Optofluidic flow meter for sub–nanoliter per minute flow measurements

Performance improvements in microfluidic systems depend on accurate measurement and control of fluids on the micro- and nanoscale, and new applications are continuously moving the needle to lower volumetric flow rates. This work focuses on improving an optofluidic system for the measurement and calibration of microflows to the sub-nanoliter per minute range. The experimental measurements rely on an optofluidic system that delivers excitation light and records fluorescence in a precise interrogation region of a microfluidic channel. Using a scaling relationship between flow rate and the fluorescence emission after photobleaching, the system enables real-time determination of flow rates. Here we demonstrate improved calibration of a flow controller to 1 % uncertainty and improved resolution of the optofluidic flow meter to less than 1 nL/min using molecules with lower diffusion coefficients.