A selective fluorescent probe for relay detection of Zn2+ and tartrate: Application to logic circuit and living cell imaging

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.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

Phenolphthalein Conjugated Schiff Base as a Dual Emissive Fluorogenic Probe for the Recognition Aluminum (III) and Zinc (II) Ions

In this study, a new phenolphthalein derivative, FFIZNA, has been planned and successfully prepared in an uncomplicated way. The probe FFIZNA could selectively monitor Al³⁺ and Zn²⁺ among other relevant cations with diverse colors through a turn-on emission response in EtOH:HEPES (9/1;v/v) media owing to the chelation enhanced fluorescence (CHEF), prevention of ESIPT, -C=N- isomerization and PET of the probe FFIZNA. The interactions of Al³⁺ and Zn²⁺ with the probe FFIZNA were confirmed by emission spectroscopy, Job's plot and ¹H-NMR titration substantiated 1:2 reaction stoichiometry between FFIZNA and Al³⁺ and Zn²⁺. The time-response study displayed that the emission of FFIZNA with Al³⁺ and Zn²⁺, rapidly boosted and reached the stable value in less than 3.0 and 4.0 min, respectively. Therefore, the FFIZNA has successfully been utilized to the dual recognition of Al³⁺ and Zn²⁺ in solutions. Phenolphthalein conjugated schiff base as a dual emissive fluorogenic probe for the detection aluminum (III) and zinc (II) ions.

Discovery of a novel camphor-based fluorescent probe for Co2+ in fresh vegetables with high selectivity and sensitivity

Cobalt is an essential micronutrient for human beings. The excessive intake of cobalt may lead to heart-related diseases. In this work, a novel fluorescent probe 1,1'-(((6,11,11-trimethyl-6,7,8,9-tetrahydro-6,9-methanopyridazino[4,5-b]quinoxaline-1,4-diyl)bis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol) (PDS) was synthesized from camphor. The probe PDS could be utilized to selectively recognize Co²⁺ over other metal ions. There is a good linear relationship between fluorescence intensity of PDS and Co²⁺ concentration within 0-20 μM, and its detection limt was found to be 0.925 μM, which is far lower than the national standard for cobalt in drinking water in China. The possible coordination mechanism of PDS with Co²⁺ was determined by nuclear magnetic resonance (NMR), high resolution mass spectrometry (HRMS) and density functional theory (DFT). The probe PDS was also successfully applied in detection of Co²⁺ in tap water and fresh vegetables.

A benzyl carbazate-based fluorescent chemosensor for detecting Zn2+: Application to zebrafish

A benzyl carbazate-based fluorescent chemosensor BCS was designed and synthesized for detection of Zn²⁺ in aqueous media. BCS displayed a notable fluorescence increase with Zn²⁺. Detection limit (1.12 μM) of BCS for zinc ion was much lower than the standard of World Health Organization. BCS was used to analyze the amounts of Zn²⁺ in water samples. Importantly, sensor BCS could be used to image Zn²⁺ in zebrafish, and a fluorescent test strip of sensor BCS for detecting Zn²⁺ could be useful for practical purpose. Sensing process of Zn²⁺ by BCS was demonstrated by DFT calculations, based on an effect of chelation-enhanced fluorescence.

Fluorescent schiff base probes for sequential detection of Al3+ and F- and cell imaging applications

Two novel Schiff-base fluorescent probers SQ and NQ based on 8-hydroxyquinoline moiety were designed and synthesized. The both probes were capable of binding with Al³⁺ by naked eye detection to produce a significant fluorescence enhancement response with a detection limit of 1.48 × 10^-8 and 4.23 × 10^-8 M, respectively. At the same time, the formed complexes SQ-Al³⁺ and NQ-Al³⁺ could sequentially detect F^-, and the detection limits of F^- were determined to be 1.64 × 10^-7 and 3.58 × 10^-8 M, respectively. The "off-on-off" fluorescence response process demonstrated that the binding were reversible. The probes were further successfully utilized to detect Al³⁺ and F^- in vitro PC12 cells.

A dual fluorescence probe for Zn2+ and Al3+ through differentially response and bioimaging in living cells

A novel Schiff base fluorescent probe 7-Hydroxy-8-(((2-(hydroxymethyl)quinolin-8-yl)imino)methyl)-coumarin (XL) consist of formylcoumarin and aminoquinoline moieties was synthesized for dual detection of Zn²⁺ and Al³⁺ ions. Probe XL exhibited high selective and sensitive response towards Zn²⁺ and Al³⁺ ions through different color changes and significant fluorescence turn-on response (270 fold higher for Zn²⁺ and 230 fold higher for Al³⁺) in MeOH-H₂O (4/1, v/v) over other cations, with detection limits (LOD) as low as 3.75 × 10^-8 and 1.14 × 10^-8 M, respectively. Moreover, probe XL exhibited preferential selectivity for Al³⁺ through displacing Zn²⁺ from the XL-Zn²⁺ complex by ligand-to-ligand transfer process. The binding mechanism of intramolecular charge transfer (ICT) were proposed from fluorescence and UV-vis titrations, Job's plot, ¹H NMR titration, HRMS and DFT calculations. The probe was proven to be suitable for actual samples detection of Zn²⁺ and Al³⁺ ions. The complex XL-Zn²⁺ and XL-Al³⁺ exhibited dramatic fluorescent "turn-off" properties for PPi and PPi/F^- respectively through snatching metal ions and released free XL. Moreover, probe XL showed low biotoxicity and sequentially "off-on-off" fluorescent bio-imaging of Zn²⁺/Al³⁺ and PPi/F^- in PC12 cells.

