Ionic Mixer on a Microfluidic Chip Using Polyelectrolytic Salt Bridges

This paper reports an active mixing method using polyelectrolytic salt bridge-based electrode (PSBE). The PSBE is a key embedded unit in a microchip device that can mix a fluid stream using an ionic current perpendicular to the main stream. The PSBEs were fabricated by employing a photopolymerization technique with an aqueous monomer solution containing diallyldimethyl ammonium chloride (DADMAC). A pair of PSBEs was easily formed at the two lateral branches perpendicular to the main microchannel and was connected to an external AC signal source via their respective 1 M KCl solutions and Ag/AgCl electrodes. The external AC signal source generated an electric current. The electric current was converted to a chloride ionic current at the interface between 1 M KCl solution and Ag/AgCl electrode. The chloride ionic current in aqueous solution dragged water molecules in the microchannel and was found to be very useful for mixing the main stream. The performance of the PSBE mixer was verified with 50 μM rhodamine 6G solution and 10 mM PBS, pH 7.4.