Fluorescent Biofunctionalized Silver and Gold Nanoparticles: Bright Tools for Bioimaging Applications

Abstract The aim of this work is to evaluate different nanostructured systems based on noble metal nanoparticles suitable for drug delivery and release related to the treatment of multiple sclerosis. To this end, four different systems are thoroughly characterized from a chemical-physical and structural perspective and, then, from a biological perspective. Gold and silver nanoparticles were synthesized and stabilized with different biocompatible ligands, including poly(ethylene glycol), citrate, and cysteine, to modulate their colloidal stability and surface reactivity. UV–Vis spectroscopy revealed characteristic plasmonic absorption bands at about 400 nm for silver and nearly 550 nm for gold nanoparticles. Morphological analyses, performed by Transmission Electron Microscopy, and colloidal stability, studied by Dynamic Light Scattering, highlighted differences in size distribution and polydispersity among the systems. The nanoparticles were subsequently functionalized with fluorescein isothiocyanate, a fluorescent dye, to enable their detection and tracking within cells using an accessible analytical technique appropriate for the study of immune cells, such as flow cytometry. Nanoparticle surface properties were thoroughly investigated by means of Fourier-transform infrared, synchrotron radiation-induced X-ray photoelectron, and near edge X-ray absorption fine structure spectroscopies. Flow cytometry analyses demonstrated efficient nanoparticle–cell interaction with peripheral blood mononuclear cells, and a cell viability assay performed with the improved system highlighted the potential for applications in drug delivery and bioimaging.