Green synthesis of metal nanoparticles by microalgae

Green synthesis of metal nanoparticles through biological resources has attracted attention in recent years. The main reason for that, a lot of toxic chemicals as reducing and stabilizing agents are used in physical and chemical methods which are known as conventional methods. Organisms such as plants, fungi, bacteria, and algae are alternative sources for green nanoparticle synthesis because of their more eco-friendly nature and not be a threat to human health. Microalgae as aquatic microorganisms have been added into the formulations of food, cosmetics, and pharmaceutical for many years, due to their high value-added metabolites such as proteins, vitamins, pigments, fatty acids, intracellular and extracellular polysaccharides. In addition, microalgae have a high potential in biogenic nanoparticle synthesis because of their metal ions accumulation capability, phytoremediation potential, and rich in intracellular and extracellular metabolites that will reduce metal ions to elemental state. In recent years, the number of studies, focused on silver, gold, titanium, zinc, iron, etc. nanoparticle synthesis from many microalgae species by intracellular and extracellular pathways has increased. This review article aims to provide a brief outline of microalgae and cyanobacteria species studied in the context of nanoparticle synthesis, different approaches for nanoparticle synthesis from microalgae, the mechanism of nanoparticle synthesis, and basic characterization principles and antimicrobial activities of nanoparticles produced by green synthesis.