Abstract
The rewards of using plants and plant metabolites over other biological methods for nanoparticle synthesis have fascinated researchers to investigate mechanisms of metal ions uptake and bio-reduction by plants. Here, green chemistry were employed for the synthesis of silver nanoparticles (AgNPs) using leaf extracts of Ocimum Sanctum (Tulsi) and its derivative quercetin (flavonoid present in Tulsi) separately as precursors to investigate the role of biomolecules present in Tulsi in the formation of AgNPs from cationic silver under different physicochemical conditions such as pH, temperature, reaction time and reactants concentration. The size, shape, morphology, and stability of resultant AgNPs were investigated by optical spectroscopy (absorption, photoluminescence (PL), PL-lifetime and Fourier transform infrared), X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). The enhanced antibacterial activity of AgNPs against E-Coli gram-negative bacterial strains was analyzed based on the zone of inhibition and minimal inhibitory concentration (MIC) indices. The results of different characterization techniques showed that AgNPs synthesized using both leaf extract and neat quercetin separately followed the same optical, morphological, and antibacterial characteristics, demonstrating that biomolecules (quercetin) present in Tulsi are mainly responsible for the reduction of metal ions to metal nanoparticles.
Highlights
Over the past few decades, there have been an increased emphasis on synthesis of metal nanoparticles and quantum dots[2,3] because of their unique optical and electrical properties
It was noticed that the time required for the reduction of silver ions to silver nanoparticles was much less in the case of quercetin compared to plant extract, this fact can be explained by taking into account the structural property of quercetin
The structure of quercetin includes an extended system of conjugated double bonds and contains five hydroxyl groups which provide the high reductive ability[28]
Summary
Over the past few decades, there have been an increased emphasis on synthesis of metal nanoparticles and quantum dots[2,3] because of their unique optical and electrical properties. Two new biosynthetic sources, Pomegranate peel extract and cochineal dye were employed and reported to obtained AgNPs25 Another natural source for feasible bioreduction of metal ions to metal nanoparticles is by the use of flavonoids. To the best of our knowledge, there are very few reports on the synthesis of silver nanoparticles using pure flavonoid reduction, which makes the mechanism of metal ions uptake by plants and their reduction to nanostructures less explored. This is with a view to verify whether the obtained particles using only quercetin as precursor exhibit the same characteristics as that of particles obtained using Tulsi leaf extract Perhaps, this investigation might provide basis for understanding the exact mechanism of how biomolecules present in plants interact with metal ions and unravel the process of their transformation into nanostructures
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