Structural origin of hierarchical chirality in Pt@Au nanostructures with step-rich surfaces.

Hierarchical chirality, arising from the coupling of chiral surfaces, units, assemblies, and overall architectures, represents a structural paradigm with profound implications for enantioselective catalysis, molecular recognition, and chiral photonics. Unraveling and regulating its formation across multiple length scales is crucial for understanding structure-property relationships and guiding the design of chiral nanomaterials. Here, we present a strategy for constructing step-rich Pt@Au nanostructures with multilevel chirality. Using octahedral Pt nanoframes as templates and cysteine as a chiral inducer, rotated and oriented Au triangular pyramids with high-Miller-index chiral facets are generated, leading to the formation of fishbone-like, pinwheel-like, and tilted-step surface features that collectively constitute a hierarchical chiral nanostructure. Mechanistic studies identify cysteine and Pt nanoframes as indispensable for directing step formation and hierarchical growth, thereby defining the overall morphology and chiroplasmonic responses. Leveraging the abundant chiral surface area and the strong chiral electromagnetic nearfields generated under plasmonic excitation, we fabricate monolayer-modified electrodes based on the Pt@Au nanostructures that enabled plasmon-enhanced enantioselective electrochemical recognition of penicillamine enantiomers and determination of their enantiomeric purity. This strategy clarifies the origin of multilevel chirality in step-rich architectures and establishes a structural engineering approach for designing chiral nanomaterials with enhanced near-field properties for enantioselective recognition.