Modulation of energy thresholds for laser-induced cavitation using gold nanoparticles

The precise control of laser-induced cavitation (LIC) at the micro and nanoscale holds significant promise for biomedical applications ranging from targeted drug delivery and microsurgery to materials processing and microfluidics. Gold nanoparticles (AuNPs) are known to act as potent enhancers for LIC by reducing cavitation energy thresholds. However, a quantitative understanding of how AuNP properties regulate cavitation events remains limited, which is crucial for optimizing the aforementioned applications. In this study, we systematically investigate AuNP-mediated modulation of LIC energy thresholds using nanosecond laser pulses and ultra-highspeed imaging. While LIC in deionized (DI) water typically exhibits a sharp transition from no cavitation to large bubble formation (maximum bubble radius Rmax >100 μm) once a critical energy threshold is exceeded. In contrast, the introduction of AuNPs reveals four distinct cavitation regimes: (i) no observable bubbles, (ii) single small bubbles (Rmax ~ 1-20 μm), (iii) multiple small bubbles forming bubble clouds, and (iv) single large bubbles (Rmax ~ 100-1000 μm). Each AuNP system exhibits a characteristic energy threshold at which large cavitation emerges. We attribute these differences to a shift in the dominant cavitation nucleation mechanisms. These results demonstrate that AuNP optical properties play a critical role in governing LIC mechanisms, cavitation regimes, and energy thresholds. By enabling tunable and predictable cavitation behavior, this work provides a framework for the rational design of nanoparticle-assisted cavitation in advanced biomedical and engineering applications.