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Poly(L-DOPA)-mediated bimetallic core−shell nanostructures of gold and silver and their employment in SERS, catalytic activity, and cell viability

Core–shell gold nanorod (AuNR)@silver (Ag) nanostructures with their unique properties have gained enormous interest and are widely utilized in various applications including sensor systems, catalytic reactions, diagnosis, and therapy. Despite the recent progress, simple, effective, low-cost, and easy-to-tune strategies are heavily required to fabricate these nanoparticles (NP) systems. For this, we propose the employment of the polymer of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) as a ligand molecule. A conformal thin layer of polymer of L-DOPA (PLDOPA) with its various functional groups enabled the reduction of silver ions onto the AuNRs and stabilization of the resultant NPs without using any surfactant, reducing agent, and seed material. The shape and growth model of the AuNR@Ag nanostructures was manipulated by simply tuning the amount of silver ions. This procedure created different NP morphologies ranging from concentric to acentric/island shape core–shell nanostructures. Also, even at the highest Ag deposition, the PLDOPA layer is still conformally present onto the Au@Ag core–shell NRs. The unique properties of NP systems provided remarkable characteristics in surface-enhanced Raman spectroscopy, catalytic activity, and cell viability tests.