Nano-Conveyor Belt on 2D Microsphere Arrays Levitated by Optical Quasi-Standing Wave

In this letter, we have proposed a two-dimension (2D) non-contact optically levitated nano-conveyor belt based on the photonic nanojet (PNJ) effect of microspheres array which is embedded in the cover layer of optofluidic channel. Au-layer plate at the shadow side of microsphers is also introduced and its specular reflection will form the quasi-standing wave of PNJ, which can largely enhance the trapping stiffness for nano-objects in the transport and other two directions. Furthermore, since its spherical symmetry, a periodical tuning of the incident deflection angle may transport the trapped targets from one to another. The validations of the ability in particle manipulation have been conducted numerically. Results show that the transporting efficiency of 200-nm particles can reach up to ~96.9% when excited at the wavelength of 1064 nm and power density of 0.2 mW/ $\mu \text{m}^{2}$ . In addition, the samples can also be successfully sorted after several periods. We believe that the mechanism reported here provides a promising method for 2D arbitrary transport and manipulation of nanoparticles in optical sensing and biomedical applications.