Trapping plasmonic nanoparticles with MHz electric fields

Abstract

Dielectrophoresis drives the motion of nanoparticles through the interaction of their induced dipoles with a non-uniform electric field. We experimentally observe rf dielectrophoresis on 100 nm diameter gold nanoparticles in a solution and show that for MHz frequencies, the nanoparticles can reversibly aggregate at electrode gaps. A frequency resonance is observed at which reversible trapping of gold nanoparticle “clouds” occurs in the gap center, producing almost a 1000-fold increase in density. Through accounting for gold cores surrounded by a conducting double layer ion shell, a simple model accounts for this reversibility. This suggests that substantial control over nanoparticle separation is possible, enabling the formation of equilibrium nanoarchitectures in specific locations.

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“…But what surprised us was the increase in speed by increasing the atomic weight in each group. Harlaftis et al demonstrated that for spherical nanoparticles, the dielectrophoretic forces depend linearly on the particle volume, when external electric field, field density gradient, and frequency are constant 38 . So, according to this theory, in samples with identical ion charges, the increase in the speed according to the particle radius is logical.…”