Two-dimensional optical trapping and clustering of magnetic nanoparticles

Abstract

The dynamics of Fe3O4 magnetic nanoparticles under the irradiation of a tightly focused laser beam was investigated by using a dark-field microscope. It was found that the magnetic nanoparticles were pushed away from the laser spot by the optical scattering force and the absorption force when the laser focus was located between the two cover slips of the sample cell. A depletion region of magnetic nanoparticles was formed in the laser spot. However, when the focus of the laser was located at the bottom of the upper cover slip of the sample cell, the magnetic nanoparticles could be trapped by the optical forces combined with the opposite force of the upper cover slip and formed magnetic clusters. In addition, the evolution of the incandescent light transmission spectrum of the magnetic fluid under the irradiation of the 532 nm laser with different powers was studied. It was observed that the intensity of the transmission spectrum of the incandescent light decreased and the peak wavelength of the transmission spectrum shifted towards the longer wavelength with the increase of the laser power.