Assessment of antioxidant, antibacterial and anti-proliferative (lung cancer cell line A549) activities of green synthesized silver nanoparticles from Derris trifoliata

Abstract

In this work, silver nanoparticles (AgNP-DTa) were prepared using an aqueous seed extract of D. trifoliata. The importance of the present piece of work is viewed specially with respect to ascertaining the potential of a widely distributed under-utilized mangrove associated plant, Derris trifoliata (DT), as medicine. The as-prepared AgNP-DTa were well dispersed and stabilised in aqueous solution through biological ligands extracted from the seeds of DT. The functional groups present in the bio-ligands of DT act as reducing and stabilising agents in the formation of nanoparticles. Besides, in the present work, sunlight could induce and catalyse the reduction process of Ag⁺ to its corresponding silver atoms of nanoscale dimensions. The size of AgNP-DTa decreased with an increase in the duration of sunlight irradiation. Bio-augmented nanoparticles were characterized by UV-vis spectroscopy, XRD, HR-TEM, DLS, AFM and photoluminescence measurements. Preliminary phytochemical studies and FTIR analysis confirmed the presence of secondary metabolites with hydroxyl, amine and carbonyl groups as reducing/capping agents. AgNP-DTa demonstrated high DPPH scavenging activity with an IC 50 value of 8.25 μg ml^-1. Greater antioxidant activity of AgNP-DTa was also confirmed from total antioxidant capacity (TAC) assay where it was found that the reducing power of 1 g of AgNP-DTa is almost equivalent to that of 1.3 g of Trolox. In addition, highly stable AgNP-DTa showed antibacterial activities against Gram positive and Gram negative bacteria. The as-prepared AgNP-DTa were observed to inhibit the growth of Klebsiella pneumonia, Staphylococcus aureus and Escherichia coli and no clear zone was obtained for Pseudomonas aeruginosa. With reference to the anti-proliferative activities, AgNP-DTa exhibited moderate activity on A549 lung cancer cell lines with a median effective concentration of 86.23 ± 0.22 μg ml^-1.

Fig. 1. (a) DT seeds (; http://www.NatureLoveYou.sg), (b) AgNO₃ solution, (c) aqueous seed extract and (d) brownish-yellow AgNP-DTa nanoparticles.

Fig. 2. (a) UV-vis spectra of AgNP-DTa; inset of (a) shows the gradation in colour with the irradiation time. (b) XRD pattern of AgNP-DTa and (c) PL emission at 360 nm.

Fig. 3. (a) FTIR spectrum of the DT extract and (b) FTIR spectrum of AgNP-DTa.

Fig. 4. (a), (b) and (c) TEM images of AgNP-DTa, (d) SAED pattern of AgNP-DTa, (e) AFM image of AgNP-DTa and (f) zeta potential of AgNP-DTa.

Fig. 5. Percentage inhibition of DPPH radicals with the concentrations of AgNP-DTa, seed extract and ascorbic acid.

Fig. 6. (a) Photographs of the antimicrobial plates of Klebsiella pneumonia, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa; 1, 2, 3, 4 and 5 contain 0.015 mg AgNO₃, 0.01 mg AgNP-DTa, 0.02 mg AgNP-DTa, 0.03 mg AgNP-DTa and aqueous seed extract, respectively.

Fig. 7. Plot showing the variation of % cell viability with the concentration of AgNP-DTa.

Fig. 8. An inverted phase contrast tissue culture microscopy image of A549 cell lines on treatment with (I) a decoction of seeds of DT and (II) AgNP-DTa.