A Systematic Study of Coumarin-Tetrazine Light-Up Probes for Bioorthogonal Fluorescence Imaging.
TL;DR: 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: 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.
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Heidelberg University1, École Polytechnique Fédérale de Lausanne2, Delft University of Technology3, European Bioinformatics Institute4, University of Mainz5, Harbin Institute of Technology6, Max Planck Society7, Singapore University of Technology and Design8, University of Birmingham9, University of Nottingham10
TL;DR: In this paper, the authors report close proximity tetrazine-dye conjugates with minimal distance between tetrazines and the fluorophore, and demonstrate their potential for live cell imaging in combination with unnatural amino acids, wash-free multicolor and super-resolution STED, and SOFI imaging.
Abstract: Small-molecule fluorophores enable the observation of biomolecules in their native context with fluorescence microscopy. Specific labeling via bio-orthogonal tetrazine chemistry combines minimal label size with rapid labeling kinetics. At the same time, fluorogenic tetrazine-dye conjugates exhibit efficient quenching of dyes prior to target binding. However, live-cell compatible long-wavelength fluorophores with strong fluorogenicity have been difficult to realize. Here, we report close proximity tetrazine-dye conjugates with minimal distance between tetrazine and the fluorophore. Two synthetic routes give access to a series of cell-permeable and -impermeable dyes including highly fluorogenic far-red emitting derivatives with electron exchange as the dominant excited-state quenching mechanism. We demonstrate their potential for live-cell imaging in combination with unnatural amino acids, wash-free multicolor and super-resolution STED, and SOFI imaging. These dyes pave the way for advanced fluorescence imaging of biomolecules with minimal label size.
29 citations
TL;DR: In this paper, the effect of the dienophile on the fluorescence enhancement obtained upon reaction with a tetrazine-quenched fluorophore and study the possible mechanisms of fluorescence quenching by both the tetrazines and its reaction products.
Abstract: Inverse electron demand Diels-Alder reactions between s-tetrazines and strained dienophiles have numerous applications in fluorescent labeling of biomolecules. Herein, we investigate the effect of the dienophile on the fluorescence enhancement obtained upon reaction with a tetrazine-quenched fluorophore and study the possible mechanisms of fluorescence quenching by both the tetrazine and its reaction products. The dihydropyridazine obtained from reaction with a strained cyclooctene shows a residual fluorescence quenching effect, greater than that exerted by the pyridazine arising from reaction with the analogous alkyne. Linear and ultrabroadband two-dimensional electronic spectroscopy experiments reveal that resonance energy transfer is the mechanism responsible for the fluorescence quenching effect of tetrazines, whereas a mechanism involving more intimate electronic coupling, likely photoinduced electron transfer, is responsible for the quenching effect of the dihydropyridazine. These studies uncover parameters that can be tuned to maximize fluorogenic efficiency in bioconjugation reactions and reveal that strained alkynes are better reaction partners for achieving maximum contrast ratio.
15 citations
TL;DR: In this paper, the authors highlight strategies that rely on modification of natural lipids or lipid-like small molecules ex cellula, where organelle specificity is provided by the structure of the chemically modified lipid, or in cellula using cellular machinery.
14 citations
25 Jan 2021
TL;DR: This work demonstrates that a shrewd redesign of common bioorthogonal reagents can lead to their transformation into organelle-specific probes, opening the possibility to activate prodrugs and manipulate biological processes at the subcellular level by using purely chemical tools.
Abstract: The development of abiotic chemical reactions that can be performed in an organelle-specific manner can provide new opportunities in drug delivery and cell and chemical biology. However, due to the complexity of the cellular environment, this remains a significant challenge. Here, we introduce structurally redesigned bioorthogonal tetrazine reagents that spontaneously accumulate in mitochondria of live mammalian cells. The attributes leading to their efficient accumulation in the organelle were optimized to include the right combination of lipophilicity and positive delocalized charge. The best performing mitochondriotropic tetrazines enable subcellular chemical release of TCO-caged compounds as we show using fluorogenic substrates and mitochondrial uncoupler niclosamide. Our work demonstrates that a shrewd redesign of common bioorthogonal reagents can lead to their transformation into organelle-specific probes, opening the possibility to activate prodrugs and manipulate biological processes at the subcellular level by using purely chemical tools.
14 citations
TL;DR: A review of tetrazine derivatives for electronic devices, luminescent elements, photoelectric conversion elements, and image sensors has been published recently as discussed by the authors, covering reported data on the modern trends in the design of functionalized tetrazines obtained within the period 2010-2020.
Abstract: Extensive research on the synthesis and application of tetrazine derivatives for electronic devices, luminescent elements, photoelectric conversion elements, and image sensors has been published recently. This review covers reported data on the modern trends in the design of functionalized tetrazines obtained within the period 2010–2020. Aryl(heteroaryl) and arylvinyl derivatives of tetrazines and their photoluminescence and application for fluorogenic probes are discussed. Examples of photosensitive oligomers and polymer 3,6-dithienyltetrazines are reviewed.
