A novel fluorescent probe for cascade detection of hydrogen sulfide and hypochlorous acid and its application in bioimaging.

Herein we developed a cascade detection mode for the detection of HS- and ClO- by the novel probe NM-Cl bearing a conjugating naphthalene-dicyanoisophorone unit. The probe displayed sensitive and remarkable fluorescent enhancement in response to HS-, but not to other analytes. The mixture of probe and HS- constructed a specific sensing system for ClO- by fluorescent quenching response. The mechanism studies indicated that the successive reacting of HS- substitution Cl atom in probe and then addition of ClO- facilitation a thiofuran ring-forming induced differentiated fluorescence emission. This study provides a novel mechanism for the detection of HS- and ClO-, the imaging of cell and living animal further indicating the good application prospects of the probe in biosensing and bioimaging.

A novel near-infrared fluorescent probe with large Stokes shift for imagining hydrogen sulfide.

Hydrogen sulfide (H2S) plays an important role in regulating varieties of important physiological and pathological processes. Thus the development of fluorescent probe for the detection of H2S is of great significance and has attracted much attention recently. Herein, we reported a novel near-infrared (NIR) emitting fluorescent probe WFP-PC, which contained a positive charged hemicyanine-based WFP-OH as fluorophore and thiobenzoate unit as a specific reaction site. After treated with H2S, the probe exhibited significant fluorescence enhancement and response time within 4 min and detection limit as low as 0.47 µM, accompanied by color changes from purple to blue. The probe was successfully applied to imaging the exogenous/endogenous H2S in cells and mice, suggesting it could be a promising molecular tool for H2S detection in living systems.

A hemicyanidin-based NIR fluorescent probe for detection of H2S and imaging study in cells and mice.

The selective detection of hydrogen sulfide in physiological and pathological processes has gained substantial attention in recent years. However, the real-time detection of hydrogen sulfide remains an elusive goal. In this work, a new type of hemicyanidin-based fluorescent "turn-on" probe NTR-HS (Ex = 680 nm, Em = 760 nm) was developed to detected H2S in a very short time (3 min). The fluorescence quantum yield is 0.15 and accompanied with a noticeable color change from violet to blue that can be used to detect H2S in the range 1.04 × 10-7-4 × 10-5 M with a limit of detection of 1.04 x 10-7 M. The NTR-HS probe was also used for imaging of endogenous hydrogen sulfide and mitochondrial localization in HCT116 and HeLa cells. The detection mechanism was studied through fluorescence, UV-Vis, NMR, and mass analysis. Notably, the probe was successfully used to imaging H2S in mice and locating hydrogen sulfide in the large intestine of mice.

A novel reversible fluorescent probe for Cu2+ and S2-ions and imaging in living cells.

A novel fluorescent probe TSOC (thiazole salicylaldehyde oxazole chlorinated) was synthesized based on benzothiazole conjugated olefinic bonds with salicylicaldehyde unit as fluorophore and a phenyl oxazole unit as bonding unit. The probe could reversibly detect of Cu2+and S2-over other common ions with longer emission and large stokes shift in an aqueous solution at pH 7.3 (DMSO-Hepes, v/v, 5:1, 10 mM). The bonding mechanism was supported through the titration experiment of fluorescence and absorption spectroscopy,1H-NMR titration, HR-MS and DFT calculations. Moreover, the probe further exhibited good cell permeability and were successfully used to visualize Cu2+and S2-in living cells.

A hemicyanine-based "turn-on" fluorescent probe for the selective detection of Cu2+ ions and imaging in living cells.

A novel hemicyanine-based fluorescent probe was developed for the fast, selective, and reversible detection of Cu2+ ions with "turn-on" fluorescence response in the aqueous solution. The sensing mode was demonstrated through fluorescence, UV-vis, HRMS, 1H NMR, and DFT calculations. The probe was successfully used for the imaging of Cu2+ ions in living cells.

Visible and Reversible Restrict of Molecular Configuration by Copper Ion and Pyrophosphate.

Molecular configuration strongly impacts on its functions; however, due to complicated and diverse configuration as well as easy and rapid conversion among various configurations, research of molecular configuration is extremely difficult. If the free rotation of a molecule could be "slowed down" or even "frozen" by an external stimulus, such as ultralow temperature, then one configuration of the molecule could be captured and characterized relatively easily. Here, we show that the rotation of a hemicyanine-labeled 2-(2'-hydroxyphenyl)-4-methyloxazole (H-HPMO) molecule could be specifically and reversibly restricted by sequential additions of copper ion (Cu2+) and pyrophosphate (P2O74-), reflecting as remarkable fluorescence quenching and recovery, which could be directly observed by naked eyes. Binding affinity tests and cryogenic 1H NMR indicate that Cu2+ forms intensive coordinate bonds with phenolic hydroxyl, oxazole, and methoxyl groups of HPMO, which strongly restricts the free rotations of these groups and blocks charge transfer. This study provides a precise, rapid, visible, reversible, and low-cost method to monitor the molecular configuration, indicating the broad application prospects of near-infrared fluorescent sensors in configuration analysis, biosensing, and drug-substrate complexation.

