Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Abstract

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains. Video LinkThe video component of this article can be found at

Acoustofluidics and Whole-Blood Manipulation in Surface Acoustic Wave Counterflow Devices

“…The top and bottom layer were aligned so that the microchannel was centered with the IDT and the channel outlet was at 670 μm from the IDT front and joined via conformal bonding. Further fabrication specific details can be found in ref . Devices with microchannel heights ranging from 14 to 70 μm were tested, with the microchannel widths held constant at w = 300 μm since this was found to enable efficient pumping at the operating frequency used here ( w = 7.5 λ SAW ) …”

Modeling of Microdevices for SAW-Based Acoustophoresis — A Study of Boundary Conditions

“…However, during the last three decades, microfluidic devices have proven to be a valuable alternative [ 1 , 7 , 8 ], as they allow for lower sample sizes and decentralized preparations of biological samples, increasing the potential for point-of-care testing. Microfluidic methods for separating particles suspended in a medium include passive methods where particle separation is solely determined by the flow and the size or density of particles [ 2 , 9 , 10 , 11 , 12 ], and active methods where particles migrate due to the application of various external fields each targeting specific properties for particle sorting [ 1 , 3 , 4 , 6 , 13 , 14 , 15 , 16 ]. Acoustophoresis is an active method, where emphasis is on gentle, label-free, precise handling of cells based on their density and compressibility relative to the suspension medium as well as their size [ 17 ].…”

Nanoliter‐Droplet Acoustic Streaming via Ultra High Frequency Surface Acoustic Waves

“…SAW microfluidic devices, as shown in Figure 1 , were fabricated at nominal frequencies of 50, 100, 200, 400, 833, and 1250 MHz, and the reflection coefficients were measured to find the resonant frequency at which to operate ( Table 1 ; details of similar fabrication techniques can be found in Travagliati et al[ 18 ]). Each SAW device consisted of straight-fingered titanium:gold (10 nm:100 nm) interdigital transducers (IDT) patterned on 128° Y-cut, X-propagating lithium niobate (LN) substrates.…”