Tuning the Properties of Conjugated Polyelectrolytes through Surfactant Complexation

Chen, Liaohai; Xu, Shengbo; McBranch, and Duncan; Whitten, David G.

doi:10.1021/ja001248r

Cited by 281 publications

(292 citation statements)

References 21 publications

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“…As shown elsewhere, the fluorescence of conjugated polyelectrolytes in aqueous solution is easily perturbed by the addition of various reagents (37,40,41). In the present investigation, we found that when proteins were added to the polyelectrolyte solutions, the PL from the conjugated polymers was altered.…”

Section: Experimental Methodssupporting

confidence: 78%

Biosensors from conjugated polyelectrolyte complexes

Wang

Gong

Heeger

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

284

192

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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.C onjugated polymers are a versatile class of organic materials that promise utility in a variety of applications ranging from antistatic coatings, electrodes, and transistors, to light-emitting diodes, large area displays, photodetectors, photovoltaic cells, and lasers (1-3). The electrical, optical, and electrochemical properties of conjugated polymers can be modified by chemical synthesis and are strongly affected by relatively small perturbations, including changes in temperature, solvent, or chemical environment. As a result of this sensitivity, conjugated polymers are promising as sensory materials (4, 5); sensing may be accomplished by transducing and͞or amplifying physical or chemical changes into electrical, optical, or electrochemical signals. Conjugated polymers have been used to detect chemical species (chemosensors) (6), such as ions (7-11), gases (for example, trinitrotoluene) (6,(12)(13)(14), and other chemicals (15), or biomolecules such as proteins, antibodies (16-27), and DNA (28-31), using electrical (13, 15), chromic (7, 8, 16-19), electrochemical (7-9, 20-25, 28-31), photoluminescent (11, 26), chemoluminescent (27), or gravimetric (14) responses.Contemporary biosensor and bioassay developments have focused on mimicking natural host-receptor (''lock-and-key'') interactions. ''Lock-and-key'' molecular recognition can be between enzyme and substrate, ligand and receptor, antibody and antigen, or between two strands of nucleic acids with complementary sequences. Although antibody-based ELISAs are widely used for detection of biological species with high sensitivity, these assays are relatively labor-intensive and timeconsuming (hours to days) and require two different antibodies of defined specificities to adequately detect the target molecule (potentially making them cumbersome to perform) (32). Additionally, the detection of small molecules using ELISA can seldom be accomplished because of the recognition of one epitope by both capture and detection antibodies. Therefore, competition assays have to be performed that are both less accurate and more time consuming.Biosensors based on conjugated polymers as sensory materials exhibit real-time response [electrochemical (20-25) or optical (16-19, 26)] to the ligand-receptor recognition event. The coupling of a recognition event to photoinduced electron...

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Section: Experimental Methodssupporting

confidence: 78%

Biosensors from conjugated polyelectrolyte complexes

Wang

Gong

Heeger

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

284

192

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“…We initially searched for conditions that would enable the encapsulation of MPS-PPV within lipid vesicles while minimizing and/or suppressing MPS-PPV binding to the lipid walls, ultimately preserving MPS-PPV freedom of motion within vesicles. Lipid-polymer self-assembly has been observed in mixtures containing surfactants and conjugated polyelectrolytes of opposite charge (17)(18)(19) as well as in mixtures of zwitterionic lipids and conjugated polyelectrolytes (16,20,21). Experimental conditions involving a lipid mixture of 75% dioleoyl phosphatidic acid (DOPA, an anionic lipid) and 25% dioleoylphosphatidylcholine (DOPC, a zwitterionic lipid) were thus chosen.…”

Section: Resultsmentioning

confidence: 99%

“…Both an intensity enhancement and a blue shift in intensity, as well as FRET, are observed upon mixing vesicles consisting of 100% DOPC with MPS-PPV. These features are signatures of the association of lipids around the MPS-PPV backbone (16)(17)(18)(19). Studies on the encapsulation of MPS-PPV within the 3∶1 DOPA∶DOPC vesicles and within 100% DOPC vesicles (SI Appendix, Fig.…”

Section: Resultsmentioning

confidence: 99%

Unraveling electronic energy transfer in single conjugated polyelectrolytes encapsulated in lipid vesicles

