Intrinsic Morphological Chirality Governs Spin Selectivity in Gold Nanoparticles

Chirality-induced spin selectivity (CISS) enables chiral materials to generate spin-polarized currents, yet the structural origin of spin selectivity in intrinsically chiral inorganic nanostructures remains unclear. A central mechanistic challenge is to determine how the molecular chirality of surface ligands and the intrinsic three-dimensional chirality of the inorganic core each contribute to the sign and magnitude of spin polarization. Here we address this challenge using cysteine-directed seed-mediated growth of chiral Au nanoparticles (NPs). Remarkably, the same cysteine enantiomer directs the formation of two distinct intrinsically chiral morphologies, trisoctahedral and petal-cube-like nanoparticles, by a simple change in cysteine concentration. This morphology transition reverses the effective plasmonic handedness, as reflected by the sign of the circular dichroism response, and simultaneously reverses the sign of spin polarization. Magnetic conductive-probe atomic force microscopy shows that l-cysteine-derived trisoctahedral and petal-cube-like particles exhibit opposite spin selectivity, although they bear the same chiral ligand. In contrast, achiral Au NPs modified with l-cysteine show only weak spin polarization, approximately 1 order of magnitude smaller than that of intrinsically chiral particles. By combining ensemble circular dichroism, single-particle circular differential scattering, electromagnetic simulations, and spin-dependent transport measurements, we show that spin polarization follows the local morphological handedness of individual particles more closely than the ensemble-averaged chiroptical response. These results establish intrinsically chiral plasmonic NPs as a robust platform for CISS and demonstrate that the three-dimensional handedness of the metallic core, rather than ligand handedness alone, can dictate spin-selective charge transport.