In this study, a surface acoustic wave (SAW)-based microfluidic device has been developed to separate heterogeneous
particle or cell mixtures in a continuous flow using acoustophoresis. 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 along the cross-section of the channel.
Solid particles immersed in the standing SAW field are accordingly pushed to the pressure node arising from the acoustic
radiation force acting on the particles, referring to the acoustic particle-focusing phenomenon. Acoustic radiation force
highly depends on the particle properties, resulting in different acoustic responses for different types of cells. A
numerical model, coupling the piezoelectric effect in the solid substrate and acoustic pressure in the fluid, was developed
to provide a better understanding of SAW-based particle manipulation. Separation of two types of fluorescent particles
has been demonstrated using the developed SAW-based microfluidic device. An efficient separation of E. coli bacteria
from peripheral blood mononuclear cell (PBMC) samples has also been successfully achieved. The purity of separated E.
coli bacteria and separated PBMCs were over 95% and 91%, respectively, obtained by a flow cytometric analysis. The
developed microfluidic device can efficiently separate E. coli bacteria from biological samples, which has potential
applications in biomedical analysis and clinical diagnosis.