Dynamic Nanoparticle Trapping By Cascaded Nanophotonic Traps in a Silicon Slot Waveguide

Nanophotonic traps integrated in a microfluidic channel are promising for next-generation multifunctional and flexible lab-on-chip systems, especially for researches in nanobiophotonics. Here we propose a slot waveguide with a nano-slit to produce a high gradient of optical field in a tiny space, which exhibits strong optical force to trap nanoparticles. Moreover, the slits can be cascaded along the direction of light propagation to form a large array of optical traps, with negligible reflection and loss, which is expected to be useful in study of biological nanoparticles. The trapping dynamics of nanoparticles to the proposed nanophotonic traps is analyzed, which reveals physically cascaded trapping processes enabled by the slot and the slit, respectively. The motion trajectories of the particles of 50 nm in diameter are obtained with the Brownian motion taken into account, which shows successful trapping of the nanoparticles.