Sheathless Focusing and Separation of Microparticles Using Tilted-Angle Traveling Surface Acoustic Waves

Abstract

Sheathless focusing and separation of microparticles is an important preprocessing step in various biochemical assays in which enriched sample isolation is critical. Most of the previous microfluidic particle separation techniques have used sheath flows to achieve efficient sample focusing. The sheath flow dilutes the analyte and requires additional microchannels and accurate flow control. We demonstrated a tilted-angle traveling surface acoustic wave (taTSAW)-based sheathless focusing and separation of particles in a continuous flow. The proposed device consists of a piezoelectric substrate with a pair of interdigitated transducers (IDTs) deposited at two different angles relative to the flow direction. A Y-shaped polydimethylsiloxane (PDMS) microchannel having one inlet and two outlet ports was positioned on top of the IDTs such that the acoustic energy coupling into the fluid was maximized and wave attenuation by the PDMS walls was minimized. The two IDTs independently produced high-frequency taTSAWs, which propagated at ±30° with respect to the flow direction and imparted a direct acoustic radiation force onto the target particles. A sample mixture of 4.8 and 3.2 μm particles was focused and then separated by the actuation of the IDTs at 194 and 136 MHz frequencies, respectively, without using an additional sheath flow. The proposed taTSAW-based particle separation device offered a high purity >99% at the both outlets over a wide range of flow speeds (up to 83.3 mm/s).

Acoustic Microfluidic Separation Techniques and Bioapplications: A Review

“…The location and angle of IDTs have also been studied for TSAW-based separation. Ahmed et al exploited a tilted-angled TSAW (TaTSAW)-generated acoustic radiation force onto the 4.8 and 3.2 µm particles in continuous flow [ 66 ]. In their system, two tilted-angled IDTs can produce TaTSAWs that propagate at 30 degrees with reference to the fluid flow directions ( Figure 3 f).…”

“…( f ) Tilted-angled TSAW (TaTSAW)-induced radiation force for particle focusing and particle separation. Reprinted with permission from reference [ 66 ]. SAW—surface acoustic wave.…”

Evaluation of acoustic-based particle separation methods

“…To minimize the surface contact between the substrate and the microchannel, the channel is placed on micro-rails above the substrate and a PDMS post is used to integrate the channel and substrate for acoustic coupling (Skowronek et al, 2013). Recently, Ahmed et al (2018) presented double stage tilted angled TSAW based system to separate a mixture of 4.8 and 3.2 mm particles in a continuous flow. In the first stage 194 MHz acoustic waves are applied to align the mixture along microchannel wall.…”

3D numerical simulation of acoustophoretic motion induced by boundary-driven acoustic streaming in standing surface acoustic wave microfluidics

“…Acoustofluidic methods are capable of cell/particle manipulation based on relative density and compressibility and are not restricted by the target particles' electric, magnetic, and optical properties. Moreover, excellent cell/microorganism viability, contact/label-free manipulation, relatively simple and compact devices, and versatility to readily integrate with other microfluidic technologies make acoustofluidic approaches, especially standing surface acoustic wave (SSAW) based methods, a promising platform for the future of LoC technologies, and, consequently, the focus of numerous experimental and theoretical investigations 10 – 12 . To fully grasp the potential of acoustofluidic devices, further development in the reliability and efficiency of the available devices is mandatory, which can be achieved through optimization and conceiving innovative device design.…”