Plasmonic nanorod and dimer chiral molecule sensing from cysteine monolayer to bi-layers and multilayered shells

Chirality plays a crucial role in biomedical and pharmaceutical sciences, where enantiomers can have vastly different effects. Circular dichroism (CD) spectroscopy is commonly used to detect chiral molecules, but its weak signals limit sensitivity. Plasmonic nanostructures, particularly gold nanorods (AuNRs), enhance these signals through plasmon resonances. This study investigates the enhancement of CD signals using single AuNRs, dimers, and chains for detecting cysteine (Cys) layers. By controlling pH and other buffer conditions, we precisely grow Cys layers from monolayer, bilayer to multilayer shells. Our results show that AuNR dimers significantly boost CD signals, with enhancements similar to those observed for much larger AuNR chains. Single AuNRs, meanwhile, are effective for detecting Cys layers down to a monolayer. Validated by simulations, this work provides insights into plasmonic nanoparticle assembly and chiral sensing, paving the way for advanced plasmon-based chiral molecule detection technologies.