Mallotus oppositifolius-mediated biosynthesis of bimetallic nanoparticles of silver and nickel: antimicrobial activity and plausible mechanism(s) of action

This study demonstrated the green synthesis route of silver (Ag), nickel (Ni), and silver-nickel bimetallic nanoparticles (Ag-Ni BNPs) using Mallotus oppositifolius leaf extract and their antimicrobial activity against bacteria and fungi. The capping ability of the leaf extract was explored and several analytical techniques confirmed the nanoparticles’ biosynthesis. The antimicrobial activity of the nanoparticles was evaluated by the agar diffusion method. Optical property revealed colour change from colourless silver nitrate to brown for silver nanoparticles, the bright green of nickel chloride to dark reddish brown for nickel nanoparticles and brown for the silver-nickel nanoparticles after treatment with the extract of M. oppositifolius. FTIR showed the chemical functionalities of the possible molecules responsible for the bio-reduction of the metals. Secondary metabolites such as terpenoids, polyols, alkaloids, phenolic acids, and proteins (containing hydroxyl, aromatic amine, carbonyl groups, etc.) are present in plant extracts, and they play a crucial role in the biosynthesis of metal-based nanoparticles. UV-visible spectroscopy revealed surface plasmon resonance (SPR) at 454, 420, and 437 nm. SEM image revealed AgNPs and NiNPs nanoclusters and well-defined and less agglomerated morphology of Ag-Ni BNPs, respectively. Preliminary antimicrobial studies showed that the bimetallic nanoparticles (Ag-Ni BNPs) exhibited better antibacterial activity than their monometallic forms (AgNPs and NiNPs) but were not as effective against fungi. These findings urge future research into this hybrid material as a practical countermeasure to microbial contamination. Graphical Abstract: (Figure presented.)