Quantifying the Plasmonic Nanoparticle Size Effect on Photoacoustic Conversion Efficiency

Efficient contrast agents such as plasmonic nanoparticles (PNPs) are highly desirable for good-performance photoacoustic (PA) imaging. Owing to the small size effect, PNPs have a unique microscopic mechanism of PA conversion from photons to ultrasound. Here, by quantitatively modeling the optical absorption, the time-resolved temperature field, and thermal expansion based on the analytical and finite element analysis (FEA) method, we obtained the quantitative size-dependent PA conversion efficiency of nanospheres/nanorods spanning a comprehensive range of particle sizes, which also provides a deep understanding of the microscopic PA conversion mechanism for nanoprobes. Results show that both the plasmon-mediated absorption and energy conversion from absorbed laser energy to ultrasound are strongly dependent on the PNPs’ size, which comes from their sharply increased surface-to-volume ratios. The gold nanospheres and nanorods possess peak size values for maximizing the PA conversion efficiency. Our work gi...