Luminescence emission of copper nanoclusters by ethanol-induced aggregation and aluminum ion-induced aggregation

Abstract

Metal nanoclusters (MNCs), as a new type of nano-material, possess excellent properties such as facile synthesis, strong light stability, low toxicity, excellent biocompatibility, and high luminous efficiency. Aggregation-induced emission (AIE), which can enhance the luminescence properties of MNCs, has resulted in MNCs attracting significant attention. In this thesis, L-glutathione (GSH)-protected copper nanoclusters (GS@CuNCs) were prepared by a “one-pot” method in aqueous solution without additional reducing agents. The GS@CuNCs were characterized by UV-Vis absorption spectroscopy and fluorescence spectroscopy. Upon excitation at 370 nm, the fluorescence spectrum of GS@CuNCs displayed the maximum emission peak at 610 nm. The as-prepared CuNCs generate a striking fluorescence intensity via aggregation-induced emission (AIE). The AIE property of GS@CuNCs was examined for the aggregates in different organic solvents, such as ethanol, methanol, and dimethylformamide. Since the aggregation degree was controlled by the content of organic solvent, we further measured the fluorescence intensity of GS@CuNCs in different volume ratios of a water-ethanol mixture solution. The fluorescence intensity of GS@CuNCs exhibited an approximately 30-fold increase at 85% of ethanol content, as compared to that in aqueous solution. A possible mechanism may be that intramolecular motions are restricted in ethanol, resulting in a significant increase of fluorescence intensity. Moreover, only very weak emissions were recorded for the CuNC dispersion in aqueous solution; however, an apparent luminescence enhancement was observed in both luminescence spectra and by naked eyes under UV light, with a gradual increase in the ethanol content in the water-ethanol mixture from 0% to 85%. Additionally, we developed a new selective and sensitive turn-on fluorescent sensor for the detection of trivalent aluminum ions (Al3+) based on cation-induced aggregation methods. Among the 15 types of metal cations studied, only Al3+ visibly increased the fluorescence emission of the GS@CuNCs. These results indicated that the GS@CuNCs were highly selective to Al3+ than other metal ions, which may result from the electrostatic and coordination interactions between the trivalent aluminum ions and monovalent carboxylic anions from GSH in the CuNCs. The response of the probe to Al3+ exhibited a good linear range of 2–20 μmol·L-1 and the detection limit was 33 nmol·L-1. Thus, the weak fluorescence intensity of CuNCs was increased markedly by the AIE of Al3+, and could construct an interesting fluorescent platform for sensing aluminum ions. The property of AIE of GS@CuNCs may expand the potential applications of nanocluster materials to biosensors and cell imaging.