A novel near-infrared turn-on fluorescent probe for the detection of Fe3+ and Al3+ and its applications in living cells imaging.

In this study, a new hemicyanidine-based colorimetric-fluorescent probe L has been synthesized and characterized by X-ray single crystal diffraction, NMR, HRMS and other technologies. The probe L serves as a "turn-on" probe for the detection of Fe3+ and Al3+ ions in DMF-HEPES system with a high sensitivity and an excellent selectivity. The probe L manifesting the color of the solution containing L turns red on the addition of Fe3+, and turns pink on the addition of Al3+. The fluorescence turn-on detection of Fe3+ and Al3+ ions is attributed to the photo-induced electron transfer (PET) process and the exertion of the chelation-enhanced fluorescence effect (CHEF) mechanism. The results of thin layer silica gel plate coloration experiments also present the same characteristics. Additionally, we further demonstrate that the probe L exhibit good cell permeability and could be employed to monitor Fe3+ and Al3+ ions in the living 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.

Coumarin-based colorimetric-fluorescent sensors for the sequential detection of Zn2+ ion and phosphate anions and applications in cell imaging.

Two novel coumarin based fluorescent sensors CHP and CHS have been synthesized for the sequential detection of Zn2+ ion and phosphate anion (PA) in DMF/HEPES buffer medium (1/5 v/v, 10 mM, pH = 7.4). On the addition of Zn2+ ion to the solution of CHP or CHS resulted in a pronounced fluorescence enhancement, accompanying noticeable color change (under UV or daylight), while there was hardly obvious change with other competing metal ions co-existing. The detection limits (DL) of CHP and CHS toward Zn2+ were separately determined as 1.03 × 10-7 (R2 = 0.9886) and 1.87 × 10-7 (R2 = 0.9902). The PET binding processes were affirmed by spectroscopic techniques, HRMS experiments and theoretical calculations. Subsequently, the CHP-Zn2+ or CHS-Zn2+ complexes showed high selectivity fluorescence quenching toward PA by snatching Zn2+ ion from its complex and the binding processes were reversible. DLs were calculated as 2.07 × 10-7 M (R2 = 0.9928) and 2.63 × 10-7 M (R2 = 0.9954), respectively. Furthermore, the cell imaging experiments demonstrated that the sensors were capable of detecting of Zn2+ and PA in vitro cells.

Indole-based colori/fluorimetric probe for selective detection of Cu2+ and application in living cell imaging.

A highly sensitive and selective indole-based probe IHT exhibited obvious color change from colorless to violet easily detected by naked eye as well as 'turn on' fluorescence response to Cu2+ ion at physiological pH condition. The detection limit was determined to be as low as 8.93 × 10-8 M, which was much lower than drinking water permission concentrations by the United States Environmental Protection Agency. The 1:2 binding mechanism was well confirmed by fluorescence titration, Job's plot, HRMS, IR analysis and DFT calculations. Furthermore, the probe IHT was successfully used for fluorescence imaging of Cu2+ ion in living cells.

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 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 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 novel coumarin-based fluorescent sensor for Ca2+ and sequential detection of F- and its live cell imaging.

A novel fluorescent sensor CPM for relay detecting Ca2+ and F- based on coumarin has conveniently synthesized and characterized. The sensor CPM showed highly fluorescence enhancement to Ca2+ over other metal ions, and the CPM-Ca2+ complex could selectively recognize F- among other anions. The limits of detection for Ca2+ and F- were 5.81 × 10-7 M and 4.28 × 10-7 M in aqueous solution (DMF/HEPES buffer 1:1 v/v, 10 mM, pH = 7.2), respectively. Their sensing mode had been testified by Job's plots, UV-vis titration, 1H NMR titrations, ESI-mass, fluorescence and DFT calculations. The fluorescence imaging indicated that CPM was cell-permeable and could be used to effectively detect Ca2+ and F- within living cells.

Novel fluorescent probes for relay detection copper/citrate ion and application in cell imaging.

Two novel fluorescent probes, 2­(2'­hydroxyphenyl)­4­(2'­hydroxymethyl­8­quinolinamino)methyloxazole (L1), and 2­(2'­hydroxyphenyl)­4­(2'­methyl­8­quinolinamino)methyloxazole (L2), exhibited colorimetric and "turn off" fluorometric response to Cu2+ ion in DMSO/H2O solution (v/v = 1/1, 0.01 M, Tris-HCl buffer, pH 7.20) and the corresponding detection limit were found to be 2.14 × 10-8 and 2.70 × 10-8 M, which were much lower than drinking water permission concentrations by the United States Environmental Protection Agency (U.S. EPA) and World Health Organization (WHO). The L1-Cu2+ and L2-Cu2+ complexes ensemble detected citrate anions (CA) sequentially through fluorescence recovery response due to the extrusion of Cu2+ ion from the complexes. The binding processes were investigated by UV-vis, fluorescence, IR and DFT calculation. Furthermore, the vivo sensitivity experiments of Cu2+ ion and CA was demonstrated through fluorescence imaging in living cells.

