Optical manipulation of metal-silica hybrid nanoparticles

Metallic nanoparticles are known to experience enhanced optical trap strengths compared to dielectric particles due to the increased optical volume, or polarizability. In our experience, larger metallic particles (similar tomum) are not easily trapped because momentum effects due to reflection become significant. Hybrid particles comprised of both metal and dielectric materials can circumvent this limitation while still utilizing a larger polarizabitity. Heterogeneous nanosystems were fabricated by embedding/coating silica nanoparticles with gold or silver in varying amounts and distributions. These compound particles were manipulated via optical tweezers, and their trapping characteristics quantitatively and qualitatively compared to homogeneous particles of comparable size. The parameters explored include the dependence of the trapping force on the percentage of loading of gold, the size of the embedded colloids, and the distribution of metal within the surrounding matrix or on its surface.