Gas Microbubble Formation via Near-Infrared Femtosecond Laser Ablation in Live Cells.

Abstract

Focused near-infrared femtosecond (NIR fs) laser irradiation induces efficient photochemical breakdown of intracellular molecules, resulting in the formation of gas microbubbles that ultimately lead to cell death and removal. This study characterizes these microbubbles using high-speed imaging. Microbubbles generated within cells by single-pulse irradiation were consistently larger than those formed in the surrounding culture medium across a broad pulse energy range. Notably, the energy threshold for intracellular microbubble formation was several tens of nanojoules lower than in the culture medium, enabling precise cell ablation without inducing extracellular bubbling. Repeated pulse irradiation at 1 kHz frequency further reduced the energy threshold and increased bubble size, with saturation observed after approximately 30 pulses. Near-threshold pulse irradiation was then employed to develop a precise method for investigating cellular motility in vitro. Cell-free zones were created within cell monolayers, enabling motile cells to migrate into the cleared zones. This method was validated using the A549 lung cancer cell line and the plant flavonoid apigenin, which exhibited dose-dependent reduction in A549 cell motility. These findings highlight the method's potential for evaluating cellular behaviours and screening chemical compounds.