Methionine-directed fabrication of gold nanoclusters with yellow fluorescent emission for Cu(2+) sensing

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 530nm), a long fluorescence lifetime (181ns and 1651ns), high colloidal stability (pH-, temperature-, salt- and time-stability), and a large Stoke's shift (110nm), 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 Cu(2+) by fluorescence quenching. The limit of detection for Cu(2+) was determined to be 7.9nM and linear response over the Cu(2+) concentrations range from 50nM to 8μM. Furthermore, the new-constructed probe allows simple and rapid detection of the concentrations of Cu(2+) in soil, with results demonstrating its great feasibility for the determination of copper in real samples.