Green synthesis of iron oxide nanoparticles using Ceratonia siliqua L. aqueous extract: improvement of colloidal stability by optimizing synthesis parameters, and evaluation of antibacterial activity against Gram-positive and Gram-negative bacteria

Abstract

Abstract This study focused on the colloidal stability enhancement of iron oxide nanoparticles synthesized using aqueous extract of the Ceratonia siliqua L. (carob pod) by optimizing the synthesis parameters. The synthesis parameters were determined as the concentration of iron ions, the concentration of extract, pH of extract, temperature, stirring rate, and reaction time. The significance of the studied factors in controlling the particle size distribution of nanoparticles was quantitatively evaluated via analysis of variance (ANOVA). Iron oxide nanoparticles were produced with an average zeta potential of +41 ± 0.8 mV, hydrodynamic size of 78 ± 22 nm, and a polydispersity value of 0.42 ± 0.06, respectively. As a result of the stability study by measuring the zeta potential, it was determined that the colloidal stability was maintained for 3 months. Green iron oxide nanoparticles (gIONPs) showed inhibition zones of 24.27 ± 0.12 mm and 20.83 ± 0.11 mm in 250 mg/mL concentration against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial strains, respectively. S. aureus was susceptible to the gIONPs according to the standard antibiotics of Cefotaxime (≥23 mm), Tetracycline (≥19 mm), Gentamicin (≥15 mm), and Cefoxitin (≥22 mm). E. coli was susceptible to the gIONPs according to the standard antibiotics of Tetracycline (≥19 mm) and Gentamicin (≥15 mm), but showed resistance to the Cefotaxime (15–22 mm) and Cefoxitin (≤21 mm) standard antibiotics. This study suggests that the green synthesized iron oxide nanoparticles could be used as an antimicrobial agent and a promising candidate for usage in sensor, biomedical, and electronics applications for being in a highly stable structure.