If you had to sort a bunch of nanoparticles by size, what would you use? A microscope, tweezers, and a very finely-calibrated caliper? Actually, you’d probably use the nanofluidic “multi-tool” created by researchers at the National Institute of Standards and Technology (NIST) in the U.S. Before you start picturing a teeny-tiny Leatherman, which would admittedly be pretty cool, you should be aware that the NIST device is more like a coin separator, that sorts your nickels, dimes and quarters. In this case, however, they would be nickels, dimes and quarters that are smaller than a bacterium.
The device was actually created a year ago, but has just been showcased in an article in the journal Lab on a Chip. That article outlined how the device recently performed the first of a planned series of nanoscale tasks – it successfully separated and measured a mixture of spherical nanoparticles of different sizes (ranging from about 80 to 250 nanometers in diameter) dispersed in a solution.
Viewed in cross-section, the device is a wedged-shaped chamber, with a flat roof and a broad, staircase-like floor. That chamber is taller at the front, but becomes narrower at the back, as the roof and floor close together one precisely-calibrated step at a time.
Using electrophoresis, a method of moving charged particles through a solution by forcing them forward with an applied electric field, the nanoparticles were channeled into the chamber and up the staircase. The larger particles got stuck relatively near the front, as they could no longer squeeze between the floor and the roof, while the smaller particles were able to move farther back before they also were stopped. Ultimately, all the particles ended up at specific steps of the chamber, as dictated by their size.
“Integrated into a microchip, the device could enable the sorting of complex nanoparticle mixtures, without observation, for subsequent application” NIST stated in its press release. “This approach could prove to be faster and more economical than conventional methods of nanoparticle sample preparation and characterization.”
The research team is now looking at using the device for sorting nanoparticles by other criteria, such as shape or composition, instead of size.