Active density-based separation using standing surface acoustic waves

In this paper, we demonstrate active, sheathless density-based particle separation using standing surface acoustic waves. Density-based separation is critical for many biological applications, such as white blood cell classification, stem cell isolation, fetal cell collection from maternal blood, and specific bacterium sorting. Current gold standard separation techniques are only capable of separation based on particle size; hence, separation cannot be achieved for same-size particles with different densities. Here, the separation is accomplished with an acoustic force field (active technique) without using sheath flow. We demonstrate the separation of two 10 μm diameter, different-density particle streams (polystyrene: 1.05 g/cm3, melamine: 1.71 g/cm3) with 98.8% separation efficiency.