Optical trapping of gold nanoparticles using a radially polarized laser beam

In this work we present new results regarding the optical trapping of single gold nanoparticles with a radially polarized laser beam. Since a radially polarized laser beam possesses a strong longitudinal component of the electric field in the center of the focal area, it opens up new advantages for optical manipulation. We describe a procedure of coating the experimental chamber with a charged polymer and the gold nanoparticles with ligands carrying the same charge as the polymer, thus generating electrostatic repulsion which prevents the nanoparticles from depositing on the bottom surface of the experimental chamber. Our experimental results show that a radially polarized laser beam focused with a high numerical aperture objective lens forms a stable trap of a single gold nanoparticle in aqueous solution. By comparing the duration of the interaction of particles with the trapping laser, we found that the average duration of the interactions with a radial beam is two times longer than with a Gaussian beam. Thus, we demonstrate that a radially polarized laser beam exerts stronger forces on the nanoparticles than the Gaussian beam. These findings provide a new insight into the complex interaction of a nanoparticle with the electromagnetic field of optical tweezers.

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