Harnessing Efficient ROS Generation in Carbon Dots Derived from Methyl Red for Antimicrobial Photodynamic Therapy

Area of Science:

• Materials Science
• Nanotechnology
• Microbiology
• Photochemistry

Background:

• Rising antimicrobial resistance poses a significant public health threat, necessitating novel therapeutic strategies.
• Carbon dots are nanomaterials with unique optical and electronic properties, showing potential in biomedical applications.
• Methyl red, an azo dye, can be a precursor for synthesizing functionalized carbon dots.

Purpose of the Study:

• To synthesize and characterize carbon dots (CD-MR) from methyl red azo dye.
• To evaluate the physicochemical properties, including photoluminescence and cytotoxicity, of CD-MR.
• To investigate the potential of CD-MR in bioimaging and as an antimicrobial agent, particularly through reactive oxygen species (ROS) generation.

Main Methods:

• Synthesis of carbon dots (CD-MR) from methyl red.
• Morphological and structural characterization (e.g., nitrogen content analysis).
• Photoluminescence spectroscopy, cytotoxicity assays against mammalian cells, and ROS generation studies (singlet oxygen quantum efficiency).
• Antimicrobial activity testing against *Staphylococcus aureus*, *Candida albicans*, and *Cryptococcus neoformans* using Kirby-Bauer susceptibility tests and photoexcitation at 532 nm.

Main Results:

• CD-MR exhibited tunable photoluminescence and low cytotoxicity against mammalian cells.
• CD-MR demonstrated efficient generation of reactive oxygen species, including high singlet oxygen quantum efficiency.
• Upon photoexcitation at 532 nm, CD-MR showed significant antimicrobial activity against *S. aureus*, *C. albicans*, and *C. neoformans*, inhibiting the growth of *C. neoformans*.

Conclusions:

• Nitrogen-doped carbon dots derived from methyl red are effective ROS generators.
• CD-MR possess strong antimicrobial properties against clinically relevant pathogens, especially when photoactivated.
• These findings highlight the potential of CD-MR as a dual-functional nanomaterial for bioimaging and combating microbial infections.