Temperature-dependent dielectric function in plasmonic nanobubble formation

Plasmonic nanobubbles generated from noble metals are widely employed in biomedical theranostics. The dynamic photothermal properties of plasmonic nanoparticles during nanobubble formation are crucial for the optical detection of nanobubbles. This work establishes a coupled model that incorporates the temperature dependence of the dielectric constants of gold and water. Based on the Lattice Boltzmann Method (LBM), the size of nanobubbles generated by gold nanoparticles under laser irradiation is determined. Simultaneously, the absorption, scattering, and extinction cross-sections of the particles are obtained using the Mie theory for multilayered spheres. The results reveal a gradual decrease in the absorption cross-section of the gold nanoparticles during nanobubble formation. Such variation in optical properties reduces the heat generation of the gold nanoparticles, thereby prolonging the nanobubble nucleation time. Furthermore, this work investigates the role of SiO₂ coating in modulating the optical properties of nanobubbles. The work provides theoretical foundations for achieving flexible control in biomedical diagnostics and therapeutic applications.