Synthesis and Optical Properties of Surface Stabilized Gold Nanoparticles with Poly(Vinyl Pyrrolidone) Polymer Molecules of a Nanofluid

Surface stabilized gold nanoparticles (Au-NPs) and self-assembly of them offer tailored functional properties useful for biological reactions, biodiagnostic assays, and other applications. This paper describes a simple synthesis of Au-NPs from a sonication assisted caloric dissociation reaction of a gold salt HAuCl₄·3H₂O in presence of reactive polymer molecules such as poly(vinyl pyrrolidone) (PVP) in form of a nanofluid in water. Size of the Au-NPs, ranging from 10 to 110 nm, is easily controlled by varying the content of PVP molecules (0.01–10 g/dL) relative to an aqueous salt precursor. Reactions carried out in a batch of 5.1 mL sample demonstrate that the PVP molecules not only tailor the basic size and shape of resulting Au-NPs but also two-dimensional assembles of them that develop in part of the reaction. Light-absorption (460–960 nm) in Au-NPs in these nanofluids is influenced by content of PVP molecules used during the reaction. A maximum absorption extinction coefficient 1.1 × 10⁴ L-mol^–1 cm^–1 is achieved in 1.0 g/dL PVP with 0.001 mM Au-NPs. An intense light emission 280–560 nm is obtained in this sample in combined effects of the surface enhanced light-absorption in Au-NPs and a dielectric surrounding with metal-insulator interfaces. Results are discussed in correlation with shape, size and assemblies in the Au-NPs with a polymer surface layer.