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  • 1
    Online Resource
    Online Resource
    Beyond superquenching: Hyper-efficient energy transfer from conjugated polymers to gold nanoparticles
    Proceedings of the National Academy of Sciences ; 2003
    In:  Proceedings of the National Academy of Sciences Vol. 100, No. 11 ( 2003-05-27), p. 6297-6301
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 100, No. 11 ( 2003-05-27), p. 6297-6301
    Abstract: Gold nanoparticles quench the fluorescence of cationic polyfluorene with Stern–Volmer constants ( K SV ) approaching 10 11 M — 1 , several orders of magnitude larger than any previously reported conjugated polymer–quencher pair and 9–10 orders of magnitude larger than small molecule dye–quencher pairs. The dependence of K SV on ionic strength, charge and conjugation length of the polymer, and the dimensions (and thus optical properties) of the nanoparticles suggests that three factors account for this extraordinary efficiency: ( i ) amplification of the quenching via rapid internal energy or electron transfer, ( ii ) electrostatic interactions between the cationic polymer and anionic nanoparticles, and ( iii ) the ability of gold nanoparticles to quench via efficient energy transfer. As a result of this extraordinarily high K SV , quenching can be observed even at subpicomolar concentrations of nanoparticles, suggesting that the combination of conjugated polymers with these nanomaterials can potentially lead to improved sensitivity in optical biosensors.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1132025100
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2003
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  • 2
    Online Resource
    Online Resource
    Probing π-coupling in molecular junctions
    Proceedings of the National Academy of Sciences ; 2005
    In:  Proceedings of the National Academy of Sciences Vol. 102, No. 25 ( 2005-06-21), p. 8821-8825
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 102, No. 25 ( 2005-06-21), p. 8821-8825
    Abstract: Charge transport characteristics for metal–molecule–metal junctions containing two structurally related π-conjugated systems were studied to probe π–π interactions in molecular junctions. The first molecule contains a typical π-conjugated framework derived from phenylene vinylene units, whereas the second has the phenylene vinylene structure interrupted by a [2.2]paracyclophane (pCp) core. Electrochemical investigations were used to characterize the defects and packing density of self-assembled monolayers of the two molecules on gold surfaces and to enable quantitative comparison of their transport characteristics. Current–voltage measurements across molecular junctions containing the two species demonstrate that the pCp moiety yields a highly conductive break in through-bond π-conjugation. The observed high conductivity is consistent with density functional theory calculations, which demonstrate strong through-space π–π coupling across the pCp moiety.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0500002102
    RVK:
    TA 1000
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2005
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 3
    Online Resource
    Online Resource
    The fluorescence resonance energy transfer (FRET) gate: A time-resolved study
    Proceedings of the National Academy of Sciences ; 2005
    In:  Proceedings of the National Academy of Sciences Vol. 102, No. 3 ( 2005-01-18), p. 530-535
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 102, No. 3 ( 2005-01-18), p. 530-535
    Abstract: The two-step energy-transfer process in a self-assembled complex comprising a cationic conjugated polymer (CCP) and a dsDNA is investigated by using pump-dump-emission spectroscopy and time-correlated single-photon counting; energy is transferred from the CCP to an ethidium bromide (EB) molecule intercalated into the dsDNA through a fluorescein molecule linked to one terminus of the DNA. Time-dependent anisotropy measurements indicate that the inefficient direct energy transfer from the CCP to the intercalated EB results from the near orthogonality of their transition moments. These measurements also show that the transition moment of the fluorescein spans a range of angular distributions and lies between that of the CCP and EB. Consequently, the fluorescein acts as a fluorescence resonance energy-transfer gate to relay the excitation energy from the CCP to the EB.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0408568102
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2005
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 4
    Online Resource
    Online Resource
    SNP detection using peptide nucleic acid probes and conjugated polymers: Applications in neurodegenerative disease identification
    Proceedings of the National Academy of Sciences ; 2005
    In:  Proceedings of the National Academy of Sciences Vol. 102, No. 1 ( 2005-01-04), p. 34-39
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 102, No. 1 ( 2005-01-04), p. 34-39
