One probe, two-channel imaging of nuclear and cytosolic compartments with orange and red emissive dyes

Highly Fluorescent Dianionic Polymethines with a 1,3,2-Dioxaborine Core

The difluoroboron β-diketonate ring is ever more used for creating bright polymethine-type fluorophores for the visible and NIR range. Here, we report the synthesis and spectral properties of a series of dianionic cyanine dyes of the rare A¹-π-A-π-A¹ type, with the central dioxaborine ring (A) embedded into the polymethine chain and various electron-acceptor terminal groups A¹. Depending on the nature of the end group, the maxima of their intensive (with molar extinctions up to 380 000 M^-1 cm^-1) and narrow long-wavelength absorption band lie in the range of 530-770 nm. Their absorption and fluorescence bands are nearly mirror-like and characterized by weak solvatochromism; the marked hypsochromic shifts are observed only when going from polar aprotic solvents to methanol. The designed dianionic dyes have fluorescence quantum yields up to 92 % in the visible range, and even for the NIR dyes, the values of 18-37 % are observed in DMF.

Recent advances in dioxaborine-based fluorescent materials for bioimaging applications

Fluorescent materials are continuously contributing to important advances in the field of bioimaging. Among these materials, dioxaborine-based fluorescent materials (DBFM) are arousing growing interest. Due to their rigid structures conferred by a cyclic boron complex, DBFM possess appealing photophysical properties including high extinction coefficients and quantum yields as well as emission in the near infrared, enhanced photostability and high two-photon absorption. We herein discuss the recent advances of DBFM that found use in bioimaging applications. This review covers the development of fluorescent molecular probes for biomolecules (DNA, proteins), small molecules (cysteine, H₂O₂, oxygen), ions and the environment (polarity, viscosity) as well as polymers and nanomaterials used in bioimaging. This review aims at providing a comprehensive and critical insight on DBFM by highlighting the assets of these promising materials in bioimaging but also by pointing out their limitations that would require further developments.

Influence of Polymer Charge on the Localization and Dark- and Photo-Induced Toxicity of a Potential Type I Photosensitizer in Cancer Cell Models

A current trend within photo-dynamic therapy (PDT) is the development of molecular systems targeting hypoxic tumors. Thus, type I PDT sensitizers could here overcome traditional type II molecular systems that rely on the photo-initiated production of toxic singlet oxygen. Here, we investigate the cell localization properties and toxicity of two polymeric anthracene-based fluorescent probes (neutral Ant-PHEA and cationic Ant-PIm). The cell death and DNA damage of Chinese hamster ovary cancer cells (CHO-K1) were characterized as combining PDT, cell survival studies (MTT-assay), and comet assay. Confocal microscopy was utilized on samples incubated together with either DRAQ5, Lyso Tracker Red, or Mito Tracker Deep Red in order to map the localization of the sensitizer into the nucleus and other cell compartments. While Ant-PHEA did not cause significant damage to the cell, Ant-PIm showed increased cell death upon illumination, at the cost of a significant dark toxicity. Both anthracene chromophores localized in cell compartments of the cytosol. Ant-PIm showed a markedly improved selectivity toward lysosomes and mitochondria, two important biological compartments for the cell’s survival. None of the two anthracene chromophores showed singlet oxygen formation upon excitation in solvents such as deuterium oxide or methanol. Conclusively, the significant photo-induced cell death that could be observed with Ant-PIm suggests a possible type I PDT mechanism rather than the usual type II mechanism.

Classification of Multiple DNA Dyes Based on Inhibition Effects on Real-Time Loop-Mediated Isothermal Amplification (LAMP): Prospect for Point of Care Setting

LAMP has received great interest and is widely utilized in life sciences for nucleic acid analysis. To monitor a real-time LAMP assay, a fluorescence DNA dye is an indispensable component and therefore the selection of a suitable dye for real-time LAMP is a need. To aid this selection, we investigated the inhibition effects of twenty-three DNA dyes on real-time LAMP. Threshold time (T_t) values of each real-time LAMP were determined and used as an indicator of the inhibition effect. Based on the inhibition effects, the dyes were classified into four groups: (1) non-inhibition effect, (2) medium inhibition effect, (3) high inhibition effect, and (4) very high inhibition effect. The signal to noise ratio (SNR) and the limit of detection (LOD) of the dyes in groups 1, 2, and 3 were further investigated, and possible inhibition mechanisms of the DNA dyes on the real-time LAMP are suggested and discussed. Furthermore, a comparison of SYTO 9 in different LAMP reactions and different systems is presented. Of the 23 dyes tested, SYTO 9, SYTO 82, SYTO 16, SYTO 13, and Miami Yellow were the best dyes with no inhibitory effect, low LOD and high SNR in the real-time LAMP reactions. The present classification of the dyes will simplify the selection of fluorescence dye for real-time LAMP assays in point of care setting.

Design, Synthesis, and Crystallization-Induced Emission of Boron Difluorides β-Ketoiminates

A series of new nitrogen-containing analogues of boron difluoride benzoylacetonates with hydrogen and methyl substituents at the nitrogen atom have been synthesized. A comparative study of boron difluoride β-ketoiminates and their oxygen-containing analogues by means of luminescence and IR spectroscopic methods as well as quantum chemistry simulations was also performed.

