Driving Micro‐Objects Using Optical Force due to Fluorescence Emission From Molecules

Abstract 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 small objects anisotropically emitting fluorescence from molecules in the objects only by photo‐irradiation without any spatio‐temporal control of light field. To demonstrate the movement by the emission force, we fabricated dye‐doped cylinder‐shaped polymer micro‐objects (PMOs) with gold thin films on their top surfaces. The single PMOs in water on a glass substrate, the side surfaces of which were facing to the substrate, were photoexcited with a continuous wave visible (532 nm) laser. The dyes in a PMO emitted strong fluorescence toward the non‐coated end (bottom) of the micro‐cylinder due to the reflection by the gold thin film on the top. The individual motions of the PMOs under photoexcitation are detected with fluorescence microscopy. Analysis of the trajectories of the PMOs confirmed that the anisotropic fluorescence emission led to the transportation of the PMOs in the opposite direction of the fluorescence. The emission force acting on the PMO is quantitatively evaluated through computational simulation considering the emission force and Brownian motion.