In this paper, small plasmonic nanobumps, which consist of metal/dielectric layers are placed on the ring of optical vortex to enhance electric field ampltiude. In this paper, a plasmonic nanobump is placed on the ring of smaller optical vortex. The smaller optical vortex form from the resultant topological phase between the handedness of the incident circular polarized light and the nanoslits spiral. Different designs of plasmonic nanobump are investigated, and tapered nanobump produced higher field enhancement due to higher surface charge density at the tapering end. Higher field intensity at the tip of the plasmonic nanobump produces lower potential, which attract nanoparticle to the region. The optical force increases by the square of the electric field amplitude. This high electric field intensity at the plasmonic nanobump functions as attractive node, which trap molecules inside the optical vortex. Additional plasmonic nanobumps are added onto the other locations of the optical vortex to manipulate the particle trapping positions. This allows the precise control of molecule's position and movement for imaging, characterization and analysis, which is useful for mobile lab-on-chip devices. [ABSTRACT FROM PUBLISHER]
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