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A novel ratiometric fluorescent probe HB‐2 based on benzothiazole for hypobromous acid (HBrO) was synthesized and studied. After HBrO was added to the CH3CN‐HEPES solution of the HB‐2, the probe cyclized to form a sulfimine bond, which increased the conjugated degree of the system. The fluorescence emission peak of the reaction system at 447 nm gradually decreased, while the newly generated emission peaks gradually increased at 580 nm. The ratio of the fluorescence intensity at the two wavelengths of 447 nm and 580 nm increased about 234 times. Moreover, it has successfully been used to stain and record microscopy images of 4T1 cells, and the presence of exogenous HBrO could be judged by the change of fluorescence intensity. [ABSTRACT FROM AUTHOR]

Selective detection of H2S in the cellular systems using fluorescent CPs/MOFs is of great scientific interest due to their outstanding aqueous stability, biocompatibility and real‐time detection ability. Fabrication of such materials using complete biologically essential elements and applying them as an efficient biosensor is still quite challenging. In this context, two newly synthesized CPs containing biologically essential metal ion (Zn) and nitro/azido functional groups into the framework to sense extracellular and intracellular H2S by reducing into respective amines are presented. The CP‐1 containing the azide group acted as an efficient fluorescent turn‐on probe with the lowest detection limit (7.2 μM) and shortest response time (30 s) among the Zn‐based probes reported till date. Moreover, CP‐1 exhibited green luminescence in live cells after imaging a very low concentration of H2S, whereas the nitro analogue CP‐2 could not detect the target analyte due to its framework disruption. [ABSTRACT FROM AUTHOR]

As one of the most important minerals in the body, potassium is vital for the heart and neurons. Methods that can non‐invasively and accurately monitor changes in potassium balances would benefit disease diagnoses as well as offer insight into pathologies. Among the sensing approaches, fluorescent probes serve as a unique detection method for its simplicity, tunable detection range, and bioimaging ability. The design of new probes with highly selective K+ receptors and transduction functionality remains a challenge that is motivated by numerous sensing and detection applications. In this minireview, fluoroionophores are summarized that undergo transduction, producing fluorescence signals when interacting with, e. g. potassium ions. The properties of ionophores (afford selective interaction with potassium) and fluorophores (generate signal read‐out) are discussed. Molecular structure design and sensing mechanisms are included along with cell imaging applications. The selectivity towards K+ and the absorption/emission characteristics of the probes are of particular interest. [ABSTRACT FROM AUTHOR]

Live‐cell imaging with fluorescent probes is an essential tool in chemical biology to visualize the dynamics of biological processes in real‐time. Intracellular disease biomarker imaging remains a formidable challenge due to the intrinsic limitations of conventional fluorescent probes and the complex nature of cells. This work reports the in cellulo assembly of a fluorescent probe to image cyclooxygenase‐2 (COX‐2). We developed celecoxib‐azide derivative 14, possessing favorable biophysical properties and excellent COX‐2 selectivity profile. In cellulo strain‐promoted fluorogenic click chemistry of COX‐2‐engaged compound 14 with non/weakly‐fluorescent compounds 11 and 17 formed fluorescent probes 15 and 18 for the detection of COX‐2 in living cells. Competitive binding studies, biophysical, and comprehensive computational analyses were used to describe protein‐ligand interactions. The reported new chemical toolbox enables precise visualization and tracking of COX‐2 in live cells with superior sensitivity in the visible range. [ABSTRACT FROM AUTHOR]

A novel boron dipyrromethene (BODIPY)‐based fluorescent probe BDP−Pd was designed and synthesized. Upon coordination with Pd2+, the emission of the probe at 508 nm significantly increased, showing an 'OFF‐ON' fluorescence response. The complexation of BDP−Pd with Pd2+ in both acetonitrile and aqueous solution were then studied by absorption and fluorescence spectra. The binding stoichiometry between the probe and Pd2+ was found to be 1 : 2, and the binding constant was determined to be 8.5×1010 M−2 and 8.2×1010 M−2 in acetonitrile and aqueous solution, respectively. The probe exhibited a detection limit as low as 0.72 ppb toward Pd2+ with no obvious interference from up to 21 species of common metal ions, suggesting BDP−Pd as a sensitive and selective fluorescent probe for Pd2+ detection. The fast fluorescence 'OFF‐ON' phenomenon of the probe upon coordination with Pd2+ ions could be easily observed by a hand‐hold UV lamp under naked eye in solution as well as on homemade test trips. Density functional theory (DFT) calculations were carried out to give the optimized structure of complex BDP−Pd : 2Pd2+ and rationalize the detection mechanism through a prohibited intramolecular photoinduced electron transfer (PET) process. The bio‐imaging application of the probe was investigated and it showed excellent cell permeability for fluorescent imaging of Pd2+ ions in A549 human non‐small cell lung cancer cells. [ABSTRACT FROM AUTHOR]

