The fungal cell filtrate,

after incubation with 1 mM AgNO

The fungal cell filtrate,

after incubation with 1 mM AgNO3 (tube 3), underwent a distinct change in its color to brown within 24 h, which indicated the formation of silver nanoparticles due to the A-769662 cell line conversion of Ag+ ions to elemental Ag by extracellular reductase activity of M. phaseolina filtrate. The color intensity of the silver nanoparticle solution persisted even after 72 h, which indicated that the particles were well dispersed and stable in the solution. The mycosynthesis of silver nanoparticles involves trapping of Ag + ions at the surface of the fungal cells and the subsequent reduction of the silver ions by the extracellular enzymes like naphthoquinones and anthraquinones present in the fungal system. One earlier study with Fusarium oxysporum shows that NADPH-dependent RepSox concentration nitrate reductase see more and shuttle quinine extracellular process are responsible for nanoparticle formation [31]. Extracellular secretion of enzymes is especially advantageous for large-scale nanoparticle synthesis since large quantities of relatively pure enzyme can be obtained, free from other cellular proteins associated with the organism. The nanoparticles thus produced can be easily isolated by filtering from the reaction mix [28]. Figure 1 Synthesis of silver nanoparticles

using cell-free filtrate of Macrophomina phaseolina and spectroscopic analysis. (a) Photograph of 1 mM AgNO3 solution without cell filtrate (1, control), mycelia-free cell filtrate of M. phaseolina (2), and 1 mM AgNO3

with cell ADAM7 filtrate after 24-h incubation at 28°C (3). (b) UV–vis spectra recorded as a function of time of reaction at 24, 48, and 72 h of incubation of an aqueous solution of 1 mM AgNO3 with the M. phaseolina cell filtrate showing absorption peak at 450 nm. UV–vis spectroscopy of the silver nanoparticles The silver nanoparticles were subjected to spectral analysis by UV–vis spectroscopy. The absorption spectra of nanoparticles showed symmetric single-band absorption with peak maximum at 450 nm for 24, 48, and 72 h of incubation of cell filtrate with AgNO3 which steadily increased in intensity as a function of time of reaction without any shift in the peak (Figure 1b). This indicates the presence of silver nanoparticles, showing the longitudinal excitation of surface plasmon, typical of silver nanoparticles. Morphological study of the silver nanoparticles with scanning electron microscopy The morphology (viz shape and size) of the silver nanoparticles studied under scanning electron microscopy (SEM) (magnification × 50,000) revealed that the nanoparticles were mostly spherical in shape and polydisperse in nature (Figure 2a). The nanoparticles were not in direct contact even within the aggregates, indicating stabilization of the nanoparticles by a capping agent. Figure 2 Electron micrographs of silver nanoparticles. (a) Scanning electron microscopy micrograph of silver nanoparticles produced with M. phaseolina at 50,000 magnification (bar = 1 μm).

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