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

A novel fluorescent probe 2-(2'-hydroxyphenyl)-4-(phenylethylamino)methyloxazole (HPO) has been synthesized, which performed highly selective and sensitive detection of Zn2+ ion with a discriminating enhancement over the other metal ions. The binding constant was calculated as 3.07 × 103 M-1 with detection limit of 1.22 × 10-6 M in aqueous solution (CH3CN-Tris v/v, 1/1, Tris, 10 mM, pH = 7.4). Moreover, the HPO-Zn2+ complex could serve as an excellent tartrate anion (TA). The detection mode maybe due to TA detach Zn2+ ion from HPO-Zn2+ complex leading to resulting in the release of the free probe HPO. As a result, a logic circuit has also been constructed on the basis of Zn2+ and TA as chemical inputs. Furthermore, fluorescence imaging experiments showed that probe HPO could be used as an effective fluorescent probe for detecting Zn2+ and TA in living cells.

Acridine-based fluorescence chemosensors for selective sensing of Fe3+ and Ni2+ ions.

Two novel acridine-based fluorescence chemosensors (L1 and L2) were prepared and their metal ions sensing properties were investigated. L1 (L2) exhibited an excellent selective fluorescence response toward Fe3+ (Ni2+) and the stoichiometry ratio of L1-Fe3+ and L2-Ni2+ were 1:1. The detection limits of L1 and L2 were calculated by the fluorescence titration to be 4.13µM and 1.52µM, respectively, which were below the maximum permissive level of Fe3+ and Ni2+ ions in drinking water set by the EPA. The possible mechanism of the fluorescence detection of Fe3+ and Ni2+ had been proposed according to the analysis of Job's plot, IR spectra and ESI-MS. The determination of Fe3+ and Ni2+ ions in living cells had been applied successfully.

Colorimetric chiral fluorescent sensors for Eu3+ and sequential enantioselective sensing of malate anion.

Novel phenanthroline Schiff base fluorescent sensors L1, L2, and D1 were designed and synthesized. The sensing abilities of the compounds in the presence of metal cations (Li+ , Na+ , K+ , Ag+ , Mg2+ , Ba2+ , Ca2+ , Mn2+ , Pb2+ , Hg2+ , Ni2+ , Zn2+ , Cd2+ , Co2+ , Cu2+ , Cr3+ , Fe3+ , Fe2+ , Al3+ , and Eu3+ ) were studied by UV-vis and fluorescent spectroscopy. The compounds L1, L2, and D1 could act as Eu3+ ion turn-off fluorescent sensors based on ligand-to-metal binding mechanism in DMSO-H2 O solution (v/v = 1:1, 10 mM Tris, pH = 7.4). Additionally, the L1-Eu3+ and D1-Eu3+ complexes could be applied as turn-on enantioselective sensors sensing of malate anion isomers with color changes. Furthermore, biological experiments using living PC-12 cells demonstrated that L1 and D1 had excellent membrane permeability and could be used as effective fluorescent sensors for detecting Eu3+ and malate anion in living cells.

A novel turn-on fluorescent probe for Al3+ and Fe3+ in aqueous solution and its imaging in living cells.

A quinoline-based fluorescence probe has been prepared and characterized. Probe 1 showed a selective sensing ability for Al3+ and Fe3+ ions through fluorescence enhancement response at 515nm when it was excited at 360nm. In the presence of Fe3+ ion, probe 1 exhibited a detection limit of 2.10×10-6M. As for Al3+, its detection limit of 3.58×10-7M was significantly lower than the highest limit of Al3+ in drinking water recommended by the WHO (7.41µM), representing a rare example in reported fluorescent probe for Al3+ ion. The fluorescence microscopy experiments have demonstrated that probe 1 could be used in live cells for the detection of Al3+ and Fe3+ ions.

Novel enantioselective fluorescent sensors for tartrate anion based on acridinezswsxa.

Novel chiral fluorescence sensors L-1 and D-1 incorporating N-Boc-protected alanine and acridine moieties were synthesized. The recognition ability of the sensors was studied by fluorescence titration, 1 H NMR spectroscopy and density functional theory (DFT) calculations. The sensors exhibited good enantioselective fluorescent sensing ability toward enantiomers of tartrate anion for the selected carboxylate anions and formed 1: 1 complexes by multiple hydrogen bonding interactions.