Study On Droplet-based Micro-reactor With Saw As Energy

Microfluidic chip has been used in biochemical analysis, single molecule analysis, single cell analysis, food testing, and national security. It is often difficulty for complex microanalysis systems to be integrated into one substrate. At the meantime, different substrate materials will be choosen in one microanalysis system to take their advantages. Thus, the transportation of droplet between different substrates is inevitable. Compared with continuous flow microfluidic chip, the microfluidic chip working in digital flow (droplet) has more advantages due to its higher analysis accuracy, more simple operation, and smaller size. Micro-reactor is an important and indispensable unit for a microfluidic chip, and is receiving more and more attention at home and abroad. In this paper, a microreactor system with a double-substrate structure using SAW as the energy source has been designed, and a new method to transport microdroplet between substrates and compact droplet mixing and reaction with SAW have been proposed.The micro-reactor system excites SAW with vertical or horizontal arrangement IDTs which were fabricated on 128°YX-LiNbO₃ substrates. It consists of above, below substrate and arc-shaped microchannel. The IDTs were fabricated on the substrates with microelectronics technique, the arc-shaped microchannel was made by polymer; and their surfaces were hydrophobic treated for transporting droplets.When the amplified RF signal with 27.5MHz center frequency is added on the IDTs, SAW is excited and drives the droplet to move along its propagation direction. Then the micro-droplet slides off the arc-shaped polymer and falls on the bellow substrate. Experiment results showed that curvature radius of the arc-shaped polymer, volumes and physical characteristics of droplet would affect the transportation. Theoretical analyses of the forces on micro-droplet depending on different considerations would be given in paper.After arriving at the down substrate, the microdroplet mixes with the other microdroplet under the influence of SAW, which is excited by the RF signal of a 25.5MHz center frequency added on the IDTs on the down substrates. Physical and chemical reaction was implemented in this microreactor system. The results showed that reaction velocity increases with RF signal power. The results also showed that the reactants with oil encapsulation can reduce evaporation rate. The reaction mechanism was analysized and relation of the reaction velocity to the SAW power was also given in the paper.