Comparative analysis of synthesis techniques for citrate-capped gold nanoparticles: insights into optimized wet-chemical approaches for controlled morphology and stability

Gold nanoparticles (AuNPs) hold immense potential in biomedical and technological applications due to their unique optical and physicochemical properties. While several studies have compared selected citrate-based AuNP synthesis methods, a comprehensive, side-by-side evaluation of multiple widely used protocols-tested both under their literature-reported conditions and under fully standardized parameters-remains limited. This study presents a systematic comparison of six wet-chemical synthesis techniques-including the classical Turkevich-Frens, reverse Turkevich-Frens, Slot-Geuze-based approaches, and both standard and reverse Natan reductions. By controlling key parameters-such as citrate-to-gold ratio and reagent addition sequence-we investigated how these factors influence particle size, shape, monodispersity, and colloidal stability. Among the methods tested, the reverse Turkevich-Frens technique reliably yielded the most monodisperse AuNPs (7-14 nm), while the rNR and rSG methods enabled the formation of ultrasmall AuNPs (2-6 nm) when paired with elevated citrate concentrations. These findings highlight the synergistic effects of citrate availability and reagent addition sequence in tuning AuNP properties. This work provides a robust comparative framework for selecting optimized synthesis methods of citrate-capped AuNPs and lays the foundation for surface functionalization and stabilization using biocompatible polymers in future studies.