Abstract
A straightforward and green method for the synthesis of gold, silver, and silver chloride nanoparticles (Au NPs and Ag/AgCl NPs) was developed using three different microbial exopolymers (EP) as reducing and stabilizing agents. The exopolysaccharides EPS B3-15 and EPS T14 and the poly-γ-glutamic acid γ-PGA-APA were produced by thermophilic bacteria isolated from shallow hydrothermal vents off the Eolian Islands (Italy) in the Mediterranean Sea. The production of metal NPs was monitored by UV−Vis measurements by the typical plasmon resonance absorption peak and their antimicrobial activity towards Gram-positive and Gram- negative bacteria (Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa), as well as fungi (Candida albicans) was investigated. The biological evaluation showed no activity for EP-Au NPs, except against E. coli, whereas EP-Ag NPs exhibited a broad-spectrum of activity. The chemical composition, morphology, and size of EP-Ag NPs were investigated by UV–Vis, zeta potential (ζ), dynamic light scattering (DLS) measurements and transmission electron microscopy (TEM). The best antimicrobial results were obtained for EPS B3-15-Ag NPs and EPS T14-Ag NPs (Minimum Inhibitory Concentration, MIC: 9.37–45 µg/mL; Minimum Bactericidal Concentration/Minimum Fungicidal Concentration, MBC/MFC: 11.25–75 µg/mL).
Highlights
Noble metal nanoparticles, gold and silver (Au NPs and Ag NPs, respectively), have attracted increasing interest due to their potential applications in several fields ranging from catalysis, sensors, optoelectronics, biotechnology to medicine [1]
The best antimicrobial results were obtained for EPS B3-15-Ag NPs and EPS T14-Ag NPs (Minimum Inhibitory Concentration, MIC: 9.37–45 μg/mL; Minimum Bactericidal Concentration/Minimum Fungicidal Concentration, MBC/MFC: 11.25–75 μg/mL)
The EP-mediated production of Au NPs was completed at 100 ◦ C within 3 h for EPS B3-15 and after 1 h and 30 min for γ-PGA-APA, as demonstrated by UV–Vis analysis monitoring the typical plasmon resonance absorption peak of Au NPs (Figure 1)
Summary
Gold and silver (Au NPs and Ag NPs, respectively), have attracted increasing interest due to their potential applications in several fields ranging from catalysis, sensors, optoelectronics, biotechnology to medicine [1]. They possess a unique combination of advantageous physicochemical features, different from those of the bulk metal, such as high surface-to-volume ratio, versatile surface functionalization, surface plasmon resonance properties, making them suitable to be used in advanced application fields [2]. Au NPs and Ag NPs can be advantageously synthesized by an eco-friendly laser ablation method, using a pulsed laser beam to ablate a metal target immersed in a solvent, without reducing and capping agents [7,8]
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