Synergistic Effect\nin Hybrid Plasmonic Conjugates\nfor Photothermal Applications

Photothermal conversion efficiency (η) plays a\ncrucial role\nin selecting suitable gold nanoparticles for photothermal therapeutic\napplications. The photothermal efficiency depends on the material\nused for the nanoparticles as well as their various parameters, such\nas size and shape. By maximizing the light-to-heat conversion efficiency\n(η), one can reduce the concentration of nanoparticle drugs\nfor photothermal cancer treatment and apply lower laser power to irradiate\nthe tumor. In our study, we explored a new hybrid plasmonic conjugate\nfor theranostic (therapy + diagnostic) applications. We conjugated\nPEG-functionalized 20 nm gold nanospheres with cyanine IR dyes via\na PEG linker. The resulting conjugates exhibited significantly enhanced\nphotothermal properties compared with bare nanoparticles. We experimentally\nshowed that a proposed new hybrid plasmonic conjugate can achieve\nalmost four times larger conversion efficiency (47.7%) than 20 nm\ngold nanospheres (12%). The enhanced photothermal properties of these\ngold conjugates can provide the required temperature for the photothermal\ntreatment of cancer cells with lower concentrations of gold nanoparticles\ninjected in the body as well as with lower applied incident laser\npower density. Moreover, the improved photothermal properties of the\nconjugates can be explained by a synergistic effect that has not been\nobserved in the past. This effect results from the coupling between\nthe metal nanosphere and the organic dye.