A highly selective and sensitive turn-on fluorescent probe for the detection of Al3+ and its bioimaging

A new NCDs@ZIF-90-based sensor: fluorescent "turn-on" detection of Al3+ ions with high selectivity and sensitivity

A new NCDs@ZIF-90 composite as fluorescence sensor was designed and prepared by encapsulation of N-doped carbon dots (NCDs) in metal-organic framework (MOF) ZIF-90 in one-pot synthesis. NCDs@ZIF-90 retained the crystal structure and high thermal stability of ZIF-90; meanwhile, it also displayed the good chemical stability. NCDs@ZIF-90 dispersion in ethanol exhibited selective "turn-on" fluorescence response towards Al³⁺. The other coexisting competing metal ions had no obvious influence on the sensing performance of NCDs@ZIF-90 for Al³⁺. The fluorescence intensity at 447 nm of NCDs@ZIF-90 dispersion in ethanol had good linear relation with the concentrations of Al³⁺ with a low detection limit of 3.196 μM. The fluorescence enhancement after the addition of Al³⁺ was attributed to the release of NCDs from the inside of ZIF-90 to ethanol solution. In addition, NCDs@ZIF-90 displayed good recovery in detection of Al³⁺ in water samples indicating its practical application capability. The high selectivity and sensitivity indicate that NCDs@ZIF-90 is a good candidate as a "turn-on" fluorescence chemosensor to identify and detect Al³⁺.

Theoretical investigation on the fluorescence properties and ESIPT mechanism of the Al3+ ion sensor 1-((2-hydroxynaphthalen-1-yl)methylene)urea(OCN)

A new action mechanism for the fluorescent detection on the Al³⁺ ion of the sensitive 1-((2-hydroxynaphthalen-1-yl)methylene)urea(OCN) is theoretically studied. The extensive theoretical calculations on the OCN and the isomer structure OCN-T are performed. The emission and absorption spectra consistent with the experiment value. The absorption spectra peaks (362 nm and 326 nm) of OCN and OCN-T molecules are attributed to the experimentally observed absorption spectra at 356 nm and 314 nm, respectively. The calculated fluorescence value of the OCN-AL structure is 460 nm, while the OCN-T-AL structure has no fluorescence. These results better explain that OCN and its isomers OCN-T are involved in the absorption, and the detection spectrum signal is emitted from the OCN-AL complex. The OCN and OCN-T molecules are obvious hydrogen bonding systems. The excited state intramolecular proton transfer photochemical behaviors and detecting Al³⁺ ion photophysical changes were explained for the first time at the molecular level. As driving force of excited state intramolecular proton transfer (ESIPT) reaction, the bond parameters and vibrational frequencies of intramolecular hydrogen bond were analyzed by optimizing structures and calculating infrared spectra, analysis of frontier molecular orbitals. To further elucidate the proton transfer reactive paths, the scanned the potential energy curves (PECs) of OCN and OCN-T chemosensor in different electronic states are plotted. This work proposes a reasonable explanation for the detection mechanism of the OCN sensor.

A New Coumarin-Acridone Compound as a Fluorescence Probe for Fe3+ and Its Application in Living Cells and Zebrafish

A new coumarin-acridone fluorescent probe S was designed and synthesized, and the structure was confirmed with ¹H/¹³C NMR spectrometry, single-crystal X-ray diffraction, and high-resolution mass spectrometry. This probe has high sensitivity and selectivity for Fe³⁺ over other testing metal ions at 420 or 436 nm in acetonitrile-MOPS (3-Morpholinopropanesulfonic Acid) buffer solution (20.0 μM, pH = 6.9, 8:2 (v/v)). Under physiological conditions, the probe displayed satisfying time stability with a detection limit of 1.77 µM. In addition, probe S was successfully used to detect intracellular iron changes through a fluorescence-off mode, and the imaging results of cells and zebrafish confirmed their low cytotoxicity and satisfactory cell membrane permeability, as well as their potential biological applications.

A highly selective aggregation-induced emission fluorogen for sensitive detection of Al3+ in living cells

A Schiff's base derivative was synthesized using a condensation reaction between 8-formyl-7-hydroxy-4-methylcoumarin and furan-2-carbohydrazide that produced marked aggregation-induced emission and had excellent ability to specifically recognize aluminium ions (Al³⁺ ). This compound displayed faint fluorescence in the benign solvent dimethyl formamide, and exhibited obvious green fluorescence following addition of specific amounts of water. Moreover, it exhibited strong blue fluorescence after combination with Al³⁺ even in the presence of other interfering ions. These experimental results demonstrated that this derivative could be used as a fluorescence probe for Al³⁺ . The advantages, including significant fluorescence change, high selectivity and sensitivity, and fast response, meant that this probe could be used both to detect Al³⁺ in water samples and for fluorescence imaging in living cells.

New fluorescent chemosensors based on mononuclear copper complex for highly selective and sensitive detection of phosphate anion in aqueous solution and living cells

Three new probes, named, [Cu(L1)₂]Cl₂ (C1), [Cu(L2)₂]Cl₂ (C2) and [Cu(L3)₂]Cl₂ (C3) were synthesized and well characterized. The probes C1, C2 and C3 were successfully achieved for the efficient detection of PO₄^3- as turn-on fluorescence chemosensors in DMSO/H₂O (v:v = 2:8, Tris-HCl pH = 7.20). The limit of detection (LOD) of probes C1, C2 or C3 for PO₄^3- could be as low as 0.029 μM, 0.048 μM, 0.079 μM, respectively, which were effectively applied for the determination of the PO₄^3- concentration in environmental water of swimming pool. What's more, the binding constant between probes C1, C2, C3 and PO₄^3- are estimated to be 3.11 × 10⁷ M^-1 (R² = 0.9992), 1.84 × 10⁷ M^-1 (R² = 0.9956), 1.93 × 10⁷ M^-1 (R² = 0.9976), respectively. The proposed mechanism for the "on-off-on" fluorescence response was confirmed by ESI-MS and fluorescence spectrum. Moreover, the membrane-permeable probe C1 was successfully demonstrated in monitoring of PO₄^3- in cultured HepG2 cells.

A multifunctional selective “turn-on” fluorescent chemosensor for detection of Group IIIA ions Al3+, Ga3+ and In3+

A versatile chemosensor was developed for highly distinguishable and selective recognition of group IIIA metal ions (Al³⁺, Ga³⁺ and In³⁺).