Metal-insulator-metal waveguides for particle trapping and separation.

Optical particle trapping and separation are essential techniques in the fields of biology and chemistry. In many applications, it is important to identify passive separation techniques that only rely on intrinsic forces in a system with a fixed device geometry. We present a dual-waveguide sorter that utilizes the loss of metal-insulator-metal (MIM) waveguides for completely passive particle trapping and separation and is created using a unique angle sidewall deposition process. Our experiments show that an inner Au–Si3N4–Au waveguide is able to trap particles within the propagation distance of its dominant modes and release the particles into an outer Au–H2O–Au waveguide. The outer waveguide then propels the particles and separates them by size. The separation results are accurately modeled by a first-principles, analytical model.