Ratiometric fluorescence nanoprobe based on carbon dots and terephthalic acid for determining Fe in environmental samples.

A ratiometric fluorescent nanoprobe using carbon dots (CDs) and involving oxidation of terephthalic acid (TPA) induced by hydroxyl radicals (·OH) was developed for sensitively and selectively determining Fe ions. When Fe ions are added to the TPA@CDs/HO system, ·OH produced through the Fenton reaction oxidizes the non-fluorescent TPA to give 2-hydroxyl terephthalic acid, which fluoresces at 423 nm when excited at 286 nm. The ·OH and Fe produced quench CD fluorescence at 326 nm. The 2-hydroxyl terephthalic acid to CD fluorescence intensity ratio linearly increased as the Fe concentration increased in the range 0.5-50 μM, and the detection limit was 0.25 μM. The new assay is very selective because it involves dual-emission reverse change ratio fluorescence sensing, which can exclude matrix effects. The new nanoprobe was used to determine Fe concentrations in real water samples, and the recoveries were found to be acceptable. Schematic of the ratiometric fluorometric method for determining Fe based on CDs and TPA.