Enhanced photoresponsive polyethyleneimine/citric acid co-carbonized dots for facile and selective sensing and intracellular imaging of cobalt ions at physiologic pH

Whether as an important biological element or as a radioactive source/medicine, the monitoring of trace levels of cobalt ions (Co) has become a non-negligible factor for human health and green environment. Current technologies for the detection of Co are cost-expensive and time-consuming, and require cumbersome sample pretreatment process. Herein a novel sensing platform has been developed for Co detection based on the quenching of the enhanced fluorescence signal of polyamine functionalized C-dots. Amine groups at the surface of the C-dots can capture Zn²⁺/Cd²⁺ to form coordination compound, which can inhibit the photoinduced electron transfer pathways of C-dots and then induce the fluorescence enhancement of the C-dots by ∼80% margin. Also, Co interacts with these amine groups to form an absorbent complex, which can strongly quench the enhanced fluorescence of C-dots via an inner filter effect. This C-dots-based probe showed a wide linear response to Co with a concentration ranging from 0.012 to 12 μM, and a detection limit of 8.0 nM and RSD of 5.7% (n = 5). Significantly, the C-Dots exhibit excellent properties, such as negligible cytotoxicity, excellent biocompatibility, low-cost and high photostability, etc., which make C-dots favorable for label-free monitoring of Co and then successfully applied to the confocal imaging of intracellular Co. - Highlights: • Polyethyleneimine/citric acid co-carbonized dots were prepared. • Zn²⁺ can enhance fluorescence of C-dots by inhibiting PET pathways. • Co²⁺ can quench the enhanced fluorescence by an inner filter effect. • Bioprobe has been established for intracellular imaging Co.