Green biosynthesis of gold nanoparticles using Galaxaura elongata and characterization of their antibacterial activity

The synthesis of gold nanoparticles (Au) using Galaxaura elongata (powder or extract) is demonstrated here. The rapid formation of stable Au nanoparticles has been found using G. elongata extract in aqueous medium at normal atmospheric condition. Transmission electron microscopy (TEM) analysis revealed that the particles are spherical in shape along with a few rod, triangular, truncated triangular and hexagonal shaped nanoparticles. Zeta potential measurements indicated that the Au nanoparticles were in the size range of 3.85–77.13 nm. Fourier transform infrared spectroscopy (FTIR) showed that nanoparticles were capped with alga compounds. The chemical constituents, viz. Andrographolide, Alloaromadendrene oxide, glutamic acid, hexadecanoic acid, oleic acid, 11-eicosenoic acid, stearic acid, gallic acid, Epigallocatechin Catechin and Epicatechin gallate of the algal extract were identified which may act as a reducing, stabilizing and capping agent. The nanoparticles were also evaluated for their antibacterial activities which showed better antibacterial effects with maximum inhibition zones of 17–16 mm by AuNPs synthesized by ethanolic extract against Escherichia coli, Klebsiella pneumoniae and MRSA, respectively, followed by Staphylococcus aureus and Pseudomonas aeruginosa (13 mm). Furthermore, the nanoparticles synthesized by the powder of G. elongata were found to be highly effective against E. coli and K. pneumoniae (13.5 and 13 mm), respectively. On the other hand, the free ethanolic extract of G. elongata exhibits high activity only against MRSA (14 mm).