Green synthesis of gold nanoparticles from the rind extract of Garcinia mangostana and its synergistic effect with antibiotics against human pathogenic bacteria

The present investigation reports a facile method for the biosynthesis of gold nanoparticles from the rind extract of Garcinia mangostana, a medicinal plant which acts as a reducing agent. It was observed that the aqueous gold ions, when exposed to the rind extract of G.mangostana were reduced in the solution, thereby leading to the formation of gold nanoparticles (GMREGNP). The structural characterization was performed using HR-TEM; the micrographs showed the well dispersed spherical nanoparticles ranged from 25 - 60 nm. The SAED diffraction rings suggested that the GMREGNP were polycrystalline in nature. The peaks in the XRD were in good agreement with the standard values of the spherical form of metallic gold and no peaks of impurities were detected. From the Fourier Transformed-Infrared Spectra (FT-IR) of the rind extract and phytosynthesised gold nanoparticles, the possible functional groups involved in the gold ions reduction and capping of the gold nanoparticles were identified. The particle size (DLS) and the electro kinetic measurement (zeta potential) of the GMREGNP was also evaluated. The nanoparticles were assessed for their increased antimicrobial activity with various antibiotics against potential human pathogens. Further the fabrication of the bio-inspired GMREGNP with the drug and the changes on the characteristics of the nanoparticles were studied using various techniques like UV-VIS spectroscopy and FT-IR. The minimal inhibitory concentration (MIC) of the GMREGNP and drug fabricated GMREGNP has been recorded. The topological changes stamped by the nanoparticles on the surface of the bacteria have been recorded by SEM images. Experiments are underway to prove the possible mechanism for the synergistic effect of the nanoparticles with antibiotics.