Metal-free visible light photocatalytic carbon nitride quantum dots as efficient antibacterial agents: An insight study

Graphitic carbon nitride (g-CN, commonly called as g-C3N4) quantum dots exhibiting excellent photoluminescence behaviour is explored as metal-free visible light photocatalytic antibacterial agents. The g-CNQDs were synthesized by two-step thermal polymerization and selective dialysis approach yielding particle size in the range of 2–7 nm with a large specific surface area of 264 m2/g. The fluorescent g-CNQDs could efficiently generate superoxide and hydroxyl radicals under visible light irradiation, inhibiting∼99% of Gram negative E.coli and ∼90% of Gram positive S.aureus at a concentration of 0.1 mg/mL. A strong correlation between the TEM, SEM and confocal microscopic analysis is observed demonstrating that g-CNQDs cause light induced photo toxicity. This toxicity is caused by the physical interaction (between the QDs and cells) and due to the generation of ROS in presence of light. The g-CNQDs were found to be non-toxic to fibroblast cells up to a concentration of 3.2 mg/mL. A comprehensive comparison of g-CNQDs with bulk non-porous g-CN, mesoporous CN, silver loaded mesoporous CN and bare silver nanoparticles indicated them to be promising photo induced bactericidal material.