Synthesis of metal nanoclusters and study of their influence on the bacterial copper resistance

Abstract

Metal nanoclusters (NCs) are promising ultra-small nanomaterials with attractive properties for sensing and various biomedical applications. Unlike metal nanoparticles, NCs often have a stable fluorescence with large Stokes shift, high photostability, low toxicity and significant antibacterial activity (especially, in a case of silver). For evaluation of bioactivity we synthesized a three types of glutathione-capped silver nanoclusters (Ag-SG NCs) with different reductants (L-glutathione, NaBH4 and L-ascorbic acid) and different conditions of the reaction. According to spectral data, all types of Ag-SG NCs were demonstrated a strong absorption in ultra-violet and visible region (up to ~450 nm). Moreover, only silver clusters fabricated in the presence of NaBH4 have a significant fluorescence (λex/λem = 509/645 nm) with a large Stokes shift (>130 nm).
The obtained NCs were studied for the manifestation of antimicrobial activity towards the copper-resistant bacterium Achromobacter insolitus LCu2. A well-known gold glutathione-capped nanoclusters was used for comparison with antibacterial effect of Ag-SG NCs. In the optimal culture medium, antimicrobial activity was detected only for Ag-SG NCs synthesized in the presence of NaBH4 (MIC = 24.4 μM) and L-ascorbic acid (MIC = 4.81 μM). However, when the clusters were introduced into the bacterial culture medium containing 3 mM Cu2+, the antimicrobial activity sharply increased for all Ag-SG NCs: the MIC values for the nanoclusters obtained by various methods were 25.1 nM (reductant – L-glutathione), 0.76 nM (reductant – NaBH4), and 0.16 nM (reductant – L-ascorbic acid). Gold nanoclusters did not demonstrate antimicrobial activity towards A. insolitus LCu2 in both types of media.


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Margarita Filippova
Saratov State University, Saratov, Russia
Russia

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