Vesicular polydiacetylene sensor for colorimetric signaling of bacterial pore-forming toxin

A vesicle-based polydiacetylene biosensor for colorimetric detection of bacterial pore-forming toxin streptolysin O (SLO) is reported. The sensor was constructed with three lipid constituents: glycine-terminated diacetylene lipid Gly-PCDA, cell membrane-mimicking component PC-DIYNE, and cholesterol (CHO), which serves as the bait molecule. UV irradiation led to photopolymerization of the diacetylene lipids that gave the material a blue appearance. Incubation of the vesicles with SLO from Streptococcus pyrogenes turned the vesicle solution red, and the color change was found to be correlated to SLO concentration. The optimal sensing performance was found with vesicles consisting of 71% Gly-PCDA, 25% CHO, and 4% PC-DIYNE, and a correlation relationship was obtained for 20 HU to 500 HU/mL, or 100 pM to 6.3 nM of SLO toxin. Transmission electron microscopy and dynamic light scattering was used for further characterization of the vesicular assemblies. Transmembrane pores (holes) with diameter around 30 nm were observed on the vesicle membranes, in particular on the peripheral of the membrane structures, suggesting pore formation by SLO toxin provides the driving force for the color change of the functional vesicles.     

A selective turn-on fluorescent sensor for Fe and application to bioimaging

A novel compound FD1 was demonstrated as a turn-on fluorescent sensor for imaging of iron(III) ion in biological samples. Based on the spirolactam (nonfluorescence) to ring-open amide (fluorescence) equilibrium, FD1 exhibited high selectivity and sensitivity for Fe³⁺ over other metal ions. Moreover, fluorescent microscopy experiments further established that FD1 could be used for sensing Fe³⁺ within living cells.     

A selective turn-on fluorescent sensor for imaging copper in living cells

We present the synthesis, properties, and biological applications of Coppersensor-1 (CS1), a new water-soluble, turn-on fluorescent sensor for intracellular imaging of copper in living biological samples. CS1 utilizes a BODIPY reporter and thioether-rich receptor to provide high selectivity and sensitivity for Cu+ over other biologically relevant metal ions, including Cu2+, in aqueous solution. This BODIPY-based probe is the first Cu+-responsive sensor with visible excitation and emission profiles and gives a 10-fold turn-on response for detecting this ion. Confocal microscopy experiments further establish that CS1 is membrane-permeable and can successfully monitor intracellular Cu+ levels within living cells.     

A colorimetric and fluorescent turn-on sensor for pyrophosphate anion based on a dicyanomethylene-4H-chromene framework

A new red fluorescent sensor DCCP-Cu2+ based on dicyanomethylene-4H-chromene shows turn-on fluorescence with high selectivity for pyrophosphate over other anions.     

Antioxidant-substituted tetrapyrazinoporphyrazine as a fluorescent sensor for basic anions

Tetrapyrazinoporphyrazine substituted at its periphery with eight antioxidant 3,5-di-t-butyl-4-hydroxyphenyl groups behaves as a turn-on fluorescent sensor for fluoride anions. Conversely, the precursor antioxidant-substituted 1,2-phthalonitrile was found to act in turn-off mode suggesting that the origin of the phenomenon lies at the phenolate-substituted 1,4-pyrazinyl moiety.     

Ratiometric and turn-on monitoring for heavy and transition metal ions in aqueous solution with a fluorescent peptide sensor

A novel fluorescent peptide sensor containing tryptophan (donor) and dansyl fluorophore (acceptor) was synthesized for monitoring heavy and transition metal (HTM) ions on the basis of metal ion binding motif (Cys-X-X-X-Cys). The peptide probe successfully exhibited a turn on and ratiometric response for several heavy metal ions such as Hg²⁺, Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ in aqueous solution. The enhancements of emission intensity were achieved in the presence of the HTM ions by fluorescent resonance energy transfer (FRET) and chelation enhanced fluorescence (CHEF) effects. The detection limits of the sensor for Cd²⁺, Pb²⁺, Zn²⁺, and Ag⁺ were lower than the EPA's drinking water maximum contaminant levels (MCL). We described the fluorescent enhancement, binding affinity, and detection limit of the peptide probe for HTM ions.     

