Optically Induced Structural Instability in Gold-Silica Nanostructures: A Case Study

Optical excitation of plasmonic nanoparticles that generate heat or induce photoacoustic signals is gathering immense attention in biomedical applications such as imaging, photothermal therapy, and drug delivery. Generally, these nanoparticles are encompassed by a silica coating that enhances their overall activity and that imparts stability. Intuitively, only an extreme high pressure and temperature can lead to the morphological rupture of these heterogeneous composites; however, herein, we report a study which shows that these drastic structural defects can also be mimicked by simple optical pulse irradiation. This happens because of the heat and pressure waves generated in these hybrids. The structural differential expansion of constituent materials induces a thermal stress in the system which causes a structural instability and ultimately ruptures the coating. To demonstrate this phenomenon, a comprehensive theoretical and experimental study has been conducted on silica-coated gold nanoparticles, with diameter ca. 80 nm. The heat and pressure waves generated because of the irradiation initiate a crack in the silica coating and rupture the structure eventually. The mechanism of this phenomenon has also been elucidated in this paper via theoretical and experimental means.