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Chiral plasmonic nanoparticles (NPs) can amplify chiral optical signals, but actual enantioselective sensing often stalls because the huge structural asymmetry (g value) alone does not ensure that the analyte reaches the strongest chiral near-field. Here, we demonstrate that the decisive design variable is not merely dielectric tuning, but rather the realization of dielectric tuning within the nano-gap of a single helical gold nanoparticle in a conformal, accessible manner. The ultrathin (approximately 1.5 nanometers) polystyrene sulfone (PS-SH) layer regulates the local refractive index contrast (Δn can reach ∼0.45), while maintaining the chiral nano-gap open for molecular permeation. This accessible conformal nano-gap concentrates the optical chirality and electric dipole (ED) - magnetic dipole (MD) coupling in the analyte-related volume, thereby amplifying the molecular response dependent on chirality, rather than merely transferring resonance through scalar refractive index changes. Transmission electron microscopy - electron energy loss spectroscopy (TEM-EELS) and three-dimensional finite element method (FEM) show selective enhancement of the gap local mode and optical chirality, while fixed total concentration L/D ratio measurements, hand and non-hand regulation, and even/odd decomposition of resonance shift distinguish scalar dielectric contributions from κ-dependent chiral interactions. Therefore, the surface-modified helix III (M-H3) in colloidal suspensions has a larger enantioenantiomer-specific spectral shift, with an induction sensitivity up to 66% higher than the bare H3. These results establish chiral nano-gap engineering as the dominant design principle for chiral nanophotonic enantioselective sensing, rather than merely g value enhancement. This research was published in ACS Nano under the title "Specifying the Origin of Chiral Sensitivity through Conformal Nanogap Engineering in a Single Helicoid Gold Nanoparticle".
References:
DOI: 10.1021/acsnano.6c01492
