The Rise of Structurally Anisotropic Plasmonic Janus Gold Nanostars

Nanostructures intrinsically possessing two different structural or functional features, often called Janus nanoparticles, are emerging as a potential material for sensing, catalysis, and biomedical applications. Herein, we report the synthesis of plasmonic gold Janus nanostars (NSs) possessing a smooth concave pentagonal morphology with sharp tips and edges on one side and, contrastingly, a crumbled morphology on the other. The methodology reported herein for its synthesis using a single-step growth reaction is unique to any other Janus nanoparticle preparation involving either template-assisted growth or a masking technique. Interestingly, a coexistence of lower and higher index facets has been found in these Janus NSs. The general paradigm for synthesizing Au Janus NSs was investigated by understanding the mechanism of its kinetic control with the combinatorial effect of all the reagents responsible for its structure. Optical property of the Janus NSs has been realized by corelating their extinction spectrum with the simulated data. The size-dependent surface-enhanced Raman scattering (SERS) activity of these Janus NSs has been studied with 1,4-BDT as the model analyte. Finite-difference time-domain (FDTD) simulations for different sized particles revealed the distribution of electromagnetic hot-spots over the particles resulting in the enhancement of the SERS signal in a size dependent manner.