Fluorescence quenching of L-histidine-protected copper nanoclusters by closed-shell heavy metal ions.

Abstract

We investigated the interaction of L-histidine (L-His) protected copper nanoclusters (L-His-CuNCs) with heavy metal ions having closed-shell electronic configurations (Pb2+, Cd2+, Zn2+, and Ag+) using fluorescence spectroscopy. Paramagnetic interactions, energy transfer, and electron transfer were excluded as possible quenching mechanisms. The fluorescence of the L-His-CuNCs is sensitive and exponentially decreased upon interaction with Pb2+ in the concentration range of 0.16-7.69 mM, due to the formation of cluster aggregates. Such aggregates were detected by dynamic light scattering (DLS) and high-resolution transmission electron microscopy (HRTEM) studies. This amplified luminescence quenching effect by Pb2+ is due to its large ionic radius, high polarizability, and high affinity for oxygen and nitrogen donor ligands like carboxylate and imidazole nitrogen functionalities. Supporting analyses include FTIR, UV-visible absorption, and time-resolved fluorescence spectroscopic studies. Ultimately, the study concluded that aggregation-induced quenching is due to a combined static and dynamic quenching mechanism followed by the heavy atom effect. We believe that understanding how closed-shell heavy metal ions interact with L-His-CuNCs is not only fundamental to unravelling their photophysical quenching mechanism but also vital for developing sensing platforms for toxic metals in aqueous environments.

Abstract as supplied by the indexing source. © the authors / publisher.