Distinct Fluorescence Enhancement Research Articles

Pyrene excimer-based fluorescent chemosensor for cascade detection of Zn(II) and phosphate ions and its applications

There is growing research on developing fluorescent chemosensors that can detect multiple analytes. Herein, a pyrene-naphthaldehyde based Schiff base PNY was synthesized, characterized, and employed for the cascade fluorescent ‘Off-On-Off’ detection of Zn2+ and phosphate ions. The interaction of PNY with Zn2+ led to a distinct fluorescence enhancement at 450 nm, and the fluorescent color of PNY was changed from blue to cyan-blue due to the complexation-induced formation of a pyrene excimer. PNY, as a fluorescent turn-on sensor can be employed to detect Zn2+ down to 2.20 × 10−7 M. Subsequently, the in-situ formed PNY-Zn2+ complex gets decomplex upon the addition of phosphate ion among other tested anions with a detection limit of 3.42 × 10−7 M. With the addition of phosphate ion, fluorescence intensity of PNY-Zn2+ at 450 nm was quenched with the concomitant formation of an emission peak at around 396 nm. The excimer-monomer mechanism was used to explain the sensing ability of PNY. Further, to complement the phosphate ion selectivity, the ability of PNY-Zn2+ to detect adenosine triphosphate (ATP) was explored. At last, the analytical novelty of PNY and PNY-Zn2+ was explored by quantifying Zn2+ and phosphate ions in real environmental and biological samples.

An efficient tetrahydroquinazolin-2-amine derivative-grafted cellulose fluorescent probe for detection of Cu2+ and Zn2+

Cu2+ and Zn2+ play crucial roles in many physiological processes, and their disorder will cause harm to human health. An efficient difunctional fluorescent probe CMC-GE-PQA for simultaneous detection of Cu2+ and Zn2+ was synthesized based on carboxymethyl cellulose. The probe CMC-GE-PQA exhibited a moderate blue fluorescence color. Interestingly, this probe showed a distinct fluorescence enhancement response toward Zn2+, while it displayed a significant fluorescence quenching response toward Cu2+. The detection limits of CMC-GE-PQA for Cu2+ and Zn2+ were calculated as low as 5.0 × 10−8 M and 1.0 × 10−7 M, respectively. The detection mechanisms of CMC-GE-PQA for Cu2+ and Zn2+ were fully verified by Job's plot, X-ray photoelectron spectroscopy analysis. The probe CMC-GE-PQA was applied to determine the trace amounts of Cu2+ and Zn2+ in environmental water samples. In addition, the probe CMC-GE-PQA-based fluorescent film and hydrogel were manufactured to achieve the portable detection of Cu2+ and Zn2+.

Facile fluorescent detection of o-nitrophenol by a cucurbit[8]uril-based supramolecular assembly in aqueous media

The efficient and selective detection of isomers is an attractive but challenging area. In this study, a supramolecular fluorescent probe based on cucurbit[8]uril (Q[8]) and a pyrene-based derivative (G) was prepared, which effectively recognized and removed o-nitrophenol (o-NP) from a mixture of nitrophenol isomers. The newly designed probe G@Q[8] was characterized by NMR spectroscopy, fluorescence emission and UV–Vis spectroscopy, and its host-guest properties in aqueous solution were investigated. The results revealed that the system forms a stable inclusion complex with a stoichiometric ratio of 1:1, which was accompanied by a distinct fluorescence enhancement of G. Moreover, it was employed for the rapid detection of nitrophenol isomers where o-NP showed a dramatical quenching efficiency with a detection limit of 1.53 × 10−7 mol·L-1. This highly efficient supramolecular fluorescent probe offers a new strategy for the convenient detection and removal of o-NP from mixtures in aqueous medium.

Visualization of ligand-induced c-MYC duplex-quadruplex transition and direct exploration of the altered c-MYC DNA-protein interactions in cells.

