Identification of phytochemicals capping the exogenously biosynthesized silver nanoparticles by T. apollinea (Delile) DC. living plants and evaluation of their cytotoxic activity

The exogenous synthesis of nanoparticles (NPs) by living plant systems was considered a sustainable way to synthesize NPs. It is cost-effective and more eco-friendly compared to the currently used chemical and physical methods. In this study, silver NPs (AgNPs) were exogenously synthesized by the desert Tephrosia apollinea (Delile) DC. living plants under different levels of drought stress simulated by polyethylene glycol (PEG). The phytochemicals capping the AgNPs were characterized by gas chromatography-mass spectrometry (GC-MS). Different phytochemicals, such as palmitic acid, stearic acid, eicosane, oxalic acid, and 1,3-propanediol, were identified as possible capping agents. Hierarchical clustering and principal component analysis of the GC-MS data indicated that the levels and types of phytochemicals encapsulating the AgNPs were affected by the drought stress levels and its duration applied during AgNPs synthesis. Furthermore, the cytotoxic activities of the synthesized AgNPs were varied. The cytotoxic activity was higher with AgNPs synthesized at higher drought stress levels. The lowest half-maximal inhibitory concentration (IC50) toxicity levels were observed at −0.4 MPa, which is 5.66 ± 1.69 μg/mL for human MDA-MB-231 breast cancer cells and 4.65 ± 0.52 μg/mL for human HaCat normal skin cells. Our data collectively indicate that drought stress pre-treatment of living plants could synthesize NPs with variable capping phytochemicals. Hence, variable promising biomedical applications could be possible.