Green Synthesis of Silver Nanoparticles Using Flavonoids and Assessment of Their Antimicrobial Properties

Flavonoids are a group of bioactive compounds present in a larger group of plant species. Chemically, these compounds have the basic C15 phenyl benzopyrone skeleton structure. Flavonoid compounds were extracted from germinating seeds of black gram (Vigna mungo L.), a popular edible legume cultivated in most of the countries of Asia. Most crude extracts obtained from plants and animals are used for biosynthesis of silver nanoparticles, but less compounds have yet been identified which are responsible for conversion of silver nitrate to silver nanoparticles. Flavonoids, a secondary metabolite, were extracted from germinated black gram seeds (25 g) with acetone, and the total flavonoid content was determined by spectrophotometric method. The solution of 100 mM silver nitrate (AgNO3) solution was mixed with flavonoids in a ratio of 2:1 in a glass vial and kept at room temperature (27 °C) for 24 h. The transformation of the aliquot from colourless to brown colour was considered an incidence of reduction reaction, and the end results in the formation of silver nanoparticles. The optimum conversion time was recorded as 5 h of incubation. The confirmation and characterization of synthesized nanoparticles were ascertained by absorption study by UV–visible spectrophotometer, transmission electron microscopy (TEM) photograph, and X-ray diffraction (XRD) analysis. The nanoparticles had absorption maxima (λmax) of 440 nm. Transmission electron microscopy photographs indicated that the prepared nanoparticles were globular in shape. X-ray diffraction graph analysis of the nanoparticles indicated that the particles are rounded and have a more or less homogenous structure. The ratio of silver nitrate solution and the flavonoid extract was 2:1, and the same solution was considered a yardstick combination to biosynthesize the nanoforms. Slightly alkaline environment (pH 8.0) proved to be an appropriate environment for the bioconversion process. The extracted flavonoids have efficacy to catalysing the conversion of silver ions to nanoforms. The flavonoids present in germinated seeds of black gram synthesize stable silver nanoparticles. Silver nanoparticles encompass antimicrobial activity towards all the studied pathogenic microorganisms viz. Escherichia coli, Staphylococcus aureus and Salmonella typhimurium. Therefore, the synthesized silver nanometals have a great therapeutic value.