Carbon Nitride Dots: A Selective Bioimaging Nanomaterial

Abstract

In contrast to the recent immense attention in carbon nitride quantum dots (CNQDs) as a heteroatom-doped carbon quantum dot (CQD), their biomedical applications have not been thoroughly investigated. Targeted cancer therapy is a prominently researched area in the biomedical field. Here, the ability of CNQDs as a selective bioimaging nanomaterial was investigated to assist targeted cancer therapy. CNQDs were first synthesized using four different precursor sets involving urea derivatives, and the characteristics were compared to select the best candidate material for bioapplications. Characterization techniques such as UV–vis, luminescence, X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy, and transmission electron microscopy were used. These CNQDs were analyzed in in vitro studies of bioimaging and labeling using pediatric glioma cells (SJGBM2) for possible selective biolabeling and nanodistribution inside the cell membrane. The in vitro cellular studies were conducted under long-wavelength emission without the interference of blue autofluorescence. Thus, excitation-dependent emission of CNQDs was proved to be advantageous. Importantly, CNQDs selectively entered SJGBM2 tumor cells, while it did not disperse into normal human embryonic kidney cells (HEK293). The distribution studies in the cell cytoplasm indicated that CNQDs dispersed into lysosomes within approximately 6 h after the incubation. The CNQDs exhibited great potential as a possible nanomaterial in selective bioimaging and drug delivery for targeted cancer therapy.

Recent development of carbon quantum dots regarding their optical properties, photoluminescence mechanism, and core structure

“…In addition, the composition (functional groups) of the shell is vital to subsequent functionalization required for many applications. [137][138][139] Furthermore, the shell involves in the unique optical properties and electron donor/acceptor of CDs. For example, CDs have pH-dependent PL, which has been widely reported, and the PL can be monitored by different pH to study the effect of the surface groups on optical properties.…”

Carbon Dots: A Future Blood–Brain Barrier Penetrating Nanomedicine and Drug Nanocarrier

“…They possess a higher fluorescence quantum yield (QY) than typical CDs and usually have emission wavelengths skewed towards the blue light. 36 , 37 …”

“… 12 CNDs typically possess an s-triazine or other carbon nitride structures in their cores. 37 While each class of CDs owns a different core structure, their surfaces are believed to be composed of simple functional groups or small organic molecules.

Scheme 1 ( A ) Graphical representation of the overall structure of CDs; ( B ) number of references per year based on search results using “carbon dots” and “blood-brain barrier” from Google Scholar.

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“…Furthermore, under microwave irradiation (700 W, 7 min), citric acid and urea were applied by Liyanage et al to fabricate CNDs that owned an excitation-dependent PL and diverse surface functional groups, such as -COOH, -OH, C-O and C=N. 37 In comparison, remarkably distinct structures and optical properties were obtained in the CDs prepared using the same precursors or synthetic approaches, which suggests the importance of both factors in determination of the structure and optical properties of CDs. Furthermore, Table 1 summarizes a few classic CD synthetic methodologies and resulting surface structures and optical properties.…”

Nanoparticles in Biomedicine-Focus on Imaging Applications

“…Calcium phosphate NPs are biocompatible, multilayer nanocomposites that are more rigid than liposomal structures. Because of their composition, calcium phosphate NPs are usually less toxic than other types of NPs and diagnostic or therapeutic agents can be trapped Their results showed that CNQDs selectively entered pediatric glioma cells (SJGBM2), but not normal human embryonic kidney cells (HEK293) and excitation-dependent emission of CNQDs was proved to be advantageous in the in vitro cellular studies, highlighting a great potential in selective bioimaging and drug delivery for targeted cancer 91 therapy. nanodiamonds conjugated UCNPs in bio-imaging and drug delivery.…”