# Photodynamic Antibacterial Nanofibers with Tunable Pro- and Antioxidant Activity via N,S-Doped Carbon Quantum Dots for Corneal Tissue Engineering

## TL;DR

Researchers developed nanofibers with light-responsive carbon quantum dots that can kill bacteria and protect cells, offering a new approach for treating antibiotic-resistant eye infections.

## Contribution

N,S-doped carbon quantum dots with tunable pro- and antioxidant activity are integrated into core–shell nanofibers for photodynamic antibacterial applications in corneal tissue engineering.

## Key findings

- Illuminated nanofibers reduced Escherichia coli and Staphylococcus aureus populations by 90% and 80%, respectively.
- In the dark, the nanofibers showed up to 90% radical-scavenging activity, increasing BJ human fibroblast viability by 35%.
- N,S-doped CQDs have a high quantum yield and blue fluorescence, enabling potential imaging and diagnostic applications.

## Abstract

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 (λem = 445 nm, λex = 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.