Methionine-directed fabrication of gold nanoclusters with yellow fluorescent emission for Cu2+ sensing

• Synthesis of AuNCs by using methionine as reducing agent and protection ligand.
• Fluorescent property and colloidal stability of methionine-AuNCs.
• Fluorescent nanoprobes for rapid, sensitive and selective Cu2+ sensing.
• The detection limit is 7.9 nM.

In the past few years, fluorescent gold nanoclusters (AuNCs) have gained much attention in many areas of physics, chemistry, materials science, and biosciences due to their unique physical, electrical, and optical properties. Herein, we reported for the first time the synthesis of water soluble, monodispersed AuNCs by using methionine both as a reductant and a stabilizer. The synthetic process is green and simple, and the resulting AuNCs capped by methionine (Met-AuNCs) would be biocompatible with bioorganisms. UV–visible absorption, photoluminescence, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) were carried out to demonstrate the chemical composition and optical properties of the as-prepared Met-AuNCs. The Met-AuNCs possess many attractive features including intense yellow fluorescence (emission maximum at 530 nm), a long fluorescence lifetime (181 ns and 1651 ns), high colloidal stability (pH-, temperature-, salt- and time-stability), and a large Stoke's shift (110 nm), holding great promise as late-model analytical tools for life science and environmental studies. Moreover, the as-synthesized Met-AuNCs can serve as an efficient fluorescent probe for selective detection of Cu2+ by fluorescence quenching. The limit of detection for Cu2+ was determined to be 7.9 nM and linear response over the Cu2+ concentrations range from 50 nM to 8 μM. Furthermore, the new-constructed probe allows simple and rapid detection of the concentrations of Cu2+ in soil, with results demonstrating its great feasibility for the determination of copper in real samples.