Flow Rate Measurement in Microfluidics Using Optical Sensors

A system using low-cost and off-the-shelf electronic components for measuring very low flow rates of liquids is reported. The system records the time duration a liquid column needs to travel, in a transparent capillary, between two optical sensors. The average flow rate is then calculated from the time duration, the distance of the two sensors, and the diameter of the capillary. Our first prototype was capable of measuring flow rates as low as 280 nl/s with an average error of 1.37 %. However, with small modifications, the system could achieve a volumetric resolution <0.1 nl. The system could be an ideal tool to characterize microfluidic devices or calibrate liquid micro flow sensors.