Fluorescence and confocal imaging of mammalian cells using conjugated oligoelectrolytes with phenylenevinylene core.

Over the last few years, considerable efforts are taken, in order to find a molecular fluorescent probe fulfilling their applicability requirements. Due to a good optical properties and affinity to biological structures conjugated oligoelectrolytes (COEs) can be considered as a promising dyes for application in fluorescence-based bioimaging. In this work, we synthetized COEs with phenylenevinylene core (PV-COEs) and applied as fluorescent membranous-specific probes. Cytotoxicity effects of each COE were probed on cancerous and non-cancerous cell types and little to no toxicity effects were observed at the high range of concentrations. The intensity of cell fluorescence following the COE staining was determined by the photoluminescence analysis and fluorescence activated cell sorting method (FACS). Intercalation of tested COEs into mammalian cell membranes was revealed by fluorescent and confocal microscopy colocalization with commercial dyes specific for cellular structures including mitochondria, Golgi apparatus and endoplasmic reticulum. The phenylenevinylene conjugated oligoelectrolytes have been found to be suitable for fluorescent bioimaging of mammalian cells and membrane-rich organelles. Due to their water solubility coupled with spontaneous intercalation into cells, favorable photophysical features, ease of cell staining, low cytotoxicity and selectivity for membranous structures, PV-COEs can be applied as markers for fluorescence imaging of a variety of cell types.

Covalent Surface Modification of Gallium Arsenide Photocathodes for Water Splitting in Highly Acidic Electrolyte.

Efficient water splitting using light as the only energy input requires stable semiconductor electrodes with favorable energetics for the water-oxidation and proton-reduction reactions. Strategies to tune electrode potentials using molecular dipoles adsorbed to the semiconductor surface have been pursued for decades but are often based on weak interactions and quickly react to desorb the molecule under conditions relevant to sustained photoelectrolysis. Here, we show that covalent attachment of fluorinated, aromatic molecules to p-GaAs(1 0 0) surfaces can be employed to tune the photocurrent onset potentials of p-GaAs(1 0 0) photocathodes and reduce the external energy required for water splitting. Results indicate that initial photocurrent onset potentials can be shifted by nearly 150 mV in pH -0.5 electrolyte under 1 Sun (1000 W m-2 ) illumination resulting from the covalently bound surface dipole. Though X-ray photoelectron spectroscopy analysis reveals that the covalent molecular dipole attachment is not robust under extended 50 h photoelectrolysis, the modified surface delays arsenic oxide formation that results in a p-GaAs(1 0 0) photoelectrode operating at a sustained photocurrent density of -20.5 mA cm-2 within -0.5 V of the reversible hydrogen electrode.

Phenylenevinylene conjugated oligoelectrolytes as fluorescent dyes for mammalian cell imaging.

Conjugated phenylenevinylene oligoelectrolytes, which consist of a phenylenevinylene core equipped at each end with hydrophilic pendent groups, are shown to be good candidates for mammalian cell membrane staining. When used in the micromolar concentration range, they express low to moderate cell toxicity for selected regular and cancerous cell lines as tested for adherent and suspension cells.

Self-assembly of poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} with oppositely charged phenylenevinylene oligoelectrolytes.

The interaction of the water-soluble conjugated polyelectrolyte (CPE) poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) (degree of polymerization, DP, ∼3-6) with various concentrations of a homologous series of oppositely charged amphiphilic phenylenevinylene oligomers was investigated in water:dioxane mixtures and in aqueous micellar solutions of the non-ionic surfactant n-dodecylpentaoxyethylene glycol ether. The excellent spectral overlap between the CPE fluorescence and the conjugated oligoelectrolyte (COE) absorption indicates that energy transfer between these is a highly favored process, and can be tuned by changing the COE chain length. This is supported by time-resolved fluorescence data. The overall results provide support for different types of self-assembly, which are sensitive to the solvent environment and to the size of the phenylenevinylene oligoelectrolyte chain. It is suggested that large aggregates are formed in water:dioxane mixtures, while decorated core-shell structures are present in the surfactant solutions.

Increased ion conductance across mammalian membranes modified with conjugated oligoelectrolytes.

