Module for real time non-invasive control of the electroosmotic flow in microfluidic systems

A module is introduced that allows setting and maintaining the flow rate in microfluidic systems (analytical chips) using electroosmotic flow (EOF) for mobile phase propulsion. The sensing principle is compatible with any type of microanalytical device, where the mobile phase is drawn from a reservoir. It allows continuous monitoring of the EOF and does not require any manipulation or compositional changes (additives/heating) of the mobile phase. Instead the sensor optically records the speed of displacement of the liquid level in the chip reservoirs as the liquid flows out. Readings are taken with a frequency of 1000 Hz allowing flow rate measurements in less than 0.4 s. Based on these measurements, the flow rate can be maintained to a preset value ('flow control') using a simple control circuit/algorithm that compares the actual with the desired flow rate and adjusts the former if necessary via the applied field strength. The potential of the module to stabilize the flow after disturbances is demonstrated.