Abstract

A Billion-Droplet AC Electrospray Digital PCR Platform for Large-Dynamic Range Nucleic Acid Quantification

Hsueh-Chia Chang, Bayer Professor of Engineering / Director, University of Notre Dame

An AC-electrospray technology is shown to be able to generate 1 billion femto-liter (micron diameter) aqueous drops in immiscible silicone oil in less than 20 minutes.  Unlike DC sprays, which tend to suffer from dielectric breakdown in liquid, and droplet generation technologies based on hydrodynamic shear, which can only generate pico-liter drops, we have shown that a properly tuned AC field can entrain low-mobility anions at a meniscus and the Coulombic repulsion among such entrained ions can deform the meniscus into unique 11 degree AC cones that are quite distinct from and much stable than DC cones (Phys Rev Lett, 101, 204501(2008); 109, 224301(2012); LabChip, 15, 1656(2015)).   The sharper AC cones can generate 1 million femto-liter drops per second.  The larger drop number and concentration (nM) allow us to get significantly better accuracy (without using Poisson statistics), dynamic range (8 decades) and reduction of inhibition and interfering effects in heterogeneous media.  We have fabricated an integrated AC electrospray chip with PCR and imaging modules and have favorably compared the performance of this new droplet digital PCR platform against qPCR. The new AC droplet digital PCR platform is, however, a low-cost turn-key technology that requires no or minimum sample pretreatment.