1′-hydroxy-2′-acetonaphthone: A simple fluorescence turn-on signaling probe with high selectivity and sensitivity for Al3+ in pure water

A simple chromone-derived fluorescent "Turn-on" probe for accurate detection of Al3+ Ions: Applications in food Analysis, test strips and bioimaging

To address the toxicity concerns of aluminum ions (Al3+) due to their widespread environmental presence, a novel chromone-derived fluorescent probe, (E)-N'-((4-oxo-4H-chromen-3-yl)methylene)benzohydrazide (NMA), was developed for dual-mode detection combining colorimetric and fluorometric channels. Upon chelation with Al3+ in a 1:1 stoichiometric ratio, NMA exhibited a significant fluorescence enhancement at 510 nm, accompanied by a rapid and visible color change due to the chelation-enhanced fluorescence (CHEF) effect, achieving an exceptional detection limit of 9 nM-well below the World Health Organization's recommended threshold. The reversible binding of NMA, demonstrated through sequential addition of Al3+ and EDTA, enabled the construction of an INHIBIT molecular logic gate, broadening its potential for smart sensing applications. Structural interactions and selectivity were confirmed through 1H NMR, FT-IR spectroscopy, and density functional theory (DFT) calculations. NMA proved highly effective in diverse applications, including detecting Al3+ in food samples, bioimaging in living cells, and environmental monitoring via smartphone-assisted platforms and test strips, making it a powerful tool for addressing aluminum toxicity in practical and real-time settings.

Fluorescence sensing of metal ions in solution using a morpholine-containing phenolic Mannich base of 1'-hydroxy-2'-acetonaphthone

A phenolic Mannich base derived from 1'-hydroxy-2'-acetonaphthone (HAN) as a substrate and morpholine as an amine reagent was synthesized and structurally characterized. The sensing ability toward various metal ions of the s-, p- and d-block of this molecule that has the binding site for metal ions in the starting ortho-hydroxyphenone preserved was examined. Interaction between this phenolic Mannich base and Al3+, Cr3+, Cu2+ and Co2+ leads to modifications of the sensing molecule's absorption spectrum. Fluorescence spectroscopy showed that Al3+ acts as a fluorescence enhancer, whereas Cu2+ functions as a fluorescence quencher for the aminomethylated derivative. The phenolic Mannich base may be employed either as a sensitive "turn-on" chemosensor for Al3+ or as a sensitive "turn-off" chemosensor for Cu2+. However, in the presence of these ions at identical concentrations, the Mannich base becomes a selective chemosensor for Al3+. The sensing ability of this phenolic Mannich base toward rare earth ions showed that Eu3+, Dy3+ and Gd3+ induce changes in the absorption spectrum of the Mannich base. Fluorescence spectroscopy showed that the response of the sensing molecule toward Eu3+ and Dy3+ is weak, and this phenolic Mannich base may be used as a "turn-off" chemosensor for these two lanthanide ions only in a narrow concentration range (1-16 × 10-5 M).

A Novel AIE-Active Salicylaldehyde-Schiff Base Probe with Carbazole Group for Al3+ Detection in Aqueous Solution

A donor-acceptor Schiff-base fluorescent probe BKS with chelation enhanced fluorescence (CHEF) mechanism was designed and synthesized via benzophenone(Acceptor), salicylaldehyde and carbazole(Donor) for Al3+ detection, which exhibited typical aggregation-induced emission (AIE) characteristic. BKS probe could provide outstanding selectivity to Al3+ with a prominent fluorescence "turn-on" at 545 nm in a wide pH range from 2 to 11. By the Job's plot, the binding stoichiometry ratio of probe BKS to Al3+ was determined 1:1. The proposed strategy offered a very low limit of detection at 1.486 µM in THF/H2O(V/V = 1:4, HEPBS = 10 mM, pH = 7.40), which was significantly lower than the standard of WHO (Huang et al., Microchem J 151:104195, 2019)-(Yongjie Ding et al., Spectrochim Acta Mol Biomol Spectrosc 167:59-65, 2021) guidelines for drinking water. BKS probe could provide a wider linear detection range of 50 to 500 µM. Furthermore, the probe could hardly be interfered by other examined metal ions. The analysis of Al3+ in real water samples with appropriate recovery (100.72 to 102.85) with a relative standard deviation less than 2.82% indicated the accuracy and precision of BKS probe and the great potential in the environmental monitoring of Al3+.

