Photothermal Cavitation-Driven Micromotor to Penetrate Cell Membrane

Abstract

Photothermally driven micro/nanomotors efficiently convert light into mechanical motion, making them highly attractive for biomedical applications due to their exceptional biocompatibility and safety. However, one mystery of the photothermally driven micro/nanomotor is the wide range of reported light intensities applied, ranging from 1 W cm^–2 to over 10⁵ W cm^–2. To address this mystery, we systematically investigated the propulsion of a carbon microbottle-based micromotor under three illumination conditions: continuous laser, pulsed laser, and scanning laser, where a new cavitation-driven mechanism is identified. Using a high-speed camera, we find that the instantaneous deposition of laser energy on the micromotors can lead to transient and localized evaporation of the solvent, creating cavitation bubbles to drive micromotors with ultrafast speed, where instantaneous velocity over 1 m s^–1 is observed. Through precise modulation of the scanning orientation and intensity of the laser, directional propulsion and targeted explosions of the microbottles are achieved, where the instant force is strong enough to penetrate live cell membranes. Finally, the cavitation-driven micromotors are exploited as gene transfection tools, where targeted cytoplasmic transfection is demonstrated.