Micromixing using a conductive liquid-based focused surface acoustic wave (CL-FSAW)

•Using the concentrated acoustic force of a conductive liquid-based focused surface acoustic wave (CL-FSAW) device, rapid and efficient mixing can be achieved.•In the CL-FSAW mixer, high efficiency mixing performance can be achieved (efficiency ∼97%) at a flow rate of Q≤80μLmin−1 with an applied voltage of 21V.•For further application, CL-FSAW mixer device was applied to continuous synthesis of monodispersed silver nanoparticles at Q=100μLmin−1 and V=21V. Acoustic manipulation of fluids and particles has gained much attention in microfluidics, owing to its advantages of non-invasive manipulation and low power consumption. Microchannel mixing has been limited to diffusion-based mixing, because of low Reynolds number that has a low mixing efficiency. In this study, we firstly introduce a conductive liquid-based focused surface acoustic wave (CL-FSAW) device for mixing. Using the concentrated acoustic force of CL-FSAW, rapid and efficient mixing of deionized water and fluorescent particle suspension was demonstrated in a microfluidic channel. Effects of the applied voltage and the flow rate on the mixing efficiencies were investigated. As the flow rate decreased or the applied voltage increased, the mixing efficiency increased. At 21V, mixing efficiencies were higher than 90% at a flow rate lower than 120μLmin−1. In addition, our device was applied to silver nanoparticle synthesis at the optimal mixing condition (100μLmin−1 and 21V).