Porphyrinic metal–organic framework@alumina nanocomposite fluorescent probe: Two-stage stimuli-responsive behavior and phosphate sensing

Abstract

Phosphate (PO 4 3− ) is not only a typical indicator of water quality monitoring but also a well-established essential nutrient in biological systems. The quantification of PO 4 3− is of great importance for environment protection and human health. Herein, a novel two-stage stimuli-responsive MOF nanocomposite fluorescent probe was proposed for PO 4 3− sensing. This MOF nanocomposite is composed of an inner two-dimensional (2D) Zr-BTB (BTB = 1,3,5-tris(4-carboxyphenyl)benzene) nanosheet-anchoring TCPP (TCPP = tetrakis(4-carboxyphenyl)porphyrin) MOF and an outer amorphous Al 2 O 3 film, namely PMOF@Al 2 O 3 . Due to the protective effect of Al 2 O 3 , it possesses excellent stability in water. Meanwhile, the Al 2 O 3 nanolayer on the surface can be selectively destroyed by low concentrations of PO 4 3− , exposing the water-unstable PMOF, and water molecules attack Zr nodes, causing the release of free TCPP and resulting in near-infrared fluorescence. And, high concentrations of PO 4 3− will also attack Zr nodes, which will not only separate TCPP molecules, but also lead to the structure collapse of MOF. The PMOF@Al 2 O 3 shows a fast (10 min) and highly selective response to PO 4 3− with two linear ranges and the detection limit is as low as 0.16 μM. Moreover, this MOF nanoprobe was successfully used for PO 4 3− detection in the seawater and the intracellular imaging of PO 4 3− . 1. A novel Al 2 O 3 -protected 2D porphyrinic MOF nanocomposite fluorescent probe was successfully synthesized. 2. PMOF@Al 2 O 3 presented high water stability, fast response, selectivity and sensitivity to phosphate. 3. The two-stage stimuli-responsive sensing mechanism was proposed. 4. PMOF@Al 2 O 3 was used for phosphate detection in the seawater and the intracellular imaging of phosphate.