Ultrafast star-shaped acoustic micromixer for high throughput nanoparticle synthesis

We present an acoustically actuated microfluidic mixer, which can operate at flowrates reaching 8 ml min^-1, providing a 50-fold improvement in throughput compared to previously demonstrated acoustofluidic approaches. The device consists of a robust silicon based micro-mechanical oscillator, sandwiched between two polymeric channels which guide the fluids in and out of the system. The chip is actuated by application of an oscillatory electrical signal onto a piezoelectric disk coupled to the substrate by adhesive. At the optimal frequency, this acoustofluidic system can homogenise two fluids with a relative mixing efficiency of 91%, within 4.1 ms from first contact. The micromixer has been used to synthesize two different systems: Budesonide nanodrugs with an average diameter of 80 ± 22 nm, and DNA nanoparticles with an average diameter of 63.3 ± 24.7 nm.