Photoluminescent nanographitic/nitrogen-doped graphitic hollow shells as a potential candidate for biological applications

Abstract

Water-dispersible graphitic hollow spheres were synthesized using a soft chemical route under hydrothermal conditions by glucose carbonization using a magnetite/silica-encapsulated core–shell sphere as a template. Carbonization on the templates happens as the magnetite core is partially or completely eliminated depending on the reaction conditions. Therefore, nano-sized graphitic hollow spheres or magnetite-core-encapsulated graphitic shells could be obtained. Also nitrogen-doped graphitic spheres were synthesized by a hydrothermal reaction. The graphitic and nitrogen-doped graphitic spheres show wavelength dependent photoluminescence in 300–600 nm range. The photoluminescence seems to depend on the fraction of the sp² domains and N-doping, therefore, tunable PL emission can be achieved by controlling the nature of sp² sites. In addition the cellular uptake of the graphitic hollow spheres was evaluated in human HeLa cells, demonstrating its main localization in the cytoplasm. A blue fluorescence signal was the most intensively observed in the cellular uptake process, although some green and red fluorescence was also observed. Since the cores of Fe₃O₄ could be completely or partly eliminated in a controllable way, it can be used as a magnetic resonance imaging agent. In addition, their easily modifiable hydrophilic surfaces for multi-functionality and hydrophobic voids covered by oxidized graphite make them promising candidates for applications in cellular photo-imaging and targeted drug delivery.