Construction of coumarin-Cd2+ fluorescent probe with sequential sensing of Cu2+ and NO as well as application in water sample and bioimaging.

As an indispensable trace element, copper (Cu) is fundamental to numerous physiological processes. Similarly, nitric oxide (NO), a key signaling molecule, exhibits broad biological activity and participates in the physiological regulation of numerous systems. Abnormal concentrations of Cu2+ and NO are associated with many diseases in the body. Therefore, the detection of Cu2+ and NO holds considerable significance. Herein, a novel ABX-Cd2+ complex probe with coumarin as the skeleton has been constructed. Based on the metal ion displacement mechanism, the probe ABX-Cd2+ achieves a highly selective response to Cu2+ through a significant fluorescence quenching. Subsequently, the in-situ formed ABX-Cu2+ complex can further detect NO with high sensitivity through the fluorescence "OFF-ON" switching. The detection limits of the probe ABX-Cd2+ for Cu2+ and NO are 1.2 μM and 0.59 nM, respectively. The recognition mechanisms of the probe ABX-Cd2+ towards Cu2+ and NO are investigated using density functional theory (DFT), high-resolution mass spectrometry (HR-MS) and cyclic voltammetry (CV). Smartphone-assisted ABX-Cd2+ test strips facilitate visual analysis of Cu2+ in actual water samples. Importantly, the probe ABX-Cd2+ is successfully utilized for fluorescence imaging of Cu2+ and NO in live mice. This research achievement provides a novel technical platform for related research in environmental monitoring and biomedicine.