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Significantly amplified photoacoustic effect for silica-coated gold nanoparticles by interface heat transfer mechanisms

Plasmonic gold nanoparticles (AuNPs) are effective photoacoustic (PA) signal agents and have found important biomedical applications. The silica coating on the surface of AuNPs showed enhanced PA efficiency, however, the PA amplification mechanism remains unclear. Here, we systematically studied the silica coating effect on PA generation of AuNPs under different laser pulse durations. We experimentally demonstrated up to 4-fold PA amplification under thin silica coating (<5 nm) and a picosecond laser excitation. The theoretical model further suggests that the PA amplification originates from two interface heat transfer mechanisms including 1) the enhanced interface thermal conductance on the silica-water interface and 2) the electron-phonon energy transfer channel on the gold/silica interface. This study discovers a regime of large PA amplification and provides a new rationale for plasmonic nanoparticle design to achieve better PA efficiency.