Ligand-Induced duplex-quadruplex transition within the c-MYC promoter region is one of the most studied and advanced ideas for c-MYC regulation. Despite its importance, there is a lack of methods for monitoring such process in cells, hindering a better understanding of the essence of c-MYC G-quadruplex as a drug target. Here we developed a new fluorescent probe ISCH-MYC for specific c-MYC G-quadruplex recognition based on GTFH (G-quadruplex-Triggered Fluorogenic Hybridization) strategy. We validated that ISCH-MYC displayed distinct fluorescence enhancement upon binding to c-MYC G-quadruplex, which allowed the duplex-quadruplex transition detection of c-MYC G-rich DNA in cells. Using ISCH-MYC, we successfully characterized the induction of duplex to G-quadruplex transition in the presence of G-quadruplex stabilizing ligand PDS and further monitored and evaluated the altered interactions of relevant transcription factors Sp1 and CNBP with c-MYC G-rich DNA. Thus, our study provides a visualization strategy to explore the mechanism of G-quadruplex stabilizing ligand action on c-MYC G-rich DNA and relevant proteins, thereby empowering future drug discovery efforts targeting G-quadruplexes.

Smart dual-response probe reveals an increase of GSH level and viscosity in Cisplatin-induced apoptosis and provides dual-channel imaging for tumor

Both glutathione (GSH) and viscosity play an important role in mitochondria. They are closely related to various physiological and pathological processes and are important biomarkers in cancer analysis. Herein, we developed the first dual responsive fluorescence probe MGV that can simultaneously detect mitochondrial GSH and viscosity. MGV is smart and shows a selective ratiometric response to GSH at 535/650 nm with a significant increase of green fluorescence. MGV can also show a distinct red fluorescence enhancement at 627 nm as viscosity increases. In addition, MGV has low cytotoxicity and good mitochondrial-targeting ability. With these features, MGV was successfully applied to image mitochondrial GSH at dual fluorescence channels and track mitochondrial viscosity changes on the red fluorescence channel. With MGV, the formation of mitochondrial bleb vesicles was observed with nystatin stimulation, and during the Cisplatin-induced apoptosis, both the level of GSH and the viscosity showed an increase. Finally, based on the dual-response to GSH and viscosity, MGV was successfully used for dual-channel imaging of cancer cells/tumors. Overall, this work provided a smart probe for GSH and viscosity and new insights/methods for apoptosis and tumor imaging.

A dual-response fluorescent probe for Al3+ and Zn2+ in aqueous medium based on benzothiazole and its application in living cells

A new benzothiazole-based fluorescent chemosensor (BZDM), namely 2-amino-3-(((E)-3-(benzo[d]thiazol-2-yl)-2-hydroxy-5-methylbenzylidene)amino)maleonitrile, has been designed and synthesized for detection of Al3+/Zn2+ in aqueous medium. The sensing behavior displayed that BZDM possessed an excellent selectivity towards Al3+/Zn2+ with a distinct fluorescence enhancement in DMSO/Tris-HCl buffer solution. The binding stoichiometry was determined to be 1: 1 between BZDM and Al3+/Zn2+ according to Job’s plot method and NMR analysis. The sensing of Al3+/Zn2+ was almost free from interference of other relevant metal ions. Under optimal conditions, the LOD value for Al3+ and Zn2+ was found to be 7.06 μM and 2.98 μM, separately. Notably, the probe was found to have good biological compatibility and was employed to detect Al3+/Zn2+ in living Hela cells.

A tetraphenylethylene-based aggregation-induced emission sensor: Ultrasensitive “turn-on” fluorescent sensing for phosphate anion in pure water

