Acoustofluidic black holes for multifunctional in-droplet particle manipulation

Abstract

Acoustic black holes offer superior capabilities for slowing down and trapping acoustic waves for various applications such as metastructures, energy harvesting, and vibration and noise control. However, no studies have considered the linear and nonlinear effects of acoustic black holes on micro/nanoparticles in fluids. This study presents acoustofluidic black holes (AFBHs) that leverage controlled interactions between AFBH-trapped acoustic wave energy and particles in droplets to enable versatile particle manipulation functionalities, such as translation, concentration, and patterning of particles. We investigated the AFBH-enabled wave energy trapping and wavelength shrinking effects, as well as the trapped wave energy–induced acoustic radiation forces on particles and acoustic streaming in droplets. This study not only fills the gap between the emerging fields of acoustofluidics and acoustic black holes but also leads to a class of AFBH-based in-droplet particle manipulation toolsets with great potential for many applications, such as biosensing, point-of-care testing, and drug screening.

A solution to the biophysical fractionation of extracellular vesicles: Acoustic Nanoscale Separation via Wave-pillar Excitation Resonance (ANSWER)

“…To further reduce the cut-off size, new mechanisms and theories may need to be developed as acoustic radiation force decays in a cubic velocity to the particle size. In addition, developing hybrid nanotweezers by combining acoustofluidic technologies (60)(61)(62)(63)(64)(65) with other nanoscale manipulation technologies, such as plasmonic tweezers (66), dielectrophoresis (67), and Brownian motors (33), may be a promising route toward developing a solution. Furthermore, implementing two-dimensional van der Waals materials holds promise, as they support quasi-particle half-light and half-matter excitations, and exhibit a long lifetime, with low loss and strong field confinement (68).…”

Microfabricated acoustofluidic membrane acoustic waveguide actuator for highly localized in-droplet dynamic particle manipulation

“…Likewise, finding the substrate's acoustic focal points, in relation to the position of the transducers, 36 and adding micromachined sound-trapping dimples onto the substrate can amplify converging flexural waves and their resulting acoustic fields. 37 IDTs on a bulk piezoelectric substrate can generate surface acoustic waves (SAWs) and Lamb waves and are utilized in various settings, from the generation of streaming inside a sessile droplet to particle separation inside a microfluidic channel. To accurately control the acoustic fields induced by the mechanical deformations originating from the IDTs, several approaches have been investigated, such as shaping the electrodes into focused IDTs, 38,39 slanted IDTs 40,41 and holographic IDTs, 42,43 and pairing IDTs with each other, 15,[44][45][46][47] with microfluidic channels 23,48 or with other structural obstacles such as boundaries 24,49 and phononic crystals.…”

“…Furthermore, the open and flat surface of the device makes it compatible with various manipulations and assays carried out inside sessile droplets. 37,87…”

Active coating of a water drop by an oil film using a MHz-frequency surface acoustic wave

“…The piezoelectric effect in the substrate of the actuator linearly transforms the electrical signal to a nanoscale oscillating mechanical vibration of maximum amplitude near the surface of the devices -SAW. [5] SAW actuators are scalable in size, may be powered by a pocket size source, and are devoid of moving parts, [6][7][8][9] and hence are attractive for introducing low power and portable strategies for SAW actuated unit operations. Lithium-niobate (LN) based actuators, [10] known for their high pyroelectricity and chemically inert surface, have been showing great promise for microfluidics and small scale manufacturing.…”