Surface acoustic wave-based micromixing enhancement using a single interdigital transducer

The realization of efficient mixing of samples inside a microfluidic channel is essential for performing numerous biological assays in miniaturized total analysis systems. The low Reynolds number flows at the microscale create laminar streams inside the microchannel, limiting flow mixing to a molecular diffusion level. In this paper, we propose a simple and efficient acoustofluidic mixing technique inside a single-layered polydimethylsiloxane (PDMS) microfluidic channel. The proposed surface acoustic wave (SAW)-based system composed of a straight interdigitated transducer (IDT) is positioned beneath the PDMS microchannel. Fluorescein dye dissolved in deionized water (sample fluid) and deionized water (sheath fluid) was introduced through the first and second inlets of the PDMS microchannel, respectively. Their flow rates were controlled such that the sample fluid with fluorescein dye was hydrodynamically focused close to the bottom of the microchannel by the sheath fluid. High-frequency (140 MHz) SAWs, ge...