Benincasa hispida seed mediated green synthesis of gold nanoparticles and its optical nonlinearity

The paper reports the biosynthesis of stable and nearly spherical gold nanoparticles using the extract of Benincasa hispida seeds as reducing and capping agents. The particle size could be easily tuned by the reaction conditions including quantity of extract, temperature and pH. Gold nanoparticles having different sizes in the range from 10 to 30 nm could be obtained by controlling the synthesis parameters. The nanoparticles were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. The high crystallinity of nanoparticles is evident from clear lattice fringes in the HRTEM images, bright circular spots in the SAED pattern and peaks in the XRD pattern. FTIR spectrum indicates the presence of different functional groups present in the biomolecule capping the nanoparticles. The possible mechanism leading to the formation of gold nanoparticles is suggested. The optical nonlinearity of the samples is studied by open aperture Z-scan technique. The as-prepared gold nanoparticles shows good optical limiting behavior and the two-photon absorption coefficient is found to decrease with increase in particle size.