On-chip detection of beads with a new electrical impedance sensor

Electrical impedance measurements in microfluidic chips are used for single cell analysis. Parallel electrodes are more suited than planar ones since the electrical field distribution is more homogenous. Previous studies showed methods to make parallel electrodes by incorporating an additional layer between two glass wafers, making electrical connections to both sides needed. Also alignment of electrodes is necessary, making the fabrication of parallel electrodes more elaborate. Therefore a new, simpler fabrication method is developed for the fabrication of parallel electrode chips by incorporating a floating electrode in the microchannel just by adding one step in the fabrication process. In this way, only one side of the chip contains electrical connections. Finally, electrical impedance measurements with 3 and 6 μm polystyrene beads were done. All beads were detected and we have shown that it is possible to distinguish the two beads sizes from each other with a confidence level of 95%, based on the relative change in the electrical impedance.