Korean scientists have created a microfluidic abacus that allows them to add droplets together. They say the system can mimic the logic operations of an electronic chip. 

The droplets merge at the abacus groove to form larger droplets

Je-Kyun Park and Eujin Um at KAIST, Daejeon, created a wide microfluidic chamber with a sharply bending groove cut into it. When droplets enter the chamber, they are guided by the groove but get stuck at its rectangular corners. As more droplets enter the groove, they merge at the bend to form a bigger droplet, which is eventually forced out of the chamber as the pressure builds up behind it. Although the droplets enter the chamber at a fixed rate, Park introduced a control flow to vary the number of merging droplets - as the flow rate increases, the number of droplets merging decreases because the merged droplet is forced out the chamber more quickly. 

'Scientists have been attempting to mimic the logic operations of electronic chips using droplets and bubbles,' says Park. Each droplet can represent a unit of information, he explains, and being able to control the retention and addition of drops means they can be used as on-off switches, for example. 'This work will lead to the automation of lab-on-a-chip processes without external power sources,' Park predicts. 

Park also showed that multiple droplet adding chambers can be linked together to form more complex droplet counters, and different types of droplets can be merged in different ratios at the bend. 'As the system becomes more complex, we will have to develop elaborate means to provide pumping and tubing,' says Park. 

Rachel Cooper