Direct observation of one-dimensional plasmon coupling in metallic nanofibers prepared by evaporation-induced self-assembly with DNA.

Here we report a simple method for the preparation of highly aligned metallic nanofibers with anisotropic aggregates of silver nanoparticles (AgNPs) as well as a direct observation of localized plasmon field and its coupling in the prepared metallic nanofibers. Metallic nanofibers of several tens of nanometers wide and millimeters long were prepared. The preparation method, which is based on the process of evaporation-induced self-assembly with DNA and drying front movement, eliminates the need for lithography and an external field, and it is fast, cheap and easy. Dark-field scattering spectroscopy was used to study the strong plasmon coupling of AgNPs in the metallic nanofibers. We observed strong near-field coupling between neighboring nanoparticles, which results in red-shifted multipolar plasmon modes that are highly polarized along the fiber axis. The polarization dependence of plasmon coupling in the metallic nanofibers observed in this study was satisfactorily explained by the morphology of the metallic nanofibers, which was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Furthermore, Raman spectra imaging of the metallic nanofibers revealed the existence of intense hot spots localized along their axes, which played a significant role in the intensity of surface enhanced Raman scattering (SERS) signals from DNA bases in the metallic nanofiber. Our results demonstrate the use of evaporation-induced self-assembly with DNA as a straightforward method to produce one-dimensional coupling of localized plasmons with a longer scale.