Single-nanowire-morphed mechanical slingshot for directional shooting delivery of micro-payloads

Stretching elastomer bands to accumulate strain energy, for a sudden projectile launching, has been an old hunting skill that will continue to find new applications in miniaturized worlds. In this work, we explore the use of highly resilient and geometry-tailored ultrathin crystalline silicon nanowires (SiNWs) as elastic medium to fabricate the first, and the smallest, mechanical slingshot. These NW-morphed slingshots were first grown on a planar surface, with desired layout, and then mounted upon standing pillar frames, with a unique self-hooking structure that allows for a facile and reliable assembly, loading and shooting maneuver of microsphere payloads. Impressively, the elastic spring design can help to store 10 times more strain energy into the NW springs, compared with the straight ones under the same pulling force, which has been strong enough to overcome the sticky van der Waals (vdW) force at the touching interfaces that otherwise will hinder a reliable releasing onto soft surface with low-surface energy or adhesion force, and to achieve a directional shooting delivery of precise amount of tiny payload units onto delicate target with the least impact damage. This NW-morphing construction strategy also provides a generic protocol/platform to fast design, prototype, and deploy new nanoelectromechanical and biological applications at extremely low costs.