Driving water uphill

Canadian chemists have developed an all-terrain droplet actuation (ATDA) method to move droplets across chips at a wide range of angles.

Aaron Wheeler and colleagues at the University of Toronto said digital microfluidic devices using ATDA could be used to move fluids rapidly between different environments, for example to cycle between heating and cooling, in research published in the Royal Society of Chemistry journal Lab on a Chip.

Wheeler developed ATDA on flexible, water-repellent polyimide surfaces, clad with copper, which can be bent into a variety of shapes including steps, twists and overhangs. The fluid beads are moved by sequentially activating a series of electrode pairs, which is thought to pull the droplet forward by reducing water repellence in front of the droplet. This process gives the team full control of the droplet, including up and down vertical surfaces.

Wheeler suggests several potential uses for the technique, including PCR (the polymerase chain reaction), which is used in DNA analysis. PCR depends on rapid temperature cycling - and Wheeler showed the method can be used to move fluids between a cooling structure and a hot plate. Automating the droplet movement would allow very rapid temperature cycling, Wheeler said.