Synthesis of tuneable gold nanostars: the role of adenosine monophosphate

The seed-mediated growth of gold nanostructures is known to be strongly dependent not only on the gold seed nanocrystal structure but also on the presence of different additives that may influence the morphology, and therefore the crystalline structure of the final nanoparticle. Among the different additives or capping ligands, biomolecules are an interesting family due to their potential biomedical applications such as drug delivery, bioimaging, biosensing, phototherapy, and antimicrobial activities. Here, we develop a seed-mediated strategy for synthesizing uniform Au nanostars with tuneable optical properties which involves adenosine monophosphate (AMP) as a capping ligand. The experimental data reveal the key role of AMP not just providing colloidal stability and directing the reduction of the gold precursor via complexation but also mediating the anisotropic growth of the Au seeds via its selective adsorption on the different crystalline facets of Au nanoparticles. These observations agree with theoretical simulations carried out using molecular dynamics and density functional theory (DFT) calculations. Interestingly, the obtained Au nanostars showed high thermal stability as well as colloidal stability in polar organic solvents, which allowed their direct silica coating via the Stöber method. Importantly, we also explored the mimic enzymatic activity of the resulting gold nanostars and observed a superior catalytic activity compared with other gold nanoparticles reported in the literature.