An intra-droplet particle switch for droplet microfluidics using bulk acoustic waves

Abstract

To transfer cell- and bead-assays into droplet-based platforms typically requires the use of complex microfluidic circuits, which calls for methods to switch the direction of the encapsulated particles. We present a microfluidic chip where the combination of acoustic manipulation at two different harmonics and a trident-shaped droplet-splitter enables direction-switching of microbeads and yeast cells in droplet microfluidic circuits. At the first harmonic, the encapsulated particles exit the splitter in the center daughter droplets, while at the second harmonic, the particles exit in the side daughter droplets. This method holds promises for droplet-based assays where particle-positioning needs to be selectively controlled.

On-chip background dilution in droplets with high particle recovery using acoustophoresis

“…The microfluidic channels were etched using a standard dry etching process 7 (Fig. 2) on a high-resistivity silicon wafer (resistivity ≥ 30 000 Ω cm, Topsil).…”

Intra-droplet particle enrichment in a focused acoustic field

“…Although this method is kind of tricky, it is more direct and easier to operate than using acoustic eld to separate droplets directly. 26 The acoustic method of particle enrichment has the advantages of continuous, label free. Compared with the direct concentration of particles in a certain area in the channel, the intra-droplet particle enrichment can offer an independent working environment for particles, but it is more difficult to control.…”

Binary particle separation in droplet microfluidics using acoustophoresis

“…7,8 In many applications, the precise control of the individual droplets and the content inside the droplets is required. 9 For this purpose, unit-operators to sort, 10,11 trap, 12,13 and manipulate particles inside droplets [14][15][16][17][18][19][20] have been developed. Manipulation of particles encapsulated inside droplets is of high interest since it can be used for numerous applications such as particle enrichment and washing.…”

“…Manipulation of particles encapsulated inside droplets is of high interest since it can be used for numerous applications such as particle enrichment and washing. Recently, several methods to control the position of particles inside droplets have been reported including acoustophoresis, 14,15 dielectrophoresis, 16 magnetophoresis, 17,18 and methods relying on sedimentation and the hydrodynamic flow patterns inside the droplets. 19,20 However, methods to separate one particle species from another encapsulated in the same droplet are still missing.…”

“…During the last few years, acoustic particle manipulation (acoustophoresis) has been used to focus, concentrate, and separate particles in various one-phase microfluidic systems, [21][22][23] and recently, acoustics has also been implemented in two-phase systems to sort whole droplets and to manipulate particles inside droplets. 11,14,15,24,25 Particles in an acoustic standing wave-field will experience an acoustic radiation force (F rad ), and the force on a particle in a 1-dimensional k/2-standing wave-field is described by…”