Hybrid inorganic-organic fluorescent silica nanoparticles—influence of dye binding modes on dye leaching

Silica nanoparticles with embedded fluorescent dyes represent an important class of markers for example in biological imaging. We systematically studied the various incorporation mechanisms of fluorescent xanthene dyes in 30–40 nm silica nanoparticles. An important parameter was the interaction of the dye with the matrix material, either by weak electrostatic or strong covalent interactions, which also has implications on the stability of fluorescence and brightness of the dyes. Factors that can influence leaching of dyes such as the position of the dyes in particles and the intensity of the particle-dye interaction were investigated by using the solvatochromic effect of xanthene dyes and by stationary fluorescence anisotropy measurements. We compared uranine and rhodamine B, which were physically embedded, with modified fluorescein isothiocyanate and rhodamine B isothiocyanate, which were covalently bound to the silica matrix within a usual Stöber synthesis. Systematic leaching studies of time spans up to 4 days revealed that covalent bonding of dyes like fluorescein isothiocyanate or rhodamine B isothiocyanate is necessary for fluorescence stability, since dyes bound by physical interaction tend to leach out of porous silica networks. Coverage of silica particles with hydrophobic protection layers of alkyltrialkoxysilanes or hydrophilic polyethylene glycol (PEG) groups resulted in a better retention of physisorbed dyes and provides the possibility to adapt the particles to the polarity of the medium. Best results were archived with PEG groups, but even small trimethylsilyl (TMS) groups already reduce leaching.

Unprecedented Coumarin-Pyronin Hybrid Dyes: Synthesis, Fluorescence Properties and Theoretical Calculations

A novel class of rosamine dyes bearing a 7-substituted 4-hydroxycoumarin unit as <i>meso</i>-heteroaryl ring is presented. The latent <i>C</i>-nucleophilic character of 4-hydroxycoumarin derivatives (<i>i.e.</i>, their C-3 position as nucleophilic center) has been drawn on in the designing of two unprecedented synthetic routes towards these atypical xanthene dyes. They are based on an effective formal Knoevenagel condensation with either pyronin derivatives or a mixed bis-aryl ether bearing both an aldehyde and a masked phenylogous amine, possibly applicable to a wide range of latent cyclic <i>C</i>-nucleophiles. We also report experimental and theoretical photophysical investigations of these unique coumarin-pyronin hybrid structures and particularly their form low-lying quenching states, some of dark twisted intramolecular charge transfer (TICT) nature, depending on the medium (CHCl₃ and water). Furthermore, two fluorophore compounds <b>9</b> and <b>11</b> have been applied for imaging in paraformaldehyde-fixed A549 cells to gain insights into their permeation and localization.

Unprecedented Coumarin-Pyronin Hybrid Dyes: Synthesis, Fluorescence Properties and Theoretical Calculations

A novel class of rosamine dyes bearing a 7-substituted 4-hydroxycoumarin unit as <i>meso</i>-heteroaryl ring is presented. The latent <i>C</i>-nucleophilic character of 4-hydroxycoumarin derivatives (<i>i.e.</i>, their C-3 position as nucleophilic center) has been drawn on in the designing of two unprecedented synthetic routes towards these atypical xanthene dyes. They are based on an effective formal Knoevenagel condensation with either pyronin derivatives or a mixed bis-aryl ether bearing both an aldehyde and a masked phenylogous amine, possibly applicable to a wide range of latent cyclic <i>C</i>-nucleophiles. We also report experimental and theoretical photophysical investigations of these unique coumarin-pyronin hybrid structures and particularly their form low-lying quenching states, some of dark twisted intramolecular charge transfer (TICT) nature, depending on the medium (CHCl₃ and water). Furthermore, two fluorophore compounds <b>9</b> and <b>11</b> have been applied for imaging in paraformaldehyde-fixed A549 cells to gain insights into their permeation and localization.

XANTHENE DYES-MEDIATED IN VITRO PHOTODYNAMIC TREATMENT OF CANCER AND NON-CANCER CELL LINES

Rose bengal and erythrosin B are xanthene dyes mainly known and used as antimicrobial agents, but due to their photodynamic activity they are also potential photosensitizers for cancer photodynamic therapy. The aim of this work is to study a photodynamic efficacy of rose bengal and erythrosin B against human skin melanoma and mouse fibroblast cell lines, compare them with each other and find out their photodynamic properties induced by light emitting diodes with total light dose of 5 J/cm2. To fully identify and understand photodynamic properties of both potentially effective photosensitizers, a set of complex in vitro tests such as cell cytotoxic assay, measurement of reactive oxygen species production, mitochondrial membrane potential change assay, mode of cell death determination or comet assay were made. Although both photosensitizers proved to have similar properties such as increasing production of reactive oxygen species with the higher concentration, predominance of necrotic mode of death or genotoxicity, the more effective photosensitizer was rose bengal because its EC50 was over 20 times lower for both cell lines than in case of erythrosin B.

