Highly N,P-doped carbon dots: Rational design, photoluminescence and cellular imaging

The authors describe the synthesis of carbon dots (CDs) that are highly doped with both nitrogen and phosphorus. Synthesis is accomplished via a hydrothermal reaction starting from diethylenetriaminepenta(methylenephosphonic acid) and m-phenylenediamine as the precursors. The high N,P-doping ratios renders the codoped CDs excellently water soluble, photostable over a wide range of pH values, and photostable in the presence of various metal ions. Ferric ions acts as a strong quencher of fluorescence. Their low cytotoxicity and strong green fluorescence (with excitation/emission peaks at 440/510 nm and a quantum yield of 0.32) make the CDs well suited for purposes of cell imaging, and this is demonstrated by fluorescent bioimaging of human lung carcinoma cells (type A549) and human breast cancer cells (type KB). Furthermore, the CDs were used as an effective probe for monitoring Fe(III) in both aqueous solution and living cells.