Photothermal properties of gold nanoparticles under exposure to high optical energies

Photothermal (PT) efficacy and damage thresholds of gold nanoparticles (NP)-spheres, rods and silica-gold shells-were experimentally studied during their excitation with nanosecond laser pulses at the fluence levels at and above the NP damage threshold. The maxima of PT efficacy of gold NPs with near-infrared (NIR) plasmon resonances (gold rods and shells) and the minima of their damage thresholds were found to be shifted from their plasmon resonance NIR wavelengths into non-resonant visible wavelengths. This suppression of PT efficacy of NIR plasmon resonances (bleaching) was found to be up to 18 times for the rods and up to 22 times for the shells. During laser-induced deterioration the NPs maintained their PT properties at least within 40-150 ns after exposure to laser pulses. PT properties of the gold NPs can be enhanced with the pulse train mode within the above time. The PT bubbles generated around superheated NPs were used as their optical markers and allowed us to quantify PT efficacy of plasmon resonance through the bubble parameters under the conditions when other methods of NP detection are not applicable.