Water-soluble coumarin oligomer based ultra-sensitive iron ion probe and applications

Organic molecular probes are the main method for metal ion detection because of their excellent selectivity, while the approach remains limited due to the hydrophobic properties of highly efficient fluorescent molecules. Herein, the internal hydrophobic-external hydrophilic molecule design strategy was proposed to improve the water solubility and the sensing performance. Based on a coumarin-molecule-based iron ion probe, we further introduced a central hydrophobic molecule tribromophenol to connect the hydrophobic part of coumarin molecules. By investigating the experimental conditions and molecular structure, the trimeric phenolic coumarin (TPC) molecules with the largest hydrophilic/hydrophobic ratio exhibited excellent water solubility, fluorescent property and ultra-sensitive iron ion detection performance. Greatly enhanced iron ions binding ability lead to ultralow detection limit of 9.6 pM which is much lower than that of coumarin molecule probes and other reported iron ion probes (nM level). And more, this molecular design also enabled sun-excited naked eye Fe 3+ detection. Due to the remarkable biocompatibility of the probe, the sensitive intracellular iron ions are achieved with a very low detection limit of 0.2 mM. This molecule design provides a promising and powerful method for enhanced water soluble and effective metal ion detection.