A novel report on synthesis of gold nanoparticles using bacterial exopolysaccharide and synthesized nanocrystals (5–20 nm) capped with polysaccharide layer.

Exopolysaccharides (EPSs) are structurally and functionally valuable biopolymer secreted by different prokaryotic and eukaryotic microorganisms in response to biotic/abiotic stresses and to survive in extreme environments. Microbial EPSs are fascinating in various industrial sectors due to their excellent material properties and less toxic, highly biodegradable, and biocompatible nature. Recently, microbial EPSs have been used as a potential template for the rapid synthesis of metallic nanoparticles and EPS-mediated metal reduction processes are emerging as simple, harmless, and environmentally benign green chemistry approaches. EPS-mediated synthesis of metal nanoparticles is a distinctive metabolism-independent bio-reduction process due to the formation of interfaces between metal cations and the polyanionic functional groups (i.e. hydroxyl, carboxyl and amino groups) of the EPS. In addition, the range of physicochemical features which facilitates the EPS as an efficient stabilizing or capping agents to protect the primary structure of the metal nanoparticles with an encapsulation film in order to separate the nanoparticle core from the mixture of composites. The EPS-capping also enables the further modification of metal nanoparticles with expected material properties for multifarious applications. The present review discusses the microbial EPS-mediated green synthesis/stabilization of metal nanoparticles, possible mechanisms involved in EPS-mediated metal reduction, and application prospects of EPS-based metal nanoparticles.

A simple naphthoquinone−dopamine hybrid (2CND) was designed and fabricated as a colorimetric and fluorescence chemosensor for the selective recognition of Sn 2+ in the aqueous medium. This simply accessible chemosensor was prepared by connecting of naphthoquinone acceptor and dopamine donor moieties via Michael-like addition reaction. The chemosensor 2CND showed a turn-on fluorescence response which operated through the inhibited photoinduced electron transfer effect. The sensor probe shows remarkable performance, such as high selectivity, sensitivity, excellent water solubility, and rapid response to Sn 2+ (less than 5 s). The detection mechanism of the 2CND−Sn 2+ complex was supported by FT-IR analysis, 1 H NMR titration, and DFT calculations. Besides, the 1:1 binding stoichiometry was confirmed by the ESI-MS spectral analysis. Furthermore, the chemosensor 2CND has been successfully employed as a fluorescence probe to monitor trace Sn 2+ in live cells and zebrafish. The sensor probe 2CND could serve as an effective fluorescence bioimaging probe for the discriminative detection of diseased and normal human cells.

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