In this paper, AuNRs colloids with SPR L located at ~810 nm and ~1100 nm were synthesized using an improved seed method. Based on the NIR lasers available, photothermal conversion of AuNRs were systematically studied compared with that of water. Under low power irradiation, the highest temperature is obtained when the SPR L wavelength of AuNRs is equal to the laser wavelength, and temperature of colloid increases from ~20˚C to ~65˚C. With increasing laser power (such as 6 W), the AuNRs colloid boils within a few minutes, and nanorods undergo a shape deformation from rod to spherical particle and even fusion, and the SPR L disappears. For further investigation, the obtained AuNRs were coated with SiO 2 shell to form a core-shell nanostructure (Au@SiO 2). The surface coating can be used not only in keeping the stability of AuNRs for further treatment, but also in increasing plasmonic property and biocompatibility. This work will be useful for designing plasmonic photothermal properties and further applications in nanomedicine.
Gold and silver nanostructures (such as Au nanorods and Ag nanoplates) exhibit strong and tunable surface plasmon resonance in the near-infrared region (NIR). Under a certain NIR laser irradiation, noble metal nanostructrues achieve a high photo-thermal effect, which would be useful in the therapy. In this work, Au nanorods with longitude surface plasmon resonance (SPRL) shifting in the region of 650 ~1100 nm were synthesized by a seed method. Ag nanoplates and nanocubes with SPR located in the region of 650~850 nm were produced by a hydrothermal method. Through adjusting laser power and irradiating time, the photo-thermal conversions of these nanostructures were studied under NIR laser irradiation. Under low power laser (808 nm, <1W) irradiation, the shape of the Au nanorods are stable and the temperature of colloid increase from room temperature to ~57°C. However, Au nanorods undergo deformation from rod to spherical particle under irradiation of high power (808 nm laser; 6W; 1064nm laser, 7W), resulting in the disappearance of SPRL. Morphology evolutions and photo-thermal conversion of Ag nanostructures were also studied. Ag nanostructures have a lower photo-thermal conversion compared with that of Au nanorods colloid. Snipping and dendrite can be observed for Ag nanoplates after irradiating, while Ag nanocubes have no obvious shape change.
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