Tunable and Linker Free Nanogaps in Core–Shell Plasmonic Nanorods for Selective and Quantitative Detection of Circulating Tumor Cells by SERS

2017 
Controlling the size, number, and shape of nanogaps in plasmonic nanostructures is of significant importance for the development of novel quantum plasmonic devices and quantitative sensing techniques such as surface-enhanced Raman scattering (SERS). Here, we introduce a new synthetic method based on coordination interactions and galvanic replacement to prepare core–shell plasmonic nanorods with tunable enclosed nanogaps. Decorating Au nanorods with Raman reporters that strongly coordinate Ag+ ions (e.g., 4-mercaptopyridine) afforded uniform nucleation sites to form a sacrificial Ag shell. Galvanic replacement of the Ag shell by HAuCl4 resulted in Au–AgAu core–shell structure with a uniform intra-nanoparticle gap. The size (length and width) and morphology of the core–shell plasmonic nanorods as well as the nanogap size depend on the concentration of the coordination complexes formed between Ag+ ions and 4-mercaptopyridine. Moreover, encapsulating Raman reporters within the nanogaps afforded an internal st...
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