Glass-based microfluidic device fabricated by parylene wafer-to-wafer bonding for impedance spectroscopy

The paper reports the realization of a glass-based microfluidic device for characterization of cells in suspensions using impedance spectroscopy. The device consists of two glass wafers: a bottom wafer comprising a microfluidic channel with two electrodes added for impedance measurement, and a top glass wafer in which inlets and outlets are realized. The main focus of this work is the original fabrication process of this device, which combines three key techniques: firstly, successfully applying a through-wafer wet etching method in order to pattern the inlets and outlets in the top glass wafer; secondly, patterning the electrodes not only on flat surfaces but also in the microfluidic channel etched in the bottom wafer; and thirdly, employing indirect wafer to wafer bonding using an intermediate polymer layer. No external pumping is required as capillarity enables direct suction of a sample droplet in the channel. The device can be reusable if a thorough cleaning procedure is carried out. Devices with three different electrode geometries were successfully tested in electrochemical impedance spectroscopy (EIS) measurements using DI water and HepG2 cells. Although clear differences between DI water and live HepG2 cells have been observed in all cases, different results were obtained for various electrode geometries, highlighting the critical importance of the device design in performing EIS measurements and especially when making comparisons with other reported results. (c) 2006 Elsevier B.V. All rights reserved.