We demonstrate three-dimensional optical trapping and orientation of individual Au nanorods in solution, taking advantage of the longitudinal surface-plasmon resonance to enhance optical forces. Stable trapping is achieved using laser light that is detuned slightly to the long-wavelength side of the resonance; by contrast, light detuned to the short-wavelength side repels rods from the laser focus. Under stable-trapping conditions, the trapping time depends exponentially on laser power, in agreement with a Kramers escape process. Trapped rods have their long axes aligned with the trapping-laser polarization, as evidenced by a suppression of rotational diffusion about the short axis. The ability to trap and orient individual metal nanoparticles may find important application in assembly of functional structures, sorting of nanoparticles according to their shape, and development of novel microscopy techniques.

Date Published: 30 August 2006
PDF: 9 pages
Proc. SPIE 6323, Plasmonics: Metallic Nanostructures and their Optical Properties IV, 63230E (30 August 2006); doi: 10.1117/12.680146

Published in SPIE Proceedings Vol. 6323:
Plasmonics: Metallic Nanostructures and their Optical Properties IV
Mark I. Stockman, Editor(s)