Detection electrodes are used to measure the local electrical conductivity or impedance of the liquid in a fluidic channel. These electrodes are used for example for detection on capillary electrophoresis chips, but can also be used to count and characterize particles or biological cells.

The electrolyte conductivity in the channel can be measured using a planar integrated interdigitated electrode structure. The number of electrode fingers can be tuned in order to obtain for example a cell constant of approximately 1 cm^-1, which is comparable to conventional conductivity cells. By increasing or decreasing the number or size of the electrode fingers other cell constants can be reached.

For special applications such as end column conductivity detection on capillary electrophoresis chips or chromatography chips the size of the electrode area is usually very small in order not to affect the separation resolution adversely. With space for only a couple of finger electrodes this will result in a larger cell constant.


Position
Depending on the application the electrodes are placed in direct contact with the liquid or they are electrically insulated from the liquid. In the latter case the signal is coupled capacitively through the insulating layer to probe the liquid. These capacitively coupled electrodes can be placed directly below or above the fluidic channel using an silicon oxide layer for insulation, but more commonly the electrodes are positioned in the same plane slightly aside of the channels.

Detection electrodes can be integrated into almost any glass chip, standard or customized. Integration of electrodes in silicon chips is done on request.