Chiral nanoparticle-induced amplification in optical activity of molecules with chiral centers

Sensitive differentiation of an enantiomer from its mirror image (ie, enantiodifferentiation), a perennial challenge for pharmaceutical production and disease diagnosis, is technically limited by the weak optical activity (OA) of enantiomers, mainly due to their dimensional mismatch with light wavelengths in the ultraviolet (UV)-visible region. Here we use silver chiral nanoparticles (Ag CNPs) with nominally sub-5 nm helical pitch (P) to amplify the OA of (2′R, 3′R, 4′S)-riboflavin-5′-phosphate sodium salts (RP), which have been found to indirectly affect metabolic processes, through the formation of an RP thin film (TF) covering a close-packed array of Ag CNPs. The OA of the RP in the deep-UV region can be amplified up to 80-fold, ascribed to the aggregation of RP in the TFs and the interactions between RP and the atomically chiral lattices at the CNPs' surfaces. The former contribution, not associated with the chiral Ag topographies, plays a dominant role by thickening the RP TFs, so that the observed amplification has no enantioselective dependence on the chirality of the Ag CNPs. This study extends progress in the sensitive detection of bio-enantiomers, which is highly desired for advanced bio-detection in disease diagnosis and production of single-enantiomer pharmaceuticals. (Figure presented.)