Chirality transfer from penicillamine to gold nanoparticles enables enantioselective electrochemical sensing of cysteine.

Abstract

Chiral nanoparticles offer new opportunities for designing functional materials with tunable optical and electrochemical properties. While cysteine and cysteine-containing peptides are commonly used as chiral agents in the synthesis of such nanoparticles, the use of alternative ligands remains limited. In this study, we introduce penicillamine as a new chiral agent in the seed-mediated growth of gold nanoparticles (AuNPs). The presence of L- or D-penicillamine induces chirality during nanoparticle growth, and its extent is examined at different growth stages using SEM. Structural evidence for enantioselective growth is also provided with high-resolution STEM. Circular dichroism spectroscopy of particle suspensions and dark-field scattering measurements at the single-particle level further suggest that the chirality is encoded in the nanoparticle morphology rather than being limited to surface-bound ligands. Importantly, dark-field scattering indicates that the AuNPs' chiral morphology is also preserved after drying on an Au electrode. To evaluate whether this morphological chirality translates into functional enantioselectivity, electrochemical measurements are performed using L- and D-cysteine as analytes on electrodes modified with chiral AuNPs. Cyclic voltammetry and electrochemical impedance spectroscopy show that electrodes modified with L-penicillamine-induced chiral AuNPs exhibit higher current densities (ca. 36%) and lower charge-transfer resistance toward L-cysteine oxidation. Similarly, D-penicillamine-induced chiral AuNPs show higher current densities for D-cysteine oxidation. This enantioselective interaction between enantio-matched pairs demonstrates that the encoded chirality influences molecular recognition processes at the electrode interface. Overall, this study establishes penicillamine-induced chiral AuNPs as versatile, label-free platforms for enantioselective electrochemical sensing.