Two red‐emitting dicyanomethylene‐4H‐pyran (DM) based fluorescent probes were designed and used for peroxynitrite (ONOO−) detection. Nevertheless, the aggregation‐caused quenching effect diminished the fluorescence and restricted their further applications. To overcome this problem, tetraphenylethylene (TPE) based glycoclusters were used to self‐assemble with these DM probes to obtain supramolecular water‐soluble glyco‐dots. This self‐assembly strategy enhanced the fluorescence intensity, leading to an enhanced selectivity and activity of the resulting glyco‐dot comparing to DM probes alone in PBS buffer. The glyco‐dots also exhibited better results during fluorescence sensing of intracellular ONOO− than the probes alone, thereby offering scope for the development of other similar supramolecular glyco‐systems for chemical biological studies. [ABSTRACT FROM AUTHOR]

The hydrothermal treatment of green carbon dots (CDs) is an appropriate fluorescent probe synthesis method. CDs are exploited as biological staining agents, especially for cellular detection and imaging. The nitrogen‐doped green carbon dots (N‐CDs) formation can improve the fluorescence intensity property in a one‐step process. Here, we report two N‐CDs from lemon and tomato extraction in the presence of hydroxylamine. Lemon and tomato N‐CDs showed the blue fluorescence under ultraviolet radiation of about 360 nm. The characterization of CDs and N‐CDs showed the presence of N‐H and C–N bonds which enhanced the fluorescence efficiency. The mean size of lemon and tomato N‐CDs were about 2 and 3 nm with an increased quantum yield (QY) of 5% and 3.38%, respectively. The CDs and N‐CDs cytotoxicity assay exhibited high cell viability approximately 85% and 73%, respectively. N‐CDs show superior fluorescent intensity in different solvents and significant stability under long‐time UV irradiation, different PH and high ionic strength. Our results indicated that the use of N‐CDs in cell imaging can lead to fluorescence intensity enhancement as well as proper biocompatibility. Therefore, the safe and high fluorescence intensity of green N‐CDs can be utilized for fluorescent probes in biolabeling and bioimaging applications. [ABSTRACT FROM AUTHOR]

Fluorescent probes that light‐up upon reaction with complementary bioorthogonal reagents are superior tools for no‐wash fluorogenic bioimaging applications. In this work, a thorough study is presented on a set of seventeen structurally diverse coumarin–tetrazine probes that produce fluorescent dyes with exceptional turn‐on ratios when reacted with trans‐cyclooctene (TCO) and bicyclononyne (BCN) dienophiles. In general, formation of the fully aromatic pyridazine‐containing dyes resulting from the reaction with BCN was found superior in terms of fluorogenicity. However, evaluation of the probes in cellular imaging experiments revealed that other factors, such as reaction kinetics and good cell permeability, prevail over the fluorescence turn‐on properties. The best compound identified in this study showed excellent performance in live cell‐labeling experiments and enabled no‐wash fluorogenic imaging on a timescale of seconds. [ABSTRACT FROM AUTHOR]

The near‐infrared window of fluorescent heptamethine cyanine dyes greatly facilitates biological imaging because there is deep penetration of the light and negligible background fluorescence. However, dye instability, aggregation, and poor pharmacokinetics are current drawbacks that limit performance and the scope of possible applications. All these limitations are simultaneously overcome with a new molecular design strategy that produces a charge balanced and sterically shielded fluorochrome. The key design feature is a meso‐aryl group that simultaneously projects two shielding arms directly over each face of a linear heptamethine polyene. Cell and mouse imaging experiments compared a shielded heptamethine cyanine dye (and several peptide and antibody bioconjugates) to benchmark heptamethine dyes and found that the shielded systems possess an unsurpassed combination of photophysical, physiochemical, and biodistribution properties that greatly enhance bioimaging performance. [ABSTRACT FROM AUTHOR]

