Surface Plasmon Resonance (SPR) Based Optimization of Biosynthesis of Silver Nanoparticles from Rhizome Extract of <Emphasis Type="Italic">Curculigo orchioides</Emphasis> Gaertn. and Its Antioxidant Potential

The present study for the first time explores the use of Central composite design (CCD) of RSM to optimize the process parameters of biosynthesis of AgNPs from rhizome extract of Curculigo orchioides based on the absorbance of surface plasmon resonance (SPR) band at 430 nm that corresponds to the synthesis of mono-disperse, spherical AgNPs. A polynomial model was established as a functional relationship between the synthesis of AgNPs and four independent variables such as concentration of AgNO₃, % rhizome extract, pH and temperature. The optimum conditions for maximum AgNPs synthesis were 2 mM concentration of AgNO₃, 20 % rhizome extract, pH 8, and temperature of 60 °C. A significant correlation (R ² = 0.8947) was observed between the experimental data and the predicted values indicating the adequacy of the model. Transmission electron microscopy (TEM) revealed spherical particles with size range of 5–28 nm. Selected area electron diffraction pattern and X-ray diffraction analysis confirmed the face-centered cubic structure of metallic silver. The plausible mechanism for the reduction of AgNO₃ to AgNPs was proposed following the identification of functional groups by FTIR. The antioxidative activity of AgNPs was demonstrated with scavenging of hydrogen peroxide (H₂O₂), 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and superoxide radicals.