Micro Programmable Object Navigation Gadget (micro-PONG) for Studying Electroosmotic Flow in PDMS Microchannel

Abstract

Precise control of fluid delivery in analytical devices may be achieved by harnessing electroosmotic flow (EOF) in oxidized poly(dimethylsiloxane) microfluidic channels fabricated via soft lithography. However, the magnitude of this flow depends on a number of parameters, including the geometry and surface chemistry of the channel walls, and is known to attenuate over time. In order to characterize these parameters and calibrate the magnitude of EOF in our devices, we have developed a versatile automated control and measurement system called micro-PONG (Micro Programmable Object Navigation Gadget). The system detects, controls, and measures the movement of polystyrene beads caused by EOF in the channel. The micro-PONG system consists of a LabView program, a DAQ board, an external voltage switching circuit, and a camera. A computer algorithm reverses the direction of the EOF each time the bead enters one of two user-specified "goalpost" areas, thus keeping the bead trapped and moving back and forth between the goalposts (similar to a game of ping pong) for extended periods of time. From the recorded motion of the bead, the three-dimensional velocity profile of the fluid in the channel may be estimated using a novel ImageJ macro for determining motion in three dimensions. This analysis may then be used to determine the magnitude of the EOF, inertia, and response time of the system as well as the time-dependent effects of PDMS surface properties on EOF. The micro-PONG system may also be useful for other purposes that require the automated manipulation of particles or cells.