Planophila laetevirens-Mediated Synthesis of Silver Nanoparticles: Optimization, Characterization, and Anticancer and Antibacterial Potentials

Algal-mediated synthesis of nanoparticles (NPs) opensthe horizonfor green and sustainable synthesis of NPs that can be used in manyfields, such as medicine and industry. We extracellularly synthesizedsilver NPs (Ag-NPs) using the novel microalgae Planophilalaetevirens under optimized conditions. The isolatewas collected from freshwater/soil, purified, morphologically identified,and genetically identified using light, inverted light, scanning electronmicroscopy, and 18S rRNA sequencing. The phytochemicals in the algalextract were detected by GC-MS. Aqueous biomass extracts andcell-free media were used to reduce silver nitrate to Ag-NPs. To getsmall, uniformly shaped, and stable Ag-NPs, various abiotic parameters,including precursor concentration, the ratio between the reductantand precursor, temperature, time of temperature exposure, pH, illumination,and incubation time, were controlled during the synthesis of Ag-NPs.B-P@Ag-NPs and S-P@Ag-NPs (Ag-NPs synthesized using biomass and cell-freemedium, respectively) were characterized using UV-vis spectroscopy,transmission electron microscopy, scanning electron microscopy, energy-dispersiveX-ray analysis (EDX) and mapping, Fourier transform infrared (FTIR)spectroscopy, and a zeta sizer. S-P@Ag-NPs had a smaller size (10.8 & PLUSMN; 0.3 nm) than B-P@Ag-NPs (19.0 & PLUSMN; 0.6 nm), while their shapeswere uniform quasispherical (S-P@Ag-NPs) and spherical to oval (B-P@Ag-NPs).EDX and mapping analyses demonstrated that Ag was the dominant elementin the B-P@Ag-NP and S-P@Ag-NP samples, while FTIR revealed the presenceof O-H, C-H, N-H, and C-O groups, indicatingthat polysaccharides and proteins acted as reductants, while polysaccharides/fattyacids acted as stabilizers during the synthesis of NPs. The hydrodynamicdiameters of B-P@Ag-NPs and S-P@Ag-NPs were 37.7 and 28.3 nm, respectively,with negative charges on their surfaces, suggesting their colloidalstability. Anticancer activities against colon cancer (Sw620 and HT-29cells), breast cancer (MDA-MB231 and MCF-7 cells), and normal humanfibroblasts (HFs) were screened using the MTT assay. B-P@Ag-NPs andS-P@Ag-NPs had a greater antiproliferative effect against colon cancerthan against breast cancer, with biocompatibility against HFs. Thebiocidal effects of the B-P@Ag-NPs and S-P@Ag-NPs were evaluated against Escherichia coli, Bacillus cereus, and Bacillus subtilis using agarwell diffusion and resazurin dye assays. B-P@Ag-NPs and S-P@Ag-NPscaused higher growth inhibition of Gram-negative bacteria than ofGram-positive bacteria. B-P@Ag-NPs and S-P@Ag-NPs synthesized by P. laetevirens are promising antitumor and biocidalagents.