Comparative analysis of synthesis techniques for citrate-capped gold nanoparticles: insights into optimized...

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.