Boundary element method for optical force calibration in microfluidic dual-beam optical trap

Abstract

The potential use of optical forces in microfluidic environment enables highly selective bio-particle manipulation. Manipulation could be accomplished via trapping or pushing a particle due to optical field. Empirical determination of optical force is often needed to ensure e cient operation of manipulation. The external force applied to a trapped particle in a microfluidic channel is a combination of optical and drag forces. The optical force can be found by measuring the particle velocity for a certain laser power level and a multiplicative correction factor is applied for the proximity of the particle to the channel surface. This method is not accurate especially for small microfluidic geometries where the particle size is in Mie regime and is comparable to channel cross section. In this work, we propose to use Boundary Element Method (BEM) to simulate fluid flow within the micro-channel with the presence of the particle to predict drag force. Pushing experiments were performed in a dual-beam optical trap and particle's position information was extracted. The drag force acting on the particle was then obtained using BEM and other analytical expressions, and was compared to the calculated optical force. BEM was able to predict the behavior of the optical force due to the inclusion of all the channel walls.

Assessment of Lagrangian Modeling of Particle Motion in a Spiral Microchannel for Inertial Microfluidics

“…Strictly speaking, the prediction of a particle trajectory requires the solution of the flow field with the presence of the particle(s). For low applications, owing to the linear nature of the governing equations (i.e., Stokes equation), the boundary element method can be implemented for a rigorous simulation of particle motion inside microchannels [ 28 ] even with the presence of an external field [ 29 , 30 , 31 ]. However, inertial effects, which are the driving mechanism for inertial microfluidics, require the solution of non-linear Navier–Stokes equations.…”