Precise Partition of Micro/Nanoparticles in an Electro-Optofluidic Platform

Integrated optofluidics, when controlled electro-optically, can facilitate the high-throughput on-chip manipulation and detection of biomolecules and micro/nanoparticles. Previously we demonstrated stable trapping and precise manipulation of trapped microspheres, with positions of trapped microspheres dictated by antinodes of a standing wave formed along a nanofabricated waveguide [1]. Using this nanophotonic platform, we now report a method of generating an optical binding effect on-chip. We show that an array of microspheres can be stably trapped and uniformly spaced with a travelling wave. The direction of the travelling wave is rapidly switched using the thermo-optic effect via an integrated electric microheater which modulates the phase of a wave in a waveguide in a Mach-Zehnder interferometer. Our theoretical work suggests that the periodic trapping potential is a result of multiple-interference of the wave due to its interactions with the microspheres. Such a demonstration of on-chip optical binding provides a novel mode of manipulation and spacing of trapped micro/nanoparticles on an optofluidic platform.[1] M. Soltani, J. Lin, R. A. Forties, J. T. Inman, S. N. Saraf, R. M. Fulbright, M. Lipson & M. D. Wang, Nanophotonic trapping for precise manipulation of biomolecular arrays. Nature Nanotechnology 9, 448-452 (2014).