A HBT-based bifunctional fluorescent probe for the ratiometric detection of fluoride and sulphite in real samples

A novel ratiometric fluorescence probe based on the FRET-ICT mechanism for detecting fluoride ions and viscosity

Fluoride ion is not only important for dental health, but also a contributing factor in a variety of diseases. At the same time, fluoride ions and cell viscosity are both important to the physiological environment of mitochondria. We developed a dual-response ratiometric fluorescent probe BDF based on Förster resonance energy transfer (FRET) and intramolecular charge transfer (ICT) mechanism for the detection of F- and viscosity. BDF has an outstanding intramolecular energy transfer efficiency of 97.7% and shows excellent performance for fluorine ion detection. In addition, when the system viscosity increases, the fluorescence emission intensity of BDF is greatly heightened, indicating the possibility of viscosity detection. Finally, based on the fluorescence properties of BDF, we used the probe to detect F- in the toothpaste sample and image exogenous fluoride ions in HeLa cells.

A coumarin based Schiff Base: An effective colorimetric sensor for selective detection of F- ion in real samples and DFT studies

Chemosensors are molecular devices which react with target and give a visible signal, which is a degree of its sensitivity. Herein, a novel coumarin based Schiff Base has been synthesized for F^- ions detection. The chemosensor showed an intense color change upon the addition of F^- ions (light yellow to purple). The chemosensor has fewer effects of competing anions. The limit of detection is calculated as low as 1.1 × 10^-6 and the binding constant was determined as 1.61 × 10⁴. The job's plot confirmed 1:1 stoichiometry between chemosensor and F^- ion. The reverse reaction of chemosensor with MeOH is useful to construct a combinatorial logic circuit gates. The interaction mechanism of chemosensor was deliberated by ¹H NMR, FTIR, and DFT studies. Finally, the chemosensor was useful to detect F^- ions in tooth-paste sample and test strip is prepared for F^- ions detection.

Small-Molecule Fluorescent Probe for Detection of Sulfite

Sulfite is widely used as an antioxidant additive and preservative in food and beverages. Abnormal levels of sulfite in the body is related to a variety of diseases. There are strict rules for sulfite intake. Therefore, to monitor the sulfite level in physiological and pathological events, there is in urgent need to develop a rapid, accurate, sensitive, and non-invasive approach, which can also be of great significance for the improvement of the corresponding clinical diagnosis. With the development of fluorescent probes, many advantages of fluorescent probes for sulfite detection, such as real time imaging, simple operation, economy, fast response, non-invasive, and so on, have been gradually highlighted. In this review, we enumerated almost all the sulfite fluorescent probes over nearly a decade and summarized their respective characteristics, in order to provide a unified platform for their standardized evaluation. Meanwhile, we tried to systematically review the research progress of sulfite small-molecule fluorescent probes. Logically, we focused on the structures, reaction mechanisms, and applications of sulfite fluorescent probes. We hope that this review will be helpful for the investigators who are interested in sulfite-associated biological procedures.

A novel ICT-based chemosensor for F- and its application in real samples and bioimaging

A novel colorimetric and fluorescent chemosensor MQS-Si with intramolecular charge transfer character has been designed and synthesized. The chemosensor shows exclusively "off-on" fluorescence response toward F^- at 620 nm in HEPES (pH 7.4): DMSO solution (7:3, v/v), which is attributed to the specific cleavage of Si-O bond. The ultrasensitive detection limit for F^- in the fluorescence measurement is down to 30 nM. Application of the chemosensor has been demonstrated by selective detection of F^- in drinking water, urine and serum samples and fluorescence imaging of F^- in living cells and zebrafish, which proves that MQS-Si has a promising application in vitro and in vivo detection of F^- and may be utilized for the diagnosis of fluorosis and esteofluorosis.