A novel colorimetric-fluorescent probe for Al3+ and the resultant complex for F- and its applications in cell imaging

A novel quinoline-based Schiff-base probe QL had been synthesized, which could sequentially monitor Al³⁺ and F^- in MeOH-H₂O solution (v/v = 8/1, 0.01 M, HEPES buffer, pH = 7.3). The probe QL expressed a high selective and sensitive "OFF-ON-OFF" fluorescent response for Al³⁺ and F^- (excitation at 460 nm and emission at 530 nm) accompanying visible color changed, which was ascribed to intramolecular charge transfer (ICT) process and chelation-enhanced fluorescence (CHEF) mechanism. The binding stoichiometry of QL with Al³⁺ was 2:1 counting on Job's plot and HRMS, while F^- could pull Al³⁺ to depart from the complexation 2QL-Al³⁺ and released free QL. The limit of detections of probe QL for Al³⁺ and F^- ions were calculated to be 0.10 μM and 0.50 μM. The ¹H NMR experiments and density functional theory (DFT) calculations were carried out to further prove the binding mode between QL and Al³⁺. Furthermore, fluorescence imaging studies demonstrated that the probe QL was low cytotoxicity and could be applied to detect Al³⁺ and F^- in living PC12cells.

A multiple fluorescein-based turn-on fluorophore (FHCS) identified for simultaneous determination and living imaging of toxic Al3+ and Zn2+ by improved Stokes shift

A multiple turn-on fluorophore (FHCS), combining fluorescein, hydrazone, cyanuric chloride and salicylaldehyde chromone into a molecule, was identified and developed based on density functional theoretical calculation. It was expected that FHCS could express exclusive fluorescent signals and improved Stokes shifts when chelating Al³⁺ or Zn²⁺. After it was synthesized and characterized in detail, it was noted that FHCS could turn-on fluorescently discriminate trace Al³⁺ and Zn²⁺ under the optimized conditions, i.e., from no-fluorescence to strong blue fluorescence for Al³⁺ and to green fluorescence for Zn²⁺ with low detection limits of 5.37 × 10^-8 M and 7.90 × 10^-8 M respectively. Owing to its low toxicity, FHCS was successfully applied for quantitative determination of Al³⁺ and Zn²⁺ in natural aqueous samples and toxicity evaluation of Al³⁺ and Zn²⁺ in living cells and bio-tissues with excellent linear relationships. The action mechanisms for FHCS with Al³⁺ and Zn²⁺ were confirmed to form stable 5-member-co-6-member condensed rings between Al³⁺/Zn²⁺ and N/O atoms in FHCS by both theoretic and experimental methods, which resulted in turn-on fluorescence with different dipolar moments and improved Stokes shifts.

Dual recognition of Al3+ and Zn2+ ions by a novel probe based on diarylethene and its application

We synthesized a new fluorescent probe 1O by attaching a diarylethene molecule to a functional group. The probe can be used to detect Al3+ and Zn2+ at the same time with high selectivity, and its detection limit is very low. When Al3+ was added, the fluorescence intensity was increased 310 folds, and was accompanied by a fluorescent color change from black to grass-green. Similarly, after the addition of Zn2+, the fluorescence intensity was enhanced 110 folds, with a concomitant color change from black to yellow-green. Moreover, based on the properties of 1O, we designed a logic circuit, and that also can be used for water sample testing.

A novel fluorescent-colorimetric probe for Al3+ and Zn2+ ion detection with different response and applications in F- detection and cell imaging

A novel Schiff base fluorescence probe (HL) was synthesized by the condensation of salicylaldehyde and an 8-aminoquinoline derivative. This probe acts as a "turn-on" dual selectivity fluorescence probe for Zn²⁺ and Al³⁺ ions, providing different colors and detection limits (DL) of 11.5 and 23.5 nM, respectively. Moreover, when Zn²⁺ and Al³⁺ co-exist, HL exhibits a preference for Al³⁺ by displacing Zn²⁺ from the HL-Zn²⁺ complex, realizing a dual-channel signal output for Al³⁺. The HL-Al³⁺ system could further discern F^- by a "turn-off" fluorescence response with a DL of 86.0 nM. Furthermore, the probe HL was capable of monitoring intracellular Al³⁺, Zn²⁺ and F^- in living PC12 cells in vitro through fluorescence imaging, which proved its value in potential in vivo applications.

A novel probe for colorimetric and near-infrared fluorescence detection of cysteine in aqueous solution, cells and zebrafish

Cysteine(Cys) is tightly related to physiological and pathological of human, and the imbalance of concentration of cysteine in the intracellular are associated with many diseases. Here, a novel NIR fluorescent probe TCF-Cys was designed and synthesized, and both the optimal excitation and emission wavelength of them were between 650 and 900 nm, that within the "optical window" of biological tissues. In aqueous solution, TCF-Cys, which with an acrylate extremity as a recognizing unit, exhibited excellent "turn-on" fluorescence response for Cys superior to other amino acids and thiols with a limit of detection of 0.1323 μM. Moreover, as an excellent naked-eye colorimetric indicator, TCF-Cys could effectively distinguishing the Cys, Hcy and GSH in aqueous solution through color change. Then, the response mechanism of TCF-Cys for Cys was revealed by TLC, ¹H NMR, HPLC, HRMS and DFT calculation. Finally, TCF-Cys was successfully employed to fluorescence specifically map of exogenous and endogenous Cys in living cells and zebrafish with low toxicity.

A dual functional fluorescent sensor for the detection of Al3+ and Zn2+ in different solvents

A new fluorescent sensor, X, was designed and synthesized based on imidazo[2,1-b]thiazole and 2-hydroxy-1-naphthaldehyde, which could be used to detect Al³⁺ in methanol buffer solution and detect Zn²⁺ in ethanol buffer solution, respectively.