Sulfonated rhodamines as impermeable labelling substrates for cell surface protein visualization

Sulfonated rhodamines that endow xanthene dyes with cellular impermeability are presented. We fuse charged sulfonates to red and far-red dyes to obtain Sulfo549 and Sulfo646, respectively, and further link these to SNAP- and Halo-tag substrates for protein self-labelling. Cellular impermeability is validated in live cell imaging experiments in transfected HEK cells and neurons derived from induced pluripotent stem cells (iPSCs). Lastly, we show that Sulfo646 is amenable to STED nanoscopy by recording membranes of SNAP/Halo-surface-labelled human iPSC-derived neuronal axons. We therefore provide an avenue for rendering dyes impermeable for exclusive extracellular visualization via self-labelling protein tags.

Phosphonofluoresceins: Synthesis, Spectroscopy, and Applications

<p>Xanthene fluorophores, like fluorescein, have been versatile molecules across diverse fields of chemistry and life sciences. Despite the ubiquity of 3-carboxy and 3-sulfuonofluorescein for the last 150 years, to date, no reports of 3-phosphonofluorescein exist. Here, we report the synthesis, spectroscopic characterization, and applications of 3-phosphonofluoresceins. The absorption and emission of 3-phosphonofluoresceins remain relatively unaltered from the parent 3-carboxyfluorescein. 3-phosphonofluoresceins show enhanced water solubility compared to 3-carboxyfluorescein and persist in an open, visible light-absorbing state even at low pH and in low dielectric media while 3-carboxyfluoresceins tend to lactonize. In contrast, the spirocyclization tendency of 3-phosphonofluoresceins can be modulated by esterification of the phosphonic acid. The bis-acetoxymethyl ester of 3-phosphonofluorescein readily enters living cells, showing excellent accumulation (>6x) and retention (>11x), resulting in a nearly 70-fold improvement in cellular brightness compared to 3-carboxyfluorescein. In a complementary fashion, the free acid form of 3-phosphonofluorescein does not cross cellular membranes, making it ideally suited for incorporation into a voltage-sensing scaffold. We develop a new synthetic route to functionalized 3-phosphonofluoresceins to enable the synthesis of phosphono-voltage sensitive fluorophores, or phosVF2.1.Cl. Phosphono-VF2.1.Cl shows excellent membrane localization, cellular brightness, and voltage sensitivity (26% ΔF/F per 100 mV), rivalling that of sulfono-based VF dyes. In sum, we develop the first synthesis of 3-phosphonofluoresceins, characterize the spectroscopic properties of this new class of xanthene dyes, and utilize these insights to show the utility of 3-phosphonofluoresceins in intracellular imaging and membrane potential sensing. </p> <p> </p>

Phosphonofluoresceins: Synthesis, Spectroscopy, and Applications

<p>Xanthene fluorophores, like fluorescein, have been versatile molecules across diverse fields of chemistry and life sciences. Despite the ubiquity of 3-carboxy and 3-sulfuonofluorescein for the last 150 years, to date, no reports of 3-phosphonofluorescein exist. Here, we report the synthesis, spectroscopic characterization, and applications of 3-phosphonofluoresceins. The absorption and emission of 3-phosphonofluoresceins remain relatively unaltered from the parent 3-carboxyfluorescein. 3-phosphonofluoresceins show enhanced water solubility compared to 3-carboxyfluorescein and persist in an open, visible light-absorbing state even at low pH and in low dielectric media while 3-carboxyfluoresceins tend to lactonize. In contrast, the spirocyclization tendency of 3-phosphonofluoresceins can be modulated by esterification of the phosphonic acid. The bis-acetoxymethyl ester of 3-phosphonofluorescein readily enters living cells, showing excellent accumulation (>6x) and retention (>11x), resulting in a nearly 70-fold improvement in cellular brightness compared to 3-carboxyfluorescein. In a complementary fashion, the free acid form of 3-phosphonofluorescein does not cross cellular membranes, making it ideally suited for incorporation into a voltage-sensing scaffold. We develop a new synthetic route to functionalized 3-phosphonofluoresceins to enable the synthesis of phosphono-voltage sensitive fluorophores, or phosVF2.1.Cl. Phosphono-VF2.1.Cl shows excellent membrane localization, cellular brightness, and voltage sensitivity (26% ΔF/F per 100 mV), rivalling that of sulfono-based VF dyes. In sum, we develop the first synthesis of 3-phosphonofluoresceins, characterize the spectroscopic properties of this new class of xanthene dyes, and utilize these insights to show the utility of 3-phosphonofluoresceins in intracellular imaging and membrane potential sensing. </p> <p> </p>