Optofluidic flow-ratio sensor system for microchannels

We present an optofluidic sensor system to monitor the ratio of dual-liquid flows in a microchannel, for liquids with different refraction indices. With an image sensor, the interference minima and maxima are registered from the combination of a flow-channel containing a single liquid (reference) and a channel with dual-liquid flows. The device works both for non-mixing and mixing liquids because of the averaging of the refractive indices of the liquids. For liquids with a refraction index difference of 0.09 or more, the flow-rate ratio can be determined with a resolution of better than 1%. This is valid for a flow-rate range covering more than 2 decades; from 20 nL/s to 4000 nL/s. Because of the out-of-plane concept, the device can be used as a non-invasive and robust table-top system. Flow-rate stability tests were performed showing the differences between the application of glass and plastic syringes to pump the liquids.