Here we first demonstrate the pH-dependent synthesis of pepsin-mediated gold nanoclusters (Au NCs) with blue-, green-, and red-fluorescent emission from Au5 (Au8), Au13, and Au25, respectively. Pepsin is a gastric aspartic proteinase (molecular weight 34,550 g/mol) that plays an integral role in the digestive process of vertebrates.  We found that the pH of the reaction solution was critical in determining the size of Au NCs (i.e. the number of gold atoms of Au NCs). Interestingly, the enzyme function of pepsin contributes to the formation of these Au NCs. The photo-stability of Au25 (or Au13) NCs is much higher than that of Au5 NCs (i.e. Au25 - Au13 >> Au5). The pepsin-mediated Au25 NCs were also found to be useful as fluorescent sensors for the detection of Pb2+ ions by enhanced fluorescence and the detection of Hg2+ ions by fluorescence quenching. Although the detailed formation mechanisms of these Au NCs require further analysis, the synthetic route using proteinase demonstrated here is promising for preparing new types fluorescent metal nanoclusters to apply in catalysis, opyics, biological labeling, and sensing.

pH-dependent synthesis of pepsin-mediated gold nanoclusters with blue-, green-, and red-fluorescent emission

243rd National Meeting (2012)

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