The near‐infrared window of fluorescent heptamethine cyanine dyes greatly facilitates biological imaging because there is deep penetration of the light and negligible background fluorescence. However, dye instability, aggregation, and poor pharmacokinetics are current drawbacks that limit performance and the scope of possible applications. All these limitations are simultaneously overcome with a new molecular design strategy that produces a charge balanced and sterically shielded fluorochrome. The key design feature is a meso‐aryl group that simultaneously projects two shielding arms directly over each face of a linear heptamethine polyene. Cell and mouse imaging experiments compared a shielded heptamethine cyanine dye (and several peptide and antibody bioconjugates) to benchmark heptamethine dyes and found that the shielded systems possess an unsurpassed combination of photophysical, physiochemical, and biodistribution properties that greatly enhance bioimaging performance. [ABSTRACT FROM AUTHOR]

Lipid droplets (LDs) are important organelles associated with many physiological processes as well as diseases. To visualize LDs and study their versatile functions, the fluorescence imaging technique is one of the most powerful tools. Thus, the development of fluorescent probes for LDs imaging has attracted increased attention in recent years. Herein, a new LDs fluorescent probe Ph‐Red is developed and its application in fluorescence imaging is carefully demonstrated. The probe Ph‐Red has a compact single‐benzene‐based molecular structure and can be easily synthesized via a one‐step reaction. Impressively, the probe displays strong red emission based on a very small π‐system consisting of only one benzene ring. Moreover, the probe shows high LDs staining selectivity and good cellular viability, and is tolerant for repeatedly fluorescence imaging. Given these advantages, the 3D confocal imaging in fixed cells as well as multicolor confocal imaging in live cells are successfully realized, highlighting the utility of the single‐benzene‐based fluorescent probe Ph‐Red for LDs imaging. In addition, the hydrophobicity of the probe and the molecular size are revealed to play critical roles for efficiently staining LDs, which are important insights for the development of new LDs fluorescent probes. [ABSTRACT FROM AUTHOR]

Herein, a facile method to synthesize the fluorescence probe 1‐(4‐(1,5‐diphenyl‐4,5‐dihydro‐1H‐pyrazol‐3‐yl)phenyl)‐1H‐pyrrole‐2,5‐dione (probe 10) was reported. The relative quantum yield determined using quinine sulfate for the probe 10 is 42% in 100% acetonitrile (ACN), which was reduced to 6% in 10% ACN‐water system. The turn‐off probe 10 becomes turn‐on selectively in the presence of glutathione (GSH). The Probe 10 is highly sensitive to GSH in the presence of common interfering molecules like cysteine, N‐acetylcysteine, thioglycolic acid, mercaptoethanol, and mercaptopropionoic acid. The limit of detection is 0.06 μM. The practical use of the probe 10 was demonstrated through quantifying GSH (1.68 mM) in the blood serum of healthy person, artificial cerebrospinal fluid, and artificial urine. Probe 10 works on a wide range of pH 2–12. Cells expressing GSH can be imaged using probe 10 and also useful in analysing the percentage of GSH in the cells under oxidative stress. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is a critical gasotransmitter playing an important role in various physiological and pathological processes. The development of fluorescent probes for rapid, sensitive, and selective lysosomal H2S sensing has attracted much attention. Herein we report a rhodamine based probe MF‐N3 that can selectively accumulate in lysosomes and give turn‐on fluorescence in the presence of both H2S and protons. Results show that MF‐N3 has an exclusive response to H2S in the acidic lysosomal environment but does not respond in other organelles or in neutral environments. This strategy can circumvent the fluorescence interference from H2S of other sources, thus providing a high sensitivity and selectivity on lysosomal H2S imaging by fluorescence microscopy. This pH‐dependent lysosome‐targeting fluorescent probe has been successfully applied to lysosomal H2S imaging in living cells and is of great potential for applications to the environmental and biological systems. [ABSTRACT FROM AUTHOR]