Variation in conjugated oligoelectrolyte (COE) repeat units is shown to affect the rate of COE insertion into mammalian membrane patches and membrane patch stabilities. These findings suggest that it is possible to find COE structures that do not destroy membranes while at the same time allow for more facile transmembrane movement of ions/substrates.

Aggregation properties of p-phenylene vinylene based conjugated oligoelectrolytes with surfactants.

The amphiphilic properties of conjugated oligoelectrolytes (COE) and their sensitivity to the polarity of their microenvironment lead to interesting aggregation behavior, in particular in their interaction with surfactants. Photoluminescence (PL) spectroscopy, liquid-phase atomic force microscopy, small-angle neutron scattering, small-angle X-ray scattering, and grazing-incidence X-ray diffraction were used to examine interactions between cationic p-phenylene vinylene based oligoelectrolytes and surfactants. These techniques indicate the formation of COE/surfactant aggregates in aqueous solution, and changes in the photophysical properties are observed when compared to pure aqueous solutions. We evaluate the effect of the charge of the surfactant polar headgroup, the size of the hydrophobic chain, and the role of counterions. At low COE concentrations (micromolar), it was found that these COEs display larger emission quantum efficiencies upon incorporation into micelles, along with marked blue-shifts of the PL spectra. This effect is most pronounced in the series of anionic surfactants, and the degree of blue shifts as a function of surfactant charge is as follows: cationic < nonionic < anionic surfactants. In anionic surfactants, such as sodium dodecyl sulfate (SDS), the PL spectra show vibronic resolution above the critical micelle concentration of the surfactant, suggesting more rigid structures. Scattering data indicate that in aqueous solutions, trimers appear as essentially 3-dimensional particles, while tetra- and pentamers form larger, cylindrical particles. When the molar ratio of nonionic C12E5 surfactant to 1,4-bis(4-{N,N-bis-[(N,N,N-trimethylammonium)hexyl]amino}-styryl)benzene tetraiodide (DSBNI) is close to one, the size of the formed DSBNI-C12E5 particles corresponds to the full coverage of individual oligomers. When these particles are transferred into thin films, they organize into a cubic in-plane pattern. If anionic SDS is added, the formed DSBNI-SDS particles are larger than expected for full surfactant coverage, and particles may thus contain several oligomers. This tendency is attributed to the merging of DSBNI oligomers due to the charge screening and, thus, reduced water solubility.

Improving charge collection in Escherichia coli-carbon electrode devices with conjugated oligoelectrolytes.

It is important to tailor biotic-abiotic interfaces in order to maximize the utility of bioelectronic devices such as microbial fuel cells (MFCs), electrochemical sensors and bioelectrosynthetic systems. The efficiency of electron-equivalent extraction (or injection) across such biotic-abiotic interfaces is dependent on the choice of the microbe and the conductive electrode material. In this contribution, we show that spontaneous intercalation of a conjugated oligoelectrolyte, namely 4,4'-bis(4'-(N,N-bis(6''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+), into the membranes of Escherichia coli leads to an increase in current generation in MFCs containing carbon-based electrodes. A combination of scanning electron microscopy (SEM) and confocal microscopy was employed to confirm the incorporation of DSSN+ into the cell membrane and biofilm formation atop carbon felt electrodes. Current collection was enhanced by more than 300% with addition of this conjugated oligoelectrolyte. The effect of DSSN+ concentration on electrical output was also investigated. Higher concentrations, up to 25 µM, lead to an overall increase in the number of charge equivalents transferred to the charge-collecting electrode, providing evidence in support of the central role of the synthetic system in improving device performance.

Conjugated oligoelectrolytes increase power generation in E. coli microbial fuel cells.

A series of conjugated oligoelectrolytes with structural variations is used to stain E. coli. By taking advantage of a high-throughput screening platform that incorporates gold anodes, it is found that MFCs with COE-modified E. coli generate significantly higher power densities, relative to unmodified E. coli. These findings highlight the potential of using water-soluble molecules inspired by the work on organic semiconductors to improve electrode/microbe interfaces.

Self-assembly of an optically active conjugated oligoelectrolyte.

