Guazuma ulmifolia bark-synthesized Ag, Au and Ag/Au alloy nanoparticles: Photocatalytic potential, DNA/protein interactions, anticancer activity and toxicity against 14 species of microbial pathogens.

In the present study, we focused on a quick and green method to fabricate Ag, Au and Ag/Au alloy nanoparticles (NPs) using the bark extract of Guazuma ulmifolia L. Green synthesized metal NPs were characterized using different techniques, including UV-Vis spectroscopy, FT-IR, XRD, AFM and HR-TEM analyses. The production of Ag, Au and Ag/Au alloy NPs was observed monitoring color change from colorless to brown, followed by pink and dark brown, as confirmed by UV-Vis spectroscopy characteristic peaks at 436, 522 and 510nm, respectively. TEM shed light on the spherical shapes of NPs with size ranges of 10-15, 20-25 and 10-20nm. Biosynthesized NPs showed good catalytic activity reducing two organic dyes, 4-nitrophenol (4-NP) and Congo red (CR). UV-vis spectroscopy, fluorescence, circular dichroism spectroscopy and viscosity analyses were used to investigate the NP binding with calf thymus DNA. The binding constant of NPs with DNA calculated in UV-Vis absorption studies were 1.18×104, 1.83×104 and 2.91×104M-1, respectively, indicating that NPs were able to bind DNA with variable binding affinity: Ag/Au alloy NPs>Ag NPs>Au NPs. Ag/Au alloy NPs also showed binding activity to bovine serum albumin (BSA) over the other NPs. Ag and Ag/Au alloy NPs exhibited good antimicrobial activity on 14 species of microbial pathogens. In addition, the cytotoxic effects of Ag/Au alloy NPs were studied on human cervical cancer cells (HeLa) using MTT assay. Overall, our work showed the promising potential of bark-synthesized Ag and Ag/Au alloy NPs as cheap sources to develop novel and safer photocatalytic, antimicrobial and anticancer agents.