Ultrabright and Fluorogenic Probes for Multicolor Imaging and Tracking of Lipid Droplets in Cells and Tissues

Lipid droplets (LDs) are intracellular lipid-rich organelles that regulate the storage of neutral lipids and were recently found to be involved in many physiological processes, metabolic disorders, and diseases including obesity, diabetes, and cancers. Herein we present a family of new fluorogenic merocyanine fluorophores based on an indolenine moiety and a dioxaborine barbiturate derivative. These so-called StatoMerocyanines (SMCy) fluoresce from yellow to the near-infrared (NIR) in oil with an impressive fluorescence enhancement compared to aqueous media. Additionally, SMCy display remarkably high molar extinction coefficients (up to 390 000 M^-1 cm^-1) and high quantum yield values (up to 100%). All the members of this new family specifically stain the LDs in live cells with very low background noise. Unlike Nile Red, a well-known lipid droplet marker, SMCy dyes possess narrow absorption and emission bands in the visible, thus allowing multicolor imaging. SMCy proved to be compatible with fixation and led to high-quality 3D images of lipid droplets in cells and tissues. Their high brightness allowed efficient tissue imaging of adipocytes and circulating LDs. Moreover their remarkably high two-photon absorption cross-section, especially SMCy5.5 (up to 13 300 GM), as well as their capacity to efficiently fluoresce in the NIR region led to two-photon multicolor tissue imaging (liver). Taking advantage of the available color palette, lipid droplet exchange between cells was tracked and imaged, thus demonstrating intercellular communication.

Bis(dioxaborine) Dyes with Variable π-Bridges: Towards Two-Photon Absorbing Fluorophores with Very High Brightness

Bis(dioxaborine) dyes of the A-π-A format (A: acceptor, π: conjugated bridge) were prepared and photophysically characterized. The best performing dyes feature (a) visible-light absorption (>400 nm), (b) high molar absorption coefficients (up to 70000 m^-1  cm^-1 ), (c) Stokes shifts in the range of ca. 2500-5800 cm^-1 , and (d) strong fluorescence emission with quantum yields of up to 0.74. This yields very bright-emitting dyes for one-photon excitation. However, the most intriguing feature of the dyes is their strong two-photon absorption. This was achieved by means of increased π-conjugation in the phenylene or phenylene-thiophene bridges through the variation of the conjugation length and rigidity. This provided two-photon absorption cross sections of up to 2800 GM (1 Goeppert-Mayer (GM)=10^-50  cm⁴  s photon^-1 ). Considering the mentioned high fluorescence quantum yields, exceptionally bright-emitting A-π-A two-photon absorbing dyes with low molecular mass are obtained. Time-dependent density-functional theory calculations corroborated the experimental results.

A highly fluorescent water soluble spirobifluorene dye with a large Stokes shift: synthesis, characterization and bio-applications

The first water-soluble highly emitting spirobifluorene-based dye and its applications for live cell imaging and BSA detection are reported.

Emergence through delicate balance between the steric factor and molecular orientation: a highly bright and photostable DNA marker for real-time monitoring of cell growth dynamics

A bright and biostable molecular fluorogenic material for real-time monitoring of in vitro cellular growth dynamics.

A New Design Strategy and Diagnostic to Tailor the DNA-Binding Mechanism of Small Organic Molecules and Drugs

The classical model for DNA groove binding states that groove binding molecules should adopt a crescent shape that closely matches the helical groove of DNA. Here, we present a new design strategy that does not obey this classical model. The DNA-binding mechanism of small organic molecules was investigated by synthesizing and examining a series of novel compounds that bind with DNA. This study has led to the emergence of structure-property relationships for DNA-binding molecules and/or drugs, which reveals that the structure can be designed to either intercalate or groove bind with calf thymus dsDNA by modifying the electron acceptor properties of the central heterocyclic core. This suggests that the electron accepting abilities of the central core play a key role in the DNA-binding mechanism. These small molecules were characterized by steady-state and ultrafast nonlinear spectroscopies. Bioimaging experiments were performed in live cells to evaluate cellular uptake and localization of the novel small molecules. This report paves a new route for the design and development of small organic molecules, such as therapeutics, targeted at DNA as their performance and specificity is dependent on the DNA-binding mechanism.

Thienyl Difluoroboron β-Diketonates in Solution and Polylactide Media

Difluoroboron β-diketonates have impressive optical properties in both solution and the solid state. In particular, both fluorescence and room-temperature phosphorescence are present when the dyes are confined to a rigid matrix, such as poly(lactic acid) (PLA). To expand current knowledge and color range capabilities of this unique type of multi-emitting chromophore, a series of thienyl-substituted BF₂bdk complexes have been synthesized. The photophysical properties were investigated in methylene chloride solution and in the solid state as dye/PLA blends. By varying donor ability, i.e. methyl, phenyl, methoxyl, and thienyl substituents, and by changing the dye loading in the PLA media (0.1-10% dye loading) red-shifted emission was achieved, important for biological imaging applications. In dilute CH₂Cl₂ solution, complexes exhibited absorptions ranging from 350 - 420 nm, solid-state fluorescence in PLA ranging from 390 - 500 nm, and oxygen sensitive phosphorescence ranging from 540 - 585 nm in PLA blends. Promising candidates as dye/PLA blends serve as models for dyepolymer conjugates for application as biological oxygen nanoprobes.

Photochemically-assisted synthesis and photophysical properties of difluoroboronated β-diketones with fused four-benzene-ring chromophores, chrysene and pyrene

We report synthesis and photophysical properties of difluoroboronated β-diketone complexes having chrysene and pyrene. Intense fluorescence is observable in solution and the solid state.