Consistent with these observations, Reda et al. noted in their study on the biosynthesis of copper nanoparticles that increasing concentrations (A = 25, B = 50, C = 100, and D = 200 µg/mL) resulted in enhanced antibacterial activity. This finding supports the direct proportionality between nanoparticle concentration and antibacterial efficacy, as highlighted by Reda and colleagues . It was also reported that copper nanoparticles attach to the cell membrane, disrupting its function and directly interacting with the bacterial outer membrane, leading to the release of Cu ions . The high reactivity of copper nanoparticles, owing to their elevated surface area to volume ratio, facilitates extensive interaction with the cell membrane, causing damage to cellular genetic materials and ultimately inducing cell death . figure 7. Antimicrobial susceptibility test of P.guajava extract, P.g-CuNPs(pH 5) and P.g-CuNPs (pH 8)