A new naphthalimide-picolinohydrazide derived fluorescent "turn-on" probe for hypersensitive detection of Al3+ ions and applications of real water analysis and bio-imaging

The development of high-selective chemosensors for trace Al³⁺ detection in the ecosystem is crucially importance due to its detrimental effects. In this work, a simple Schiff-base fluorescent probe NPP derived from naphthalimide and picolinohydrazide was rationally designed and prepared for efficient detection of Al³⁺. NPP exhibited prominent sensing behaviors toward Al³⁺ with low detection limit (LOD) (39 nM), rapid response time (1 min), strong binding affinity (4.02 × 10⁴), good anti-interference characteristics and visual detection. Binding ratio of NPP-Al³⁺ complex was determined to be 1:1 by Job's plot analysis. In addition, the chelation mechanism of NPP with Al³⁺ ions was proposed and substantiated by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT), IR spectrum and ¹H NMR titration experiments. Furthermore, this "signal-on" probe NPP was efficiently utilized as a promising indicator for Al³⁺ detection in environmental and biological samples.

Naphthalimide appended isoquinoline fluorescent probe for specific detection of Al3+ ions and its application in living cell imaging

Herein, a novel Schiff base fluorescent probe NIQ based on naphthalimide and iso-quinoline units has been readily prepared for the selective detection of Al³⁺ ions. The obviously visible color changes and prominent fluorescence enhancement were observed upon the addition of Al³⁺ to NIQ, which could be attributed to the complexation of NIQ with Al³⁺ and thus leading to the inhibition of photo-induced electron transfer (PET) and the chelation-enhanced fluorescence (CHEF) progress. The limit of detection (LOD) was 52 nM that was far below the standard recommended by the WHO. Binding ratio (1:1) of NIQ with Al³⁺ ions was supported by Job's plot. The binding constant of NIQ for Al³⁺ were calculated to be 3.27 × 10⁵ M^-1 on the basis of benesi-Hildebrand plot. The plausible binding mechanism for NIQ towards Al³⁺ ions was evidenced by the density functional theory (DFT) and ¹H NMR titration experiment. Furthermore, this "turn-on" probe NIQ has been successfully applied as a biomarker for imaging the Al³⁺ ions in living cells.

A novel reversible fluorescent probe based on naphthalimide for sequential detection of aluminum (Al3+) and fluoride (F-) ions and its applications

A new Schiff base fluorescent probe NBP derived from the one-step condensation strategy of 2-butyl-6-hydroxy-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-5-carbaldehyde and N-(2-(hydrazinecarbonyl)phenyl)benzamide was synthesized and characterized. NBP exhibited high selectivity toward Al³⁺ along with naked-eye color changes and prominent fluorescence enhancement. The limit of detection (LOD) of NBP toward Al³⁺ was detected to be 80 nM. The binding ratio of NBP with Al³⁺ ions was obtained as 1 : 2 on the basis of Job's plot with the association constant K_a value of 4.22 × 10¹⁰ M^-1/2. The plausible complexation mechanism of NBP toward Al³⁺ ions was validated by the density functional theory (DFT) and IR spectrum. In addition, in situ formed "NBP + Al³⁺" could be utilized as the second sensor for selective recognition of F^-via fluorescence quenching with a low detection limit (44 nM). Furthermore, the cell imaging experiments of probe NBP in HeLa cells have successfully demonstrated that NBP could serve as an indicator for monitoring Al³⁺ ions in living cells. On top of that, NBP could be used to prepare simple test paper strips for quickly and qualitatively detecting a trace amount of Al³⁺ ions in a visible manner.