A separator-analyzer flowmeter for complex liquids in microfluidic systems

The measurement and control of the flowrate of fluids containing charged macromolecular species and particles is required for a number of applications, such as controlled-drug-delivery and microscale bioreactors. The flowrates that need to be measured for such systems can be as small as microliters per day. We are developing a novel flowmeter, called the separator-analyzer flowmeter (SAF meter), to measure the flow rate of suspensions of charged macromolecules or particles. The SAF meter consists of a channel that splits into two parts and then recombines. A pair of electrodes is positioned before the channel bifurcation. When a DC potential is applied across this pair of electrodes, the charged species are dragged toward one electrode, and the solutions flowing into the two arms downstream differ in the concentration (separator). This difference is inversely proportional to the flowrate of the original mixture. The concentration difference can be measured optically or electrochemically (analyzer). Based on the input to the separator (strength of the applied electric field), and the output from the analyzer (concentrations in the two arms), we can obtain the flowrate of the solution. A milliscale prototype has been fabricated and has been used to measure flowrates from 25-75 μl/min.