Ligand-programmed interfacial nucleation enables uniform ferrite-gold core-shell nanostructures

Precise control of heterogeneous nucleation at inorganic interfaces is essential for constructing uniform multicomponent nanostructures but remains challenging because nucleation is highly sensitive to local surface chemistry. Here, we demonstrate a ligand-programmed interfacial nucleation strategy for controlling ferrite-gold growth through regulation of surface citrate coverage. Using gold magnetic nanoparticles (GMNPs) composed of Fe₃O₄ and Au as a model system, we show that surface-bound citrate modulates gold precursor adsorption and the heterogeneous nucleation landscape, enabling interlayer-free aqueous synthesis of highly uniform nanostructures with tunable sizes. Notably, citrate transforms iterative gold deposition from a heterogeneity-amplifying process into a self-homogenizing process by suppressing secondary nucleation and excessive growth of pre-existing particles while promoting utilization of residual ferrite nanoparticles. Surface citrate quantification and density functional theory calculations reveal that increasing citrate coverage strengthens interfacial Au-O electronic coupling, charge redistribution, and gold precursor adsorption, providing a molecular basis for the observed growth behavior. The strategy is further validated in Co_0.5Fe_2.5O₄@Au and Mn_0.5Fe_2.5O₄@Au systems. The resulting GMNPs enable a 10-fold sensitivity enhancement over conventional AuNPs-based lateral flow immunoassays following magnetic enrichment. These findings establish surface ligand coverage as a molecular parameter for programming heterogeneous growth at ferrite-gold interfaces.