Amplification strategy using aggregates of ferrocene-containing cationic polythiophene for sensitive and specific electrochemical detection of DNA

We report a new electrochemical amplification strategy for an ultrasensitive electrochemical detection of DNA sequences using aggregates composed of a water-soluble, ferrocene-functionalized polythiophene. A two-step hybridization is performed at one addressing surface with PNA capture probes whereas the electrochemical detection is done on an electrode nearby. Specific and quantitative detection of DNA targets with a detection limit of 4 × 10(-16) M (about 4 zeptomoles or about 2500 copies of oligonucleotides) was achieved.

The development of a silica nanoparticle-based label-free DNA biosensor

A silica nanoparticle-based DNA biosensor capable of detecting Bacillus anthracis bacteria through the use of unlabelled ss-oligonucleotides has been developed. The biosensor makes use of the optical changes that accompany a nanoparticle-immobilized cationic conjugated polymer (polythiophene) interacting with single-stranded vs. hybridized oligonucleotides, where a fluorescence signal appears only when hybridized DNA is present (i.e. only when the ss-oligonucleotide interacting with the polymer has hybridized with its complement). In order to enhance the sensitivity of the biosensor, two different nanoparticle architectures were developed and used to elucidate how the presence of neighboring fluorophores on the nanoparticle surface affects Förster-resonant energy transfer (FRET) between the polythiophene/oligonucleotide complex (FRET donor) and the fluorophores (FRET acceptors). We demonstrate that the silica nanoparticle-based FRET platform lowers the limit of detection at least 10-fold in comparison to the polythiophene itself, and allows the detection of ∼2 × 10(-12) moles of ss-oligonucleotide in a 100 μL sample with a standard fluorimeter (i.e. has a limit of detection of ∼2 nM ssDNA). Such nanoparticle-based biosensor platforms are beneficial because of the robustness and stability inherent to their covalent assembly and they provide a valuable new tool that may allow for the sensitive, label-free detection (the target DNA that produces the fluorescence signal is unlabelled) without the use of polymerase chain reaction.

Design, Synthesis and Charaterization of Polymers Derived from Fluorene for Application in RGB Polymer Light-Emitting-Diodes

In order to obtain efficient blue, green and red light-emitters as active layers in polymer light-emitting diode (PLEDs), we report herein the design, the synthesis, and the characterization of new polyesters and copolymers derived from fluorene. We will focus on a new approach to obtain a stable, high luminance blue emitter via polyesters derived from fluorene. The versatile synthetic approach allows the easy design of a whole class of new and tunable electroactive and photoactive aromatic polyesters. Poly(1,6-hexane- 9,9′,9′,9′′,9′′-hexahexyl-7,2′;7′,2′′-terfluorene-2,7′′-dicarboxylate) (PTFHHC6) and Poly(1,6-hexane-2,7-Bis(1,1′-biphenylen-4-yl-4′-dicarboxylate)-9,9-dioctylfluorene) (PE-BP-DOF-BP) exhibit strong emission in the blue range, both in solution and in the solid state. Moreover, these polyesters present some advantages over other polyfluorene derivatives. For example, their solid-state fluorescence spectrum does not show the formation of any excimer and does not vary upon thermal treatment. We will also present copolymers derived from fluorene which emit green light and a new approach to obtain red polymer light-emitting-diode will also be shown. Optical properties such as light absorption, light emission and quantum yield of fluorescence in solution as well as electrical properties such as cyclic voltammogram and conductivity in-situ are reported. Finally, some of the polymers presented have been tested in PLEDs devices and the preliminary results seem promising for the development of multicoloured displays made from the same class of polyfluorene derivatives.

Highlighting new phylogenetic specificities of Crohn's disease microbiota

BACKGROUND

Recent studies suggest that gastrointestinal (GI) microbes play a part in the pathogenesis of Crohn's disease (CD).

METHODS

Fecal samples were collected from 16 healthy individuals and 16 CD patients (age- and sex-matched). The DNA extracted from these samples were subjected to two different methods of microbiome analysis. Specific bacterial groups were quantified by real-time polymerase chain reaction (PCR) methods using primers designed using a high-throughput in-house bioinformatics pipeline. The same DNA extracts were also used to produce fluorescently labeled cRNA amplicons to interrogate a custom-designed phylogenetic microarray for intestinal bacteria.

