Green Synthesis of Iron Nanoparticles from Spinach Leaf and Banana Peel Aqueous Extracts and Evaluation of Antibacterial Potential

Abstract

Spinacia oleracea (spinach) and Musa acuminata (banana) were chosen for the study, and aqueous extracts of spinach leaf extract (SLE) and banana peel extract (BPE) were prepared for the synthesis of iron nanoparticles (FeNPs), and their antibacterial potential against pathogenic bacteria Bacillus subtilis (MTTC 1133) and Escherichia coli (MTTC 62) was evaluated. In 10 minutes at 60°C, the color of the mixture (FeCl3+SLE) changed from light green to dark blackish-brown, and the color of the mix (FeCl3+BPE) changed from transparent yellow to dark black, confirming the synthesis of FeNPs from SLE and BPE, respectively. The UV-Vis spectra of spinach- and banana-derived FeNPs revealed two peaks ranging from 240 to 430 nm and multiple peaks at 240, 270, and 395 nm, respectively. FTIR spectroscopy was used to show different functional groups on BPE and SLE, and their role in FeNP synthesis was predicted. TEM micrographs showed that the particles were in nanoscale, ranging in size from 20 to 50 nm for BPE-derived FeNPs and 10 to 70 nm for SLE-derived FeNPs. The FeNP (BPE and SLE) XRD analysis revealed amorphism, with a weak iron characteristic peak, indicating noncrystallinity. The antibacterial potential of BPE- and SLE-FeNPs was investigated, and inhibition zones (mm) against B. subtilis ( $22.70\pm 0.4$ ) and E. coli ( $20.45\pm 1.66$ ) were observed, as well as SLE-FeNPs against B. subtilis ( $23.56\pm 1.00$ ) and E. coli ( $20.33\pm 0.58$ ). There were no significant differences in antibacterial activities between BPE-FeNPs and SLE-FeNPs. Positive controls were tetracycline and gentamicin, both standard antibiotics, at 5 μg/disk. SLE- and BPE-derived green FeNPs were also analysed in vivo of D. melanogaster life history traits, i.e., fecundity, hatchability, viability, and duration of development for toxicity evaluation. SLE- and BPE-derived green FeNPs at a concentration of 10 mg/L were fed flies compared to normal diet-fed flies (control sample), and no significant differences were observed between them. The findings suggest that FeNPs have a high antibacterial potential and could be used as antibacterial agents against pathogenic bacteria while being nontoxic in nature.