A fluorescence ratiometric sensor for hypochlorite based on a novel dual-fluorophore response approach

A fluorescence ratiometric sensor for OCl⁻ has been developed based on a novel dual fluorophore response approach. The sensor molecule contains a coumarin fluorophore and a rhodamine fluorophore, and the two fluorophores are directly linked to an OCl⁻ recognition group. The structure of the sensor was characterized by ESI-MS, NMR, and X-ray crystallographic analysis. Upon treatment with OCl⁻, both fluorophores in the sensor responded simultaneously at two separate optical windows, with large enhancement of the fluorescence ratio (I₅₇₈/I₅₀₁) from 0.01 to 39.55. The fluorescence ratios for the sensor showed a good linearity with the concentration of OCl⁻ in the range of 0.2–40 μM and the detection limits is 0.024 μM (S N⁻¹ = 3). Investigation of reaction products indicated that the sensor reaction with OCl⁻ produced two new fluorescent molecules, which were responsible for the fluorescence changes in two optical windows. In addition, the sensor showed high selectivity to OCl⁻ over other reactive oxygen species, reactive nitrogen species, cations, and anions. The sensor has also been successfully applied to detection of OCl⁻ in natural water samples with satisfactory recovery.     

An ICT-based approach to ratiometric fluorescence imaging of hydrogen peroxide produced in living cells

We present the synthesis, properties, and biological applications of Peroxy Lucifer 1 (PL1), a new fluorescent probe for imaging hydrogen peroxide produced in living cells by a ratiometric response. PL1 utilizes a chemoselective boronate-based switch to detect hydrogen peroxide by modulation of internal charge transfer (ICT) within a 1,8-naphthalimide dye. PL1 features high selectivity for hydrogen peroxide over similar reactive oxygen species, including superoxide, and nitric oxide, and a 65 nm shift in emission from blue-colored fluorescence to green-colored fluorescence upon reaction with peroxide. Two-photon confocal microscopy experiments in live macrophages show that PL1 can ratiometrically visualize localized hydrogen peroxide bursts generated in living cells at immune response levels.     

A ratiometric fluorescence sensor for caffeine

The dye disodium 3,4:3',4'-bibenzo[b]thiophene-2,2'-disulfonate can be used as a molecular probe for the fluorimetric detection of caffeine in aqueous solution. The fluorescence response is attributed to non-covalent interactions of caffeine with the dye in the ground state and in the excited state. The bimodal interaction allows performing ratiometric measurements with very good selectivity over structurally related analytes. The dye was also used to develop a simple test strip for the visual differentiation of normal and decaffeinated coffee with a standard UV lamp.     

A new phenothiazine-based fluorescence sensor for imaging Hg2+ in living cells

A new phenothiazine-based sensor PHE-Ad for monitoring Hg²⁺ has been designed and synthesized based on the intramolecular charge transfer (ICT) mechanism. The probes were characterized by FTIR, ¹H NMR, and HRMS, and their optical properties were detected by UV and FL. It's showed the probes detection of Hg²⁺ compared to other metal ions (Mg²⁺, Cu²⁺, Hg²⁺, Ag⁺, Co²⁺, Cr³⁺, Al³⁺, Ni²⁺, Zn²⁺, Ca²⁺, Fe³⁺, Fe²⁺, K⁺, Na⁺, and Cd²⁺) based on the test results. Besides, the detection limits were determined to be 2.12 × 10⁻⁸ M through the standard curve plot. In addition, sensor PHE-Ad shows high selectivity and sensitivity for Hg²⁺ with a fast response in a suitable pH range. Furthermore, taking into account its good “turn-on” fluorescent sensing behavior and low cell cytotoxicity, PHE-Ad was successfully applied to detect and image Hg²⁺ in real water samples and living cells, which shows great potentials for application in environmental and biological systems.     

A ratiometric fluorescent probe for imaging hydroxyl radicals in living cells

A novel fluorescent probe, the detection mechanism of which is based on the 'on-off' switching of a FRET triggered by the *OH-induced cleavage of a DNA strand, has been developed for the ratiometric imaging of *OH.     

A 4-hydroxynaphthalimide-derived ratiometric fluorescent chemodosimeter for imaging palladium in living cells

A highly selective ratiometric fluorescent chemodosimeter derived from 4-hydroxynaphthalimide was designed and synthesized to image palladium species in living cells by virtue of a palladium-catalyzed depropargylation reaction, and it could monitor three typical palladium species (0, + 2 and + 4) without additional reagents.     

