Optical Trapping and Separation of Metal Nanoparticles by Cylindrical Metalenses With Phase Gradients

We proposed a method for driving metal nanoparticles in the focal field by cylindrical metalens with phase gradient. It was found that the introduced gradient phase would not affect the formation of the focal line, where metal nanoparticles can be trapped. While being driven along the direction with the phase gradient, Ag nanoparticles with different sizes, and nanoparticles with different materials (Au and Ag) were successfully separated, respectively. The induced driving force has an approximately linear relationship with the phase gradient. This kind of planar thin structure can be combined with a microfluidic chip to form a miniaturized system for label-free and non-contact sorting of particles or biological cells, and it may find potential applications in biomedicine.