title: Near-Field, On-Chip Optical Brownian Ratchets.
abstract: Nanoparticles in aqueous solution are subject to collisions with solvent molecules, resulting in random, Brownian motion. By breaking the spatiotemporal symmetry of the system, the motion can be rectified. In nature, Brownian ratchets leverage thermal fluctuations to provide directional motion of proteins and enzymes. In man-made systems, Brownian ratchets have been used for nanoparticle sorting and manipulation. Implementations based on optical traps provide a high degree of tunability along with precise spatiotemporal control. Here, we demonstrate an optical Brownian ratchet based on the near-field traps of an asymmetrically patterned photonic crystal. The system yields over 25 times greater trap stiffness than conventional optical tweezers. Our technique opens up new possibilities for particle manipulation in a microfluidic, lab-on-chip environment.
authors.affiliation: Ming Hsieh Department of Electrical Engineering, Viterbi School of Engineering, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Shao-Hua
authors.initials: SH
authors.lastname: Wu
authors.affiliation: Ming Hsieh Department of Electrical Engineering, Viterbi School of Engineering, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Ningfeng
authors.initials: N
authors.lastname: Huang
authors.affiliation: Ming Hsieh Department of Electrical Engineering, Viterbi School of Engineering, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Eric
authors.initials: E
authors.lastname: Jaquay
authors.affiliation: Ming Hsieh Department of Electrical Engineering, Viterbi School of Engineering, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Povinelli
keywords: Brownian ratchets; Optical trapping; nanomanipulation; photonic crystal