Rapid microparticle separation based on acoustofluidic particle manipulation inside a sessile droplet

The precise separation of particles and cells from complex mixtures is a fundamental technique in various diagnostic and therapeutic applications. In this study, a highly efficient, non-invasive acoustic tweezers method for particle separation within a sessile droplet driven by surface acoustic waves (SAW) was introduced. By changing two typical acoustic parameters in the experiment, including the actuation frequency and the position offset factor, three particle distribution models were generated. Concentration distribution experiments were conducted using particles of 1-40 $\mu$m diameters. It was observed that the particle cluster enriched in the center and the concentric particle ring in the outer area could co-exist in a balanced state (C2), suggesting new particle manipulation possibilities. Also, the particles would concentrate at the center of the droplet (C1) or around the periphery of the droplet (C3). By adjusting acoustic parameters, particles were selectively concentrated in the sessile droplet, enabling precise separation based on particle size in complex mixtures (5 $\mu$m and 40 $\mu$m, 5 $\mu$m and 30 $\mu$m) in a short time ($\sim$30 s). This acoustic separation method offers significant advantages over traditional techniques, due to its non-invasive nature and the ability to handle a wide range of particle sizes. The ability to selectively manipulate particles based on their physical properties opens new avenues for precise and scalable particle sorting and purification.