A localized surface acoustic wave applied spatiotemporally controllable chemical gradient generator.

In many research studies and applications about microscale biochemical analysis, the generation of stable, spatiotemporally controllable concentration gradients is critical and challenging. However, precise adjustment of concentration gradients in microchannels is still a huge challenge. Because of its precise controllability, non-harmfulness, and immediacy, sound waves perfectly meet the needs of this type of problem. Utilizing the acoustofluidic platform to manipulate liquids in the microchannel accurately makes it an excellent solution to this problem. In this work, we present a tunable and reliable acoustofluidic gradient generator, which can trigger a change of medium based on acoustic streaming induced by C-shaped interdigital transducers (IDTs). By locally generating streaming via two C-shaped IDTs in the same direction but at different horizontal positions, concentration generators can produce two streams of liquids step by step, forming a stable and controllable concentration gradient within short response times (approximately second response time). Along with this gradient generator's advantages in size, tunability, and reliability, it could be widely used for micro-biological and micro-chemical applications requiring a precise concentration gradient.