Nitrogen-Doped Carbon Quantum Dots for Visible-Light Photocatalytic Disinfection

Overview

This project develops nitrogen-doped carbon quantum dots (NCQDs) as a next-generation photocatalytic disinfectant for antimicrobial applications. NCQDs are discrete, quasi-spherical nanomaterials under 10 nm in size, featuring a nanocrystalline core of predominantly sp2-bonded carbon. When activated by visible or near-UV light, positively charged NCQDs interact with negatively charged bacterial membranes, causing surface damage and cytoplasmic leakage, generating reactive oxygen species, and producing localized hyperthermia that together lead to bacterial cell death.

Unlike conventional photocatalytic sanitizers such as TiO2, which require UV light due to large band gaps exceeding 3.2 eV, NCQDs possess smaller band gaps that enable activation under visible light. This makes them practical for a broader range of real-world disinfection scenarios. NCQDs are highly dispersive, non-toxic, and capable of repeated photocatalytic oxidative cycles, offering a sustainable and effective antimicrobial solution.

Technical specifications

Core technology:

• Nitrogen-doped carbon quantum dots (NCQDs) under 10 nm with tunable size, structure, and optical properties
• Activated by visible and near-UV light at wavelengths above 280 nm
• Smaller band gap than TiO2, enabling visible-light-driven photocatalysis without UV requirements

Mechanism of action:

• Positively charged NCQDs (zeta potential up to +45 mV) disrupt negatively charged bacterial membranes, causing cytoplasmic leakage
• Generation of reactive oxygen species that damage bacterial cells
• Light absorption produces hyperthermia, contributing to cell damage and death

Demonstrated antimicrobial performance:

• EDA-derived NCQDs reduced E. coli from approximately 10^7 CFU/mL to approximately 10^2 CFU/mL within 30 minutes under visible light
• Glucose-spermine-derived NCQDs (~6 nm, +45 mV zeta potential) effective against E. coli, S. aureus, P. aeruginosa, Salmonella enterica, and methicillin-resistant S. aureus (MRSA) at concentrations as low as 2–4 µg/mL

Tunability:

• Size, excitation/absorption/emission wavelengths, and surface functionality can be modified through feedstock and production environment variations
• Adaptable to meet specific antimicrobial requirements

Technology readiness level

NCQDs have demonstrated proof-of-concept antimicrobial efficacy in published laboratory studies against multiple bacterial strains, including drug-resistant MRSA, under visible light illumination. However, key questions remain before commercial deployment: dispersive behavior in complex sanitizing solutions containing other chemicals, optimization of dosing, rate of antimicrobial degeneration at optimal doses, and duration of surface effectiveness. Florida Institute of Technology researchers are actively pursuing validation studies to address these questions and advance the technology toward practical application.