Synthesis of large and stable colloidal gold nanoparticles (AuNPs) by seeding-growth method

Colloidal gold nanoparticles (AuNPs) have been used in various applications, mainly in biomedical sciences for therapeutic and diagnostic purposes. These AuNPs can be conjugated with biomolecules and chemical substances due to their unique physical and chemical properties. The AuNPs are usually synthesized by a chemical method; namely Turkevich method or reduction method. However, this synthesis method is not suitable for synthesis of large AuNPs due to aggregation and instability of AuNPs suspension. Thus, the aim for this study is to evaluate the seeding-growth method for synthesis of large AuNPs. The seed of 15 nm AuNPs was initially produced using the citrate reduction method, then further grown to 40, 60, and 80 nm AuNPs using the mild reduction agent, hydroxylamine. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and UV–vis- NIR spectroscopy were used to characterize the as-synthesized AuNPs. The narrow particle size distribution and low polydispersity index value (PDI) for all AuNPs revealed the presence of monodisperse AuNPs. The as-synthesized AuNPs are nearly spherical as shown by the degree of ellipticity (G) close to 1.00. This result showed no agglomeration of AuNPs in the colloidal suspension. The UV–vis-NIR spectra showed peaks shifted to a longer wavelength that confirmed increasing size of AuNPs. The synthesis of different sizes of AuNPs using the seeding-growth method was successful and stable with no aggregation and agglomeration.