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Polyvinyl Alcohol (PVA) capped Ag nanoparticles (AgNPs) formed through reduction of Silver Nitrate (AgNO3) by Sodium Borohydride (NaBH4) were studied for different PVA concentrations (C, %w/w of solution) in the bulk. Diameter (DAg) of Ag metallic core, obtained from plasmon resonance in Ultraviolet-Visible spectra, had a peak (≈12.8 nm) at C~0.24, which almost exactly matched the gyration sphere diameter of PVA molecule (∼13 nm). Cluster diameter (Dcl), measured after a month through Dynamic Light Scattering (DLS) study, gave the number of NPs per cluster showing a dip at C∼0.24. Minimum inhibitory concentration (MIC) of AgNPs on Escherichia coli (E. coli), assayed from standard broth dilution method (CLSI M07-A8), showed MIC of 0.66 μg/ml at the PVA concentration of 0.24%. Scanning Electron Microscopy (SEM) showed NP clusters accumulating over E. coli to have Dcl ∼ DAg whereas those lying outside the bacteria to have Dcl ∼ 3DAg, consistent with a strong size selectivity of antimicrobial efficacy.
Parveen et al. (Fri,) studied this question.