Photodynamic Antibacterial Nanofibers with Tunable Pro- and Antioxidant Activity via N,S-Doped Carbon Quantum Dots...

Antibiotic resistance poses a critical challenge in ocular medicine, where treatments must combine antibacterial potency with tissue compatibility. Electrospun core-shell nanofibers offer an attractive solution for ocular applications as they provide a biomimetic extracellular matrix structure with controlled drug release and surface functionality. In this work, polycaprolactone (PCL) was used as the mechanically robust, biodegradable core, while polyvinylpyrrolidone (PVP) formed a hydrophilic shell to enhance wettability and ocular compatibility. The nanofibers were further functionalized with N,S-doped carbon quantum dots, exhibiting light-switchable redox behavior. Compositional and spectroscopic analyses revealed that N,S-doped CQDs possessed a significantly narrowed bandgap (3.14 eV) relative to cysteine- and tryptophan-derived CQDs, attributable to heteroatom-induced defect states and the formation of π-π conjugated domains, confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). XPS measurements showed valence band energies suitable for superoxide generation under illumination, consistent with the reported redox potentials. As a result, illuminated nanofibers produced reactive oxygen species (ROS), reducing Escherichia coli and Staphylococcus aureus populations by 90% and 80%, respectively. In the dark, the same CQDs exhibited up to 90% radical-scavenging activity, increasing BJ human fibroblast viability by 35%. Additional mechanistic evidence indicated that light enhances the adhesion of CQDs to bacterial membranes, further promoting ROS-mediated inactivation. With a high quantum yield of 50% and strong blue fluorescence (λ_em = 445 nm, λ_ex = 380 nm), the CQDs also offer imaging and diagnostic potential. Together, these findings position N,S-doped CQDs-modified core-shell nanofibers as a biologically adaptive platform capable of photodynamic antibacterial action while supporting cytoprotection and tissue regeneration─an innovative approach for combating antibiotic-resistant ocular infections.