    Abstract: A strategy employing a combination of peptide nucleic acid (PNA) probes, an optically amplifying conjugated polymer (CP), and S1 nuclease enzyme is capable of detecting SNPs in a simple, rapid, and sensitive manner. The recognition is accomplished by sequence-specific hybridization between the uncharged, fluorescein-labeled PNA probe and the DNA sequence of interest. After subsequent treatment with S1 nuclease, the cationic water soluble CP electrostatically associates with the remaining anionic PNA/DNA complex, leading to sensitized emission of the labeled PNA probe via FRET from the CP. The generation of fluorescent signal is controlled by strand-specific electrostatic interactions and is governed by the complementarity of the probe/target pair. To assess the method, we compared the ability of the sensor system to detect normal, wild-type human DNA sequences, and those sequences containing a single base mutation. Specifically, we examined a PNA probe complementary to a region of the gene encoding the microtubule associated protein tau. The probe sequence covers a known point mutation implicated in a dominant neurodegenerative dementia known as frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), which has clinical and molecular similarities to Alzheimer's disease. By using an appropriate PNA probe, the conjugated polymer poly[(9,9-bis(6′- N , N , N -trimethylammoniumhexylbromide)fluorene)-co-phenylene] and S1 nuclease, unambiguous FRET signaling is achieved for the wild-type DNA and not the mutant sequence harboring the SNP. Distance relationships in the CP/PNA assay are also discussed to highlight constraints and demonstrate improvements within the system.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0407578101
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2005
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 5
    Online Resource
    Online Resource
    Electron injection into organic semiconductor devices from high work function cathodes
    Proceedings of the National Academy of Sciences ; 2008
    In:  Proceedings of the National Academy of Sciences Vol. 105, No. 35 ( 2008-09-02), p. 12730-12735
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 105, No. 35 ( 2008-09-02), p. 12730-12735
    Abstract: We show that polymer light-emitting diodes with high work-function cathodes and conjugated polyelectrolyte injection/transport layers exhibit excellent efficiencies despite large electron-injection barriers. Correlation of device response times with structure provides evidence that the electron-injection mechanism involves redistribution of the ions within the polyelectrolyte electron-transport layer and hole accumulation at the interface between the emissive and electron-transport layers. Both processes lead to screening of the internal electric field and a lowering of the electron-injection barrier. The hole and electron currents are therefore diffusion currents rather than drift currents. The response time and the device performance are influenced by the type of counterion used.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0806494105
    RVK:
    TA 1000
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    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2008
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 6
    Online Resource
    Online Resource
    Ultrafast Long-Range Charge Separation in Organic Semiconductor Photovoltaic Diodes
    American Association for the Advancement of Science (AAAS) ; 2014
    In:  Science Vol. 343, No. 6170 ( 2014-01-31), p. 512-516
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 343, No. 6170 ( 2014-01-31), p. 512-516
    Abstract: Understanding the charge-separation mechanism in organic photovoltaic cells (OPVs) could facilitate optimization of their overall efficiency. Here we report the time dependence of the separation of photogenerated electron hole pairs across the donor-acceptor heterojunction in OPV model systems. By tracking the modulation of the optical absorption due to the electric field generated between the charges, we measure ~200 millielectron volts of electrostatic energy arising from electron-hole separation within 40 femtoseconds of excitation, corresponding to a charge separation distance of at least 4 nanometers. At this separation, the residual Coulomb attraction between charges is at or below thermal energies, so that electron and hole separate freely. This early time behavior is consistent with charge separation through access to delocalized π-electron states in ordered regions of the fullerene acceptor material.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1246249
    RVK:
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2014
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
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  • 7
    Online Resource
    Online Resource
    DNA detection using water-soluble conjugated polymers and peptide nucleic acid probes
    Proceedings of the National Academy of Sciences ; 2002
    In:  Proceedings of the National Academy of Sciences Vol. 99, No. 17 ( 2002-08-20), p. 10954-10957
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 99, No. 17 ( 2002-08-20), p. 10954-10957
