A closed-loop controlled electrochemically actuated micro-dosing system

In this paper a closed-loop controlled micromachined dosing system is prese nted, for the accurate manipulation of liquids in microsystems down to the nanoliter range. The applied driving force to dispense liquids originates f rom the electrochemical generation of gas bubbles by the electrolysis of wa ter. The proposed dosing system comprises a micromachined channel/reservoir structure in silicon, capped with a Pyrex(R) cover on which a set of plati num electrodes is patterned. By adopting an interdigitated electrode geomet ry, the electrodes can be used for electrochemical gas generation as well a s for the simultaneous determination of the total gas bubble volume, via an impedance measurement of the gas/liquid mixture in the reservoir. As this measured gas bubble volume equals the dosed liquid volume, active control o f dosed volumes can be obtained. It will be shown that the cell impedance c an be applied to accurately determine the generated gas volume and that by using this parameter in a closed-loop control system, dosed volumes can be controlled in the nanoliter range.