Influence of Poly(vinylpyrrolidone) Synthesis Conditions on the Formation of Gold Nanostars

The chemical synthesis of nanomaterials has been a driving force in the advancement of nanoscience and nanotechnology. However, minor changes in the composition of the reactants and the presence of impurities can significantly alter the outcome of synthetic procedures that have been developed for a wide range of nanomaterials. The synthesis of gold nanostars (AuNSt) using poly(vinylpyrrolidone) (PVP) in N,N-dimethylformamide (DMF) is no exception to this issue, as several studies have reported PVP batch dependency of the synthesis. In this context, we set to analyze commercial PVP using 1H NMR and show that only those containing certain impurities are suitable for the synthesis of AuNSt. Following this finding, we synthesized our own PVP with the aim of replicating the synthesis conditions of commercial PVP, including its impurities. The results confirm that PVP synthesized using hydrogen peroxide as a radical initiator and ammonium hydroxide or calcium carbonate as the base, are suitable for the formation of AuNSt. Additionally, the base used in PVP synthesis was found to influence the reaction kinetics and, in turn, the shape of the resulting AuNSt. Control reactions with purified PVP show drastically decreased nanoparticle anisotropy, suggesting that the star shape is strongly dependent on the impurity profile, resulting from the selected PVP synthetic pathway. We present a solution toward customizing AuNSt shape via PVP synthesis and avoiding dependence on commercial PVP.