GHz acoustic streaming micro-vortex arrays for reconfigurable sub-100 nm nanoparticle patterning.

Precise, parallel, and dynamically reconfigurable patterning of sub-100 nm nanoparticles plays a vital role in materials science, biochemistry, and physics. However, achieving this via acoustofluidics has remained elusive, due to the severe attenuation of acoustic radiation forces and the interference of uncontrolled acoustic streaming effects. To overcome this, we introduce GHz acoustic streaming micro-vortex arrays (GASMA) for the stable, arrayed assembly of sub-100 nm nanoparticles. By deliberately exciting specific lateral modes of GHz bulk acoustic wave (BAW) resonators, we generate a highly structured, periodic acoustic field on the device surface. When coupled into the adjacent liquid, this field gives rise to ordered micro-vortex arrays. These periodic micro-vortices rapidly transport nanoparticles to acoustic streaming potential wells (ASPWs)-the stagnation zones between adjacent vortices-where they are stably trapped. We demonstrate the precise parallel patterning of nanoparticles as small as 30 nm and validate GASMA's versatility by manipulating diverse materials, including polystyrene (PS) nanoparticles, gold nanorods, and extracellular vesicles (EVs). Critically, by simply modulating the driving frequency, we achieve dynamic, on-demand reconfiguration of these nanoparticle arrays. In summary, GASMA addresses several key limitations in manipulating sub-100 nm nanoparticles, offering a promising acoustofluidic platform for applications in tunable optoelectronics, nanofabrication, and biomedicine.