A Closed-Loop Calibration System for a Microdialysis-Based Lab-On-A-Chip

In this contribution a closed loop calibration facility for a microdialysis based lab-on-a-chip is presented. Each facility consists of a channel structure etched in silicon, closed by a Pyrex® cover comprising two small platinum electrodes. In the silicon structure the calibration liquid is stored in the meander shaped channel that starts in an electrolyte filled reservoir. By applying an electric current via both electrodes through the electrolyte in the reservoir, gas bubbles are generated by electrolysis, forcing the calibration liquid into the main carrier channel leading to the sensor area of the lab-on-a-chip. Above the electrolyte reservoir two additional interdigitated electrodes are present that are used to measure the gas bubble volume by measuring the impedance of the gas/liquid mixture in the reservoir. Since the volume of the gas bubbles is equal to the dispensed calibration liquid, its total volume can be controlled by a closed loop impedance measuring system. In this way precise plugs of 60nl calibration liquid have been dispensed into the main carrier channel.