Dual - ligand metal - organic frameworks for dual - emission ratiometric and visual detection of hypochlorous acid.

A dual-emission metal-organic framework (UiO - 66 - TCPP) was prepared using 2 - aminoterephthalic acid (BDC - NH) and tetrakis(4 - carboxyphenyl) porphyrin (HTCPP) as the dual-ligand for ratiometric fluorescent, colorimetric, and visualization triple-mode detection of hypochlorous acid (HClO). Structural and spectroscopic characterization confirmed that the dual-ligand strategy integrated the nanosize of UiO - 66 and the red emission of HTCPP, resulting in a stable monodisperse and dual-emission at 465 and 668 nm under single excitation at 390 nm for UiO - 66 - TCPP. Upon exposure to HClO, UiO - 66 - TCPP displayed the enhanced emission at 668 nm, while that at 465 nm increased a little for ratiometric sensing of HClO. Correspondingly, the color transition from yellow to pale pink achieved colorimetric detection of HClO. The detection limits were 0.15 μM for ratiometric sensing and 0.36 μM for colorimetric detection, with a linear range of 5-200 μM for both modes. A test strip was developed for visual assay, allowing on-site fluorescent detection of HClO by RGB analysis with a smartphone. The performance of UiO - 66 - TCPP was confirmed with the recovery testing for water and serum samples. The response mechanism was investigated as the oxidation of pyrrole nitrogen and amino groups, resulting in the multi-modality detection. Thus, we proposed the dual-ligand strategy to realize the nanosize and dual-emission, simultaneously, as a robust platform for sensitive and visible detection of HClO with great potential for environmental and biological monitoring.