Acoustoelectronic nanotweezers enable dynamic and large-scale control of nanomaterials
Figure: a Acoustoelectronic fields are generated via dynamic acoustic wave interactions. These acoustic waves have minimal out-of-plane vibrations and associated acoustic attenuation losses in a fluid. F is the surface electric potential. b Schematic side-view of the electric field distribution and trapping positions for particles with different polarizabilities relative to the medium (red sphere: high polarizability; green sphere: low polarizability). c Schematic mechanism of AENT on manipulating nanoparticles with lower (pnp < pm) or higher (pnp > pm) polarizability than the medium in 3D space by tuning the phases and amplitudes of the acoustic waves. Δφ1 indicates the phase variation of IDT1. ΔA12 indicates the amplitudes variation of IDT1 and IDT2. d Candidate excitation configurations based on nine potential single-crystal piezoelectric materials for AENT. κAET is the acoustoelectronic efficiency, which is defined as the ratio between the surface electric potential and the excitation voltage on the transducer in a standing wave mode. ufluid is the acoustic streaming speed under consistent excitation amplitudes on different crystals. e Macroscopic materials with pre-designed nanotextures fabricated by AENT. Insets: microscopic images of PDMS films containing aligned carbon nanotubes and 100 nm PS beads, PEG hydrogels containing textured FITC-BSA proteins (66 kDa) and FITC-dextran (3 kDa). Scale bar: 60 μm.
The ability to precisely manipulate nano-objects on a large scale can enable the fabrication of materials and devices with tunable optical, electromagnetic, and mechanical properties. However, the dynamic, parallel manipulation of nanoscale colloids and materials remains a significant challenge. Here, we demonstrate acoustoelectronic nanotweezers, which combine the precision and robustness afforded by electronic tweezers with versatility and large-field dynamic control granted by acoustic tweezing techniques, to enable the massively parallel manipulation of sub-100 nm objects with excellent versatility and controllability. Using this approach, we demonstrated the complex patterning of various nanoparticles (e.g., DNAs, exosomes, ~3 nm graphene flakes, ~6 nm quantum dots, ~3.5 nm proteins, and ~1.4 nm dextran), fabricated macroscopic materials with nano-textures, and performed high-resolution, single nanoparticle manipulation. Various nanomanipulation functions, including transportation, concentration, orientation, pattern-overlaying, and sorting, have also been achieved using a simple device configuration. Altogether, acoustoelectronic nanotweezers overcome existing limitations in nano-manipulation and hold great potential for a variety of applications in the fields of electronics, optics, condensed matter physics, metamaterials, and biomedicine.
Digital acoustofluidics enables contactless and programmable liquid handling
Figure: Digital acoustofluidics for contactless and programmable droplet manipulation. a Schematic showing one unit consisting of four IDTs (one pixel) in the digital acoustofluidic device. The four IDTs can be selectively excited to translate droplets along the ±x and ±y directions. The aqueous droplets are isolated from the piezoelectric substrate by an inert carrier fluid to prevent direct contact with surfaces. The IDT (bottom left) embedded beneath the carrier fluid generates SAWs that pumps out fluid in the ±y directions and pumps in fluid in the ±x directions. The red and blue droplets are separately trapped at the two symmetric hydrodynamic wells near the flanks of an IDT. The blue droplet is translated toward a well on the other side of the excited transducer. The reflux streamlines are shown in black. b A photo showing the digital acoustofluidic device with a drop of blood floating on the carrier layer of fluorinated oil
For decades, scientists have pursued the goal of performing automated reactions in a compact fluid processor with minimal human intervention. Most advanced fluidic handling technologies (e.g., microfluidic chips and micro-well plates) lack fluid rewritability, and the associated benefits of multi-path routing and re-programmability, due to surface-adsorption-induced contamination on contacting structures. This limits their processing speed and the complexity of reaction test matrices. We present a contactless droplet transport and processing technique called digital acoustofluidics which dynamically manipulates droplets with volumes from 1 nL to 100 µL along any planar axis via acoustic-streaming-induced hydrodynamic traps, all in a contamination-free (lower than 10−10% diffusion into the fluorinated carrier oil layer) and biocompatible (99.2% cell viability) manner. Hence, digital acoustofluidics can execute reactions on overlapping, non-contaminated, fluidic paths and can scale to perform massive interaction matrices within a single device.