Karam

Ngo²,

Rouiller³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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A method for the study of conjugated polyelectrolyte (CPE) photophysics in solution at the single-molecule level is described. Extended observation times of single polymer molecules are enabled by the encapsulation of the CPEs within 200-nm lipid vesicles, which are in turn immobilized on a surface. When combined with a molecular-level visualization of vesicles and CPE via cryo-transmission electron microscopy, these single-molecule spectroscopy studies on CPEs enable us to directly correlate the polymer conformation with its spectroscopic features. These studies are conducted with poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylene-vinylene] (MPS-PPV, a negatively charged CPE), when encapsulated in neutral and in negatively charged lipid vesicles. MPS-PPV exists as a freely diffusing polymer when confined in negatively charged vesicles. Individual MPS-PPV molecules adopt a collapsed-chain conformation leading to efficient energy migration over multiple chromophores. Both the presence of stepwise photobleaching in fluorescence intensity-time trajectories and emission from low-energy chromophores along the chain are observed. These results correlate with the amplified sensing potential reported for MPS-PPV in aqueous solution. When confined within neutral vesicles, single MPS-PPV molecules adopt an extended conformation upon insertion in the lipid bilayer. In this case emission arises from multiple chromophores within the isolated polymer chains, leading to an exponential decay of the intensity over time and a broad blueshifted emission spectrum.lipid-polymer interaction | exciton migration | water-soluble light-emitting polymer | biosensing C urrent knowledge on how the interplay of polymer conformation and chromophore coupling affect energy transfer along a conjugated polymer backbone has been established following rigorous ensemble and single-molecule spectroscopy studies. Many of these studies involve polyphenylene vinylene (PPV)-based conjugated polymers decorated with alkyl side groups that facilitate their solubility in organic solvents. This knowledge is critical for developing conjugated polymer-based electroluminescent, photovoltaic, and sensor devices (1).The prevailing organization of a polymer backbone is expected to have direct effects on the coupling of neighboring chromophores (planar segments with delocalized π orbitals along the backbone) and on the energy transfer efficiency between these chromophores. Collapsed polymers, predominantly encountered in films prepared from poor solvents, exhibit long-range order where chains are found in close proximity, folded back on themselves (2, 3). Polymers will thus undergo efficient interchain or through-space energy transfer. On the contrary, polymers in solution are highly disordered, where the presence of defects along the chains together with freely accessible bond rotations should result in globular structures with larger intramolecular distances, on average. The predominant mode of energy transfer found in this case is through-bond or intramolecular ener...

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“…18 An alternative explanation for the increase in the emission quantum yield of conjugated polymers upon interaction with surfactants is that it is not due to the disruption of polymer aggregates but is associated with changes in conformational order. [19][20][21] While it is possible that both factors are involved, the breakup of aggregates is likely to be a precursor of such conformational changes.…”

Section: Introductionmentioning

confidence: 99%

Interplay of Electrostatic and Hydrophobic Effects with Binding of Cationic Gemini Surfactants and a Conjugated Polyanion: Experimental and Molecular Modeling Studies

et al. 2007

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Understanding factors responsible for the fluorescence behavior of conjugated polyelectrolytes and modulation of their behavior are important for their application as functional materials. The interaction between the anionic poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}copolymer (PBS-PFP) and cationic gemini surfactants R,ω-(C m H 2m+1 N + (CH 3 ) 2 ) 2 (CH 2 ) s (Br -) 2 (m-s-m; m ) 12, s ) 2, 3, 5, 6, 10, and 12) has been studied experimentally in aqueous solution. These surfactants are chosen to see whether molecular recognition and self-assembly occurs between the oppositely charged conjugated polyelectrolyte and gemini surfactant when the spacer length on the surfactant is similar to the intercharge separation on the polymer. Without surfactants, PBS-PFP exists as aggregates. These are broken up upon addition of gemini surfactants. However, as anticipated, the behavior strongly depends upon spacer length (s). Fluorescence measurements show three surfactant concentration regimes: At low concentrations (<2 × 10 -6 M) quenching occurs and is most marked with the small spacer 12-2-12; at intermediate concentrations (∼2 × 10 -6 -10 -3 M), fluorescence intensity is constant, with a 12-carbon spacer 12-12-12 showing the strongest fluorescence; above the critical micelle concentration (CMC; ∼10 -3 M) increases in emission intensity are seen in all cases and are largest with the intermediate spacers 12-5-12 and 12-6-12, where the spacer length most closely matches the distance between monomer units on the polymer. With longer spacer length surfactants, surface tension measurements for concentrations below the CMC reveal the presence of polymer-surfactant aggregates at the air-water interface, possibly reflecting increased hydrophobicity. Above the CMC, small-angle neutron scattering experiments for the 12-6-12 system show the presence of spherical aggregates, both for the pure surfactant and for polyelectrolyte/gemini mixtures. Molecular dynamics simulations help rationalize these observations and show that there is a very fine balance between electrostatic and hydrophobic interactions. With the shortest spacer 12-2-12, Coulombic interactions are dominant, while for the longest spacer 12-12-12 the driving force involves hydrophobic interactions. Qualitatively, with the intermediate 12-5-12 and 12-6-12 systems, the optimum balance is observed between Coulombic and hydrophobic interactions, explaining their strong fluorescence enhancement.

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Tuning the Properties of Conjugated Polyelectrolytes through Surfactant Complexation

Cited by 281 publications

References 21 publications

Biosensors from conjugated polyelectrolyte complexes

Biosensors from conjugated polyelectrolyte complexes

Unraveling electronic energy transfer in single conjugated polyelectrolytes encapsulated in lipid vesicles

Interplay of Electrostatic and Hydrophobic Effects with Binding of Cationic Gemini Surfactants and a Conjugated Polyanion: Experimental and Molecular Modeling Studies

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