Biological Synthesis of Gold Nanoparticles from Suspensions of Green Microalga Dunaliella salina and Their Antibacterial Potential

Green synthesis of nanoparticles has been widely considered because of its applications in various fields such as medicine and pharmaceutical industries. The synthesis of nanoparticles using microalgae is less known, hence the attention of researchers in this context already has been attracted. In the present study, gold nanoparticles (GNPs) were synthesized from gold(III) chloride trihydrate (HAuCl 4 ·3H 2 O) by an ecofriendly, low-cost method using a green microalgae Dunaliella salina as a reducing and stabilizing agent simultaneously. The effect of pH, algal suspension volume, algal population, gold salt concentration, and temperature was studied for determining the optimum conditions of GNP synthesis. Biosynthesis of GNPs was monitored by UV–Visible (UV–Vis) absorption spectroscopy, which showed surface plasmon resonance band at 550 nm. The Fourier transform infrared (FT-IR) spectroscopy revealed that the functional groups of algal cells including hydroxyl (–OH), carbonyl (C = O), and amine (–NH) interact with gold ions to reduce and stabilize GNPs. The electron graphs (TEM and SEM) showed that the resulting GNPs are all almost spherical with the average size of 50 nm. The presence of sharp peaks in X-ray diffraction (XRD) patterns shows a high degree of crystallinity with the face-centered cubic (FCC) structure for GNPs generated by D. salina suspension. The antibacterial effect of 0.05 mg ml −1 of synthesized GNPs displayed a significant bactericidal power on Gram-positive bacteria. These results suggest that algae-synthesized GNPs have a high potential for clinical and pharmaceutical purposes, which support its commercial generation.