Carbon nanodots are carbon nanoparticles which are less than 10 microns (µm) in size.
They have several unique characteristics, including biocompatibility, photostability, and a large surface area. They also have a low toxicity, are water soluble and have good conductivity.
All of these properties make carbon nanodots perfect for use in protein detection, cell biology and systems biology.
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Carbon nanodots for the detection of proteins
Carbon dots are quasispherical nanoparticles and as they have low cost, high biocompatibility and stability, they are being increasing used to detect proteins within samples.
In a recent study, C-dot based aptamer was created to detect thrombin protein. This design is easy and does not require sophisticated methods.
Also, such carbon dots are environment friendly and the design can be easily adapted for proteins other than thrombin so can have a wider range of applications.
Using carbon nanodots to label proteins
Carbon dots have a very high quantum yield of 99%, making them one of the brightest probes. This, and the fact that they can be easily cultured within cells makes them an ideal candidate for live cell imaging.
However, carbon dots often interact non-specifically with many cellular targets. This makes them less suitable to labeling proteins within cells.
Recently, studies have shown that modified carbon dots can also be used to label proteins. In one study, the researchers show carboxyl functionalized carbon dots can precisely target the lysine residues on proteins, and thus can be used to label proteins containing lysine.
In contrast to carbon dots, carbon nanotubes can target specific cellular components and are widely used for this purpose.
Using carbon nanodots in drug delivery
To conjugate carbon dots to drugs, certain conditions need to be met. The drug to be conjugated needs to have a free amino acid or a free carboxylic acid group.
Covalently conjugating a drug with a carrier leads to greater loading yield, but it also causes the drug to be released more slowly. This may even cause a drug to become ineffective.
Common drugs which are conjugated to carbon dots are those used in chemotherapy. A ligand, such as nuclear localization signal peptide, can also be added to this conjugated complex to ensure a more accurate localization of the drug.
Carbon nanodots for cancer detection
Carbon dots can also be fused with specific ligands for receptors which are present on cancer cells.
For example, cancer cells often overexpress growth factor receptors (GFRs), so ligands for these GFRs can be fused to carbon dots. Other ligands which can be conjugated to carbon dots include transferrin, folic acid and hyaluronan.
These receptors which bind these ligands influence the cell death and proliferation pathway, either directly or indirectly.
Transferrin is involved in iron uptake within cells, and in cancer studies carried out on mice there is an increased uptake of transferrin receptor within cancer cells.
Folic acid is involved in producing purines and pyrimidines, which are components of DNA, and this regulates cell division and growth. Carbon dots conjugated with folic acid has shown potential to detect cancer cells which have increased levels of folic acid.
Finally, hyaluronic acid is an adhesion regulator whose levels are also altered during cancer. Carbon dots conjugated with hyaluronan has been shown to detect cancer cells with increased CD44 expression.
Carbon nanodots for catalysis
Carbon dots can act as photocatalysts and catalyze reactions by UV or visible light. Many carbon catalysts, such as sulfated-graphene, carbon tube and active carbon, have low efficiency as catalysts due to the lac of proper surface functionalization.
However, carbon dots ranging from 1-4 µm in size can be potent light driven photocatalysts for several organic reactions. They have a high conversion rate of 92% and a selectivity of 100%.
This is greater than CNP (2',3'-cyclic nucleotide 3' phosphodiesterase) and graphite which have conversion rates of 71% and 51%.