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Gold nanostars are one of the new types of nanoparticles with advantages such as plasmon resonance tunability and low toxicity. Therefore, gold nanostars are promising candidates for various biomedical applications including bioimaging, cell optoporation and plasmonic photothermal therapy (PTT) in NIR I, II, and III optical transparency windows of biotissues. However, the stability and possible transformation of gold nanostars under laser irradiation still remains unexplored. In this work, we studied the photomodification of gold nanostars under the 1064-nm nanosecond pulsed laser irradiation by the transmission electron microscopy and spectrophotometry. The photostability of nanostars depends on their morphology and the plasmonic properties. Specifically, for large nanostars with a plasmon resonance at 950 nm remarkable changes occur at a threshold pulse energy of 5 μJ. At this threshold, a significant part of nanostars spikes melts and most of the nanostars start to transform into gold spheres. For higher pulse energies of about 50 μJ, all stars transform into spheres. For smaller gold stars with a plasmon resonance at 680 nm, the changes are less pronounced. Up to pulse energy of 50 μJ, they retain the shape of stars and have spikes on their surface. Moreover, the complete transformation of these stars into spheres does not occur up to pulse energy of about 150 μJ. The obtained results can be important for optimization of PTT treatment with gold nanostars and nanosecond laser irradiation.
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