Optimization of Silver Nanoparticle Synthesis by Banana Peel Extract Using Statistical Experimental Design, and testing of their Antibacterial and Antioxidant Properties.

In this study, silver nanoparticles (AgNPs) were synthesized using Banana Peel Extract (BPE), and characterized using UV- Vis absorbance spectroscopy, X-Ray Powder Diffraction (XRD), Atomic Force Microscopy (AFM), and Fourier Transform Infrared Spectroscopy (FTIR). UV - Vis absorbance spectroscopy showed the characteristic plasmon resonance of AgNPs at 433 nm. Nanoparticle size (between 5 and 9 nm) was measured using AFM, whereas their crystallinity was shown by XRD. FTIR identified the ligands that surround the nanoparticle surface. The synthesis conditions were optimised using Central Composite Design (CCD) under Response Surface Methodology (RSM). Silver nitrate (AgNO3) and BPE concentrations (0.25- 2.25 mM, 0.2- 1.96 % v/v respectively), incubation period (24 - 120 h) and pH level (2.3 - 10.1) were chosen as the four independent factors. The fitting parameters (i.e. the wavelength at peak maximum, the peak area, and the peak width) of a Voigt function of the UV- Vis spectra were chosen as the responses. An optimum combination of all independent factors was identified (BPE concentration 1.7 % v/v, AgNO3 concentration 1.75 mM, incubation period 48 h, pH level 4.3), giving minimum peak wavelength and peak width. The antibacterial properties of the AgNPs were tested against Escherichia coli and Staphylococcus aureus using the tube dilution test. The nanoparticles inhibited the growth of E. coli, whereas S. aureus growth was not affected. However, no superiority of AgNPs compared to AgNO3 used for their fabrication (1.75 mM), with respect to antibacterial action, could be here demonstrated. AgNPs were found to present moderate antioxidant activity(44.71± 3.01%), as measured using the 1,1 - diphenyl - 2 - picrylhydrazyl (DPPH) assay, while the BPE (used for their fabrication) presented alone (100%) an antioxidant action equal to 86±1%, something expected due to its higher total phenolic content (TPC) compared to that of nanoparticles. Altogether, the results of this study highlight the potential of an eco-friendly method to synthesize nanoparticles and its promising optimization through statistical experimental design. Future research on the potential influence of other synthesis parameters on nanoparticles yield and properties could further promote their useful biological activities towards their successful application in the food industry and other settings.