We investigate experimentally and theoretically plasmon-enhanced optical trapping of metal nanoparticles. We calculate the optical forces on gold, silver and aluminium nanospheres through a procedure based on the Maxwell stress tensor in the transition T-matrix formalism. We compare our calculations with experimental results finding excellent agreement. We identify regimes where force constants obey general scaling laws with particle size and laser detuning from the plasmon resonance frequency of spherical metal nanoparticles. We also demonstrate how light-driven rotations can be generated and detected in non-symmetric nanorods aggregates. Analyzing the motion correlations of the trapped nanostructures, we measure with high accuracy both the optical trapping parameters, and the rotation frequency induced by the radiation pressure.

© 2011 Optical Society of America

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