A composite consisting of bromine-doped carbon dots and ferric ions as a fluorescent probe for determination and intracellular imaging of phosphate

A composite probe has been developed for fluorometric determination and imaging of phosphate in real water samples and in cells. The method is based on the use of weakly blue fluorescent bromine-doped carbon dots (C-dots) containing aromatic carbon-bromine groups and loaded with Fe3+ ions. The carboxy, phenolic hydroxy and aldehyde groups on the surface of the C-dots can coordinate with Fe3+ to form an adsorbed complex that reduces the blue fluorescence through an inner filter effect. If phosphate is added, it will capture Fe3+ on the surface of C-dots and restore fluorescence by ~88% via a displacement approach. The probe, best operated at excitation/emission maxima of 370/418 nm, has a linear response in the 0.4 to 22 μM phosphate concentration range and a 0.25 μM of detection limit. The relative standard deviation (at a phosphate level of 8.0 μM) is 3.6% (for n = 5). The method was applied to confocal imaging of phosphate in HeLa cells.