Separation of sub-micron particles from micron particles using acoustic fluid relocation combined with acoustophoresis

Abstract

Acoustophoresis has gained increasing attention as a gentle, non-contact, and high-throughput cell and particle separation technique. It is conveniently used to isolate and enrich particles that are greater than 2 μm; however, its use in manipulating particles smaller than 2 μm is limited. In this work, we present an alternative way of using acoustic forces to manipulate sub-micrometer particles in continuous flow fashion. It has been shown that acoustic forces can be employed to relocate parallel laminar flow streams of two impedance-mismatched fluids. We demonstrate the separation of sub-micron particles from micron particles by the combination of acoustophoresis and acoustic fluid relocation. The micron particles are focused into the middle of the flow channel via primary acoustic forces while sub-micron particles are moved to the side via drag forces created by the relocating fluid. We demonstrate the proof of the concept using binary mixtures of particles comprised of sub-micron/micron particles, micron/micron particles, and bovine red blood cells with E. coli. The efficiency of the particle enrichment is determined via flow cytometry analysis of the collected streams. This study demonstrates that by combining acoustic fluid relocation with acoustophoresis, sub-micron particles can be effectively separated from micron particles at high flow rates and it can be further implemented to separate binary mixtures of micron particles if the volumetric ratio of two particles is greater than 10 and the larger particle diameter is about 10 μm. The combined method is more appropriate to use than acoustophoresis in situations where acoustic streaming and differences in acoustic impedance of fluids can be of concern. Graphical abstract In the presence of a resonance acoustic field, the clean high-density fluid (dark gray) and the low-density sample fluid are relocated. During this process, E. coli are separated from the red blood cells (RBCs).

Gradient acoustic focusing of sub-micron particles for separation of bacteria from blood lysate

“…Purification of small particles, e.g. bacteria and platelets [25][26][27][28] has been achieved by acoustically pushing away the larger particles from the smaller particles, but this approach does not enable isolation of sub-micron-sized biological particles from a complex background of molecules, particles or debris that are of smaller size, which is essential for purification protocols. Recently sub-micron particles were pushed away from 100-nm-particles by surface acoustic waves 29,30 and the same approach was applied to separate red blood cells and microvesicles from exosomes in a two-stage process 31 .We recently found that, for bulk acoustic waves, acoustic streaming can be greatly reduced by introducing a gradient in acoustic impedance (mass density times speed of sound) in the acoustic cavity by standard gradient centrifugation media 32,33 .…”

Acoustic Microfluidic Separation Techniques and Bioapplications: A Review

“…Due to the diameter difference, micron particles were dominated by primary acoustic radiation force and focused on the midline of the microchannel, while sub-micron particles were moved toward the sidewall via drag force. Using the same mechanism, they successfully separated bovine red blood cells and Escherichia coli ( E. coli ) [ 46 ]. In addition to the size-based separation, BAW is also able to separate samples based on density or compressibility.…”

Field-Portable Microplastic Sensing in Aqueous Environments: A Perspective on Emerging Techniques

“…Second, the forces in acoustophoresis depend on bulk, mechanical properties of materials, therefore the manipulation may be effective with MPs affected by surface fouling from biofilms or other materials. Third, acoustophoresis has been shown to be effective for separating very small particles [99,100], include sub-micrometer particles [101]. The relative abundance of small MPs is very high in comparison to MPs of 100 µm in diameter or more that are retained by surface trawling nets, so acoustophoresis may be useful for analyzing smaller samples than have previously been required.…”