Dependence of the Nonlinear Photoacoustic Response of Gold Nanoparticles on the Heat-Transfer Process

Photoacoustic (PA) imaging using the nonlinear PA response of gold nanoparticles (GNPs) can effectively attenuate the interference from background noise caused by biomolecules (e.g., hemoglobin), thus offering a highly potential noninvasive biomedical imaging method. However, the mechanism of the nonlinear PA response of GNPs based on the thermal expansion mechanism, especially the effect of heat-transfer ability, still lacks quantitative investigation. Therefore, this work investigated the effect of heat-transfer ability on the nonlinear PA response of GNPs using the critical energy and fluence concept, taking into account the Au@SiO₂core-shell nanoparticles (weakened heat transfer) and gold nanochains (enhanced heat transfer). The results showed that the stronger the heat transferability, the smaller the critical energy, indicating that the nonlinear PA response of different nanoparticles cannot be contrasted directly through the critical energy. Moreover, the critical fluence can directly contrast the proportion of nonlinear components in the PA response of different GNPs as governed by the combined effect of heat transferability and photothermal conversion ability.