Nanostructural transformations of silver nanoclusters occurring during their synthesis and after interaction with UV-light

Abstract

Metal nanoclusters (NCs), composed of several to tens of atoms, are a new class of fluorescent nanoprobes. NCs present distinct and favourable optical, electrical, and chemical properties as compared to other large-scale nanomaterials or bulk materials with the same chemical composition, being attractive for bio-imaging and bio-labelling applications. As this is a new nanomaterial class, fundamental questions regarding cluster growth mechanisms, stability, and functionality remain. Thus, new analytical tools for the analysis and characterization of such NCs are urgently needed to help in their synthesis optimization and final quality control. Information obtained from the use of a gentle separation technique, asymmetric flow field-flow fractionation, coupled on-line to molecular and elemental spectroscopic detection (spectrophotometry, fluorimetry and inductively coupled plasma mass spectrometry) along with transmission electron microscopy provide new insights into the structural transformations occurring during the growth of highly fluorescent silver nanoclusters (AgNCs) and also after their continuous irradiation with UV-light. These studies reveal that the mechanism of AgNCs growth goes through the previous formation of the corresponding unstable plasmonic metal nanoparticle. Moreover, photo-stability of the synthesized fluorescent NCs was investigated, in order to establish its manipulation and possible applications. Obtained results prove that the continuous exposure of AgNCs to UV-light provokes the loss of their optical properties driven by a photo-oxidation reaction.