Investigation of antioxidant activity of silver nanoparticles with mushroom metabolites

Silver nanoparticles (AgNPs), which received great interest lately due to their nano-sized dimension and large surface area, have been applied in medicine, drug delivery systems, bio-labeling, sensing, and food preservation. The green approach in the preparation of AgNPs uses extracts from plants where the metabolites in the extract act as reducing and stabilizing agents. There are limited studies available that uses mushroom extracts for the synthesis of AgNPs. This study explored the green synthesis of AgNPs using the mushrooms Ganoderma lucidum and Laxitextum bicolor. The optimal conditions using Central Composite Design (CCD) were determined for the synthesis of AgNPs when using G. lucidum extract (pH=10, Temp= 65C, Time= 120 min, Volextract = 3.5mL, VolAgNO3= 20mL) and when using L. bicolor extract (pH=10, Temp= 55C, Time= 180 min, Volextract = 1.5mL, VolAgNO3= 20mL). The surface plasmon resonance was observed at 420 nm in UV-Vis spectrum indicating successful synthesis of AgNPs. SEM and TEM showed that G. lucidum-AgNPs and L. bicolor-AgNPs are mostly spherical having diameters of 21.66  4.22 nm and 14.38  6.96 nm, respectively. FT-IR confirmed the presence of organic compounds in the AgNPs showing similar stretching frequencies as compared to the mushroom aqueous extract. The presence of -OH stretch and -NH bend in FT-IR suggests that the capping molecules are proteins and phenolic compounds. EDS analysis also showed the presence of the elements Ag, C, N, and O. Results indicate that metabolites from the mushrooms served as capping agents to the AgNPs. Both the mushroom-mediated AgNPs were found to be relatively stable with a zeta potential of - 14.7 mV for G. lucidum-AgNPs and -25.3 mV for L. bicolor-AgNPs. LC-MS/MS analysis revelead the identities of the capping molecules. DPPH assay showed that the G. lucidum-AgNPs and L. bicolor-AgNPs possessed an antioxidant property. The activity of L.bicolor-AgNPs were significantly different from its raw aqueous extract while G.lucidum-AgNPs do not have significant difference on its antioxidant activity compared to its raw aqueous extract.