Photobleaching is a major challenge in fluorescence microscopy, in particular if high excitation light intensities are used. Signal‐to‐noise and spatial resolution may be compromised, which limits the amount of information that can be extracted from an image. Photobleaching can be bypassed by using exchangeable labels, which transiently bind to and dissociate from a target, thereby replenishing the destroyed labels with intact ones from a reservoir. Here, we demonstrate confocal and STED microscopy with short, fluorophore‐labeled oligonucleotides that transiently bind to complementary oligonucleotides attached to protein‐specific antibodies. The constant exchange of fluorophore labels in DNA‐based STED imaging bypasses photobleaching that occurs with covalent labels. We show that this concept is suitable for targeted, two‐color STED imaging of whole cells. [ABSTRACT FROM AUTHOR]

New L‐shaped fluorophores possessing five conjugated rings have been synthesized through a four‐step procedure involving diketopyrrolopyrrole synthesis and its double N‐alkylation, followed by trimethylsilyl bromide‐mediated rearrangement to thieno[2,3‐f]isoindole‐5,8‐dione and an intramolecular Friedel–Crafts reaction. In comparison with the parent isoindolediones and π‐expanded diketopyrrolopyrroles, these new dyes show red‐shifted absorption and emission (up to ≈630 nm). Their structural rigidity is responsible for both the observed small Stokes shifts and large fluorescence quantum yields. Tissue imaging studies revealed that these new dyes show advantageous features including minimal autofluorescence interference and pronounced solvent‐sensitive emission. Interestingly, there is a fundamental difference between a dye possessing an amino group and its analog bearing an N‐alkyl substituent. The former dye under two‐photon excitation at 900 nm gives bright images whereas its N‐alkylated counterpart does not. A new type of membrane localization has been discovered by an N‐alkylated isoindoledione possessing a benzofuryl substituent. In spite of the fact that the fluorescence quantum yield of this dye in a range of solvents is rather low, it does stain cell membranes exclusively. This new mode of cellular staining opens the door towards further development of membrane staining dyes. [ABSTRACT FROM AUTHOR]

Transgenic birds are commonly used for time‐lapse imaging and fate mapping studies in developmental biology. When researchers use transgenic birds expressing fluorescent protein, they need to understand the integration site of the transgene in the genome and the intensity of fluorescence in the tissues of interest. In this study, we determined the integration site of the transgene and fluorescence property of developing organs in our transgenic chicken line generated by lentivirus infection. The transgene was localized between exons 3 and 4 of MED27. Some homozygotes and heterozygotes appeared to be lethal at early embryonic stages. We performed histological analysis of EGFP expression in transgenic embryos at St. 14, 17, and 24 by immunohistochemistry with anti‐GFP antibody on paraffin sections. Next, we cut cryosections and quantified direct EGFP intensity from the transgene in each tissue without performing immunohistochemistry. These results revealed that EGFP intensity in each tissue was unique in developing embryos and changed according to developmental stages. Finally, we demonstrated that EGFP‐expressing cells in a micromass culture with co‐culturing wild‐type cells were clearly distinguishable via live cell imaging. These results provide essential information on the potential of our transgenic line and indicate that these transgenic chicken lines are useful for research associated with developmental biology. [ABSTRACT FROM AUTHOR]

