Figure 1.

Design and concept of the acoustofluidic platform for nanoparticle (NP) synthesis. a) Schematic showing the acoustofluidic synthesis device. The device is composed of a PDMS microfluidic channel constructed with multiple pairs of sharp‐edge structures, a glass slide, and an acoustic transducer. When flowing through the channel, Solution 1 and Solution 2 are rapidly yet completely mixed in the presence of the acoustic streaming effect, thus resulting in the self‐assembly of PLGA‐PEG NPs. b) Schematic showing the generation of acoustic streaming and design of sharp‐edge structure. c) Stacked fluorescent image displaying the acoustic streaming generated in the acoustofluidic device. d) Fluorescent images showing the mixing of two fluids. When the acoustic transducer is off, an unmixed, laminar flow pattern is observed, whereas a complete mixing of two fluids is achieved when the acoustic transducer is on. Results shown in (c) and (d) are obtained under the same conditions: the driving voltage of 20 V_PP, the driving frequency of 4.0 kHz, and the flow rate of 10 µL min⁻¹ for each stream. e) Bright‐field images showing the mixing of water and PLGA‐PEG precursor solution. Similarly, when the acoustic transducer is off, the two solutions form a laminar flow, where NPs may also be synthesized through a diffusion‐based mixing between the two solutions. Once the transducer in turned on, the two solutions are rapidly mixed without any fluidic interface observed; this rapid and complete mixing leads to an exchange between the solvent and water, also known as solvent exchange, and therefore produces PLGA‐PEG NPs.