Using Electroosmotic Pumps to Control the Flow Velocity in Cotton Thread-Based µTADs

Flow velocity control is of great interest for passive microfluidic devices that are used in point-of-care diagnostics. Various methods have been developed for the flow velocity control of microfluidic paper-based analytical devices (µPADs), whereas fewer attempts have been made for microfluidic thread-based analytical devices (µTADs). In this research, we attempt to control the flow velocity in cotton thread-based µTADs with electroosmotic pumping. Utilizing electroosmotic pumps, the flow velocity in the cotton thread-based µTADs can be decreased or increased by 13% and 106%, respectively. Moreover, the dynamic control of the flow velocity in the cotton thread-based µTADs is achieved by adjusting the real-time magnitude and direction of the voltage. Furthermore, we demonstrate that electroosmotic pumps can be used to overcome the hydrophobic valves in the cotton thread-based µTADs. We show that the delivery sequence of different liquid samples for a three-branch µTAD can be controlled. Finally, we show the potential application in lithium detection with a colorimetric assay. This method for flow velocity control shows promise for customizing the flow velocity and reaction time of cotton thread-based µTADs, and this method can potentially increase the sensitivity of detection.