Figure 3 HRTEM imaging of red-luminescent Au clusters and emission spectra of Au and Pt clusters. learn more (a) HRTEM imaging of red-luminescent Au clusters. (b) Emission spectra of red-luminescent, pink-luminescent, and blue-luminescent Au clusters and blue-luminescent Pt cluster. Regarding the formation mechanism, as put forward by Xie et al. [19], with the egg white as stabilizing host material providing a confined space that limits cluster growth and impedes agglomeration, the formation process consists of the trapping and interacting of metal ions, followed by reduction and growth at highly alkaline pH. During the process, the aromatic amino acids in
proteins would donate electrons to reduce metal ions; meanwhile, the broken disulphide bonds would stabilize these nucleated clusters. Considering the complexity of proteins in egg white, it might take us a long time to make buy R406 the check details mechanism clear. In spite of this, some questions remain haunting us, such as the following: What happened during the 12 h of evolution of clusters in the mixed proteins [28]? Is one or more proteins
involved in the formation of metal clusters? What is the number of metal atoms in the cluster core? Is it possible to synthesize metal clusters using plant or animal extracts by adopting a similar method [29–31]? What is the luminescent mechanism Nutlin3 of metal clusters in mixed proteins? Further
work in our group is being actively explored towards these questions. There are many reports about fabricating luminescent sensors based on metal clusters [32–35]. Herein, the as-prepared Au clusters were also used as a highly sensitive sensor for the identification of H2O2, which is a kind of important small-molecule compounds in the environment and bioanalytical sciences. We found that the luminescence of the Au cluster is quenched in the presence of H2O2. From Figure 4, one can see that more and more quenching occurs with increasing H2O2 concentrations. The quenching mechanism could be attributed to the strong oxidative ability of H2O2, which disrupted the egg white-protected Au clusters, leading to their aggregation and growth, becoming larger Au nanoparticles. The destructive products were also imaged by TEM (Additional file 1: Figure S2). Figure 4 Fluorescence quenching of red-luminescent Au clusters by the addition of different concentrations of H 2 O 2 . (black) 1.0 × 10−2 M, (red) 1.0 × 10−3 M, (blue) 1.0 × 10−4 M, (green) 1.0 × 10−5 M, (pink) 1.0 × 10−6 M, (yellow) 1.0 × 10−7 M. Conclusions In conclusion, we have developed ‘a real green way’ to synthesize noble metal clusters (Au and Pt) by using chicken egg white as template. The method is simple; source-, energy-, and cost-effective; and environmentally friendly.
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