In recent years, particle transport at microscopic level has become an important research topic which has led to the understanding of directed particle transport subjected to thermal fluctuations. Brownian motors (also called ratchet mechanism) are one of the most interesting phenomena of work generation in nonequilibrium systems under random external forces. In this work, we report Brownian movement rectification of 0.5 μm diameter latex particles using pulsating ratchets. In order to implement the ratchets, an asymmetric 2D potential saw tooth phase pattern is displayed on a spatial phase modulator and then transformed into an intensity pattern by using the phase contrast method. This pattern is focused down with a 100x microscope objective obtaining a pattern of ~40x40 μm² at the focal plane. The patterns parameters can be dynamically controlled: periodicity, asymmetry, and on/off rate, which allows optimization of directed transport. We found that there is an optimum value for the on/off rate and particle diameter/spatial period obtaining an average speed of 0.6 μm/s. The 2D pattern allow us to manipulate a large number of particles, in contrast to previous studies were only one particle has been studied, opening the opportunity to massive sorting of particles.

Date Published: 9 September 2011
PDF: 8 pages
Proc. SPIE 8097, Optical Trapping and Optical Micromanipulation VIII, 80971W (9 September 2011); doi: 10.1117/12.894450

Published in SPIE Proceedings Vol. 8097:
Optical Trapping and Optical Micromanipulation VIII
Kishan Dholakia; Gabriel C. Spalding, Editor(s)