Contactless, programmable acoustofluidic manipulation of objects on water
Figure: Contactless, programmable acoustofluidic manipulation of objects on water. (a) Schematic showing one unit of the acoustofluidic device. The oil droplets (red and blue spheres) are isolated in water to prevent direct contact with surfaces. This unit IDT has a hollow square structure and generates SAWs in ±x and ±y directions. The acoustic waves propagate, leak into the carrier liquid to form jets which propulse droplets along orthogonal axes on the surface of water. (b) Device image. The acoustofluidic chip consists of 36 pixels, each individually excitable.
Contact-free manipulation of small objects (e.g., cells, tissues, and droplets) using acoustic waves eliminates physical contact with structures and undesired surface adsorption. Pioneering acoustic-based, contact-free manipulation techniques (e.g., acoustic levitation) enable programmable manipulation but are limited by evaporation, bulky transducers, and inefficient acoustic coupling in air. Herein, we report an acoustofluidic mechanism for the contactless manipulation of small objects on water. A hollow-square-shaped interdigital transducer (IDT) is fabricated on lithium niobate (LiNbO3), immersed in water and used as a sound source to generate acoustic waves and as a micropump to pump fluid in the ±x and ±y orthogonal directions. As a result, objects which float adjacent to the excited IDT can be pushed unidirectionally (horizontally) in ±x and ±y following the directed acoustic wave propagation. A fluidic processor was developed by patterning IDT units in a 6-by-6 array. We demonstrate contactless, programmable manipulation on water of oil droplets and zebrafish larvae. This acoustofluidic-based manipulation opens avenues for the contactless, programmable processing of materials and small biosamples.
Acoustic streaming vortices enable contactless, digital control of droplets
Figure: ASV-based droplet manipulation. (A) Schematic showing a typical droplet processing unit. The droplets (i.e., red and blue spheres) over the transducers are guided into the center between the barrel-like ASVs (labeled as Vortices) following the recirculating inflow. These droplets are unidirectionally routed along the linear array of IDTs by shifting the sequence of working frequencies. The portions of the IDTs shaded in purple (e.g., IDTi) indicate that they are being excited by a high-amplitude signal with frequency fi. (B) The photo shows a bifurcated device with a particle floating above the transparent carrier oil layer. (C) The general control schematic for the droplet processing unit. The unit is composed of K + M + N interconnected IDTs [denoted as IDTkI, IDTmL, and IDTnR (k = 1,2, …, K; m = 1,2, …, M; n = 1,2, …, N)] with tuned working frequencies. Multitonal signals (i.e., SIL or SIR) encoded with a series of different frequencies, amplitudes, durations, and initiation times (i.e., [fmL,AmL,TmL,tmL]K+M or [fnR,AnR,TnR,tnR]K+N) are the excitation signals into the droplet processing unit and can direct the droplet from IDT1I to the left or right port, respectively. The blue shaded area indicates the resulting virtual bifurcated channel for droplet translation. Photo credits: Peiran Zhang, Duke University.
Advances in lab-on-a-chip technologies are driven by the pursuit of programmable microscale bioreactors or fluidic processors that mimic electronic functionality, scalability, and convenience. However, few fluidic mechanisms allow for basic logic operations on rewritable fluidic paths due to cross-contamination, which leads to random interference between “fluidic bits” or droplets. Here, we introduce a mechanism that allows for contact-free gating of individual droplets based on the scalable features of acoustic streaming vortices (ASVs). By shifting the hydrodynamic equilibrium positions inside interconnected ASVs with multitonal electrical signals, different functions such as controlling the routing and gating of droplets on rewritable fluidic paths are demonstrated with minimal biochemical cross-contamination. Electrical control of this ASV-based mechanism allows for unidirectional routing and active gating behaviors, which can potentially be scaled to functional fluidic processors that can regulate the flow of droplets in a manner similar to the current in transistor arrays.