Green synthesis of carbon quantum dots (CQDs) from oak fruit: antimicrobial and anti-biofilm efficacy against ESKAPE pathogens in wound infections

Aim: The present study aims to synthesize Carbon Quantum Dots (CQDs) using natural oak fruit as a green carbon precursor and to evaluate their antimicrobial and anti-biofilm activities against WHO priority antibiotic-resistant ESKAPE pathogens isolated from clinical wound infections. Methods: CQDs were synthesized via a one-step hydrothermal method (190°C for 5 hours). The study design consisted of four main phases: nanoparticle synthesis and characterization (TEM, FTIR, UV-Vis, fluorescence spectroscopy), in vitro microbiological evaluations (disk diffusion, minimal inhibition concentration/ minimal bactericidal concentration (MIC/MBC), and microtiter plate assays), molecular investigations (Real-Time PCR targeting biofilm-associated genes), and in vivo animal model studies using murine infected wound model. A total of 122 clinical isolates from diabetic, burn, and surgical wounds were collected over 6 months, alongside standard bacterial strains. Results: Successful synthesis of CQDs was confirmed by blue/green luminescence under 365 nm UV irradiation and the presence of surface functional groups (OH, COOH, C=O) via FTIR. TEM revealed uniform spherical morphology with an average particle size <10 nm. Molecular analysis showed that sub-MIC concentrations of CQDs significantly down-regulated key biofilm-associated genes (icaA/icaD in Staphylococcus aureus, lecA/pelA in Pseudomonas aeruginosa, mrkA/mrkD in Klebsiella pneumoniae, and bap/ompA in Acinetobacter baumannii) compared to the 16S rRNA reference gene (P<0.05). In vivo evaluation demonstrated that topical application of CQDs significantly accelerated epithelialization, improved wound contraction, and reduced wound area over 14 days compared to untreated and antibiotic-treated controls (P<0.05). Conclusion: Hydrothermally synthesized oak-derived CQDs effectively disrupt biofilm formation at the transcriptional level, reduce wound bacterial burden, and accelerate tissue regeneration. These findings highlight the potential of green-synthesized CQDs as alternative therapeutic agents for managing multidrug-resistant wound infections.