Green synthesis of ZnO nanoparticles using the mangosteen (Garcinia mangostana L.) leaf extract: Comparative preliminary in vitro antibacterial study

Abstract In the realm of public health, the rising threat caused by bacteria resistant to many drugs is a critical concern. In this work, we used the aqueous extract of mangosteen leaves to create zinc oxide (ZnO) nanoparticles (NPs) in an environmentally friendly manner. Through various analytical methods, we thoroughly characterized these biogenic ZnO NPs, including UV−visible, Fourier transform infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray powder diffraction, field emission-scanning electron microscopy with energy dispersive X-ray and high resolution-transmission electron microscopy. ZnO NPs showed distinctive properties among different characterization techniques, including a small energy bandgap of 2.80 eV, a porous, a minimum crystalline size of 16.99 nm, an average particle size of 14.21 nm, and a spherical nanostructure. Additionally, we performed preliminary antibacterial experiments to assess ZnO NPs, copper oxide (CuO) NPs, and ZnO–CuO nanocomposites for antibacterial activity. Interestingly, ZnO NPs showed significant potential in suppressing the growth of Staphylococcus aureus ATCC BAA-1026, Bacillus subtilis ATCC 6633, Escherichia coli ATCC 25922, and Klebsiella pneumoniae ATCC 13883, with decreasing order of minimum inhibitory concentrations: S. aureus = B. subtilis (15.63 μg·mL−1) > E. coli (62.50 μg·mL−1) > K. pneumoniae (125.00 μg·mL−1). These results highlight the potential of biogenic NPs, particularly ZnO NPs, as effective agents against multi-drug-resistant bacteria.