Biogenic silver nanoparticles: Green synthesis, encapsulation, thermal stability and antimicrobial activities

Biogenic silver nanoparticles (AgNPs) were synthesized using an aqueous extract of potato in presence of water soluble starch and characterized by UV-visible spectroscope, transmission electron microscope (TEM), scanning electron microscope (SEM), and Energy dispersive X-ray spectroscope (EDX). KI-I-2 colorimetric method was used to determine of amylose content in an aqueous potato extract. UV-visible measurements showed that AgNPs replace molecular iodine from starch iodine complex. TEM images of starch capped AgNPs, blue complex of starch iodine and encapsulated AgNPs showed that the morphology of encapsulated and non-encapsulated AgNPs has been changed entirely. Thermogravimetric analysis shows two step thermal degradation of potato amylose and amylose capped AgNPs. Hydrogen peroxide oxidized potato amylose contains carbonyl and carboxyl degree of oxidation 0.23 and 0.11, respectively with 4% H2O2. The antimicrobial activity of starch capped AgNPs were determined against both Gram-positive and Gram-negative human pathogens. Escherichia coli MTCC-450 (E. coli) and Staphylococcus aureus MTCC-3160 (S.aureus) bacteria used to estimate the antibacterial activity of AgNPs. Minimum inhibitory concentration was determined and found to be 6.4 mu g/ml and 82 mu g/ ml for E. coli and S. aureus, respectively. (C) 2019 Elsevier B.V. All rights reserved.