FRET-derived ratiometric fluorescence sensor for Cu

New N-(pyrenylmethyl)naphtho-azacrown-5 (1) was synthesized as an ‘On-Off’ fluorescent chemosensor for Cu²⁺. Excited at 240 nm corresponding to the absorption of naphthalene unit (energy donor) of 1, emission at 380 nm from pyrene unit (energy acceptor) is observed, indicating that intramolecular fluorescence resonance energy transfer (FRET-On) occurs in 1. When Cu²⁺ is added to a solution of 1, however, the fluorescence of pyrene is strongly quenched (FRET-Off) whereas that of naphthalene group is revived. Such FRET ‘On-Off’ behavior of 1 is observed only in the case of Cu²⁺ binding, but not for other metal cations. The high selectivity of 1 toward Cu²⁺ can be potentially applied to a new kind of FRET-based chemosensor. The FRET On-Off behavior is supported by computational studies. The calculated molecular orbitals of HOMO and LUMOs suggest the excited-state interactions leading to FRET from naphthalene to pyrene in 1, but no electron density changes in 1·Cu²⁺ complex.     

Development of an iminocoumarin-based zinc sensor suitable for ratiometric fluorescence imaging of neuronal zinc

Ratiometric imaging is a technique to reduce artifacts by minimizing the influence of extraneous factors on the fluorescence of a sensor and is particularly useful for cellular imaging studies. Here we characterized the iminocoumarin fluorophore as a new scaffold for sensors for ratiometric imaging. The iminocoumarin 4 showed a high quantum yield in aqueous media on excitation in the visible wavelength region, while its coumarin analogue showed little fluorescence. We therefore developed a novel fluorescence probe, ZnIC, for ratiometric imaging of Zn2+, using iminocoumarin as a fluorophore and (ethylamino)dipicolylamine as a Zn2+ chelator. ZnIC exhibited almost the same fluorescence properties as 4, and the emission spectrum of this probe was red-shifted on addition of Zn2+ under physiological conditions. ZnIC is selective for Zn2+ over other biologically important metal ions, such as Ca2+ and Mg2+, and has high affinity for Zn2+. To confirm the suitability of ZnIC for biological applications, we employed it for the ratiometric detection of changes in intracellular Zn2+ in cultured cells and in rat hippocampal slices. The results indicate that iminocoumarin is a useful fluorophore for fluorescence microscopic imaging and that ZnIC should be useful for studies on the biological functions of Zn2+.     

A highly selective colorimetric and ratiometric fluorescent chemodosimeter for imaging fluoride ions in living cells

A simple but highly selective colorimetric and ratiometric fluorescent chemodosimeter was designed and synthesized to detect fluoride ions (F(-)) in aqueous solution and living cells by virtue of the strong affinity of F(-) toward silicon.     

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 fluorescence enhanced probe for sulfur dioxide detection and fluorescence imaging in living cellsEI北大核心CSCD

基于香豆素和苯并吡啶基团,构建了用于二氧化硫(SO_(2))高效检测的荧光探针P1,其化学结构通过核磁氢谱(^(1)H NMR)、碳谱(^(13)C NMR)和高分辨质谱(HR-MS)确证。在缓冲溶液体系中,单独的探针P1具有微弱的荧光,识别SO_(2)后荧光发射强度明显增强,能够实现对SO_(2)的专一性裸眼识别,检出限为126 nmol/L。生物应用实验结果表明,该探针具有较低的细胞毒性,可用于生物活细胞中外源性SO_(2)的荧光成像。     

A fluorescence ratiometric nano-pH sensor based on dual-fluorophore-doped silica nanoparticles

We have synthesized dual-fluorophore-doped core-shell silica nanoparticles used as ratiometric pH sensor. The nanoparticles were prepared with a reverse microemulsion technique by simultaneously encapsulating two different fluorophores, the pH-sensitive dye fluorescein as a pH indicator and the pH-insensitive dye phenosafranine as an internal reference for fluorescence ratiometric measurement, into silica shell. The nanoparticles prevent the fluorescence dyes leaching from the silica matrix when immersed inside water. The hydrophilic silica shells were made by hydrolysing and polymerizing tetraethoxysilane (TEOS) in water-in-oil microemulsion. The fluorescence intensity ratio of the two dyes varied linearly as a function of pH in the range from 4.0 to 8.0. The sensor was also applied to measure pH of real water samples. The results are in good agreements with that using the conventional glass electrode method. The as-prepared fluorescent nanoparticles showed rapid response, excellent stability and high reproducibility as pH sensors.     

