Nanotweezers Increase Velocity of Particle Transport

Nanotweezers that exploit plasmonics, heat and an electrical field flow overcome previous limitations caused by weak convection properties.

The nanotweezer system uses a nanoantenna to concentrate and absorb light, creating plasmonic hotspots, which make it possible to manipulate nanoscale objects suspended in a fluid. Previous research had shown that convection using a single plasmonic nanoantenna was too weak to result in net transport of suspended particles.

Researchers at Purdue University have increased the velocity of particle transport to more than 10 μ/s — two orders of magnitude greater than previously predicted — by applying a low-frequency (<10 MHz) AC electric field in conjunction with laser heating of a cylindrical gold nanoantenna with a diameter of 320 nm. The local electromagnetic field intensity was enhanced more than 200 times at the plasmonic hotspot.

A rendering of hybrid nanotweezer, which could enable quantum computers and ultrahigh-resolution displays. Courtesy of Mikhail Shalaginov and Pamela Burroff-Murr/Purdue University.

The result is a hybrid nanotweezer that combines a near-infrared laser light and an electric field, inducing an electrothermoplasmonic flow, said doctoral student Justus C. Ndukaife.

"Then, once we turn off the electric field, the laser holds the particles in place, so it can operate in two modes," Ndukaife said. "First, the fast transport using alternating current, and then you turn off the electric field, and it goes into the plasmonic tweezing mode."

The technique was demonstrated with polystyrene particles.

Nanotweezers have potential applications in nanoscale sensing, as well as in quantum computers and ultrahigh-resolution displays. They could be used to create devices containing nanodiamond particles or other nanoscale light-emitting structures to enhance the production of single photons — the workhorses of quantum information processing — in turn enabling superior computers, cryptography and communications technologies.

The research is ongoing and was published in Nature Nanotechnology (doi: 10.1038/nnano.2015.248). Funding was provided by the National Science Foundation.