Thin layer copper ISE for fluidic microsystem

A miniaturized ion selective electrode (ISE) for Cu2+ ions was developed, specially for application in a microfluidic system. The electrode preparation is based on a silicon wafer substrate which is coated with a Cu deposit in the range of 50 - 200 nm. The Cu layer is quantitatively converted into CuS by treatment in a sulphidic ambient. The chip electrode has a size of 5x5 mm2 and was mounted on a spacer chip coupled to the fluidic microcell using a chip clip technology. The coupling is liquid tight and reversible, admitting an easy exchange of the chip electrodes. The effective electrode area in contact with the liquid of the microsystems flow channel amounts to about 4 mm2.
Sensitivity measurements were performed stationary and in the flow through cell. Good Nernstian response of 29 mV/pCu between pCu 5 and 1 has been found and is in agreement with reference measurements carried out with a commercial ISE.
The rapid response observed also in the most diluted solutions used, is related to the thin, non porous structure of the CuS layer, minimizing diffusion effects during changing the test solutions. The adhesion of the sensitive CuS layer is different for the substrates Si, SiO2 and Si3N4 and depends on their history, roughness and evaporation conditions.