Assembly and manipulation of Fe₃O₄/coumarin bifunctionalized submicrometer janus particles

Magnetic and fluorescent bifunctionalized Janus particles were fabricated via sequential particle embedding and surface modifications. The two hemispherical surfaces of a 500 nm silica particle were separately functionalized with Fe₃O₄ nanoparticles and coumarin dye molecules. The Fe₃O₄ hemisphere exhibited magnetically driven particle orientation and alignment, whereas the coumarin hemisphere served as an anisotropic emission indicator. The photoluminescence of these orientated and solidified Janus particles revealed anisotropic emission contrast as high as 40% between the magnet-aspect and the dye-aspect excitations. The dynamic anisotropic emission of the bifunctionalized Janus suspension under magnetic manipulation also revealed a nonsynchronized bulk correlation time that was much slower than that of an individual 500 nm particle. Under a static magnetic field, the suspended Janus particles assembled into a grape-like bunch, with random particle orientation. Unlike their microscale counterparts, the submicrometer magnetic Janus particles were less sensitive to gravity and more vulnerable to particle-particle interactions.