title: Microfluidic plug steering using surface acoustic waves.
abstract: Digital microfluidic systems, in which isolated droplets are dispersed in a carrier medium, offer a method to study biological assays and chemical reactions highly efficiently. However, it's challenging to manipulate these droplets in closed microchannel devices. Here, we present a method to selectively steer plugs (droplets with diameters larger than the channel's width) at a specially designed Y-junction within a microfluidic chip. The method makes use of surface acoustic waves (SAWs) impinging on a multiphase interface in which an acoustic contrast is present. As a result, the liquid-liquid interface is subjected to acoustic radiation forces. These forces are exploited to steer plugs into selected branches of the Y-junction. Furthermore, the input power can be finely tuned to split a plug into two uneven plugs. The steering of plugs as a whole, based on plug volume and velocity is thoroughly characterized. The results indicate that there is a threshold plug volume after which the steering requires elevated electrical energy input. This plug steering method can easily be integrated to existing lab-on-a-chip devices and it offers a robust and active plug manipulation technique in closed microchannels.
authors.affiliation: Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia. adrian.neild@monash.edu.
authors.forename: Muhsincan
authors.initials: M
authors.lastname: Sesen
authors.forename: Tuncay
authors.initials: T
authors.lastname: Alan
authors.forename: Adrian
authors.initials: A
authors.lastname: Neild
mesh_terms: D046210:Microfluidic Analytical Techniques / Q000295:instrumentation; D010316:Particle Size; D013016:Sound; D013499:Surface Properties