Green-synthesized quantum dots from quercus brantii for infected polymicrobial wound healing: mechanisms and biocompatibility.

Abstract

Background: The rise of antimicrobial resistance (AMR) has created an urgent need for alternative therapies, particularly against biofilm-driven polymicrobial wound infections. Although green-synthesized nanoparticles have emerged as promising candidates, many studies lack rigorous validation of their quantum properties, fail to clarify mechanisms of action, and omit essential cytotoxicity profiling in human cells.

Objective: To synthesize silver (Ag), copper (Cu), and zinc oxide (ZnO) quantum dots (QDs) using Quercus brantii acorn extract, confirm quantum confinement effects, and evaluate their antimicrobial efficacy, mechanistic basis, and biosafety in a clinically relevant murine wound model.

Methods: QDs were synthesized via a standardized hydrothermal approach. Quantum confinement was verified using photoluminescence (PL) spectroscopy and Tauc plot analysis. Antimicrobial activity was tested against multidrug-resistant (MDR) clinical isolates of Pseudomonasaeruginosa, methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii, and Klebsiella pneumoniae. To differentiate oxidative stress from chemical artifacts, we employed non-thiol reactive oxygen species (ROS) scavengers (Trolox, Mannitol) and electron paramagnetic resonance (EPR). Cytotoxicity was assessed in human keratinocytes (HaCaT) and dermal fibroblasts (HDF). In vivo efficacy was evaluated in a murine excisional wound model infected with a polymicrobial consortium, tracking pathogen-specific clearance. Hydrogel rheology and stability were also characterized.

Results: Monodispersed, crystalline QDs with evidence consistent with quantum confinement were obtained (Ag-QDs: 7.2 ± 1.5 nm; apparent bandgap: 2.85 eV). Ag-QDs showed strong antimicrobial activity (MIC: 4.5-18.1 µg/mL) and biofilm inhibition (up to 85% at ½×MIC). Mechanistic experiments, including EPR and ROS-scavenger assays, supported ROS-associated oxidative stress as a major contributor to bacterial killing under the tested conditions. Ag-QDs exhibited bactericidal activity at concentrations that were non-toxic to human skin cells in the employed assay (Selectivity Index for MRSA: 18.9). In vivo, topical application of an Ag-QD hydrogel (shear-thinning) accelerated wound closure to 95.3% by Day 14 (comparable to uninfected controls) and reduced the total bacterial burden by 4.2 log₁₀ CFU/g; all four pathogens were below the detection limit at the study endpoint. No overt systemic toxicity was observed based on the assessed biomarkers. Resistance development in serial passage assays was limited (2-fold MIC increase after 30 passages), noting that longer-term polymicrobial studies are required to fully evaluate resistance evolution.

Conclusion: Q. brantii-mediated Ag-QDs are a promising green-synthesized nanomaterial with physicochemical characteristics consistent with quantum-dot behavior and notable antimicrobial and antibiofilm activity against MDR polymicrobial communities. In a preclinical murine wound model, topical Ag-QD hydrogel treatment was associated with accelerated wound closure and marked reductions in bacterial burden, alongside a favorable preliminary biosafety profile based on the endpoints assessed. Further studies are warranted to validate efficacy in clinically relevant chronic wound settings (e.g., diabetic models), to expand long-term toxicology, and to clarify resistance evolution and mechanistic pathways in polymicrobial systems.