Application of a three-dimensional (3D) particle tracking method to microfluidic particle focusing.

In this paper, a defocusing-based three-dimensional (3D) particle tracking method is presented and demonstrated for microfluidic particle focusing applications. Previous work in particle focusing has verified particle position in two dimensions (2D) using micro-streak velocimetry, or confocal and stereoscopic setups for 3D tracking. The results obtained from the methodology presented are compared with the theoretical and previously observed trends, and it is shown that the defocusing technique provides a simple and precise tool for determining the 3D locations of cell-sized particles in microscale flows (Re ≤ 100). Although similar methods exist for micro-particle image velocimetry (μ-PIV) applications, this is the first implementation of this technique for particle focusing applications.