E-mail: tina. E-mail: dinesh. Covalent organic frameworks COFs have been used in cell imaging, but very rarely for imaging specific cell conditions. Fluorescence microscopy imaging shows that the material discriminates between HeLa cells grown under hypoxia and those cultured under normoxia. Various methods of both invasive and noninvasive hypoxia imaging have been developed. More recently, fluorescence imaging has likewise received significant attention in the realm of cancer imaging on account of its high sensitivity, low toxicity, good spatial and temporal resolution, emission tunability, simple operation, and non-invasive nature.
In the hypoxic tumor microenvironment, reductases, such as azo reductase and nitro reductase, are overexpressed. While the azo group is an azo-reductase-sensitive moiety, nitro-imidazole is a nitro-reductase-sensitive moiety. Various small-molecule fluorophores have been developed for imaging hypoxic conditions 7 yet it is the nanomaterials that enable passive tumor accumulation and retention due to the enhanced permeability and retention EPR effect. Due to their purely organic nature, structural and functional tunability, and porosity, which could also be exploited for drug delivery, COFs are strong candidates for the imaging of cellular conditions.
Only a few examples of COFs have been studied for bioimaging where cell imaging is primarily achieved using the inherent fluorescence of the materials, 10,11 or relying on the fluorescence of a conjugated moiety, such as dye-labeled nucleic acids 12,13 and fluorescent probes. Taking advantage of its low cytotoxicity, we implemented NI-COF as a fluorescence imaging tool for hypoxia. Our fluorescence microscopy images demonstrate the preferential accumulation of the material in HeLa cells incubated under hypoxic conditions over those incubated under normoxia.
In the final step, imine condensation between the amino groups of NH 2 -COF and the formyl group of 4-nitro-1H-imidazolecarbaldehyde Hyp , a hypoxia targeting molecule, was carried out Fig. All three materials were characterized by standard molecular-level and macroscopic characterization techniques. Upon reduction to NH 2 -COF , these three peaks either disappear entirely or become significantly reduced in intensity.
In NI-COF , peaks labelled a, b and c correspond to the carbon atoms adjacent to the keto group ppm , and the two carbon atoms in the enamine group ppm and ppm , respectively. AA stacking was found to be the preferred conformation in all three COFs. The materials show an intensive reflection at 3. A smaller reflection is observed at 6. These assignments match well with the literature reports.
