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

Phosphate (PO43−) is not only a typical indicator of water quality monitoring but also a well-established essential nutrient in biological systems. The quantification of PO43− is of great importance for environment protection and human health. Herein, a novel two-stage stimuli-responsive MOF nanocomposite fluorescent probe was proposed for PO43− 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 Al2O3 film, namely [email protected]2O3. Due to the protective effect of Al2O3, it possesses excellent stability in water. Meanwhile, the Al2O3 nanolayer on the surface can be selectively destroyed by low concentrations of PO43−, 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 PO43− will also attack Zr nodes, which will not only separate TCPP molecules, but also lead to the structure collapse of MOF. The [email protected]2O3 shows a fast (10 min) and highly selective response to PO43− with two linear ranges and the detection limit is as low as 0.16 μM. Moreover, this MOF nanoprobe was successfully used for PO43− detection in the seawater and the intracellular imaging of PO43−.