Experimental and theoretical study of biodirected green synthesis of gold nanoflowers

We report a very simple, green, and eco-friendly route to synthesize three-dimensional branched gold nanoflowers (AuNFs). The process involved reduction of gold salt in presence of two naturally occurring small biomolecules viz. L-tyrosine and sodium citrate which act as mild reducing and shape-directing agent. A detailed picture of the formation mechanism of AuNFs has been proposed after thorough experimental analysis (electron microscopy, X-ray photoelectron spectroscopy [XPS], circular dichroism [CD], UV-vis spectroscopy, dynamic light scattering [DLS] and nanoparticle tracking analysis [NTA]) as well as by theoretical simulations (cellular automata and diffusion-limited aggregation [DLA] simulations). Experimental analysis and numerical simulation pointed out that L-tyrosine molecules self-assemble in a complex way which controls the flower-like shape and structure, whereas trisodium citrate plays a crucial role in controlling the particle diameter. A second shape (quasi-spherical) could also be obtained with same formulation by just changing the sequence of addition of reactants. As such the effect of the shape on surface enhanced Raman spectroscopy [SERS] enhancement has also been evaluated. Finally, in vitro studies were performed on a model cell line of mouse brain endothelium (bEnd.3) to assess biocompatibility.