Methoxyquinoline-diethylenetriamine conjugate as a fluorescent zinc sensor

A 6-methoxyquinoline conjugated diethylenetriamine derivative, N,N'-bis(6-methoxy-2-quinolylmethyl)diethylenetriamine (6-MeOBQDIEN) has been synthesized and its fluorescent response toward zinc ion was investigated. In the presence of zinc ion, 6-MeOBQDIEN exhibits fluorescence (λ(ex) = 329 nm, λ(em) = 418 nm, φ = 0.039). The fluorescent intensity of the zinc complex of the compound is two times higher than the parent BQDIEN (φ = 0.021) under the same conditions. The crystal structure of 6-MeOBQDIEN-Zn complex shows that all five nitrogen atoms participate to the metal coordination in a distorted square-pyramidal geometry (τ = 0.145) with the aliphatic nitrogen in an apical position. Fluorescent microscopic analysis using 6-MeOBQDIEN reveals the zinc ion concentration change in living cells.     

Self-assembled fluorescent hexaazatriphenylenes that act as a light-harvesting antenna

In this paper we report the self-assembling nature of fluorescent hexaazatriphenylenes (HATs) 6a-d with six alkyl/alkoxy-chain-containing biphenyl groups and their application to light-harvesting antennae. In a nonpolar solvent and the film state, the HAT derivatives form one-dimensional aggregates with an H-type parallel stacking mode, which were analyzed by 1H NMR, UV-vis, and steady-state and time-resolved fluorescence spectroscopy. When HAT derivative 7 with six perylenediimide moieties is incorporated into the one-dimensional aggregates, an efficient energy transfer takes place from the self-assembled HAT moiety as a light-harvesting antenna to the perylenediimide moiety as an energy acceptor. Further, when HAT derivative 8 with six triphenylamino moieties is newly added to the light-harvesting system, an intermolecular electron transfer occurs subsequently between the electron-accepting perylenediimide molecule and the electron-donating triphenylamino molecule.     

A highly selective turn-on colorimetric, red fluorescent sensor for detecting mobile zinc in living cells

We describe ZRL1, a turn-on colorimetric and red fluorescent zinc ion sensor. The Zn(2+)-promoted ring opening of the rhodamine spirolactam ring in ZRL1 evokes a 220-fold fluorescence turn-on response. In aqueous media, ZRL1 turn-on luminescence is highly selective for Zn(2+) ions, with no significant response to other competitive cations, including Na(+), K(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Cd(2+), or Hg(2+). In addition to these characteristics, preliminary results indicate that ZRL1 can be delivered to living cells and can be used to monitor changes in intracellular Zn(2+) levels.     

A "turn-on" fluorescent sensor for the selective detection of mercuric ion in aqueous media

A water-soluble turn-on fluorescent sensor for Hg(II) is described. Incorporation of soft thioether donors into an aniline-derived ligand framework that can be linked to a fluorescein platform affords sensor MS1, which shows a approximately 5-fold increase in integrated emission upon addition of 1 equiv of Hg(II). The synthesis and metal-binding properties of MS1 are discussed, and its ability to detect environmentally relevant concentrations of Hg(II) is demonstrated.     

A highly selective and sensitive BODIPY-based colourimetric and turn-on fluorescent sensor for Hg2+ ions

A series of monostyryl boron dipyrromethenes appended with an NO(4), NO(2)S(2), N(3)O(4), or N(3)O(2)S(2)-type ligand have been prepared and characterised. While the UV-Vis spectra of the former three compounds in CH(3)CN/H(2)O (2?:?3 v/v) do not respond towards a wide range of metal ions, the derivative with an N(3)O(2)S(2)-ligand exhibits a highly selective and sensitive spectral response towards Hg(2+) ions. The absorption band is blue-shifted by 40 nm due to inhibition of the intramolecular charge transfer process upon metal complexation. The fluorescence is also turned on giving a strong emission band at 572 nm. The colour changes can be easily detected by the naked eye. The results suggest that this compound serves as a promising colourimetric and fluorescent sensor for Hg(2+) ions in this mixed aqueous medium.     

