Wavelength‐Dependent Differential Amplification of Raman Scattering by Chiral Gold Nanorods for Multiplexed Encoding

Abstract The application of wavelength‐dependent differential circularly polarized light‐induced surface‐enhanced Raman scattering (CPL‐SERS) is reported for codification and encryption, using colloidal chiral plasmonic nanoparticles. This study demonstrates that intrinsically chiral Au nanorods (c‐AuNRs) encoded with achiral Raman reporters display unique optical activity. Right‐handed and left‐handed c‐AuNRs show positive or negative CPL‐SERS depending on the illumination wavelength (633 and 785 nm in this case), in correlation with their respective circular dichroism (CD) spectra. This effect enables c‐AuNR enantiomeric differentiation through evaluation of the CPL‐SERS response for each excitation wavelength. To showcase the potential of this approach, four encoded c‐AuNR dispersions were prepared, each with distinct handedness and Raman reporter combinations, and used to encode a four‐letter message on paper, which can be selectively decoded through CPL‐SERS, even when using only two Raman reporters. By switching between excitation wavelengths of 633 and 785 nm, inverted CPL‐SERS signals were recorded, therefore enhancing the versatility of the coding. The integration of chiral plasmonic nanoparticles and CPL‐SERS represents a highly tunable platform for advanced sensing, encryption, and codification, thereby expanding the functionality of plasmonic nanostructures in optical technologies.