Site-selective growth and plasmonic spectral properties of L-shaped Janus Au-Ag gold nanodumbbells for surface-enhanced Raman scattering

Ligand-mediated interface control has been broadly applied as a powerful tool in constructing asymmetric multicomponent nanoparticles (AMNP), and induces the anisotropic growth with fine-tuning morphology, composition, plasmonic property and functionality. As a new kind of AMNP, the synthesis of Janus Au-Ag nanoparticles with tunable negative surface curvature is still a challenge. Here, we demonstrate that the syn-ergistic surface energy effects between gold nanodumbbells (Au NDs) with a negative surface curvature and 4-mercaptobenzoic acid (4-MBA) can direct the site-selective growth of anisotropic silver domains on gold nanodumbbells (Au NDs@Ag NPs). By adjusting the 4-MBA concentration-dependent interfacial energy, the Au NDs@Ag NPs could be continuously tuned from dumbbell-like core-shell structures, to L-shaped Janus, and then rod-like core-shell structures with directional and asymmetric spatial distributions of resizable Ag domains by site-selective growth. Based on the calculation results of discrete dipole approximation (DDA) method, it has been found that the Au NDs@Ag L-shaped Janus NPs with Ag island domains created polarization orientation -dependent plasmonic extinction spectra and hot spots around the negatively curved waist and Ag domains. The L-shaped Janus Au NDs@Ag NPs exhibited significantly plasmonic spectrum properties with four apparent LSPR peaks that cover from visible to near-infrared range and higher surface-enhanced Raman scattering (SERS) activity compared with the original Au NDs. The best SERS enhancement factor of 1.41 x 107 was achieved. This synergistic surface energy effect-based method involving the asymmetric growth of silver coating on gold nanoparticles with negatively curved surface presents a new method to design and fabricate nanometer optical devices based on asymmetric multicomponent nanoparticles.

Automated summary

In this study, Janus Au-Ag nanoparticles with tunable negative surface curvature were successfully synthesized by ligand-mediated interface control. By adjusting the interfacial energy, the nanoparticles could be continuously tuned from dumbbell-like core-shell structures to L-shaped Janus structures, and then rod-like core-shell structures with resizable Ag domains. These nanoparticles exhibited significantly enhanced plasmonic spectrum properties and surface-enhanced Raman scattering activity, providing potential applications in nanometer optical devices.