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. 2013 Jul 30;110(31):12549-54.
doi: 10.1073/pnas.1301860110. Epub 2013 Jul 15.

Acoustophoretic contactless transport and handling of matter in air

Daniele Foresti  1 , Majid Nabavi, Mirko Klingauf, Aldo Ferrari, Dimos Poulikakos
Affiliations

Affiliation

  • 1 Department of Mechanical and Process Engineering, Laboratory of Thermodynamics in Emerging Technologies, Eidgenössische Technische Hochschule Zürich, CH-8092 Zurich, Switzerland.

Acoustophoretic contactless transport and handling of matter in air

Daniele Foresti et al. Proc Natl Acad Sci U S A. .
. 2013 Jul 30;110(31):12549-54.
doi: 10.1073/pnas.1301860110. Epub 2013 Jul 15.

Authors

Daniele Foresti  1 , Majid Nabavi, Mirko Klingauf, Aldo Ferrari, Dimos Poulikakos

Affiliation

  • 1 Department of Mechanical and Process Engineering, Laboratory of Thermodynamics in Emerging Technologies, Eidgenössische Technische Hochschule Zürich, CH-8092 Zurich, Switzerland.

Abstract

Levitation and controlled motion of matter in air have a wealth of potential applications ranging from materials processing to biochemistry and pharmaceuticals. We present a unique acoustophoretic concept for the contactless transport and handling of matter in air. Spatiotemporal modulation of the levitation acoustic field allows continuous planar transport and processing of multiple objects, from near-spherical (volume of 0.1-10 μL) to wire-like, without being limited by the acoustic wavelength. The independence of the handling principle from special material properties (magnetic, optical, or electrical) is illustrated with a wide palette of application experiments, such as contactless droplet coalescence and mixing, solid-liquid encapsulation, absorption, dissolution, and DNA transfection. More than a century after the pioneering work of Lord Rayleigh on acoustic radiation pressure, a path-breaking concept is proposed to harvest the significant benefits of acoustic levitation in air.

Keywords: acoustics; fluid; manipulation; microfluidics; ultrasounds.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Schematic of the contactless multidrop…

Fig. 1.

Schematic of the contactless multidrop manipulator and its excitation mechanism. In the illustrative…

Fig. 1.
Schematic of the contactless multidrop manipulator and its excitation mechanism. In the illustrative example, droplets are introduced into the system at three locations (inlets 1, 2, and 3) in a five-one-two LPT levitator. Their numbers correspond to the number of LPTs in a certain row. All rows are on the same plane, parallel to the reflector plane. The droplets move and mix, and the final sample is delivered to the outlet. The introduction of droplets into the system can be achieved either manually with a micropipette or with an automatized syringe pump and a glass capillary (Methods). The reflector height H is adjusted with a linear micrometer stage.
Fig. 2.

Fig. 2.

Controlled approach of two droplets…

Fig. 2.

Controlled approach of two droplets in air. ( A ) Levitation potential inside…

Fig. 2.
Controlled approach of two droplets in air. (A) Levitation potential inside a five-LPT device by varying the driving voltage of the LPTs (the levitation nodes are shown in blue). The small ellipses illustrate the experimental droplet positions. For clarity, only the emitting surfaces of the LPTs are shown. (B) Experimental results for the horizontal position of two acoustophoretically transported and eventually coalesced water droplets 0.84 mm in diameter for four traveling velocities, along with the numerical predictions (Figs. S6–S8). The oscillations of the droplets during translation are due to the very low damping effect of the surrounding fluid (air). (C) Experimental movement velocity (formula image) of one of the two approaching water droplets. (D) Analytical and experimental values of total acceleration (formula image) of the droplets near collision, with respect to the center-to-center droplet distance r (V0 = 2.6 m/s, H/λ = 0.496). The dotted line marks the primary acceleration formula image due to the acoustic potential field. The experimental uncertainty in the estimation of vrms is reflected in the error bars of the analytical data.
Fig. 3.

Fig. 3.

Series of representative experiments with…

Fig. 3.

Series of representative experiments with droplets or particles using the present acoustophoretic concept.…

Fig. 3.
Series of representative experiments with droplets or particles using the present acoustophoretic concept. (A) Stable water droplet coalescence (We = 0.42). (B) Explosive atomization after water droplet coalescence. (C) Tetradecane droplets bouncing (We = 0.875) and subsequently coalescing (We = 0.25). (D) Polystyrene particle collision with tetradecane droplet (We = 0.66). (E) Collision of a porous particle (instant coffee) and a water droplet (We = 0.24). The colored image at the bottom shows an instant coffee particle before and after the mixing/evaporation process. (F) Schematic of the contactless DNA transfection process and micrographs of the transfected cells with blurred edges. The transfection agent (TA) was premixed with the DNA solution. (G) Mixing experiment of fluorescein droplet (Left), with a logarithmic acid dissociation constant of pKa = 6.4 and pH 3, and of a droplet of physiological solution with pH 12 (Right). (Scale bars: B–E, 1 mm.)
Fig. 4.

Fig. 4.

Contactless transport of an elongated…

Fig. 4.

Contactless transport of an elongated object (a toothpick with L= 8 cm ≈…

Fig. 4.
Contactless transport of an elongated object (a toothpick with L= 8 cm ≈ 6λ, H ≈ λ). Controlled rotation: top view (A) and side view (B). (C) Controlled translation: top view. In principle, there is no limit to the length of the object that can be handled.
See this image and copyright information in PMC

References

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