Biased AC electro-osmosis for on-chip bioparticle processing

Real-time detection of bioparticles is of great importance in deterring infectious diseases and bioterrorism. For bioparticle solutions with concentrations at an infectious level, culturing is typically used to increase the particle concentration to a detectable level, which is time consuming and often unfeasible under field conditions. Therefore, a real-time particle concentration technique is in demand to bridge the gap between the detectable level and infectious level of bacterial solutions. This paper describes a novel electrokinetic method that can potentially concentrate particles in real time. By studying surface flows on planar electrode pairs, two distinct ac electro-osmosis (ACEO) flows have been identified which are due, respectively, to capacitive and Faradaic charging of electrode double layers. Biased ACEO, combining dc bias with ac signals, breaks the symmetry of electrode charging, leading to asymmetric surface flows and a variety of directed surface flows that can concentrate, manipulate, and transport particles. Surface flows of opposite directions on planar electrodes produce stagnation lines that function as long-range particle traps and lead to net flows for micropumping. The device fabrication and operation are simple and compatible with integrated circuit technology.