New Fluorescent-Labelled Nanoparticles: Synthesis, Characterization and Interactions with Cysteine and Homocysteine to Evaluate Their Stability in Aqueous Solution

Fluorescent-labelled nanoparticles conjugate the SPR of nanomaterials as well as the fluorescence properties of the capping dye. In this work, we report a study on the synthesis of fluorescent l -tyrosine ( l -Tyr) and fluorescein (Fluo)-capped silver nanoparticles (AgNPs) carried out by a fine-tuning of the analytical concentration of the reagents. The AgNPs have been characterized by TEM, UV–Vis, ATR–FTIR, and photoluminescence (PL) spectroscopy and DLS. The adsorption of cysteine and homocysteine on the surface of the nanoparticles has been studied to evaluate their overall evolution in solution and their possible interactions with more complex systems, such as proteins. Opposed to homocysteine, cysteine induces aggregation either of tyrosine- and fluorescein-capped nanoparticles, which are therefore promising systems for the discrimination of biothiols. Furthermore, tyrosine-capped AgNPs, in spite of the better coordinating characteristics of this amino acid with respect to fluorescein, show aggregation abilities with cysteine greater than the fluorescein-capped ones that are unexpectedly more stable and thus less prone to aggregation phenomena.