A new fluorescent sensor of tetraphenylethylene (TPE) derivate with four dimethylformamidine and four chloride anions, sensor 1, was resoundingly synthesized. Meanwhile, the structure of sensor 1 has been characterized by 1H NMR, 13C NMR, FT-IR and mass spectrum. Sensor 1 can dissolve in water completely and showed significant fluorescence enhancement response towards PO43− with selectivity and sensitivity in pure water. The results of fluorescence spectra, turbidity measurement, dynamic light scattering (DLS) and fluorescent micrographs elucidated that the distinct fluorescence enhancement of sensor 1 with PO43− anion can be attributed to the aggregation-induced emission (AIE) of TPE. The AIE of sensor 1 with PO43− anion was reversible, proved by the alternate addition of PO43− anion and calcium ion. The fluorescence intensity of sensor 1 at 510 nm gradually increased and was obviously augmented by 266% when the added concentration of PO43− was 150 μmol L−1 (15 equiv. of sensor 1). In addition, the fluorescence intensity also displayed a good linear relationship with PO43− ions in the large concentration range of 10–150 μmol L−1 with very low detection limit for PO43− of 6.56 × 10−8 mol L−1. Furthermore, sensor 1 also presented the semi-quantitative visual detection ability for PO43− in solutions and test paper mode via the fluorescence changes and quantitative detection potential for PO43− in actual water sample.

A ratiometric and near-infrared fluorescent probe for discrimination of Cys/Hcy/GSH in aqueous solution and its intracellular imaging in living cells

In this work, a unique ratiometric and NIR fluorescent probe, Hecy-NBD, was designed and synthesized to detect cysteine/homocysteine/glutathione in aqueous solution. Hemicyanine skeleton was chosen as the major fluorophore and nitro benzoxadiazole (NBD) chromophore was selected as the recognition unit to construct a ratiometric fluorescent probe. The fluorescence of probe Hecy-NBD was very weak due to the introduction of quenching group NBD. Upon the addition of 100 μM GSH to 10 μM Hecy-NBD, the fluorescence intensity at 702 nm was very strong with the releasing of compound Hecy-OH. While upon the addition of 100 μM Cys or 100 μM Hcy, probe exhibited distinct fluorescence enhancement at 540 nm and 702 nm, which resulted from the formation of compound NBD-Cys and NBD-Hcy through the 5/6-membered cyclic transition and the fluorescence releasing of compound Hecy-OH. The proposed mechanism based on SNAr reaction and molecular rearrangement, which were confirmed by HRMS spectra. The detection limit of these three biothiols was also calculated (GSH, 50 nM; Cys, 81.0 nM; Hcy, 130 nM). Moreover, probe Hecy-NBD could function well at wide pH conditions from 4 to 10. Besides that, probe Hecy-NBD with low cell toxicity had been successfully applied to dual-channel fluorescence imaging in living cells. Considering the good characteristics, Hecy-NBD had great potential to detect biothiols-associated diseases in the future.

An “Off-On-Off” type fluorescent chemosensor for the relay detection of Zn2+ and H2PO4− in aqueous environment

A new fluorescence receptor 2-(diethylamino)-N-(quinolin-8-yl) acetamide (L) was synthesized by simple reaction condition. The ligand HL is highly selective and sensitive towards Zn2+ ions over other tested metal ions. Upon interaction HL with Zn2+, the receptor HL showed a distinct fluorescence enhancement at 496 nm due to chelation enhanced fluorescence (CHEF) leading to visible fluorescence color change from blue to cyan. Subsequently, an in-situ generated L-Zn2+ when interacted with various anions, only with H2PO4− showed fluorescence quenching while other ions did not respond. Accordingly, the receptor HL was developed for the highly selective determination of Zn2+ and H2PO4− with the lowest detection limit (LOD) of 8 nM and 55 nM respectively. The binding mechanism of HL with Zn2+ and L-Zn2+ with H2PO4− were studied by both experimental and theoretical studies. The off-on-off sequential of HL with Zn2+ and H2PO4− were successfully employed for the INHIBIT logic gate response and cellulose assisted test strips proved, the practical application for qualitative analysis of Zn2+ and H2PO4− ions. Finally, the receptor HL was applied for the detection of Zn2+ in different water and pharmaceutical samples.

The specific binding of a new 1,2,3-triazole to three blood proteins and it's appended rhodamine complex for selective detection of Hg2.

