Separation of 300 and 100 nm Particles in Fabry–Perot Acoustofluidic Resonators

Abstract

Separation of particles on the order of 100 nm with acoustophoresis has been challenging to date because of the competing natures of the acoustic radiation force and acoustic streaming on the particles. In this work, we present a surface acoustic wave (SAW)-based device that integrates a Fabry-Perot type acoustic resonator into a microfluidic channel to separate submicrometer particles. This configuration enhances the overall acoustic radiation force on the particles and thereby offers controlled manipulation of particles as small as 300 nm. Additionally, SAW-based excitation generates high-frequency acoustic waves in the system relative to bulk acoustic wave (BAW)-based actuation, which suppresses Rayleigh streaming effects on the submicrometer particles. We demonstrate a continuous-flow acoustophoretic separation of 300 and 100 nm particles in our device with a separation efficiency of 86.3%. We also present an analytical stochastic method to model the transport of submicrometer particles in the device and predict the migration trajectories as a function of acoustic and velocity potential field strengths. Our model incorporates particle diffusion, which is important for small particles, and successfully predicts the size-dependent separation modality of our system. This device can be used for several applications in microfluidics that require sorting of the submicrometer particles, and the analytical method can also be extended to predict the particle transport in other systems.

Experimental Characterization of Acoustic Streaming in Gradients of Density and Compressibility

“…For microparticles below a critical size, * weiqiu@fysik.dtu.dk † bruus@fysik.dtu.dk ‡ per.augustsson@bme.lth.se the motion of microparticles is dominated by acoustic streaming, which in many cases hinders the manipulation of sub-micrometer sized particles. Manipulation below the classical limit has previously been demonstrated by flow vortices generated by two-dimensional acoustic fields [29,30], by acoustically active seed particles [24], by a thin reflector design [31], or in systems actuated by surface acoustic waves [32][33][34].…”

Whole-System Ultrasound Resonances as the Basis for Acoustophoresis in All-Polymer Microfluidic Devices

“…Both methods are actively being used in contemporary acoustofluidics as is evident from the following examples published in the literature the past two years. BAW devices have been used for cell focusing in simple and inexpensive aluminum devices [20], for binary particle separation in droplet microfluidics [21], for hematocrit determination [22], for enrichment of tumor cells from blood [23], and for manipulation of C. elegans [24,25], while SAW devices have been used for nanoparticle separation [26,27], for self-aligned particle focusing and patterning [28], for enhanced cell sorting [29], and for in-droplet microparticle separation [30]. Currently, the acoustofluidic devices with the highest throughput are of the BAW type [5].…”

Three-Dimensional Numerical Modeling of Surface-Acoustic-Wave Devices: Acoustophoresis of Micro- and Nanoparticles Including Streaming

“…However, these streamingbased methods have low selectivity. More recently, SAW devices have been developed to focus [22] and separate [23,24] nanoparticles. In particular, Sehgal and Kirby [23] demonstrated separation between 100-nm-and 300-nmdiameter particles at a proof-of-concept stage.…”

“…More recently, SAW devices have been developed to focus [22] and separate [23,24] nanoparticles. In particular, Sehgal and Kirby [23] demonstrated separation between 100-nm-and 300-nmdiameter particles at a proof-of-concept stage. To fully utilize the potential of this and similar devices, further development is necessary to increase the efficiency and the sorting flow rates.…”