towards combining this aerosol particle microfluidic capture technique with online real–time chemical analysis using Surface-Enhanced Raman Spectroscopy (SERS). The combination of these methods will create a promising technique for the sampling and real–time field analysis of single aerosol particles using small microfluidic devices.