Background: 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.
The synthesized AgNPs were tested for their antibacterial and antioxidant properties.
Methods: 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. The antibacterial properties
of the AgNPs were tested against Escherichia coli and Staphylococcus aureus using the tube dilution
test. The synthesized nanoparticles were tested for total phenolic composition (TPC) using the
Folin - Ciocalteau method, whereas their radical scavenging activity using the 1,1-diphenyl-2-
picrylhydrazyl (DPPH) free radical assay.
Results: 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 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 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.
Conclusion: 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.