Biosynthesis of Gold Nanoparticles Using Strobilanthes crispa Aqueous Leaves Extract and Evaluation of Its Antibacterial Activity

The role of plant phytochemicals has drawn undeniable attention for synthesizing stable and eco-friendly nanoparticles. Therefore, this work explores using locally grown Strobilanthes crispa aqueous leaves extract for the biosynthesis of gold nanoparticles (AuNPs) using HAuCl4 as the metal precursor. The AuNPs were characterized using Ultraviolet-visible (UV-Vis) spectroscopy, Fourier transforms infrared (FTIR) spectroscopy, High-resolution Transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). The UV-Vis spectrum exhibits two absorption peaks due to surface plasmon resonance of gold at 530 nm and 708 nm within 2 hours. The HRTEM micrographs proved that AuNPs were predominantly spherical with mixtures of anisotropic nanoshapes. The FTIR spectra evident the presence of phytochemical compounds, which acted as the capping agent. The face-centered cubic (fcc) structure was confirmed using the XRD pattern with an average crystallite size of 9.3 nm. The antibacterial assay exhibited a positive inhibitory effect on Gram-negative bacteria (Escherichia coli ATCC 11229) compared to Gram-positive bacteria (Staphylococcus aureus ATCC 6538). Further in silico analysis between AuNPs and E. coli bacterial proteins using STITCH 5.0 revealed a high binding affinity of > 0.7 to DNA and membrane-related proteins. This result unravels the antibacterial properties of S. crispa AuNPs, leading to potent bacterial death.