NMR techniques for a structural characterization of fluorescent Carbon Dots

Abstract

Carbon Dots (CDs), since their discovery in 2004, are receiving considerable attention in the fields of optoelectronic devices, sensors and biological labelling. CDs are small carbon nanoparticles below the size of 10 nm that show a very strong photoluminescence emission. Compared to the semiconductor nanocrystals, which have raised serious health and environmental concerns, CDs present a safe, green and cheaper alternative, especially regarding the biomedical application. In fact CDs show good biocompatibility and an adequate functionalization of the surface enables the cellular uptake, opening the door to their use in optical imaging techniques and, with a further step, as drug carriers for therapeutic applications. In order to achieve these results, the comprehension of the CDs¿ chemical structure can be of great advantage, providing a starting point to understand which changes in the structure will affect the fluorescence behaviour and how. CDs can be synthetized starting from several oxygen-rich carbon sources, such us polysaccharides (top-down approach) or organic molecules (bottom-up approach). Among many different synthetic methods, pyrolysis, hydrothermal treatment and microwave irradiation offer an easy and suitable procedure to obtain CDs. In the current work nitrogen-doped CDs have been synthetized exploiting old and new synthetic approaches based on the condensation reactions of organic reagents. The as-prepared fluorescent CDs were characterized employing several powerful techniques for the structure determination, such as H1NMR, C13NMR, IR, XPS and Elemental Analysis.