A synthesized compound, ethyl 2,5-diphenyl-2H-1,2,3-triazole-4- carboxylate (EDTC) was investigated on its physiochemical parameters and structural properties by using the quantum-chemical method. The results on the theoretical spectrum of EDTC were line with experimental fluorescence and absorption spectrum in large degree. Then EDTC was successfully synthesized to a novel rhodamine-based fluorescent probe (REDTC), which showed a distinct fluorescence enhancement upon the presence of Hg2+ in dimethyl formamide-water (DMF-H2O) buffer solution (pH 7.4). Meanwhile, the triazole appended colorless compound turns to pink upon complex formation with Hg2+ ions as 1:2 molar ratios and enables naked-eye detection. The chromogenic mechanism was determined by using spectroscopic measurements and TD DFT calculation. The fluorescence imaging experiments of Hg2+ in HeLa cell revealed that the probe REDTC could be labeled and it could be used in biological systems. Also, the intermediate EDTC was developed as a sensitive fluorescent probe for specific studies on the interactions to three kinds of blood proteins including human serum albumin (HSA), human immunoglobulin (HIg) and bovine hemoglobin (BHb) by using a series of spectroscopic methods and molecular docking under the simulative physiological conditions. The interactions between EDTC and these proteins led to the distinct fluorescence enhancement. The thermodynamic measured results further suggested that hydrophobic forces play a dominating role in stabilizing the complexes, which are in correspondence with the results from molecular docking. The UV-visible, synchronous, and three-dimensional (3D) fluorescence measurements demonstrated that EDTC influences the conformational of proteins and the microenvironment surrounding HSA, HIg, or BHb in aqueous solution.

A fluorescence "turn-on" sensor for detecting hydrazine in environment

Hydrazine (N2H4) has been classified as an environmental contaminant and human carcinogen owing to its high toxicity. Being exposed to high levels of hydrazine can cause irreversible damage to human bodies. Hence, it is significant to explore an effective method to selectively recognize and detect it. In this work, a new “turn-on” fluorescence probe, coumarin-thiophene (C-T), was designed based on PET (photo-induced electron transfer) mechanism by employing 5-chlorothiophene-2-carbonyl chloride as a electron donor and coumarin as a electron acceptor. The flourescence could be recovered due to the interruption of PET by stripping the 5-chlorothiophene-2-carbonyl chloride when treated with hydrazine. The mechanism was further verified through 1H NMR titration and spectral analysis. Additionally, The probe exhibited a high selectivity towards hydrazine over other common ions and amine-containing species with a distinct fluorescence enhancement at 450 nm. The probe could operate over a wide pH region (4–10) with a detection limit as low as 0.0047 μM (1.5 ppb). Furthermore, it could selectively detect hydrazine in different water samples which indicated its potential for practical applications.

Single molecular dual analyte thio-urea based probes for colorimetric Hg2+ and fluorometric AcO− detection and its’ application in bioimaging

Two thio-urea based bifunctional probes (H2L1-S and H2L2-S) have been designed and fabricated for the colorimetric and fluorometric detection of mercury(II) and acetate ions respectively in DMSO media. Both the H2L1-S and H2L2-S were fully characterized by various spectroscopic techniques and the solid-state structure of H2L1-S was determined via single-crystal X-ray diffraction. The high sensitivity and selectivity of the probes for Hg2+ were achieved by the Hg2+ promoted desulfurization reactions utilizing the high thiophilic nature of mercury and was monitored by UV–vis spectroscopy. Most interestingly the desulfurized product was isolated and characterized by ESI-MS and single crystal X-ray diffraction. The probes H2L1-S and H2L2-S were found to be highly selective towards acetate ion (AcO−) in fluorescence channel. These probes showed a distinct fluorescence enhancement only in the presence of AcO− at 493 nm due to the inhibition of photo induced electron transfer (PET). Finally, the cytotoxicity study was carried out for biological application. The probe showed minimum cytotoxicity and was suitable for intracellular acetate ion imaging.

