Using a device consisting of a chamber with a cascading “staircase” of 30 nanofluidic channels, National Institute of Standards and Technology (NIST), USA, researchers lead by S.M. Stavis have demonstrated that the device can separate and measure a mixture of spherical nanoparticles of different sizes (80 – 250 nm in diameter) dispersed in a solution.

The steps of the device range in depth from 80 nm at the top to 620 nm at the bottom and, as expected, the nanoparticles stopped when they reached a step with a depth that corresponded to its diameter. Progress across the device was driven by electrophoresis and the nanoparticles labeled with fluorescent dye to enable tracking.

Integrated into a microchip, the device could enable the sorting of complex nanoparticle mixtures, without observation, for subsequent application. This approach could prove to be faster and more economical than current methods and could be tailored to separate by resolution, particle size, or material.

• Separation and metrology of nanoparticles by nanofluidic size exclusion
  S.M. Stavis, J. Geist, M. Gaitan,
  Lab Chip 2010, 16.
  DOI: 10.1039/C0LC00029A