Driving Micro-Objects Using Optical Force due to Photoemission

Emission of fluorescence in a specific direction generates an optical force in the opposite direction of the emission by the momentum conservation raw. This "emission force" can induce the directional transportation of a tiny object anisotropically emitting fluorescence from dye molecules incorporated in the object, leading to the realization of the controlled actuation of a tiny object only by the light irradiation. To demonstrate the movement by using the emission force, we prepared dye-doped cylinder-shaped polymer micro-object one top of which was covered with gold thin film. Under visible (532 nm) light illumination on a glass surface in water, the dyes emitted strong fluorescence towards the other non-coated end of the micro-cylinder due to the reflection by the gold thin film. Analysis of the trajectory of tiny objects confirmed that this anisotropic fluorescence emission led to the transportation of the micro-objects in the opposite direction of the fluorescence. The emission force acting on the polymeric micro-objects was quantitatively evaluated through computational simulation taking into account the emission force and Brownian motion.