Laser-Guided Liquid Marbles

Shooting marbles is no longer just a game for researchers at Harbin Institute of Technology. Led by Qinmin Pan, the team has developed nanoparticle-encased microdroplets—so-called liquid marbles—that can be steered through water using laser light (ACS Appl. Mater. Interfaces 2015, DOI: 10.1021/acsami.5b09952). This technique could lead to remotely controlled microreactors and microrobots. To make the liquid marbles, the Harbin team rolled hydrophobic chloroform microdroplets over a bed of iron oxide-polydopamine core-shell nanoparticles in a beaker of water. The nanoparticles cling to the interface between the two liquids and form a coating around the droplets. The researchers then shot individual marbles with near-infrared laser light, heating and vaporizing small pockets of the chloroform within. The vapor creates a bubble that sticks to the marble, making it more buoyant. Eventually, the marble lifts off in the beaker. The team can manipulate a marble vertically and laterally by controlling the intensity and position of the laser beam. Orlin D. Velev, a chemist at North Carolina State University, calls this microdroplet manipulation method “simple, elegant, and easy to implement.”