Sorting droplets digitally

By using microelectrodes to distinguish between droplets of different sizes and compositions, the new detector provides better scan rates and higher accuracy than current methods - which often use special cameras and optical tricks to separate droplets.

The droplets pass between a series of electrodes built into the chip, which can sequentially identify, label and separate droplets based on their capacitance, or ability to store charge. This means the chip can digitally sort the droplets based on many criteria like size, velocity or even composition. The chip can process up to 10,000 drops a second - a feat that is difficult to achieve using optical methods, the team claim, and is cheaper to make than other detectors.

Weijia Wen, associate professor at the Hong Kong University of Science and Technology and co-author of the paper, told Chemistry World the apparatus is not limited to liquid droplets. ’This chip can sort micro- or nanoparticles with high efficiency, which is not easy to realise with other methods,’ he said. ’The integration of electrical functionalities with microfluidics can greatly expand the horizon of microfluidic applications in biotechnology.’

Performing a single process on a chip is far easier than integrating several, Stephen Haswell, professor of analytical science at the University of Hull, told Chemistry World. ’None of these individual components is novel - the really neat bit of this work is the integration,’ he said. ’If we’re going to move lab-on-a-chip technology forward for use in real world applications, then integration of these components is crucial.’ 

Jonathan Edwards