The mechanisms of a bifunctional fluorescent probe for detecting fluoride and sulfite based on excited-state intramolecular proton transfer and intramolecular charge transfer

The mechanisms of 2-(Benzo[d]thiazol-2-yl)phenol-based bifunctional probe (HBT-FS) for detecting fluoride (F^-) and sulfite (SO₃ ^2-) based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) have been theoretically studied. Laplacian bond order of HBT-FS indicates that the F^- ion cleaves the Si-O bond and then forms Compound 2 possessing a six-membered ring with a hydrogen bond. Potential energy curves and dynamic simulations confirm that ESIPT in Compound 2 occurs along with this hydrogen bond and forms a keto structure with an emission at 623 nm, which agrees with the observed experimental value (634 nm) after adding F^-. Therefore, the fluorescence red-shift (from 498  to 634 nm) of HBT-FS observed in experiment after adding F^- is caused by ESIPT. The SO₃ ^2- ion is added to the C₅ site of HBT-FS, which is confirmed by orbital-weighted dual descriptor, and then forms Compound 3 with fluorescence located at 404 nm. The experimentally measured fluorescence at 371 nm after adding SO₃ ^2- is assigned to Compound 3. Charge transfer analyses indicate that the ICT extent of Compound 3 is relatively weak compared with that of HBT-FS because of the destruction of the conjugated structure by the addition reaction of SO₃ ^2-, which induces the blue-shift of the fluorescence of HBT-FS from 498 to 371 nm. The different fluorescence responses make HBT-FS a fluorescent probe to discriminatorily detect F^- and SO₃ ^2-.

A conjugated fluorescent polymer sensor with amidoxime and polyfluorene entities for effective detection of uranyl ion in real samples

It is an important challenge to develop a chemosensor for trace uranyl ion in an aqueous medium for sustainable development of nuclear energy and environmental conservation. A conjugated fluorescent polymer sensor P2 based on amidoxime groups and polyfluorene, which showed good hydrophilous resulting adequate contact with uranyl ions and selectivity and sensitivity even in the presence of other metal ions in DMA/H₂O (v/v = 20:80, pH = 6.0) solution, for uranyl ion was designed and prepared in this work. And it possesses good thermal stability and a larger Stokes shift (108 nm). Importantly, the fluorescence quenching occurred when P2 combining uranium. It had a good linear relationship with UO₂²⁺ concentration in the range of 10 to 200 nM with a fairly low LOD 7.4 × 10^-9 M. Interaction properties between the sensor P2 and UO₂²⁺ and the fluorescent mechanism were investigated by density functional theory (DFT). More importantly, the sensor can be successfully used for the detection of uranyl ion in environmental solutions. This work suggests that conjugated fluorescent polymer with amidoxime groups will be a prospective sensor of uranyl ion in the environmental sample.

A near-infrared fluorescent probe for hydrogen polysulfides detection with a large Stokes shift

Due to the crucial biological roles of hydrogen polysulfides (H₂S_n) in living systems, the selective determination of H₂S_n is essential. In this work, we reported a turn-on fluorescent probe, JSI-Sn, for H₂S_n with high sensitivity and good selectivity. Probe JSI-Sn displayed a near-infrared emission (λ_max^Em = 701 nm) and a large Stokes shift (123 nm) in the presence of H₂S_n in solution. Using probe JSI-Sn as an indispensable tool, the monitoring of intracellular H₂S_n in living cells and zebrafish were realized.

A novel ratiometric fluorescent probe for "naked-eye" detection of sulfite ion: Applications in detection of biological SO32- ions in food and live cells

A new "turn-on" luminescent probe PI has been designed and synthesized for the selective detection of sulfite ions based on the mechanism of nucleophilic addition. The designed probe PI owns naked eye detection, excellent selectivity, sensitivity, rapid response (150 s) and low limits of detection (LOD) of 0.57 μM, which is an agreeable limit by the world wide expert food additive committees. Furthermore, the probe PI was used to recognize the sulfite ions level in realistic samples and live cells.

A naphthalimide-indole fused chromophore-based fluorescent probe for the detection of biothiol with red emission and a large Stokes shift

This probe exhibited red emission (λ_max = 590 nm) and a large Stokes shift (143 nm) for the detection of biothiols.