Hypochlorous/Hypochlorite(HClO/ClO−) plays an important biochemistry roles in normal operation of the life system. Herein, a fluorescent probe 7‐chloro‐3‐((E)‐3‐(4‐(dimethylamino)phenyl)‐ acryloyl)‐2H‐chromen‐2‐one (CCO) was rationally designed and synthesized via aldehyde ketone condensation reaction to detect ClO− in Tris‐HCl (pH=7.2, 60% DMF) solution. Probe CCO was cleaved conceivably in the coumarin lactone ring by an oxidation reaction with ClO− and emitted intensive bright yellow fluorescence. The sensing mechanism was further confirmed by ESI‐MS and DFT calculation. The fluorescence emission of probe CCO triggered by ClO− was obviously enhanced within 20 s. The limit of detection of probe CCO was calculated as low as 2.6 nM. Furthermore, probe CCO can be given as an effective and outstanding fluorescent exogenous ClO− probe in living HEK293T cells for microscopic cell imaging. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) is associated with many diseases, and its accurate detection is of great significance. Fluorescent compounds with aggregation‐induced emission (AIE) feature show beneficial advantages for serving as fluorescent probes. Herein, an AIE‐active "turn on" probe for ALP detection was synthesized through incorporating a strong electron‐withdrawing group (cyano) in the middle and the recognition moiety phosphate group at the end, thereby rendering a D–A–D structure with a relatively high conjugation degree and good water solubility. It was found that the probe TPE‐CN‐pho is highly sensitive to ALP in aqueous solution. In the presence of ALP, the hydrophilic phosphate group on the probe is rapidly removed, resulting in a decrease in water solubility and subsequent formation of aggregates, thereby achieving aggregation‐induced emission. Moreover, the probe TPE‐CN‐pho has also been successfully applied to imaging ALP in living cells. The joy of being a DAD: An AIE‐active "turn‐on" probe, TPE‐CN‐pho, for alkaline phosphatase (ALP) detection has been developed with a donor–acceptor–donor (D–A–D) structure, in which phosphate acts as both the recognition moiety and hydrophilic moiety. The probe has been successfully applied in detecting ALP in aqueous media as well as imaging ALP in living cells. [ABSTRACT FROM AUTHOR]

Abstract: The chemical biology of reactive sulfur species, including hydropolysulfides, has been a subject undergoing intense study in recent years, but further understanding of their “intact” function in living cells has been limited owing to a lack of appropriate analytical tools. In order to overcome this limitation, we developed a new type of fluorescent probe that reversibly and selectively reacts to hydropolysulfides. The probe enables live‐cell visualization and quantification of endogenous hydropolysulfides without interference from intrinsic thiol species such as glutathione. Additionally, real‐time reversible monitoring of oxidative‐stress‐induced fluctuation of intrinsic hydropolysulfides has been achieved with a temporal resolution on the order of seconds, a result which has not yet been realized using conventional methods. These results reveal the probe's versatility as a new fluorescence imaging tool to understand the function of intracellular hydropolysulfides. [ABSTRACT FROM AUTHOR]

Chemical probes are powerful tools for interrogating small molecule-target interactions. With additional fluorescence Turn-ON functionality, such probes might enable direct measurements of target engagement in live mammalian cells. DNS-pE (and its terminal alkyne-containing version DNS-pE2) is the first small molecule that can selectively label endogenous 3-phosphoglycerate dehydrogenase (PHGDH) from various mammalian cells. Endowed with an electrophilic vinyl sulfone moiety that possesses fluorescence-quenching properties, DNS-pE/DNS-pE2 became highly fluorescent only upon irreversible covalent modification of PHGDH. With an inhibitory property (in vitro Ki=7.4 μ m) comparable to that of known PHGDH inhibitors, our probes thus offer a promising approach to simultaneously image endogenous PHGDH activities and study its target engagement in live-cell settings. [ABSTRACT FROM AUTHOR]

The development of a fluorescent probe to distinguish between cysteine (Cys) and homocysteine (Hcy) is always a challenge owing to their structural similarity, and the simultaneous detection of Cys and Hcy by utilizing different emission channels is especially difficult. In this work, we designed and synthesized a new fluorescent probe to differentiate between Cys and Hcy on the basis of a coumarin derivative with a chlorine atom and an α,β-unsaturated aldehyde. Cys and Hcy induced different cascade reactions with the probe, which led to different products with distinct photophysical properties. The nonfluorescent probe responded to Cys and emitted strong blue fluorescence, whereas it reacted with Hcy and generated yellow fluorescence without interference from glutathione. In addition, the probe was successfully applied to distinguish between Cys and Hcy in living cells. [ABSTRACT FROM AUTHOR]

