A Novel Method for the Direct Measurement of Electroosmotic Flow Velocity on Microfluidic Chips

As microfluidic technologies mature accurate methods for the measurement of electroosmotic flow velocity on microfluidic chips are becoming increasingly important. A change of migration time of Rhodamine 123 Rh123 at different pH values of the buffer was observed during the electrophoresis and it was deduced that there is uncharged molecular form of Rh123 in alkaline solution because of deprotonation. Therefore a method of direct measurement of electroosmotic flow velocity on microfluidic chip was developed based on the detection of migration time of the uncharged Rh123 because the migration speed of uncharged molecule is equal to the electroosmotic flow velocity. The electroosmotic flow velocity of glass microchip at pH 9.3 and 10. 1 of the buffer was detected to be 3.9 x 10(-4) cm(2)/s V and 4. 1 X 10(-4) cm(2)/s V respectively which were in agreement with those obtained by the traditional method.