Binary particle separation in droplet microfluidics using acoustophoresis

Abstract

We show a method for separation of two particle species with different acoustic contrasts originally encapsulated in the same droplet in a continuous two-phase system. This was realized by using bulk acoustic standing waves in a 380 lm wide silicon-glass microfluidic channel. Polystyrene particles (positive acoustic contrast particles) and in-house synthesized polydimethylsiloxane (PDMS) particles (negative acoustic contrast particles) were encapsulated inside water-in-oil droplets either individually or in a mixture. At acoustic actuation of the system at the fundamental resonance frequency, the polystyrene particles were moved to the center of the droplet (pressure node), while the PDMS particles were moved to the sides of the droplet (pressure anti-nodes). The acoustic particle manipulation step was combined in series with a trifurcation droplet splitter, and as the original droplet passed through the splitter and was divided into three daughter droplets, the polystyrene particles were directed into the center daughter droplet, while the PDMS particles were directed into the two side daughter droplets. The presented method expands the droplet microfluidics toolbox and offers new possibilities to perform binary particle separation in droplet microfluidic systems.

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].…”

Acoustic Microfluidic Separation Techniques and Bioapplications: A Review

“…In addition to the size-based separation, BAW is also able to separate samples based on density or compressibility. Fornell et al successfully separated polystyrene and PDMS particles with different acoustic contrast factors inside a water-in-oil droplet ( Figure 2 b) [ 47 ]. Since acoustic radiation forces are proportional to acoustic contrast factors, the polystyrene particles were directed to the pressure nodes while the PDMS particles were moved to the pressure antinodes when BAW is on.…”

“…( b ) BAW-based separation of polystyrene and polydimethylsiloxane (PDMS) particles with different acoustic contrast factors. Reprinted with permission from reference [ 47 ]. ( c ) Size-sensitive sorting mixture of 5 µm and 2.5 µm particles by acoustic bubble.…”

Lab-on-a-Chip Technologies for the Single Cell Level: Separation, Analysis, and Diagnostics

“…For an overview of the pros and cons of droplet microfluidics for single cell separation, analysis and diagnostics, please refer to Table 8 below. Individual droplets can be handled, for example, using acoustophoresis/SAW [134,167], hydrodynamic or microfluidic changes by geometries [168][169][170][171], elective emulsion separation [172], in-line passive filters [173], or even DLD [99]. It is also possible to manipulate the contents inside these droplets using DEP [174,175], magnetic fields [176,177], or beads and microfluidic ratchets [178].…”