Antimicrobial Activity of Green Synthesized Copper Nanoparticles (CuNPs) Using Aqueous Extract of Psidium guajava on Clinical Bacteria Isolates

Abstract

The eco-friendly synthesis of nanoparticles using an aqueous plant extract as a capping and stabilizing agent has garnered substantial attention, particularly in pharmaceuticals and drug delivery applications. This study focused on utilizing copper sulfate pentahydrate (CuSO₄·5H₂O) as a precursor to synthesize copper nanoparticles at both pH 4-5 and pH 8, with Psidium guajava (leaves and fruits) extract playing a crucial role. Fourier transform infrared (FTIR) spectroscopy identified four major functional groups at distinct peaks, confirming their responsibility for capping and stabilizing the synthesized P.g-CuNPs. Scanning electron microscopy (SEM) revealed spherical shapes with an average particle size range of 20-30 nm. Energy-dispersive X-ray (EDX) analysis confirmed the presence of pure copper (Cu) at 54.15%. The antimicrobial study demonstrated that P.g-CuNPs synthesized at pH 4-5 exhibited complete growth inhibition of all tested bacterial strains at varying concentrations. Furthermore, serially diluted P.g-CuNPs (pH 5) inhibited Salmonella spp, E. coli, and Streptococcus spp at 100 μg/mL, while P.g-CuNPs (pH 8) only inhibited E. coli at the same concentration. Notably, acid-based synthesized P.g-CuNPs exhibited higher efficacy in the antimicrobial study compared to their alkaline-based counterparts. This study suggests the potential biomedical applications of P.g-CuNPs, including therapeutic drugs for microbial infectious diseases, integration into textile coatings, and nanocapsulation for food storage to extend shelf life.