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Synthesis of silver nanoparticles (AgNPs) under different physicochemical conditions like concentration of silver nitrate (AgNO3), pH and temperature, using fungal cell filtrate of Aspergillus oryzae (MTCC No. 1846) and its antibacterial properties were demonstrated. When fungal cell filtrate having neutral pH was exposed to different concentrations of aqueous solution AgNO3 (1–10 mM), formation of stable AgNPs of different sizes was observed. The size of the AgNPs decreased with the increase of AgNO3 concentration from 1 mM to 8 mM, however, the particles size increased with the increase of AgNO3 concentration from 9 mM to 10 mM. When fungal cell filtrate exposed to aqueous solution of 1 mM AgNO3 at different pH (4–10), the silver ions (Ag+) were reduced leading to the formation of stable AgNPs of different sizes. The size of the AgNPs decreased with the increase of alkaline conditions. When aqueous solution of 1mM AgNO3 with fungal cell filtrate, having neutral pH, was exposed to different temperatures (10, 30, 50, 70 and 90 °С), formation of stable AgNPs having different sizes were obtained. The size of the AgNPs decreased with the increase of temperature. Synergetic effect with antibiotics and size dependent antibacterial activities were also demonstrated against Escherichia coli (MTCC 1687), Staphylococcus aureus (MTCC 737), Bacillus subtilis (MTCC 441) and Klebseilla pneumoniae (MTCC 4030). The formation AgNPs was characterized by UV–vis spectrophotometer. Transmission electron microscope (TEM) confirmed the sizes of the obtained nanoparticles. X-ray diffractometer (XRD) spectrum confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy (FTIR) confirmed the presence of protein as stabilizing agent around AgNPs. Scanning electron microscope (TEM) confirmed the morphological changes in the treated bacterial organisms.
Phanjom et al. (Tue,) studied this question.