Size-Based Separation of Particles and Biological Cells Using Surface Acoustic Waves

Acoustics has emerged as one of the most promising non-invasive techniques for particle manipulation in microfluidics. In this study, a surface acoustic wave (SAW)-based microfluidic device has been developed to manipulate micron-sized synthetic particles and biological cells. The microfluidic device is comprised of two components, a SAW transducer and a microfluidic channel made of polydimethylsiloxane (PDMS). The SAW transducer was fabricated by patterning two pairs of interdigital electrodes on a lithium niobate (LiNbO3) piezoelectric substrate. When exciting the SAW transducer by AC signals, a standing SAW is generated across the cross-section of the channel. Solid particles immersed in the standing SAW are accordingly pushed to the pressure-node arising from the acoustic radiation force acting on the particles, referring to the acoustic particle focusing phenomenon. The amplitude of acoustic radiation force highly depends on the properties of the particle, resulting in different acoustic responses for different types of cells. Separation of two types of fluorescent particles (Particle I: 1.2µm in diameter, green spectrum emission; Particle II: 5.8µm in diameter, red spectrum emission) has been demonstrated using the developed SAW-based microfluidic device. We also demonstrated the separation of E. coli bacteria from peripheral blood mononuclear cell (PBMC) samples. The purity of separated E. coli bacteria and separated PBMC are over 95% and 91%, respectively, obtained by a flow cytometric analysis. Conclusively, the developed microfluidic device can efficiently separate E. coli bacteria from biological samples, which has potential applications in biomedical analyses and clinical diagnosis.