Tuning the Morphology and Chiroptical Properties of Discrete Gold Nanorods with Amino Acids

The synthesis of discrete nanostructures with a strong, persistent, stable plasmonic circular dichroism (PCD) signal is challenging. We report a seed‐mediated growth approach to obtain discrete Au nanorods with high and stable chiroptical responses (c‐Au NRs) in the visible to near‐IR region. The morphology of the c‐Au NRs was governed by the concentration of l‐ or d‐cysteine used. The amino acids encapsulated within the discrete gold nanostructure enhance their PCD signal, attributed to coupling of dipoles of chiral molecules with the near‐field induced optical activity at the hot spots inside the c‐Au NRs. The stability of the PCD signal and biocompatibility of c‐Au NRs was improved by coating with silica or protein corona. Discrete c‐Au NR@SiO2 with Janus or core–shell configurations retained their PCD signal even in organic solvents. A side‐by‐side assembly of c‐Au NRs induced by l‐glutathione led to further PCD signal enhancement, with anisotropic g factors as high as 0.048. Discrete gold nanorods (Au NRs) with strong chiroptical responses in the visible and near infrared region were synthesized by a seed‐mediated approach in the presence of l‐ or d‐cysteine. The chiral Au NRs can be further stabilized by a silica coating (lower pictures). Assembly of the chiral Au NRs (right pictures) with glutathione further improved the g factor.