Synthesis of nanoparticles by biological methods using microorganisms, enzymes or plant extracts has been suggested as possible ecofriendly alternative to chemical and physical methods which involve the use of harmful reducing agents. In the current study, silver nanoparticles (AgNPs) were synthesized by green approach from methanolic leaf extract of Blighia sapida. The synthesized AgNPs were characterized by UV-visible (UV-vis) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). The antioxidant activity was evaluated using DPPH radical scavenging assay, determination of total reductive potential, total phenolics content (TPC) and total flavonoids content (TFC) of the synthesized AgNPs. SEM analysis revealed that the size of the synthesized silver nanoparticles ranged from 50-70 nm with maximum UV-vis absorbance at 413 nm. DPPH radical scavenging activity, reducing power, total phenolic and total flavonoid contents of the synthesized AgNPs increased in a dose dependent manner as compared to ascorbic acid the standard reference used. This result confirmed that Blighia sapida is a potential biomaterial for synthesizing AgNPs which can be exploited for its antioxidant activity.

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This study focused on the synthesis and application of nanoparticles using Neodesmus pupukensis (MG257914). Cell free extracts of the microalga was employed to synthesize both silver (AgNPs) and gold nanoparticles (AuNPs). The nanoparticles were characterized using UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM). The nanoparticles were screened for their antimicrobial potential and free radical scavenging activity against stable free radical (2,2-diphenyl-1-picrylhydrazyl). The UV absorption spectra showed absorbance peaks of 430 nm and 530 nm for AgNPs and AuNPs respectively. The FTIR spectra at 3283, 2102.87, 1636.02 for AgNPs and 3264.86, 2104.49, 1636.62, 1232.39, 1028.97 cm−1 for AuNPs confirms the participation of proteins in the capping and stabilization of the nanoparticles. The zone of inhibition indicating the activity of the NP-AgNPs were: Pseudomonas sp (43 mm); Escherichia coli (24.5 mm); Klebsiella pneumoniae (27 mm), Serratia marcescens (39 mm) while AuNPs showed activity to only Pseudomonas sp (27.5 mm) and Serratia marcescens (28.5 mm). The antifungal potency of NP-AgNPs was confirmed with mycelial inhibition of 80.6, 57.1, 79.4, 65.4 and 69.8% against Aspergillus niger, A. fumigatus, A. flavus, Fusarium solani and Candida albicans respectively, while NP-AuNPs had 79.4, 44.3, 75.4, 54.9 and 66.4% against A. niger, A. fumigatus, A. flavus, F. solani and C. albicans respectively. Appreciable free radical scavenging properties was obtained with NP-AuNPs (68.9%) and NP-AgNPs (41.21%). The nanoparticles of Neodesmus pupukensis showed appreciable potential as antimicrobial and antioxidant agents and could be explored for various applications in biotechnology.

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