Microfluidic flow direction control using continuous-wave laser

This paper describes a selective control of the flow direction in microfluidic chips using a laser induced thermal bubble. The bubble is generated inside the microchannel by focusing a continuous-wave laser onto the tear-drop shaped metal pad underneath the microchannel. Experiments demonstrate that the unidirectionally growing bubble acts as an in-channel directional micro-pump and can drive the flow to a freely chosen direction at a T-junction by pumping at different locations. In addition, the pumping flow rate could be adjusted in the real time and this technology is applicable to many types of common liquids. These advantages make it useful for flexible microfluidic manipulation in lab-on-a-chip systems and microchannel networks.