Attoliter-level droplet-ordered arrays based on acoustic nano-scissors

Abstract

In the field of nano-fluidics, the generation and manipulation of minuscule droplets with volumes ranging from attoliters (aL) to femtoliters (fL) represents a crucial frontier. Such ultrasmall droplets exhibit immense potential in single-molecule detection, targeted drug delivery, and fundamental research into nanoscale biochemical processes, owing to their unique physicochemical properties, such as low Reynolds number flow and interface-dominated mass transport. Furthermore, ordered liquid-patterned arrays hold promise for applications in optically tunable nano-lenses. However, generation and manipulation of attoliter-scale droplets have long posed significant challenges, particularly for open-interface operations like dispensing, merging, splitting, and patterning into arrays. This study introduces acoustic nano-scissors generated by lateral modes of high-frequency bulk acoustic waves. The induced acoustofluidic effect in thin liquid films forms shear forces between the adjacent wave peaks and wave valleys, thereby successfully cutting the liquid into attoliter-scale droplets at an open interface. This approach could produce droplets with volumes more than three orders of magnitude smaller than those from existing acoustic solutions. Furthermore, the acoustic nano-scissors could generate ordered attoliter droplet arrays with specific patterns, with fast droplet splitting and merging controlled by switching on and off the device. This work provides a novel and flexible solution for various applications requiring attoliter droplet arrays on open interfaces.