Controlled Synthesis of Bimetallic Gold-Silver Nanostars: Atomic Insights and Predictive Formation Model.

The nucleation and growth of bimetallic gold-silver nanostars (GNSs) are investigated to elucidate their atomic-scale formation mechanism. Motivated by the increasing demand for nanomaterials with enhanced optical and catalytic properties, particularly for applications in biosensing, bioimaging, and photothermal therapy, this work focuses on understanding the factors governing GNSs formation. GNSs are synthesized by reducing HAuCl₄ with ascorbic acid in the presence of AgNO₃, exploring the influence of temperature, delay time in AgNO₃ introduction, and AgNO concentration. High-resolution electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution X-ray photoelectron spectroscopy, and synchrotron-based powder X-ray diffraction are used to characterize their morphology, size, composition, and stability. These findings reveal that AgNO₃ promotes anisotropic growth through the formation of metallic Ag and AgCl on GNSs surfaces, leading to thorn-like structures. A detailed analysis of kinetics, particle concentration, and nucleation barriers enables the development of a theoretical model to predict optimal synthesis conditions. This work provides new insights into controlling GNSs morphology and properties, which are critical for optimizing their performance in catalysis, sensing, and biomedical applications. The novelty lies in the discovery of the role of AgCl in directing GNSs growth and the formulation of a predictive model for synthesis optimization.