Fabrication of a New Coumarin Based Fluorescent "turn-on" Probe for Distinct and Sequential Recognition of Al3+ and F- Along With Its Application in Live Cell Imaging

A new coumarin based fluorescent switch PCEH is fabricated which displays high selective sensing towards Al3+ among other metal cations at physiological pH. On gradual addition of Al3+, PCEH shows a brilliant "turn-on" emission enhancement in MeOH/H2O (4/1, v/v) solution. This new fluorescent switch is proven to be a reversible probe by gradual addition of F- into the PCEH-Al3+ solution. Detection limit as well as binding constant values are calculated to be in the order of 10-9 M and 104 M-1 respectively. We have also explored its potential as a biomarker in the application of live cell imaging using breast cancer cells (MDA-MB-231 cell).

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.

A Dual-Target Fluorescent Probe with Response-Time Dependent Selectivity for Cd2+ and Cu2

A novel fluorescent probe (NT) was developed by merging 2-hydrazinylbenzothiazole with 2-hydroxy-1-naphthaldehyde for the detection of Cd²⁺ and Cu²⁺. The probe alone is almost nonfluorescent due to the isomerization of C=N in the excited state. The addition of Cd²⁺ can cause an immediate strong green fluorescence owing to the suppression of C=N isomerization by Cd²⁺-coordination. Furthermore, NT gives a delayed turn-on fluorescence response to Cu²⁺ although it is a vigorous fluorescence quencher, which was thanks to the inhibition of the electron transfer between excited fluorophore and paramagnetic Cu²⁺ by sulfur donor. Based on fluorescence spectra and ESI-MS analysis, the binding modes between NT and Cd²⁺/Cu²⁺ were proposed.

Highly selective and sensitive sensing for Al3+ and F− based on green photoluminescent carbon dots

A novel sensor for metal ions by mean of CDs with a PL enhancement response, which shows high sensitivity and selectivity. Furthermore, the CDs-Al³⁺ ions system could be employed to probe F⁻ anions based on a PL “on–off” model.