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.

Colorimetric detection of sulfide based on target-induced shielding against the peroxidase-like activity of gold nanoparticles.

Colorimetric recognition and sensing of sulfide with high sensitivity was proposed based on target-induced shielding against the peroxidase-like activity of bare gold nanoparticles. Significant features of the new assay system are its simplicity and cost-effectiveness. The recognition of sulfide by bare gold nanoparticles can be fulfilled in a few seconds and the assay can be accomplished in about 10 min. Furthermore, the new assay system does not require surface modification of GNPs to obtain the specificity for sulfide, and a salt-induced aggregation step is not needed. The detection limit of this method for sulfide was 80 nM. These features make this sensor a potentially powerful tool for the quantitative determination of sulfide in water samples.

In situ growth of porous platinum nanoparticles on graphene oxide for colorimetric detection of cancer cells.

A green approach is proposed for in situ growth of porous platinum nanoparticles on graphene oxide (PtNPs/GO). The resulting nanocomposite has been proven to function as peroxidase mimetics that can catalyze the reaction of peroxidase substrate in the presence of hydrogen peroxide. On the basis of the peroxidase-like activity, we used the PtNPs/GO as a signal transducer to develop a colorimetric assay for the direct detection of cancer cells. By using folic acid as a recognition element, a total of 125 cancer cells (MCF-7) can be distinguished by naked-eye observation. We envision that this nanomaterial could be used as a power tool for a wide range of potential applications in biotechnology and medicine.