A dual functional MOF-based fluorescent sensor for intracellular phosphate and extracellular 4-nitrobenzaldehyde

Abstract

Herein, we present the successful synthesis, characterization and sensing application of a hydrazine functionalized Zr(IV)-based UiO-66 metal–organic framework (MOF) called Zr-UiO-66-N₂H₃ (1). The guest-free material 1′ shows selective and sensitive fluorimetric detection (turn-on mechanism) of phosphate (PO₄³⁻) anions in HEPES buffer (10 mM, pH = 7.4) and aqueous medium. It can also fluorimetrically detect (turn-off mechanism) 4-nitrobenzaldehyde (4-NB) in a HEPES : DMSO (9 : 1, v/v) medium with high selectivity and sensitivity. The selectivity for both analytes is retained in the presence of other potentially competitive analytes. The detection limit for PO₄³⁻ ions is 0.196 μM, which is far below the PO₄³⁻ level present in the aqueous environment. MOF 1′ can detect intracellular phosphate and it also has the capacity to exhibit differences in the intracellular phosphate level. Furthermore, the probe is capable of sensing PO₄³⁻ ions in real samples such as tap water, lake water, human urine and human blood serum. The sensitivity of the probe for sensing 4-NB is very high (detection limit = 4.7 μM). The possible mechanisms for sensing PO₄³⁻ ions and 4-NB have been explored in detail by experimental techniques.