ABSTRACT Fluorescent bioprobes are powerful analytical tools for studying biological activities in living systems. Fluorogens with aggregation-induced emission (AIE) characteristics have recently emerged as a new class of fluorescent bioprobes for biosensing and cell imaging. As discovered by Tang, AIE fluorogens are nearly nonemissive in molecular states with their intermolecular rotations being not restricted whereas their fluorescence is turned on by binding with certain biomolecules, leading to highly selective turn-on fluorescent probes for specific biomolecules and fluorescent cell imaging with a high signal-to-background noise ratio. By introducing the AIE characteristics into polymeric materials, AIE polymers could possess a good solubility and biocompatibility, excellent structural diversity, and ease for functionalization useful for efficient biosensing and cell imaging. Herein, we highlight a few recently published articles on small and macromolecular AIE molecules to provide a fundamental understanding of the AIE mechanism and illustrate the working principle for AIE based biosensing and cell imaging. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 653-659 [ABSTRACT FROM AUTHOR]

Two dipicolyamino-conjugated anthracene-1,9-dicarboximide fluorophores and their corresponding ReI complexes have been synthesised and photophysically examined. All species were fluorescent in the visible region at about 490 nm with lifetimes up to 16 ns. The anticancer potency of the ligands and complexes was demonstrated across a range of cancer cell lines (LOVO, PC3, A549, MCF-7). Cell imaging studies with MCF7 cells and Schizosaccharomyces pombe show that these fluorophores exhibit variable intracellular localisation patterns that are structure-dependent. [ABSTRACT FROM AUTHOR]

Pyrene-based turn-on ratiometric fluorescent probe 1 demonstrates high sensitivity and exceptional selectivity toward Cr3+ in the presence of other metals, including Fe3+ in aqueous media. Interaction of Cr3+ with probe 1 brings pyrene moieties close enough to have better aligned π-π stacking, thus enhancing the excimer peak many fold. On the other hand, the interaction of Fe3+ with probe 1 brings forth a negligible difference in stacking, resulting in an insignificant change in fluorescence intensity. Exceptional selectivity of probe 1 with Cr3+ over Fe3+ and other metals has been confirmed by theoretical studies in addition to experimental results. Imaging of HeLa cells observed by confocal fluorescence microscopy reveals that probe 1 can be used to monitor Cr3+ in live cells to map its subcellular distribution. [ABSTRACT FROM AUTHOR]

A novel fluorescent probe 5‐(diethylamino)‐2‐(((2‐(hydroxymethyl)quinolin‐8‐yl)imino)methyl)phenol (QS) was synthesized by condensation reaction of 8‐aminoquinoline derivative and 4‐(diethylamino)salicylaldehyde. It was found that the probe QS was capable of high selectivity and sensitivity about specific color and fluorescence changes towards Zn2+ ion in EtOH‐H2O (v/v = 4/1, 0.01 M, Tris–HCl buffer, pH = 7.30) solution. The interaction of QS with Zn2+ ion illustrated a "turn‐on" fluorescence response at 550 nm (λex: 458 nm), moreover, after the subsequent addition of inorganic phosphate (Pi) into the solution above, a "turn‐off" fluorescence response was observed. The sensing ability of the probe QS towards Zn2+ was confirmed by fluorescence titration, UV–Vis titration and HRMS analysis. Besides, the intracellular sensing behavior of QS with Zn2+ and Pi were captured in living PC12 cells. The limit of detection (LOD) for Zn2+ and Pi sensing was found to be 0.03 μM and 0.08 μM, respectively. [ABSTRACT FROM AUTHOR]

Fluorogenic labeling enables imaging cellular molecules of interest with minimal background. This process is accompanied with the notable increase of the quantum yield of fluorophore, thus minimizing the background signals from unactivated profluorophores. Herein, the development of a highly efficient and bioorthogonal nitroso‐based Diels–Alder fluorogenic reaction is presented and its usefulness is validated as effective and controllable in fluorescent probes and live‐cell labeling strategies for dynamic cellular imaging. It is demonstrated that nitroso‐based cycloaddition is an efficient fluorogenic labeling tool through experiments of further UV‐activatable fluorescent labeling on proteins and live cells. The ability of tuning the fluorescence of labeled proteins by UV‐irradiation enables selective activation of proteins of interest in a particular cell compartment at a given time point, while leaving the remaining labeled molecules untouched. [ABSTRACT FROM AUTHOR]

A correction to the article “Simultaneous Imaging of Mitochondria and Lysosomes using Two-Photon Fluorescent Probes" that was published in the 2012 issue of the journal is presented.