A novel NIR fluorescent turn-on sensor for the detection of pyrophosphate anion in complete water system

A novel fluorescent sensor DCAA-Cu(2+) was developed, showing turn-on fluorescence in NIR region with high selectivity to pyrophosphate anion in 100% aqueous solution.     

Photoswitchable fluorescent diarylethene in a turn-on mode for live cell imaging

A new diarylethene-derived photochromic compound, with little cytotoxicity, plasma membrane-permeability, and efficient photoswitchability in cells upon alternative UV and visible light irradiation, was synthesized and applied to live cell imaging.     

BODIPY based fluorescent turn-on sensor for highly selective detection of HNO and the application in living cells

On the basis of BODIPY platform, a terpyridyl-substituent BODIPY-Copper complex (Cu(II)-BTPY) was rationally designed and synthesized as a redox reaction fluorescent sensor for detecting HNO over reactive oxygen species (ROS) and reactive nitrogen species (RNS) with impressive selectivity in living cells under mild and neutral conditions. The BTPY exhibits relatively high fluorescence quantum efficiency as much as 34.8% and presents large stokes shift, about 62 nm. When a series of transition metal ions were exploited to investigate the fluorescence quench towards BTPY, copper ion (Cu²⁺) gave the optimal result. After the fluorescence of the probe being effectively quenched in the presence of Cu²⁺, it can be in turn recovered through the reduction of Cu²⁺ into Cu⁺ by HNO accompanying with a visually observable fluorescence response. Still, the sensing mechanism was evidently confirmed by EPR and ESI-MS measurement. In addition, the employment of BTPY for imaging dyes was also presented in vivo.     

A selective fluorescent turn-on NIR probe for cysteine

A selective and sensitive turn-on fluorescent NIR probe for cysteine has been developed. Cleavage of 2,4-dinitrobenzenesulfonyl (DNBS) with thiols switches the weakly fluorescent aza-BODIPY dye (λ(em) = 734 nm, Φ(f) = 0.03) to a strongly fluorescent species in the NIR region (λ(em) = 755 nm, Φ(f) = 0.14).     

A near-infrared fluorescence turn-on sensor for sulfide anions

The first NIR fluorescent sensor for sulfide anions was constructed based on the displacement approach. The sensing ensemble is composed of a cyanine dye, a piperazine linker, an 8-aminoquinoline ligand, and copper. The favorable attributes of the sensor include a large NIR fluorescence turn-on signal in aqueous ethanol, high sensitivity, and high selectivity. The transition-metal-based displacement strategy may open an avenue for development of NIR fluorescent sensors for a wide variety of anion targets.     

Conjugated polymer-based fluorescence turn-on sensor for nitric oxide

A turn-on fluorescent sensor for NO (g) in solution was synthesized using a bipyridyl-substituted poly(p-phenylene vinylene) derivative (CP1) as the sensory scaffold. The action of NO (g) upon the CP1-Cu(II) complex reduces it to the CP1-Cu(I) complex with a concomitant 2.8-fold increase in emission intensity. The reagent is selective for NO (g) versus other biological reactive nitrogen species, except for nitroxyl, and has a detection sensitivity limit of 6.3 nM. [structure: see text]     

Colorimetric detection of oligonucleotides using a polydiacetylene vesicle sensor

A new system for the colorimetric detection of oligonucleotides was developed using polydiacetylene vesicles, which play the dual role of an indicator of color transition and an amplification tag. The results are of significance in understanding the mechanism of color transition of biological recognition in polydiacetylene systems and in designing new biosensors.