Comment on AC frequency characteristics of coplanar impedance sensors as design parameters by Jongin Hong, Dae Sung Yoon, Sung Kwan Kim, Tae Song Kim, Sanghyo Kim, Eugene Y. Pak and Kwangsoo No, Lab Chip, 2005, 5, 270

In their article, ‘‘AC frequency characteristics of coplanar impedance sensors as design parameters’’, Hong et al.1 present an analytical model for the calculation of the resistance between two electrodes in a microchannel. However, their measurements fit poorly with their suggested model, and they attribute the discrepancies to electrode thickness and a ‘fringing effect’. In this note we show that the discrepancies are due to the neglected channel height in their model, and that by including two additional transforma ions, the resistance between two