Laser-Controlled Propulsion of a Microbubble Rolling on a Carbon Nanocoil Rail

Controllably propelling microbubbles in microchannels within a microfluidic chip is of great scientific significance yet remains challenging. In this work, we employ carbon nanocoils (CNCs) as a laser-energized rail for propelling microbubbles to the desired position on the inner sidewall of microchannels by laser irradiation at the liquid-CNC interface. Laser-controlled microbubbles can be generated, transported to a desired location, stopped, and re-mobilized repeatedly without a significant change in volume on the microchannel within a microfluidic chip by controlling the laser spot. The microbubbles exhibit a rolling motion at the liquid-CNC interface due to stronger convectional flow induced by a dynamic, mobile thermal gradient generated by a scanning laser spot. The photothermal conversion properties and hydrophobic surface of the CNCs enable the CNCs to function as a laser-energized rail for microbubble propulsion. These results demonstrate that laser-controlled microbubbles rolling on CNC rails have good mobility and can be accurately manipulated in a microchannel chip. This approach leverages a dynamic thermal gradient, departing from static control methods to enable on-demand, reconfigurable manipulation of microbubbles, which opens up new possibilities for lab-on-a-chip and microfluidic applications.