Refractive-index-based optofluidic particle manipulation

Abstract

This letter describes optofluidic particle manipulation based on the refractive index contrast between the particle and the surrounding medium. A laser beam propagated along one sidewall of a microfluidic channel will introduce a force that pushes a high-refractive-index particle toward the Gaussian-shaped laser beam center axis. By contrast, a low-refractive-index particle will be pushed away from the beam center axis and toward the other sidewall of the channel because the direction of the gradient forces acting on such a particle is opposite the direction of the forces acting on a high-refractive-index particle. The gradient forces acting on a particle were calculated to predict and interpret the particle behavior. High-refractive-index and low-refractive-index particles, prepared from polystyrene latex (PSL) and hollow glass particles with refractive indices of 1.59 and 1.22, respectively, were employed. The PSL and hollow glass particles could be separated based on their refractive indices. Doubly attached identical particles behaved as a single particle. (C) 2013 AIP Publishing LLC.