Electronic and Charge-Transfer Properties of Bimetallic Nanocluster–Graphene Hybrids with Stone–Wales Defects for Biosensing Applications

Abstract Graphene-based materials functionalized with bimetallic nanostructures have emerged as promising platforms for electrochemical sensing. However, the mechanisms governing complex–surface interactions are often oversimplified and commonly attributed to net charge transfer, despite the complex electronic redistribution occurring at the interface. In particular, the role of interfacial polarization and its relationship with the electronic structure of bimetallic nanoclusters remain poorly understood. In this work, density functional theory (DFT) is employed to investigate Stone–Wales-defective graphene functionalized with NiFe and AuNi bimetallic nanoclusters (NCs) as model platforms for tryptophan detection. The influence of nanocluster composition and atomic configuration on adsorption behavior and electronic response is systematically analyzed. Tryptophan adsorption induces a pronounced reorientation of the interfacial dipole moment, evidencing substantial spatial charge redistribution despite negligible net charge transfer. This response is accompanied by d–p orbital hybridization and configuration-dependent modulation of the Ni d-states near the Fermi level. In particular, the NiFe configuration exhibits an upward displacement of the Ni d-band feature by approximately 1.0 eV toward the Fermi level upon adsorption, highlighting its distinct electronic response compared with the FeNi configuration. The substantial reduction of the effective band gap further demonstrates the adsorption-induced modulation of the electronic structure. Comparison with pristine graphene further shows that the Stone–Wales defect provides a stable anchoring environment for the nanoclusters while influencing the interfacial electronic polarization. Overall, these findings demonstrate that the sensing-related response is governed primarily by interfacial polarization, localized charge redistribution, and electronic coupling rather than substantial net charge transfer, highlighting the potential of defect-engineered graphene-supported bimetallic nanoclusters for electrochemical detection of aromatic biomolecules.