Abstract
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.
Highlights
Sorting particles or biological cells plays an important role in colloidal physics, analytical chemistry, and biomedicine
We proposed a method for driving metal nanoparticles in the focal field by cylindrical metalens with phase gradient
The instantaneous velocity of the particle at each position was taken as the average velocity at 1 μm interval between two positions. It takes 23.307 s for a Ag nanoparticle with a radius of 50 nm to travel through the whole focal line, while it takes only 3.341 s for a Ag nanoparticle with a radius of 100 nm. These results demonstrate that metal nanoparticles of different sizes can be separated by the phase gradient metalens
Summary
Sorting particles or biological cells plays an important role in colloidal physics, analytical chemistry, and biomedicine. Based on lab-on-a-chip, several microfluidic methods including fluorescence-activated cell sorters [1], electrodynamics mobilization of fluid [2], dielectrophoretic forces [3], and hydrodynamic flow control [4] have been developed. Fluorescent labels, microfluidic buffers, and electrophoretic damage can either contaminate the sample or affect the result. There is a need to develop label-free and non-invasive methods for particle sorting. The focal field can selectively deflect running particles in solution. That is, when two groups of particles flow through the focal field, after the competition between optical force and fluid force, one group of particles deviates from the original direction of motion, while the other group of particles continues
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