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

Modulating carbon dots from aggregation-caused quenching to aggregation-induced emission and applying them in sensing, imaging and anti-counterfeiting

Aggregation Induced Emission Carbon Dots (AIE-CDs) address the problem of conventional CDs being quenched in the solid-state. However, there are still challenges in comprehending the luminescence mechanism. This work proposed a strategy for preparing green, yellow, and near-infrared CDs by modifying the functional groups on the precursor from hydroxyl and amino to p-methylenediamine, in which electronic supply capacity determined the redshift. Additionally, The CDs' properties transformed from Aggregation-Caused Quenching (ACQ) to AIE was realized by substituting non-rotatable hydroxyl or amino groups with the rotatable p-methylenediamine on the precursor. The resulting CDs were then applied in multifield. C-CDs was used for ratiometric detection of Al3+ and F- in pure water through three methods including fluorometer, test strip and smartphone. R-CDs was used for imaging cell nucleus and zebrafish. NIR-CDs (λem = 676 nm) exhibits dual emission, AIE and phosphorescent characteristics was used for triple anti-counterfeiting and binary information encryption. In summary, our finding presented a strategy for preparing multicolor CDs, proposed a mechanism for the transition of CDs from ACQ to AIE, and explore their multiple applications in anti-counterfeiting, information encapsulation, sensing and imaging.

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).

Vitamin B6-based fluorescence chemosensor for selective detection of F- ions: design, synthesis, and characterization

The present paper reports on the synthesis and characterization of a new chemosensor for fluoride ions, a hydrazone derived from pyridoxal 5'-phosphate and benzothiazole. The structure of the chemosensor was confirmed using 1H and 13C NMR, FT-IR and mass spectroscopy. The conformational diversity of the chemosensor influencing the sensor activity was studied by the quantum chemistry methods on the B3LYP/6-311++G(d, p) (H, C, N, O, P, S) level, and the optimal structure of the chemosensor was chosen. The selective capability of detecting F- in the aqueous solution, which also contains Cl-, Br-, I-, NCS-, ClO4-, HSO4-, and NO3- was demonstrated. The detection limit (LOD) for fluoride ions was 0.22 µM as determined by the 3σ method. The turn-on effect in the presence of fluoride ions is based on the deprotonation of the chemosensor and its subsequent aggregation in DMSO. In addition, the chemosensor was used for the detection and estimation of F- in real samples using fluorescence spectroscopy.

Ferrocene/ β-cyclodextrin based supramolecular nanogels as theranostic systems

A supramolecular redox responsive nanogel (NG) with the ability to sense cancer cells and loaded with a releasing therapeutic agent was synthesized using hostguest interactions between polyethylene glycol-grafted-β-cyclodextrin and ferrocene boronic acid. Cyclic voltammetry matched with other spectroscopy and microscopy methods provided strong indications regarding host-guest interactions and formation of the NG. Moreover, the biological properties of the NG were evaluated using fluorescence silencing, confocal laser scanning microscopy, and cell toxicity assays. Nanogel with spherical core-shell architecture and 100-200 nm sized nanoparticles showed high encapsulation efficiency for doxorubicin (DOX) and luminol (LU) as therapeutic and sensing agents. High therapeutic and sensing efficiencies were manifested by complete release of DOX and dramatic quenching of LU fluorescence triggered by 0.05 mM H2O2 (as an ROS component). The NGs showed high ROS sensitivity. Taking advantage of a high loading capacity, redox sensitivity, and biocompatibility, the NGs can be used as strong theranostic systems in inflammation-associated diseases.

An Acid-triggered Reactive and Enhanced Fluorescent Probe for Selective Detection of Al3+/H+ and its Application in Real Water Samples and Living Cells

A reactive fluorescent "turn-on" probe (di-PIP) with imine-linked dual phenanthro[9,10-d]imidazole luminophore have been conveniently prepared as an Al³⁺ and H⁺ dual functional receptor. di-PIP displayed high selectivity and sensitivity towards Al³⁺ ion in DMF/HEPES accompanied by fluorescence blue-shift and a good linear relationship as well as a low detection limit of 30.5 nmol·L^-1, which can root from the synergetic functions of the decomposition reaction of di-PIP promoted by acidic Al³⁺ and the coordination effect between decomposition product and Al³⁺. Intriguingly, it was found that hydrogen ion H⁺ can be sufficient for simulating the fluorescence enhancing of di-PIP. ¹H NMR titration and MS analyses for elucidation of the intermediate structure further revealed that the acid-triggered decomposition reaction resulted in the rapid, and sensitive sensing to Al³⁺ and H⁺. In addition, the probe di-PIP could be successfully applied to the detection of Al³⁺ in real water samples, and also utilized to visualize Al³⁺ and H⁺ in the living cells.

A new chromone functionalized isoqunoline derived chemosensor with fluorogenic switching effect for selective detection of Zn2+ in real water samples and living cells

In this work, a selective chemosensor, (E)-N'-((4-oxo-4H-chromen-3-yl)methylene)isoquinoline-1-carbohydrazide (ENO), was rationally developed for colorimetric and fluorogenic detection of Zn²⁺ ions. It was readily synthesized from 4-oxo-4H-chromene-3-carbaldehyde and isoquinoline-1-carbohydrazide via one-step Schiff reaction. ENO exhibited excellent fluorescent response performances toward Zn²⁺ over a wide pH range in EtOH/H₂O media, including a distinguished color change from colorless to gold, a low limit of detection (LOD) value (34 nM), strong complexation ability (1.36 × 10⁵ M^-1) and rapid identification (2 min). The sensing mechanism of ENO toward Zn²⁺ was proposed on the basis of the chelation-enhanced fluorescence (CHEF) process, which was further supported by IR studies and the density functional theory (DFT) calculation. Moreover, ENO presented here demonstrated outstanding capability in monitoring trace level of Zn²⁺ ions in real water samples, living cells as well as the on-site assay kit.

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.

A novel water-soluble naphthalimide-based turn-on fluorescent probe for mercury ion detection in living cells and zebrafish

Mercury (Hg), as the only heavy metal that can complete the cycle in the biosphere, can further accumulate in the human body through the food chain, causing irreversible damage to...