    Abstract: The light-harvesting properties of cationic conjugated polymers are used to sensitize the emission of a dye on a specific peptide nucleic acid (PNA) sequence for the purpose of homogeneous, “real-time” DNA detection. Signal transduction is controlled by hybridization of the neutral PNA probe and the negative DNA target. Electrostatic interactions bring the hybrid complex and cationic polymer within distances required for Förster energy transfer. Conjugated polymer excitation provides fluorescein emission 〉 25 times higher than that obtained by exciting the dye, allowing detection of target DNA at concentrations of 10 pM with a standard fluorometer. A simple and highly sensitive assay with optical amplification that uses the improved hybridization behavior of PNA/DNA complexes is thus demonstrated.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.162375999
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2002
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 8
    Online Resource
    Online Resource
    Time-resolved energy transfer in DNA sequence detection using water-soluble conjugated polymers: The role of electrostatic and hydrophobic interactions
    Proceedings of the National Academy of Sciences ; 2004
    In:  Proceedings of the National Academy of Sciences Vol. 101, No. 32 ( 2004-08-10), p. 11634-11639
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 101, No. 32 ( 2004-08-10), p. 11634-11639
    Abstract: We have investigated the energy transfer processes in DNA sequence detection by using cationic conjugated polymers and peptide nucleic acid (PNA) probes with ultrafast pump-dump-emission spectroscopy. Pump-dump-emission spectroscopy provides femtosecond temporal resolution and high sensitivity and avoids interference from the solvent response. The energy transfer from donor (the conjugated polymer) to acceptor (a fluorescent molecule attached to a PNA terminus) has been time resolved. The results indicate that both electrostatic and hydrophobic interactions contribute to the formation of cationic conjugated polymers/PNA-C/DNA complexes. The two interactions result in two different binding conformations. This picture is supported by the average donor–acceptor separations as estimated from time-resolved and steady-state measurements. Electrostatic interactions dominate at low concentrations and in mixed solvents.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0404574101
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2004
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 9
    Online Resource
    Online Resource
    Methods for strand-specific DNA detection with cationic conjugated polymers suitable for incorporation into DNA chips and microarrays
    Proceedings of the National Academy of Sciences ; 2005
    In:  Proceedings of the National Academy of Sciences Vol. 102, No. 3 ( 2005-01-18), p. 589-593
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 102, No. 3 ( 2005-01-18), p. 589-593
    Abstract: A strand-specific DNA sensory method is described based on surface-bound peptide nucleic acids and water-soluble cationic conjugated polymers. The main transduction mechanism operates by taking advantage of the net increase in negative charge at the peptide nucleic acid surface that occurs upon single-stranded DNA hybridization. Electrostatic forces cause the oppositely charged cationic conjugated polymer to bind selectively to the “complementary” surfaces. This approach circumvents the current need to label the probe or target strands. The polymer used in these assays is poly[9,9′-bis(6′′- N,N,N -trimethylammonium)hexyl)fluorene- co -alt-4,7-(2,1,3-benzothiadiazole) dibromide], which was specifically designed and synthesized to be compatible with excitation sources used in commonly used DNA microarray readers. Furthermore, the utility of poly[9,9′-bis(6′′- N,N,N -trimethylammonium)-hexyl)fluorene- co -alt-4,7-(2,1,3-benzothiadiazole) dibromide] has been demonstrated in homogenous and solid-state assays that involve fluorescence resonance energy transfer to a reporter dye (Cy5) and that can benefit from the light harvesting properties observed in water-soluble conjugated polymers.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0408561102
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2005
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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  • 10
    Online Resource
    Online Resource
    Biosensors from conjugated polyelectrolyte complexes
    Proceedings of the National Academy of Sciences ; 2002
    In:  Proceedings of the National Academy of Sciences Vol. 99, No. 1 ( 2002-01-08), p. 49-53
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 99, No. 1 ( 2002-01-08), p. 49-53
    Abstract: A charge neutral complex (CNC) was formed in aqueous solution by combining an orange light emitting anionic conjugated polyelectrolyte and a saturated cationic polyelectrolyte at a 1:1 ratio (per repeat unit). Photoluminescence (PL) from the CNC can be quenched by both the negatively charged dinitrophenol (DNP) derivative, (DNP-BS − ), and positively charged methyl viologen (MV 2+ ). Use of the CNC minimizes nonspecific interactions (which modify the PL) between conjugated polyelectrolytes and biopolymers. Quenching of the PL from the CNC by the DNP derivative and specific unquenching on addition of anti-DNP antibody (anti-DNP IgG) were observed. Thus, biosensing of the anti-DNP IgG was demonstrated.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.012581399
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2002
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
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