RESULTS

Even though the intersubject variability was high, differences in the fecal microbiomes of healthy and CD patients were detected. Faecalibacterium prausnitzii and Escherichia coli were more represented in healthy and ileal CD patients, respectively. Additionally, probes specific for Ruminococcus bromii, Oscillibacter valericigenes, Bifidobacterium bifidum, and Eubacterium rectale produced stronger hybridization signals with the DNA samples from healthy subjects. Conversely, species overrepresented in CD patients were E. coli, Enterococcus faecium, and species from the Proteobacteria not normally found in the healthy human GI tract. Furthermore, we detected "healthy specific" molecular species or operational taxonomic units (OTUs) that are not closely related to any known species (Faecalibacterium, Subdoligranulum, and Oscillospora species), indicating that the phylogenetic dysbiosis is broader than at strain or species level.

CONCLUSIONS

These two techniques of microbiome analysis provided a statistically robust new picture of the dysbiosis in fecal microbiota from ileal CD patients. Specifically, we identified a set of six species discriminant for CD, which provides a preliminary diagnostic tool.

Exciton formation, relaxation, and decay in PCDTBT

The nature and time evolution of the primary excitations in the pristine conjugated polymer, PCDTBT, are investigated by femtosecond-resolved fluorescence up-conversion spectroscopy. The extensive study includes data from PCDTBT thin film and from PCDTBT in chlorobenzene solution, compares the fluorescence dynamics for several excitation and emission wavelengths, and is complemented by polarization-sensitive measurements. The results are consistent with the photogeneration of mobile electrons and holes by interband π-π* transitions, which then self-localize within about 100 fs and evolve to a bound singlet exciton state in less than 1 ps. The excitons subsequently undergo successive migrations to lower energy localized states, which exist as a result of disorder. In parallel, there is also slow conformational relaxation of the polymer backbone. While the initial self-localization occurs faster than the time resolution of our experiment, the exciton formation, exciton migration, and conformational changes lead to a progressive relaxation of the inhomogeneously broadened emission spectrum with time constants ranging from about 500 fs to tens of picoseconds. The time scales found here for the relaxation processes in pristine PCDTBT are compared to the time scale (<0.2 ps) previously reported for photoinduced charge transfer in phase-separated PCDTBT:fullerene blends (Phys. Rev. B 2010, 81, 125210). We point out that exciton formation and migration in PCDTBT occur at times much longer than the ultrafast photoinduced electron transfer time in PCDTBT:fullerene blends. This disparity in time scales is not consistent with the commonly proposed idea that photoinduced charge separation occurs after diffusion of the polymer exciton to a fullerene interface. We therefore discuss alternative mechanisms that are consistent with ultrafast charge separation before localization of the primary excitation to form a bound exciton.

Intramolecular energy transfer in molecules with a large number of conformations

The equations representing the decay kinetics of fluorescence of a donor luminophore in the presence of an acceptor in the same flexible molecule are discussed. The assumption that distances between luminophores attached to chain ends are not correlated with the relative orientations of luminophores is tested by theoretical calculations for the unperturbed chains Tyr-(Ala)(n)-Tyr with n equal to 4 and 9. It appears that for these chains, in which the conformation is dominated by entropic factors, the above assumption is satisfactory even for chains with a small number of repeating units (n = 4).

Solar-energy production and energy-efficient lighting: photovoltaic devices and white-light-emitting diodes using poly(2,7-fluorene), poly(2,7-carbazole), and poly(2,7-dibenzosilole) derivatives

World energy needs grow each year. To address global warming and climate changes the search for renewable energy sources with limited greenhouse gas emissions and the development of energy-efficient lighting devices are underway. This Review reports recent progress made in the synthesis and characterization of conjugated polymers based on bridged phenylenes, namely, poly(2,7-fluorene)s, poly(2,7-carbazole)s, and poly(2,7-dibenzosilole)s, for applications in solar cells and white-light-emitting diodes. The main strategies and remaining challenges in the development of reliable and low-cost renewable sources of energy and energy-saving lighting devices are discussed.