Surface-roughness-adjustable Au nanorods with strong plasmon absorption and abundant hotspots for improved SERS and photothermal performances

The rational optimization of plasmonic property of metal nanocrystals by manipulating the structure and morphology is crucial for the plasmon-enhanced application and has always been an urgent issue. Herein, Au nanorods with tunable surface roughness are prepared by growing PbS, overgrowing Au, and dissolving PbS nanoparticles on the basis of smooth Au nanorods. The transverse plasmon resonance of Au nanorods is notably improved due to plasmon coupling between Au nanorods and the surface-modified Au nanoparticles, resulting in the strong and full-spectrum light absorption. Numerical simulations demonstrate that the surface-rough Au nanorods have abundant and full-surround hotspots coming from surface particle-particle plasmon coupling between ultrasmall nanogaps, sharp tips, and uneven areas on Au nanorods. With these characters, the surface-roughness-adjustable Au nanorods possess high tunability and enhancement of surface-enhanced Raman scattering (SERS) detection of Rhodamine B and significantly improved photothermal conversion efficiency. Au nanorods with the largest surface roughness have the highest Raman enhancement factor both at 532 and 785 nm laser excitation. Meanwhile, photothermal conversion experiments under near-infrared (808 nm) and simulated sunlight irradiation confirm that the Au nanorods with rough surface have prominent photothermal conversion efficiency and can be regarded as promising candidates for photothermal therapy and solar-driven water evaporation.