Table 5.
CDs as antibacterial agents.
| Material | Diameter | Toxicity | Mechanism | Observations |
|---|---|---|---|---|
| + charged, −charged, and 0 CDs [253] |
2.69–3.04 | + CDs: 100%, − CDs: ~80% 0 CDs: ~15% viability loss of E. coli incubated with 300 µg mL−1 for 6 h. |
ROS production disrupting cytoplasmic membrane by + charged CDs |
+ CDs had the highest antibacterial activity, while 0 charged had the lowest |
| CQD-EDA [263] | 5 nm | E. coli: ~95% viability loss in the light conditions after 6 h | ROS production under visible light | The first report on the visible/natural light-activated antibacterial activity of CDs |
| GQDs [26] | 20–67 nm |
E. coli: 80% MRSA: 90% viability loss; |
ROS production under blue light (470 nm) | Fast antibacterial action, only 15 min of exposure |
| N-GQD [240] | 8 nm, height ~ 1.03 nm | Killing 100% of E. coli in only 3 min of exposure | ROS production under 670 nm laser irradiation, the synergistic effect of ROS and RNS (reactive nitrogen species) | Higher nitrogen content in GQDs leads to more efficient PDT |
| GQD, CQDCA, and CQDNH [28] | GQD: 14 nm; CQDCA: 22.5 nm; CQDNH: 12.5 nm |
E. coli, E. aerogenes, P. aeruginosa, K. pneumoniae, B. subtilis MIC: 3.905–250 µg mL−1 |
ROS production under blue light (470 nm) | N-CQDs showed the best antibacterial properties |
| CDs three groups according to sizes [261] | Small (s-CGCD): ~2 nm Middle (m-CGCD): ~3.9 nm Large (l-CGCD): ~5.3 nm |
For E. coli: the concentration of s-CGCD ˃ 100 µg mL−1, for m-CGC and l-CGCD ˃150 µg mL−1 For S. aureus: 50, 75, and 100 µg mL−1 for s-CGCD, m-CGCD, and l-CGCD |
No ROS production. The mechanism includes destroying the cytoplasmic membrane of bacteria by causing the leaking of cellular components |
The antibacterial effect was increased with the decrease in particle size |
| Curcumin carbon dots from curcumin, neutral red, and citrate (Cur-NRCQDs) [264] |
~3.83 nm | Cur-NRCQDs inactivated 100% S. aureus and E. coli at concentrations of 10 and 15 μM | ROS production under the xenon lamp 555–850 nm | Cur-NRCQDs efficient against biofilms |
| Graphitic carbon nitride quantum dots: g-CNQDs [265] |
2–7 nm | Inhibition of ~99% of E. coli and ~90% of S. aureus at a concentration of 100 µg mL−1 | ROS production under visible light | Antibacterial activity of g-CNQDs was equivalent to silver nanoparticles |
| CDs from vitamin C [262] | ~5 nm | Killing 100% of a broad spectrum of bacteria at a concentration of 100 µg mL−1 at 150 µg mL−1, inhibiting the growth of fungus | CDs can enter the bacteria by diffusion, destroy the cell wall, bind to the DNA and RNA of bacteria, and finally kill them | These CDs could be degraded into CO2, CO, and H2O under visible light in the air after 20 days |