Chiral imprinting on discrete homochiral Au nanohelicoids for free chiral analyst recognition with high enantioselectivity

The discrimination of enantiomers is a critical challenge in our life. Herein, we propose a chemical and physical chiral imprinting strategy on discrete homochiral Au nanohelicoids (dc-Au NHs) for the effectively enantiomeric sensing. Initially, we developed a time- and energy-efficient seed-mediated overgrowth methods for the generation of dc-Au NHs using Au trioctahedron seeds with high-index-facets in the presence of chiral cysteine molecules. Subsequently, a chemical chiral capturing unity (4-Mercaptopyridine, MPY) was surface-functionalized on dc-Au NHs to discriminate the chiral targets due to their enantiomeric hydrogen interaction. In addition, the localized electromagnetic field nearby the dc-Au NHs are distributed asymmetrically for physical chiral imprinting, also contributing to the difference enhancement of surface-enhanced Raman scattering (SERS) signal toward L- and D-analyst, respectively. Upon theses chemical and physical chiral imprinting strategy, dc-Au NHs possess dual chiral recognition centers, enabling selective identification and discrimination of chiral analysts through the chirality-dependent SERS spectra. For instance, the SERS intensity of L-analyst on the L-Au NHs/MPY is stronger than that of L-analyst on D-Au NHs/MPY, as well as is stronger than that of D-analyst on the L-Au NHs/MPY. This approach enables reliable discrimination of enantiomers at concentrations as low as 10⁻⁷ M (for 1-methoxy-2-propanol and 2-butanol) and 10⁻⁶ M (for tryptophan), with an inter-batch relative standard deviation (RSD) of less than 7 %. Principal component analysis (PCA) verifies that the spectral clusters of L- and D-enantiomers are completely separated at concentrations of 10⁻⁶ M and above, with a confidence level of 85 %.