The deposition of electrodes as the final step in the microfabrication of a fluidic system avoids incompatibilities with the microfabrication, i.e., high-temperature steps, or the process environment, i.e., CMOS fabrication. The employed strategy to deposit and structure silver (Ag) electrodes in microfluidic capillaries (cross-sectional length less than 10 ¿m) is presented. First, the adhesion of the Ag layer to the silicon dioxide (SiO2) surface of the capillary was improved with an intermediate mercapto silane layer. Second, the Ag electrodes were electrolessly deposited with a modified Tollens reagent. The high conductivity of the deposited Ag layer indicated high density and purity. Third, the electrodes were structured by controlling the capillary filling of the electroless solution within the fluidic system using microfluidic stop valves. Experiments in a microfluidic system with a capillary dimension of 3 ¿m showed successful deposition and microfluidic structuring of the Ag electrode, as well as postdeposition, void-free filling by changing the solution¿s surface tension.@en

A low voltage electroosmotic (eo) pump suitable for high density integration into microfabricated fluidic systems has been developed. The high density integration of the eo pump required a small footprint as well as a specific on-chip design to ventilate the electrolyzed gases emerging at the platinum (Pt) electrodes. For this purpose, a novel liquid¿gas (lg) separator was invented. This lg-separator separated the gas bubbles from the liquid and guided them away from the eo pump. Its operational principle was solely based on the geometry of tapered sidewalls. An eo pump sandwiched by two lg separators (microchannels in the range of 10 lm, footprint of 100 lm 9 15 lm) was experimentally investigated. The lg-separator was able to reliably separate and ventilate an emerging gas flow of 2 pl s-1. The eo pump achieved flow rates of 50 pl s-1 at actuation voltages of 5 V.@en