Nannochloropsis Extract-Mediated Synthesis of Biogenic Silver Nanoparticles, Characterization and In Vitro Assessment of Antimicrobial, Antioxidant and Cytotoxic Activities.

Objective: To investigate the biogenic synthesis of silver nanoparticles (AgNPs) using partially purified ethyl acetate extract of Nannochloropsis sp. hexane (EAENH) fraction of microalga. Methods: The green synthesis of AgNPs was confirmed with UV-Vis spectrum which shows the surface plasmon resonance (SPR) at 421 nm. Fourier Transform Infrared Spectra (FTIR) presented the involvement of functional groups like carboxyl groups of fatty acids, tetraterpenoids of xanthophylls, hydroxyl groups of polyphenols, carbonyl and amide linkage of proteins in the AgNP synthesis. Gas Chromatography-Mass Spectrometry analysis (GCMS) revealed that phytochemicals like octadecanoic acid and hexadecanoic acid imply in capping, bioreduction, and stabilization of AgNps. Result: High-resolution Transmission electron microscope (HRTEM), Dynamic light scattering (DLS), X-ray diffraction (XRD) and EDX analysis showed the crystalline form of the AgNPs with Z-average size 57.25 nm. The zeta potential value of -25.7 mV demonstrated the negative surface charge and colloidal stability of AgNPs. The antimicrobial activity of AgNPs displayed effective inhibition zone against selected bacterial and fungal pathogens. In vitro, antioxidant effects were assessed by 1,1-diphenyl-2-picryl-hydrazyl (DPPH), hydrogen peroxide and reducing power assays which revealed excellent scavenging potential for AgNPs than the extracts. The anti-proliferative potential of biofabricated AgNPs and extracts on Human Non-small lung cancer cell line (A549) was assessed using 3­(4,5-dimethylthiazol-2-yl)-2,5- diphenyl-tetrazolium bromide (MTT) assay with IC50 values of 15 µgmL-1 and 175 µgmL-1 respectively. Conclusion: The study reveals that the microalgae-mediated AgNPs possesses potent antimicrobial and antioxidant activity along with the ability to stimulate apoptosis in A-549 cell line.