Bidirectional Optical Sorting of Gold Nanoparticles

M. Ploschner*†, T. Čižmár‡, M. Mazilu†, A. Di Falco†, and K. Dholakia†

^† SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, United Kingdom

^‡ School of Medicine, Medical and Biological Science Building, University of St Andrews, St. Andrews KY16 9TF, United Kingdom

Nano Lett., 2012, 12 (4), pp 1923–1927

DOI: 10.1021/nl204378r

Publication Date (Web): March 26, 2012

Copyright © 2012 American Chemical Society

We present a generic technique allowing size-based all-optical sorting of gold nanoparticles. Optical forces acting on metallic nanoparticles are substantially enhanced when they are illuminated at a wavelength near the plasmon resonance, as determined by the particle’s geometry. Exploiting these resonances, we realize sorting in a system of two counter-propagating evanescent waves, each at different wavelengths that selectively guide nanoparticles of different sizes in opposite directions. We validate this concept by demonstrating bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture.