Biomedical Letters

Green synthesis of gold nanoparticles using Tribulus terrestris extract and antibacterial activity against Gram-negative bacteria

Nighat Nawaz 1, Irshad Ahmad 2*, Simon G. Patching 3, Iqbal Hussain 1*

1 Department of Chemistry, Islamia College Peshawar, Peshawar, Pakistan

2 Institute of Basic Medical Sciences, Khyber Medical University, Peshawar, Pakistan

3 School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK

Abstract

Aqueous extract of the plant Tribulus terrestris was used to reduce chloroauric acid for synthesizing gold nanoparticles (AuNPs). In this green synthesis, the reaction proceeded to give a red/purple color that was monitored by UV-vis spectrophotometry, where the formed AuNPs had an absorption band with max of 550 nm. In terms of the highest absorbance at 550 nm, reaction conditions were optimized at a temperature of 75°C, at pH 7 and using a reaction time of 4 h. The integrity of the synthesized AuNPs was confirmed and their physical properties were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM), which also showed evidence that plant metabolites contributed to capping or stabilization of the AuNPs. XRD spectra suggested a particle size of around 40 nm and SEM images revealed spherical and relatively uniform and disperse particles with a size of less than 0.1 m. In a broth microdilution assay, the AuNPs showed inhibitory effects against Gram-negative Escherichia coli, but not against Gram-positive Enterococcus faecalis. The AuNPs showed no hemagglutination activity or cytotoxic activity against human blood cells, which is important for them to be explored as therapeutic antibacterial agents.