Microfluidic Aerobatics

Digital microfluidics, in which individual droplets are manipulated on an array of electrodes, is currently limited to a single horizontal plane. That circumstance restricts the number of samples that such microfluidic devices can handle and makes it difficult to integrate multiple physical and chemical environments on the same device. Aaron Wheeler and coworkers at the University of Toronto now describe a novel method for droplet manipulation—all-terrain droplet actuation (ATDA)—that works on a variety of device shapes (Lab Chip, DOI: 10.1039/b801516c). The researchers constructed arrays of copper electrodes on flexible polyimide substrates that can be bent into staircases, twists, and even upside-down architectures (shown). Their model shows that droplets smaller than 7.3 µL can be driven up a 90º incline; larger droplets are restricted to smaller angles. Wheeler and coworkers used ATDA to cycle droplets on oxygen- and temperature-sensitive sensors. They also have developed a device that concentrates oligonucleotides from a solution containing histone proteins. The researchers suggest that ATDA will be useful for other sample enrichment techniques and applications such as DNA amplification that require samples and reagents to be cycled between different reaction conditions.