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Keywords:
antibacterial; bioimaging; carbon quantum dots; precursor; reactive oxygen species
Abstract
Carbon quantum dots as a novel type of carbon nanomaterials have attracted the attention of many researchers because of their unique optical, antibacterial, and anticancer properties as well as their biocompatibility. In this study, for the first time, carbon quantum dots were prepared from o-phenylenediamine dissolved in toluene by a solvothermal route. Subsequently, the prepared carbon quantum dots were encapsulated into polyurethane films by a swelling-encapsulation-shrink method. Analyses of the results obtained by different characterization methods (AFM, TEM, EDS, FTIR, photoluminescence, and EPR) indicate the significant influence of the precursor on structural, chemical, and optical properties. Antibacterial and cytotoxicity tests showed that these dots did not have any antibacterial potential, because of the low extent of reactive oxygen species production, and showed low dark cytotoxicity. By investigating the cellular uptake, it was established that these dots penetrated the HeLa cells and could be used as probes for bioimaging.
Introduction Carbon quantum dots (CQDs) as a novel class of carbon nanomaterials can be prepared by using different methods and precursors [1,2]. Most of the common preparation procedures are bottom-up methods [3,4]. Depending on the used precursors and solvents, the structure of the CQDs can be modified significantly, especially, by the presence and distribution of various functional groups on the basal plane and edges of carbon network, affecting, in turn, the CQD properties. Doping of CQDs with nitrogen, chlorine, or fluorine heteroatoms induces larger a transport bandgap, increased charge transfer resistance, and better antioxidant properties compared to pristine CQDs [5]. Functionalization of CQDs with amino groups (NH2 groups) induces a redshiftof the photoluminescence because of the charge transfer from the amino groups to the carbon honeycomb core [6]. Also, grafting with NH2 groups, by means of amines such as 2-ethylenediamine, poly(ethyleneamine), or trimethylamine, enhances the affinity of CQDs to biological structures whereas incorporation of nitrogen atoms in the honeycomb structure of CQDs contributes to a reduction of photobleaching [7]. Tepliakov et al. reported that CQDs can be treated as polymer-like nanoparticles of amorphous carbon with embedded partially sp2-hybridized atomic domains [8]. In this structure, electrons are partially delocalized over the domain area, but a strong coupling of the amorphous host matrix is maintained continuously. CQDs...