Toward a molecular-level understanding of nitrogen functionalities in carbon dots for enhanced antibacterial activity...

The molecular design of antibacterial nanomaterials remains limited by insufficient understanding of how surface chemistry governs biological performance. In this study, a molecular-level understanding of how nitrogen functionalities in carbon dots (CDs) govern their dual functionality in bacterial inhibition and glutathione (GSH) sensing was developed through an integrated experimental and Time-Dependent Density Functional Theory (TD-DFT) approaches. Nitrogen-functionalized CDs were synthesized via a temperature-controlled hydrothermal method with diverse nitrogen functionalities and evaluated for their antibacterial efficacy against Staphylococcus aureus and Escherichia coli, as well as their fluorescence-based sensing performance toward GSH. All samples demonstrated strong antibacterial activity at a low concentration of 10 ppm, with CD-160 achieving the highest efficacy, reducing Escherichia coli viability to 0.07 %, and demonstrated sensitive GSH detection across a wide concentration range (0-1000 μM). TD-DFT and spectroscopic analyses revealed that Pyrrolic-N CDs possessed lower band gaps, higher chemical softness, and stronger electron localization on heteroatoms, which collectively enhanced both microbial inhibition and redox-responsive sensing behavior. These findings provide a structure-function framework that enables the rational design of multifunctional carbon-based nanomaterials for biomedical applications targeting antibiotic-resistant pathogens and oxidative stress biomarkers.