Abstract

Digital Microfluidics and Magnetic Beads

Alphonsus Ng, NSERC Canadian Graduate Scholar, University of Toronto

The marriage of magnetic beads and microfluidics systems is an emerging trend for many applications. In addition to being magnetically responsive, magnetic beads offer a dramatic increase in surface area to volume ratio, and can be functionalized with variety molecules such as antibodies and enzymes. This talk will focus on the manipulation of magnetic beads using a droplet-based fluid handling technique called Digital Microfluidics (DMF) and its applications in sample preparation, immunoassays, and catalysis.
In DMF, discrete droplets are handled by electrostatic forces on an array of electrodes coated with a hydrophobic insulator. By applying a sequence of voltage to these electrodes, droplets of magnetic bead suspension and other reagents can be individually made to move, merge, mix and dispense from reservoirs. With the help of an adjustable external magnet, the beads can be separated from the supernatant, and rapidly re-suspended in a different reagent. To automate these fluid-bead manipulations, we designed a computer-controlled system (approximately the size of a shoebox) that uses a Pogo pin interface for digital microfluidic control and a motorized magnet for magnetic bead separation.  Using this system, we developed three magnetic-bead based applications: i) a sample preparation tool that can remove unwanted proteins from a complex sample, ii) a diagnostic device that can perform competitive and sandwich immunoassays, and iii) a versatile microreactor for enzymatic catalysis. The miniaturization of these applications using digital microfluidics has resulted in several benefits, including automated operation, faster reaction and analysis time, and lower reagent and sample consumption. We anticipate that digital microfluidics and magnetic beads will be useful for other magnet bead-based applications.