CW laser-induced photothermal conversion and shape transformation of gold nanodogbones in hydrated chitosan films
We investigate the photothermal conversion and transformation of gold nanoparticles with an initial dogbone shape after dispersion in hydrated chitosan films, which is a representative model of biological tissue, and excitation by a CW diode laser for 1 min. Gold nanodogbones are observed to undergo a distinct modification above a sharp threshold of ~11 W cm−2 and 110 °C. Surprisingly, the very same modification is achieved up to at least 36 W cm−2 and 250 °C. We use an analytical model derived from Gans theory to associate the change in color of the films with the change in shape statistics of these gold nanoparticles. This model proves both convenient and dependable. We interpret the photothermal transformation as a rearrangement of particles with a dogbone shape and an aspect ratio of 4.1 into rods with an aspect ratio of 2.5, where material from the end lobes of the dogbones may relocate to the waists of the rods. In turn, additional transitions to stable gold nanospheres may exhibit fairly slower kinetics.
KeywordsGold nanorods Chitosan Gans theory Photothermal conversion Shape transformation Modeling and simulation
We are grateful to Dr. Cosimo Trono for the refractometry measurements and Prof. Stefano Cavalieri for useful discussions. This work was supported by the NANO-TREAT and NANO-CHROM projects of the Health Board of Tuscany and the FP7 NoE Photonics 4 Life.
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