Temperature Effect of Plasmonic Circular Dichroism in Dynamic Oligomers of AuNR@Ag Nanorods Driven by Cysteine: The Role of Surface Atom Migration

Achieving huge chiroptical responses is one of the driving forces for the applications of plasmonic metamaterials. Heat-assisted symmetry breaking can amplify plasmonic circular dichroism (PCD) signals in Au nanorod (AuNR) oligomers; however, the PCD responses disappear on Ag-exposed surface (AuNR@Ag core-shell nanorods) at high temperature. Thus, the inherent reason of different chiral response between Au- and Ag-surface nanorods oligomers is explored, and the chiral mechanism is further cognized. The enhanced mobility of surface Ag atoms at elevated temperatures leads to the damage of cysteine chiral networks on Ag surface. It therefore causes great reduction of chiral drive forces, thus restricting the PCD temperature amplification effect to a lower annealing temperature, compared to their Au-exposed counterparts. In addition, the PCD signals of the AuNR@Ag oligomers show a pH-dependent on-off behavior, substantiating the dominant role of chiral network. In addition, density functional theory simulation and relevant experiments reveal facet-dependent chiral response of Ag and Au oligomers. Then, Au-Ag alloy shells can suppress Ag atoms migration; the chiral network and PCD temperature amplification effect can exist in high temperature. The findings reveal the importance of understanding interface ligands, plasmonic nanoparticles, and their interactions in the rational design of chiral assemblies composed of plasmonic nano-units.

Automated summary

The differences in chiral responses between gold and silver surface nanorod oligomers are explored, revealing that enhanced mobility of surface silver atoms at high temperatures leads to the damage of cysteine chiral networks and restricts the PCD temperature amplification effect. Additionally, AuNR@Ag oligomers exhibit a pH-dependent on-off behavior in PCD signals, highlighting the dominant role of chiral networks in the system.