A highly selective, cell-permeable fluorescent nanoprobe for ratiometric detection and imaging of peroxynitrite in living cells

Peroxynitrite (ONOO(-)) is a highly reactive species implicated in the pathology of numerous diseases and there is currently great interest in developing fluorescent probes that can selectively detect ONOO(-) in living cells. Herein, a polymeric micelle-based and cell-penetrating peptide-coated fluorescent nanoprobe that incorporates ONOO(-) indicator dye and reference dye for the ratiometric detection and imaging of ONOO(-) has been developed. The nanoprobe effectively avoids the influences from enzymatic reaction and high-concentration ·OH and ClO(-). The improved ONOO(-) selectivity of the nanoprobe is achieved by a delicate complementarity of properties between the nanomatrix and the embedded molecular probe (BzSe-Cy). This nanoprobe also has other attractive properties, such as good water solubility, photostability, biocompatibility, and near-infrared excitation and emission. Fluorescence imaging experiments by confocal microscopy show that this nanoprobe is capable of visualizing ONOO(-) produced in living cells and it exhibits very low toxicity and good membrane permeability. We anticipate that this technique will be a potential tool for the precise pathological understanding and diagnosis of ONOO(-)-related human diseases.     

A novel colorimetric and ratiometric NIR fluorescent sensor for glutathione based on dicyanomethylene-4H-pyran in living cells

Glutathione (GSH) plays a critical role in maintaining oxidation-reduction homeostasis in biological systems. Considering the detection of GSH by fluorescence sensors is limited by either the short wavelength emission or the poor photostability, a highly stable colorimetric and ratiometric NIR fluorescent sensor (DCM-S) for GSH detection has been constructed on the basis of dicyanomethylene-4H-pyran (DCM) chromophore. The specific disulfide bond is incorporated via a carbamate linker as the GSH responsive group, which simultaneously blue-shifts and quenches the fluorescence. Upon addition of GSH, DCM-S exhibits outstanding colorimetric (from yellow to red) and ratiometric fluorescent response with the 6-fold enhancement of NIR fluorescence at 665 nm in quantum yield. More importantly, the GSH-treated DCM-S (DCM-NH₂ actually) possesses 20-fold longer fluorescence half-life period as well as much better photostability than the FDA-approved ICG. Finally, the ratiometric detection of GSH is also successfully operated in the living cell imaging, exhibiting NIR fluorescence and large Stokes shift (215 nm) with nearly no background fluorescence interference. As a consequence, DCM-S can be utilized as colorimetric and ratiometric NIR fluorescent sensor for GSH, with a great potential in the development of GSH-induced drug delivery system.     

Boron dipyrromethene fluorophore based fluorescence sensor for the selective imaging of Zn(II) in living cells

A simple PET fluorescence sensor (BDA) for Zn2+ that utilizes 1,3,5,7-tetramethyl-boron dipyrromethene as a reporting group and di(2-picolyl)amine as a chelator for Zn2+ has been synthesized and characterized. BDA has an excitation (491 nm) and emission wavelength (509 nm) in the visible range. The fluorescence quantum yields of the zinc-free and zinc-bound states of BDA are 0.077 and 0.857, respectively. With a low pKa of 2.1 +/- 0.1, BDA has the advantage of less sensitivity to pH than fluorescein-based Zn2+ sensors, and the fluorescence emission of zinc-binding is pH-independent in the range of pH 3-10. Under physiological conditions, metal ions such as Na+, K+, Ca2+, Mg2+, Mn2+ and Fe2+ have little interference. The apparent dissociation constant (Kd) is 1.0 +/- 0.1 nM. Using fluorescence microscopy, the sensor is shown to be capable of imaging intracellular Zn2+ changes.     

A ratiometric fluorescent probe for oxalate based on alkyne-conjugated carboxamidoquinolines in aqueous solution and imaging in living cells

A novel ratiometric fluorescent probe for oxalic acid was designed and synthesized, based on the zinc-containing [DAQZ@2Zn(2+)] complex. It shows highly selective "on-off" fluorescence changes with a more than 20 nm blue shift in wavelength for oxalic acids in aqueous solution. Moreover, it can fluorescently respond to oxalic acid in living cells.     

An ICT-based strategy to a colorimetric and ratiometric fluorescence probe for hydrogen sulfide in living cells

We present a colorimetric and ratiometric fluorescent probe Cy-N(3) that exhibits a selective response to H(2)S. The probe employs a near-infrared cyanine as a fluorophore, and is equipped with an operating azide unit. It is readily employed for assessing intracellular H(2)S levels, and confocal ratiometric imaging is achieved successfully.