A colorimetric and fluorometric dual-mode carbon dots probe derived from phenanthroline precursor for the selective detection of Fe 2+ and Fe 3+

Iron's metabolism is heavily involved in the regulation of redox balance for cell functions, however, the simultaneous monitoring of Fe 2+/3+ concentration is still a great challenge due to their transitional nature in biological systems. A novel type of carbon dots (CDs) was synthesized by solvothermal treatment with 5-amino-1,10-phenanthroline (Aphen) and salicylic acid as precursors, and the resulting targeted CDs (T-CDs) were used to simultaneously detect Fe 2+ and Fe 3+ . Comprehensive experimental characterizations revealed that the strong binding affinity of Aphen moiety to Fe 2+ leads to the formation of rigid T-CDs aggregates, which causes a substantial enhancement of fluorescence intensity, whereas Fe 3+ could cause the fluorescence quenching of T-CDs due to the oxidation‐reduction induced electron transfer. These different fluorescence responses allow T-CDs to sensitively differentiate Fe 2+ from Fe 3+ , and give the limit of detection (LOD) of 1.78 and 2.78 μM for Fe 2+ and Fe 3+ , respectively. Furthermore, the Aphen dominated structure endows the T-CDs with a colorimetric response to Fe 2+ with a LOD of 0.13 μM, which is very different from Fe 3+ . Thus, the dynamic changes of Fe 2+ and Fe 3+ in solution can be accurately monitored by T-CDs within the total iron concentration of 50 μM, which is probably the most sensitive dual-mode probe reported so far. In addition, this probe is successfully applied to detect the Fe 2+/3+ concentration in cells, demonstrating a huge application potential in the sensing of the dynamic equilibrium of these important transition metals during the cell metabolism or stimulated process. Graphical abstract The dynamic changes of Fe 2+ and Fe 3+ in solution can be accurately monitored by carbon dots based on the colorimetric and fluorometric dual-mode.