Influence of amino acid corona, metallic core and surface functionalisation of nanoparticles on their in-vitro biological behaviour

Metallic nanomaterials such as gold (Au) and silver (Ag) nanoparticles have numerous applications in biology and medicine. However, these nanoparticles have not been fully explored for their prospective utility in biomedicine. Furthermore, it is imperative to understand nanomaterial behaviour at the Nano-Bio interface based upon various physicochemical properties to control their toxicity in biological entities. In current study, we have developed synthetic methodologies to prepare Au and Ag nanoparticles, wherein amino acids were utilised as reducing, capping and stabilising agents. Tyrosine (Tyr) and tryptophan (Trp) amino acids were chosen for this purpose because the side functional group present in Tyr and Trp reduces metal ions to form Au and Ag nanoparticles, while leaving their amine and carboxylic acid groups intact. All these Tyr and Trp synthesised AuNPsTyr, AuNPsTrp, AgNPsTyr and AgNPsTrp were thoroughly characterised by UV-Vis, transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR) and zeta potential techniques after removing unbound amino acids, unreduced metal ions and other chemicals from nanoparticles solutions. These materials have shown surface corona and core metal dependent free radical scavenging capacity and peroxidase enzyme-like behaviour. Captivatingly, integral presence of amine and carboxylic acid groups on the surface of nanoparticles can provide an opportunity for further functionalisation of these nanoparticles. Therefore, biocompatible AuNPsTyr and AuNPsTrp were further functionalised with fluorescent molecules like Rhodamine B and fluorescein isothiocyanante (FITC) to generate AuNPsTyr@RhoB, AuNPsTrp@RhoB, AuNPsTyr@FITC and AuNPsTrp@ FITC. Stability of Rhodamine B and FITC on the surface of Au nanoparticles has been established and it is believed that such functional Au nanoparticles will be suitable for various biological applications.