A naphthalene-quinoline based chemosensor for fluorescent “turn-on” and absorbance-ratiometric detection of Al3+ and its application in cells imaging

A new naphthalene-quinoline based chemosensor L was prepared and structurally characterized. L exhibited excellent selectivity and sensitivity to Al3+ through distinct fluorescence enhancement (335-fold) and ratiometric detection in DMF/H2O (v/v, 1/9) based on the combined mechanisms of ESIPT and CHEF. The recognizing behavior of L toward Al3+ had been investigated in detail through Job's Plot, FT-IR, HNMR, and HRMS analysis. The limit of detection (LOD) for Al3+ was as low as and 3.67 × 10−8 M. L was successfully applied in real sample detection and construction of molecular logic gate. Moreover, L was verified to be of low cytotoxicity and good imaging characteristics for the detection of Al3+ in cells HSC.

A new Al3+ selective fluorescent turn-on sensor based on hydrazide-naphthalic anhydride conjugate and its application in live cells imaging

In this communication, we have developed an optical chemosensor 2-amino N-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)benzamide (NAPH) for selective detection of Al3+ by reacting 4-bromo-1,8-naphthalic anhydride with 2-aminobenzohydrazide. In (DMSO:H2O, 1:1, v/v) medium, the selective and specific nature of NAPH towards Al3+ was observed by the quenching along with a blue-shift in the absorption of NAPH at 465 nm that resulted in the distinct colour change from light brown to colourless. The selective complexation that occurred between NAPH and Al3+ was investigated by 1H NMR and DFT methods. Under similar conditions, the weakly fluorescent receptor NAPH showed a distinct fluorescence enhancement at 555 nm in the presence of Al3+ among the other tested metal ions and anions. The NAPH·Al3+ complex formation is reversible upon addition of strong chelating agent EDTA. The receptor NAPH can be applied to detect Al3+ down to 2.9 μM without any interference from other tested metal ions. In addition, the receptor NAPH was successfully applied to detect Al3+ in live HeLa cells.

Combined use of spectrophotometer and smartphone for the optical detection of Fe3+ using a vitamin B6 cofactor conjugated pyrene derivative and its application in live cells imaging

Synthetically easy, a new chemodosimeter-type chromogenic and fluorogenic chemosensor L was developed by condensing 1-aminopyrene with the vitamin B6 cofactor pyridoxal for the selective detection of Fe3+. Receptor L exhibits a rapid colorimetric response from yellow to colourless and a distinct fluorescence enhancement at 441 nm with Fe3+ due to the cleavage of imine linkage. The optical responses from L in the presence of Fe3+ ions are highly specific, interference-free, can be monitored by smartphone and also observed within the live HeLa cells.

Dye Tool Box for a Fluorescence Enhancement Immunoassay.

Immunochemical analytical methods are very successful in clinical diagnostics and are nowadays also emerging in the control of food as well as monitoring of environmental issues. Among the different immunoassays, luminescence based formats are characterized by their outstanding sensitivity making this format especially attractive for future applications. The need for multiparameter detection capabilities calls for a tool box of dye labels in order to transduce the biochemical reaction into an optically detectable signal. Here, in a multiparameter approach each analyte may be detected by a different dye with a unique emission color (covering the blue to red spectral range) or a unique luminescence decay kinetics. In the case of a competitive immunoassay format for each of the different dye labels an individual antibody would be needed. In the present paper a slightly modified approach is presented using a 7-aminocoumarin unit as the basic antigen against which highly specific antibodies were generated. Leaving the epitope region in the dyes unchanged but introducing a side group in positon 3 of the coumarin system allowed us to tune the optical properties of the coumarin dyes without the necessity of new antibody generation. Upon modification of the parent coumarin unit the full spectral range from blue to deep red was accessed. In the manuscript the photophysical characterization of the coumarin derivatives and their corresponding immunocomplexes with two highly specific antibodies is presented. The coumarin dyes and their immunocomplexes were characterized by steady-state and time-resolved absorption as well as emission spectroscopy. Moreover, fluorescence depolarization measurements were carried out to complement the data stressing the different binding modes of the two antibodies. The binding modes were evaluated using the photophysics of 7-aminocoumarins and how it was affected in the respective immunocomplexes, namely, the formation of the intramolecular charge transfer (ICT) as well as the twisted intramolecular charge transfer (TICT). In contrast to other antibody-dye pairs reported a distinct fluorescence enhancement upon formation of the antibody-dye complex up to a factor of 50 was found. Because of the easy emission color tuning by tailoring the coumarin substitution for the antigen binding in nonrelevant position 3 of the parent molecule, a dye tool box is on hand which can be used in the construction of competitive multiparameter fluorescence enhancement immunoassays (FenIA).

