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Site-selected growth of L-shaped Janus Au-Ag gold nanodumbbells with appropriate concentration of 4-MBA embedded on the Au NDs and polarization orientation-dependent plasmonic extinction spectra and local electric field enhancement. [Display omitted] • The synergistic 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. • 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. • The Au NDs@Ag L-shaped Janus NPs with Ag island domains locaed on one tip-side of Au NDs created polarization orientation-dependent plasmonic extinction spectra. • The Au NDs@Ag L-shaped Janus NPs with Ag island domains created hot spots around the negatively curved waist and Ag domains. • The best SERS enhancement factor of 1.41 × 107 for 4-MBA was achieved. 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 synergistic 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 × 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. [ABSTRACT FROM AUTHOR]

A metal-organic semiconductor-molecule model was developed with Ag nanoparticles (NPs), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and 4-mercaptobenzoic acid (4-MBA) via the layer-by-layer self-assembly method. In the SERS spectrum of the Ag/PEDOT:PSS/4-MBA system, structural changes in the PEDOT chain were discovered, which provides a deeper understanding of the charge transfer (CT) mechanism in SERS and helps in the development of a method to construct metal-organic semiconductor SERS substrates. A quantitative calculation of the degree of charge transfer (ρ CT(κ)) determines the CT contribution of PEDOT:PSS to the SERS intensity of the Ag/PEDOT:PSS/4-MBA system. On this basis, we propose the formation of a resonance complex between Ag NPs and PEDOT:PSS to explore the CT mechanism, which is beneficial for studying interface CT and for understanding the CT mechanism in SERS. The introduction of organic semiconductors in this study not only broadens the research scope of SERS substrates but also contributes to the exploration of SERS mechanisms. A metal/organic semiconductor/molecule model was fabricated with Ag NPs, PEDOT:PSS and 4-MBA via the layer-by-layer self-assembly method. The structural changes of the PEDOT chain in the SERS spectrum of the Ag/PEDOT:PSS/4-MBA system provide a deeper understanding of the CT mechanism in SERS and helps in the development of a method to construct metal-organic semiconductor SERS substrates. The introduction of organic semiconductors in this study not only broadens the research scope of SERS substrates but also contributes to the exploration of SERS mechanisms. Unlabelled Image • A metal/organic semiconductor/molecule model was fabricated via the layer-by-layer self-assembly method. • SERS spectrum of the Ag/PEDOT:PSS/4-MBA system provided a deeper understanding of the CT mechanism. • The introduction of organic semiconductors in this study not only broadens the research scope of SERS substrates. [ABSTRACT FROM AUTHOR]