13 citations
References
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TL;DR: This tutorial review focuses on NIR fluorescent probes that have been devised to sense various biologically important species, including ROS/RNS, metal ions, anions, enzymes and other related species, as well as intracellular pH changes.
Abstract: Near-infrared (NIR) fluorescent dyes have emerged as promising modalities for monitoring the levels of various biologically relevant species in cells and organisms. The use of NIR probes enables deep photon penetration in tissue, minimizes photo-damage to biological samples, and produces low background auto-fluorescence from biomolecules present in living systems. The number of new analyte-responsive NIR fluorescent probes has increased substantially in recent years as a consequence of intense research efforts. In this tutorial review, we highlight recent advances (2010–2013) made in the development and applications of NIR fluorescent probes. The review focuses on NIR fluorescent probes that have been devised to sense various biologically important species, including ROS/RNS, metal ions, anions, enzymes and other related species, as well as intracellular pH changes. The basic principles involved in the design of functional NIR fluorescent probes and suggestions about how to expand applications of NIR imaging agents are also described.
1,459 citations
TL;DR: Inspired by molecular modeling, the N,N-dimethylamino substituents in tetramethylrhodamine are replaced with four-membered azetidine rings, which doubles the quantum efficiency and improves the photon yield of the dye in applications ranging from in vitro single-molecule measurements to super-resolution imaging.
Abstract: Specific labeling of biomolecules with bright fluorophores is the keystone of fluorescence microscopy. Genetically encoded self-labeling tag proteins can be coupled to synthetic dyes inside living cells, resulting in brighter reporters than fluorescent proteins. Intracellular labeling using these techniques requires cell-permeable fluorescent ligands, however, limiting utility to a small number of classic fluorophores. Here we describe a simple structural modification that improves the brightness and photostability of dyes while preserving spectral properties and cell permeability. Inspired by molecular modeling, we replaced the N,N-dimethylamino substituents in tetramethylrhodamine with four-membered azetidine rings. This addition of two carbon atoms doubles the quantum efficiency and improves the photon yield of the dye in applications ranging from in vitro single-molecule measurements to super-resolution imaging. The novel substitution is generalizable, yielding a palette of chemical dyes with improved quantum efficiencies that spans the UV and visible range.
1,140 citations
TL;DR: This protocol describes procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and introduces a series of eight candidate quantum yield standards for the wavelength region of ∼350–950 nm.
Abstract: Luminescence techniques are among the most widely used detection methods in the life and material sciences. At the core of these methods is an ever-increasing variety of fluorescent reporters (i.e., simple dyes, fluorescent labels, probes, sensors and switches) from different fluorophore classes ranging from small organic dyes and metal ion complexes, quantum dots and upconversion nanocrystals to differently sized fluorophore-doped or fluorophore-labeled polymeric particles. A key parameter for fluorophore comparison is the fluorescence quantum yield (Φf), which is the direct measure for the efficiency of the conversion of absorbed light into emitted light. In this protocol, we describe procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and we address typical sources of uncertainty and fluorophore class-specific challenges. For relative determinations of Φf, the sample is analyzed using a conventional fluorescence spectrometer. For absolute determinations of Φf, a calibrated stand-alone integrating sphere setup is used. To reduce standard-related uncertainties for relative measurements, we introduce a series of eight candidate quantum yield standards for the wavelength region of ∼350-950 nm, which we have assessed with commercial and custom-designed instrumentation. With these protocols and standards, uncertainties of 5-10% can be achieved within 2 h.
818 citations
TL;DR: The background to the development of mitochondria-targeted antioxidants that selectively block mitochondrial oxidative damage and prevent some types of cell death and also to develop probes of mitochondrial function are outlined.
454 citations
TL;DR: This work refined and extended the Janelia Fluor strategy, finding that incorporation of 3-substituted azetidine groups allows rational tuning of the spectral and chemical properties of rhodamine dyes with unprecedented precision.
Abstract: Pushing the frontier of fluorescence microscopy requires the design of enhanced fluorophores with finely tuned properties. We recently discovered that incorporation of four-membered azetidine rings into classic fluorophore structures elicits substantial increases in brightness and photostability, resulting in the Janelia Fluor (JF) series of dyes. We refined and extended this strategy, finding that incorporation of 3-substituted azetidine groups allows rational tuning of the spectral and chemical properties of rhodamine dyes with unprecedented precision. This strategy allowed us to establish principles for fine-tuning the properties of fluorophores and to develop a palette of new fluorescent and fluorogenic labels with excitation ranging from blue to the far-red. Our results demonstrate the versatility of these new dyes in cells, tissues and animals.
441 citations