Fluorenone based fluorescent probe for selective “turn-on” detection of pyrophosphate and alanine

To sense biologically important entities with different size and dimensions, a fluorenone based fluorescent receptor was designed and synthesized. Probe 1 displayed a distinct fluorescence enhancement emission at 565nm for pyrophosphate and 530nm for alanine in polar solvent. The fluorescence titration experiments confirm 1:1 stoichiometric ratio with high-binding constant and very low limit of detection (LoD) values. Receptor 1 showed a highly selective and sensitive recognition to HP2O73− and to alanine over other competitive anions and amino acids. In addition, the fluorescence lifetime measurement and reversible binding study results support the practical importance of 1.

A sensitive BODIPY-based fluorescent probe suitable for hypochlorite detection in living cells

Abstract A fluorescent probe composed of BODIPY and 2,4-dinitrophenylhydrazine was designed for the detection of ClO−. The oxidizing reaction between probe and ClO− resulted in a distinct fluorescence enhancement together with a color variation from pink to orange. This probe showed excellent selectivity to ClO− among various ions including common reactive oxygen species and high sensitivity with a detection limit of 228 nM. A fast response (7 min) was observed, which made the probe a promising method in real-time detection. Furthermore, this probe was successfully applied to monitor ClO− in real-life water and living cells.

A fluorescent probe for copper and hypochlorite based on rhodamine hydrazide framework

A rhodamine derivative (1) was synthesized as a fluorescence turn-on probe for copper (Cu2+) and hypochlorite (ClO−). The probe gave a fluorescence turn-on change at 587nm with a color change from colorless to pink in the presence of Cu2+ or ClO− ions in aqueous solution. It was found that the Cu2+ ion bound to 1 in a 1:1 stoichiometry and induced a spirolactam ring opening of the rhodamine moiety leading to a fluorescence turn-on, confirmed by Job’s plot, ESI-Mass, and 1H NMR analyses. In the presence of ClO− ion, probe 1 underwent a hypochlorite-mediated oxidation and hydrolysis to produce a ring-opened rhodamine B with a fluorescence enhancement. However, these changes were not monitored in case of other metal ions, anions, and reactive redox species. In addition, probe 1 can readily react with the ClO− to provide a distinct fluorescence enhancement along with a pink color even in the presence of various competitive species.

Dicyanomethylene‐benzopyran‐based alkynyl conjugatable near–infrared fluorescent probe for detection of fluoride anion

AbstractNear‐infrared (NIR) fluorophore with one functional group, which can be utilized to conjugate other molecules, could meet various requirements just through structural modification, such as for regulating their subtle equilibrium between hydrophilicity and lipophilicity. Herein, considering the favorable photophysical properties of dicyanomethylene‐benzopyran (DCMB) derivatives and the orthogonality of functional groups and the excellent biocompatibility of CuI‐catalyzed click chemistry, the synthesis of azido and phenolic hydroxyl‐bifunctionalized DCMB‐based compound N3‐DCMBOH is described, which can conjugate with other molecules by click chemistry. As a preliminary exploration, tert‐butyldiphenylsilyl group and alkynyl‐contained quaternary ammonium were successively conjugated onto N3‐DCMBOH to construct NIR fluorescent sensor QA‐DCMBSi for detection of F−. The dramatic absorption band change with 196 nm red shift and distinct NIR fluorescence enhancement at 718 nm, can be attributed to F− mediated cleavage of silicon‐oxygen bond to release QA‐DCMBOH, which was verified by MS spectrum.