Researchers from ETH Zurich have developed tiny valves that enable individual nanoparticles in liquids to be separated and sorted. The valves can be used for a very broad range of tiny particles, including individual metal and semiconductor nanoparticles, virus particles, liposomes and larger biomolecules such as antibodies.

The nanovalves work differently than classic valves, which are used to mechanically close and open flow in pipelines, as in a tap. “These mechanical valves can be miniaturised, but not as far as we would need for nanoscale applications,” explains ETH professor Poulikakos. “If channels are thinner than a few dozen micrometres, they cannot be mechanically closed and opened with any regularity.”

Bottleneck with electrodes

In order to open and close the nanoparticle flow in ultrathin channels, the ETH scientists made use of electric forces. They worked with channels etched into a silicon chip. These had a diameter of just 300 to 500 nanometres – less than a hundredth of the diameter of a human hair. They then constructed nanovalves in these channels by narrowing the channels at desired valve locations using nanolithography and placing an electrode on both sides of these bottlenecks.