Long-range AC electroosmotic trapping and detection of bioparticles

Microfluidic devices with integrated electrical detection will enable fast, low-cost or portable sensing and processing of biological and chemical samples. By employing microfabrication, microelectrical impedance spectroscopy detectors are designed to take advantage of AC electroosmosis to rapidly concentrate bioparticles, leading to enhanced sensitivity due to a reduction of the transport time to the detector. Electrodes were fabricated by integrated circuit technology. Experiments were performed to find the optimal voltage and frequency ranges such that a trapping converging flow exists on the electrodes and the assembled cells exhibit sensitive impedance spectrum signatures. Preliminary results show resolution at a concentration of 104 bacteria/mL, indicating that combining AC electroosmosis with impedance measurement can improve the sensitivity and speed of detection of bacteria in solutions with conductivity comparable to that in environmental applications. The bacterial impedance signatures are, however, different in tap water and PBS buffers, due perhaps to different ion transport properties across the cell membranes in the two solutions.