Plasmonic random nanostructures on fiber tip for trapping live cells and colloidal particles.

We demonstrate optical trapping on a gold-coated single-mode fiber tip as excited by 980-nm laser radiation. The trapping force here is not due to common plasmonic localization, but dominated by the combined effect of thermophoresis and thermal convection. The reported scheme only requires simple thin-film deposition. More importantly, efficient broadband plasmonic absorption of the gold random nanostructures, aided by purely Gaussian excitation profile from the fiber core, has led to very low trapping-power threshold typically in hundreds of microwatts. This highly versatile fiber-based trapping scheme clearly offers many potential application possibilities in life sciences as well as engineering disciplines.