Studies on Magnetically Actuated Droplets for Digital Microfluidic

Abstract

Digital microfluidic is an emerging liquid handling technique where discrete droplets are manipulated on a substrate. For the past decades, conventional microfluidic applications are based on continuous flow concept. They require complicated networks of channels, pumps and valves to manage the flow of droplets in microchannels. In digital microfluidics, droplets are moved individually on an open surface. The droplets have the flexibility to move in various directions, making a single device flexible for diverse reaction designs and applications. The manipulation of discrete droplets allows reduction in sample size, faster heat transfer and reaction rates and easier collection of samples. The droplets can be manipulated via electrostatic force, magnetic force, gravitational force, pressure gradient, pH change, surfactant concentration, temperature change, Marangoni propulsion and light-induced surface tension gradient. Magnetic actuation is an excellent candidate for digital microfluidic applications because of the simplicity of using external magnetic field for a non-contact and non-invasive control over magnetised droplets. The magnetic field can penetrate through substrates and biological materials. There is also a wide variety of available magnetic particles and it is easy to control the amount of magnetic particles loaded into the carrier liquid. Some magnetic particles can absorb nucleic acids and other biomolecules making it possible for biomolecular separation. Magnetic manipulation is not affected by factors such as surface charges, pH and ion concentration. In most cases, magnetic manipulation does not induce heating.