Conjugated oligoelectrolytes are of emerging technological interest due to their recent function in the fabrication of optoelectronic devices, application in biosensors, and as species that facilitate transmembrane charge migration. Solubility in aqueous, or highly polar, solvents is important for many of these applications; however, there are few studies on how the self-assembly of conjugated oligoelectrolytes into multichromophore species influences linear and nonlinear optical properties. Here, we examine 1,4-bis(4'-(N,N-bis(6''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)benzene tetraiodide (DSBNI) in water, a conjugated oligoelectrolyte based on the distyrylbenzene framework. We find that DSBNI aggregation leads to increased fluorescence lifetimes, coupled with hypsochromic shifts, and larger two-photon absorption cross sections. Liquid atomic force microscopy (AFM) and cryogenic transmission electron microscopy (cryo-TEM) were used to image DSBNI aggregates and to confirm that the planar molecules stack to form nanocylinders above a critical aggregation concentration. Finally, small-angle neutron scattering (SANS) was used to quantify the aggregate dimensions in situ. Comparison of the results highlights that the hydrophilic mica surface used to image via liquid AFM and the high concentrations required for cryo-TEM facilitate the propagation of the cylinders into long fibers. SANS experiments are consistent with equivalent molecular packing geometry but lower aspect ratios. It is therefore possible to understand the evolution of optical properties as a function of concentration and aggregation and the general geometric features of the resulting supramolecular structures.

Modification of the optoelectronic properties of membranes via insertion of amphiphilic phenylenevinylene oligoelectrolytes.

We report on the modification of membranes by incorporation of phenylenevinylene oligoelectrolytes with the goal of tailoring their optical and electronic properties and their applications. A water-soluble distyrylstilbene oligoelectrolyte (DSSN+), capped at each end with nitrogen bound, terminally charged pendant groups, was synthesized. The photophysical and solvatochromatic properties of DSSN+ and the shorter distyrylbenzene analogue DSBN+ were probed and found to be useful for characterizing insertion into membranes based on phospholipid vesicle systems. A combination of UV/visible absorbance and photoluminescence spectroscopies, together with confocal microscopy, were employed to confirm membrane incorporation. Examination of the emission intensity profile in stationary multilamellar vesicles obtained with a polarized excitation source provides insight into the orientation of these chromophores within lipid bilayers and indicates that these molecules are highly ordered, such that the hydrophobic electronically delocalized region positions within the inner membrane with the long molecular axis perpendicular to the bilayer plane. Cyclic voltammetry experiments provide evidence that DSSN+ and DSBN+ facilitate transmembrane electron transport across lipid bilayers supported on glassy carbon electrodes. Additionally, the interaction with living microorganisms was probed. Fluorescence imaging indicates that DSSN+ and DSBN+ preferentially accumulate within cell membranes. Furthermore, notable increases in yeast microbial fuel cell performance were observed when employing DSSN+ as the electron transport mediator.

Chemically fixed p-n heterojunctions for polymer electronics by means of covalent B-F bond formation.

Widely used solid-state devices fabricated with inorganic semiconductors, including light-emitting diodes and solar cells, derive much of their function from the p-n junction. Such junctions lead to diode characteristics and are attained when p-doped and n-doped materials come into contact with each other. Achieving bilayer p-n junctions with semiconducting polymers has been hindered by difficulties in the deposition of thin films with independent p-doped and n-doped layers. Here we report on how to achieve permanently fixed organic p-n heterojunctions by using a cationic conjugated polyelectrolyte with fluoride counteranions and an underlayer composed of a neutral conjugated polymer bearing anion-trapping functional groups. Application of a bias leads to charge injection and fluoride migration into the neutral layer, where irreversible covalent bond formation takes place. After the initial charging and doping, one obtains devices with no delay in the turn on of light-emitting electrochemical behaviour and excellent current rectification. Such devices highlight how mobile ions in organic media can open opportunities to realize device structures in ways that do not have analogies in the world of silicon and promise new opportunities for integrating organic materials within technologies now dominated by inorganic semiconductors.

Cationic zinc enolates as highly active catalysts for acrylate polymerization.

Unprecedented cationic zinc enolates have been generated by a novel activation route involving the amido to imino ligand transformation with B(C6F5)3, structurally characterized, and utilized as highly active catalysts for the production of high molecular weight polyacrylates at ambient temperature.