Hydrothermal synthesis of carbon dots codoped with nitrogen and phosphorus as a turn-on fluorescent probe for cadmium(II).

Nitrogen and phosphorus co-doped carbon dots (N,P-CDs) have been synthesized via hydrothermal method starting from o-phosphorylethanolamine and citric acid. The blue-green fluorescence of the N,P-CDs (with excitation/emission peaks at 325/435 nm) is gradually enhanced on sequential addition of Cd(II) ions. This fluorometric assay works in the 0.5 μM to 12.5 μM Cd(II) concentration range and has a 0.16 μM detection limit. The phenomenon may be attributed to chelation enhanced fluorescence that is induced by the formation of Cd(II)-N,P-CDs complex with functional groups present on the surface. The method has applied to the detection of Cd(II) in spiked serum and urine samples and gave satisfying results. Graphical abstract Schematic presentation of the synthesis of nitrogen and phosphorus co-doped carbon dots (N,P-CDs) and their application as a turn-on fluorescence probe for Cd(II) detection.