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Metal nanoparticles have gained considerable attention as versatile nanomaterials due to their size- and shape- dependent electrical, electronic, optical, and catalytic properties. Various physical and chemical approaches have been investigated for synthesizing metal nanoparticles, specifically gold nanoparticles due to their biocompatibility, antioxidant potentials, catalytic activity, and other promising characteristics. As the chemical based approaches have led to questions on toxicity, plant-based sources and microorganisms like bacteria, fungi and algae have been evaluated for synthesizing metal nanoparticles. Gold nanoparticles derived from biological sources are expected to have different properties than those derived from chemical sources, allowing for a wider range of applications. This review provides an overview of the myriad of sources explored for the synthesis of gold nanoparticles which have found useful applications in several fields. The general approach for synthesizing gold nanoparticles is provided followed by the major applications in specific fields namely medicine, biology, electrochemistry and catalysis. Additionally, the possible challenges and future prospects of biosynthesis of nanoparticles have been highlighted. This work could provide an update on the recent advances in the applications of biogenic nanoparticles for future developments. [ABSTRACT FROM AUTHOR]

The synthesis of nanoparticles from biological sources has gained significant attention recently, however, with much emphasis on the novelty of sources. This study aims to provide a comprehensive overview on the aspects of fungal age and type of cultivation on the properties of the nanoparticles. The effect of age of Fusarium oxysporum developed in submerged culture and on solid agar medium was evaluated. When the gold salt solution was added to the fungal colony on agar medium, a deep purple colored radial zone developed in the 3 days old mycelium. The nanoparticles in the radial purple zone had two distinct characteristics when the agar blocks were dried by either lyophilization or heating in a hot air oven. The lyophilized sample contained square bi-pyramidal particles (1 to 2 μm). The oven-dried sample contained abundant truncated triangular nanoplates (150 to 500 nm), decahedrons and icosahedrons (20 to 70 nm), and a few triangular and hexagonal nanoplates (50 nm). The mycelium when suspended in 1 mM HAuCl4·3H2O presented distinct geometries of the nanoparticles in the cytoplasm and periplasm. The formation of gold nanoparticles of different morphologies within the cytoplasm, and the periplasm has implications in Surface Enhanced Raman Spectroscopic (SERS) measurements. HRTEM images of hyphae of Fusarium oxysporum suspended in 1 mM HAuCl4·3H2O for 24 h. The nanoparticles present in the electron dense cytoplasm are markedly different from those in the periplasmic space. [ABSTRACT FROM AUTHOR]