Green synthesis of a CQD/AGNPS composite from guava leaf and its potent antimicrobial activity against multidrug-resistant ESKAPEE pathogens

Abstract

This study presents a green synthesis approach for fabricating CQD/AgNPs nanocomposite materials, in which carbon quantum dots (CQDs) were derived from dried guava leaves (Psidium guajava)—a widely available, low-cost, and accessible plant material in Vietnam. The resulting nanocomposite was characterized using a range of advanced techniques, including UV-Vis, PL, XRD, FTIR, Raman, SEM and TEM. These analyses confirmed the formation of uniformly dispersed, spherical nanoparticles with an average diameter of approximately 33.4 nm and good structural stability. Interestingly, the CQD/AgNPs nanocomposite demonstrated strong antibacterial activity against multidrug-resistant (MDR) pathogens of the ESKAPEE group. In particular, the material exhibited a minimum inhibitory concentration (MIC) of 25 µg mL⁻¹ towards Acinetobacter baumannii, a highly drug-resistant bacterium commonly associated with hospital-acquired infections. The nanocomposite also showed significant inhibitory effects against ciprofloxacin-resistant strains of Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Enterobacter spp., with MIC values of 50 µg mL⁻¹. This report is among the first to develop a green-synthesized CQD/AgNP nanomaterial with low production cost, good industrial scalability, and long-term stability at room temperature. Additionally, the study also comprehensively evaluates the material's antibacterial activity against five drug-resistant ESKAPEE pathogens, thereby highlighting its potential application as an alternative to conventional antibiotics.