Effect of surfactant on water-soluble conjugated polymer used in biosensor

The effect of nonionic surfactants on the cationic conjugated polymer (CCP), poly{9,9-bis[6-(N,N-trimethylammonium)hexyl]fluorene-co 1,4-phenylene} iodide 1, has been investigated. It is shown that the CCP in various solvents exists in three phases: isolated polymer chains, polymer aggregate, and variable size clusters (partially dissolved polymer). It is shown that nonionic surfactants enhance the photoluminescence (PL) quantum yield of the CCP in water by breakup of polymer aggregates, which eliminates the nonemissive interchain quenching with aggregates and increases surface-to-volume ratio of the CCP. Furthermore, the surfactants reduce quenching by incorporation of the CCP into aggregates or binary micelles. Surfactant also reduces the polar interaction strength between CCP and water and enhances CCP quenching by the counterions (iodine) by ion pairing effect. The dynamics of the interactions are complex and reveal that the surfactant induces rapid increase in the PL which imply that the main force that causes the aggregation is weak and may be due to hydrophobic interaction of the CCP in water rather than a solid, particulate-like state. Time-resolved fluorescence measurements at the exciton energy (420 nm) confirm that the CCP in water and in some organic solvents is a multiphase system in which three exponential decay terms are needed to fit the decay profile of the CCP. The change in the decay lifetime explains clearly the effect of surfactant and solvent polarity on the three CCP phases. The average lifetime of the CCP does not increase with surfactant, but the number of isolated polymer chains increases which leads to higher PL quantum yield. The association between the polymer and a quencher, single-strand deoxyribonucleic acid (ssDNA), was investigated. It indicated that CCP:ssDNA forms a weak electrostatic complex that does not alter the absorption spectra of the CCP but induces a strong CCP fluorescence quenching with association constant KS = 5 x 10(7) M(-1). At low ssDNA concentrations, the surfactant reduces quenching in the complex possibly by preventing charge-transfer processes. This may be due to an increase in the distance between the CCP and ssDNA through incorporation of the CCP into aggregates (micelles). However, at high ssDNA concentration, the quenching increases sharply which may be assigned to the increase in the electrostatic force destroying the micelles' structure around the CCP, leading to contact quenching as well as DNA induced CCP aggregation, which in turn leads to CCP-CCP quenching.     

Shape-specific detection based on fluorescence resonance energy transfer using a flexible water-soluble conjugated polymer

We present the detection of the shape-specific conformation of DNA based on the fluorescence resonance energy transfer (FRET) by using a novel flexible water-soluble cationic conjugated polymer (CCP). The flexible backbone of CCP has more conformational freedom with the potential to be responsive to analyte shape by electrostatic interaction between flexible CCP and negatively charged DNA. The analyte shape dependent recognition is accomplished by structural changes that compressed or extended the flexible CCP. The morphology-dependent spectral properties of the novel flexible polymer related to the analyte shapes are investigated in detail, where two types of chromophores, referred to as "isolated" segment and "packed" segment aggregates, within the flexible polymer are identified by means of ensemble and single molecule measurements upon binding with different geometric DNA. The change in fluorescence intensity upon binding with shape-specific DNA without obvious color shifts makes this novel flexible polymer a suitable CCP donor for FRET measurements. The results provide insights for understanding the spectral properties of flexible water-soluble CCP and CCP/DNA interaction related to the geometry of target analyte.     

Enhanced conjugated polymer fluorescence quenching by dipyridinium-based quenchers in the presence of surfactant

Poly[(2-methoxy-5-propyloxysulfonate)phenylene vinylene] (MPS-PPV) was synthesized directly from its bischloromethylated monomer, considerably reducing the total number of steps involved in the polymer preparation. For the first time, a simple technique of ultracentrifugation was employed for final purification of the polymer. The interactions among the polymer, surfactant, and quencher molecules, as well as amplified fluorescence quenching and fluorescence enhancement associated with the interactions, were investigated and discussed. When compared with methyl viologen [MV]2+, higher values of Stern-Volmer constant K(SV) values on the order of > or =10(7) M(-1) were observed for the newly synthesized N-(2-carboxyhexadecanoyl)-N'-methyl-4,4'-bipyridinium iodide bromide ([CHMB]2+) quencher in the presence of 1,2-dioleoyl-3- trimethylammonium propane (DOTAP) surfactant. Comparisons of surfactants demonstrated that the K(SV) of [CHMB]2+ was 10-fold higher in the presence of dodecyltrimethylammonium bromide (DTAB) surfactant than with DOTAP. Polymer fluorescence was totally recovered upon addition of DOTAP surfactant to a MV-quenched polymer system, whereas only 50% of fluorescence was recovered upon addition of DOTAP surfactant to the CHMB-quenched polymer solution. In contrast, no fluorescence was recovered when DTAB was added to either the MV- or CHMB-quenched polymer systems. Thus, fluorescence enhancement was observed for the polymer complex with DOTAP, whereas fluorescence quenching was predominant in the polymer complex with DTAB. Such studies will not only help to better understand the intrinsic properties of the ionic conjugated polymer and amplified fluorescence quenching and enhancement but also provide guidelines to develop the next generation of ionic conjugated-polymer-based biosensors.     

Tuning the optical properties of a water-soluble cationic poly(p-phenylenevinylene): surfactant complexation with a conjugated polyelectrolyte

In this work, we investigate the emission and absorbance properties of the novel water-soluble cationic conjugated polymer poly{2,5-bis[3-(N,N,N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene}, denoted here as P2, in the presence of varying amounts of the anionic surfactant sodium dodecylsulfate (SDS). We show that the absolute photoluminescence quantum efficiency (PLQE), the absorption wavelength, and the emission wavelength of an aqueous solution of P2 can be adjusted according to the surfactant/polymer ratio in aqueous solution. In particular, we show that the addition of SDS to P2 increases the polyelectrolyte's PLQE to approximately 40%. An observed red shift in the emission spectra upon addition of the surfactant is attributed to the reduction in electrostatic repulsive interactions between side chains that minimize the benzene ring twisting along the backbone structure. At the surfactant's critical micelle concentration, the P2 chains wrap around the outer surface of the SDS micelles. This work has implications on the development of new stable poly(p-phenylenevinylene)-based photovoltaic and electroluminescent materials with tunable optical properties.     

Investigating the effects of side chain length on the AIE properties of water-soluble TPE derivatives

The emissive properties of fluorophores in aggregated state are important for the development of bio-sensors or bio-imaging reagents. So three water-soluble TPE derivatives with different lengths of side chains have been synthesized and we investigated the effects of side chains on aggregation-induced emission (AIE) properties in the aggregated states. The results indicate that side chains on the fluorophores play a pivotal role in their emission in aggregated state mediated by heparin or solid state, because the coplanarity of these TPE derivatives was affected by side chains. The rates of radiative decay k_f and non-radiative decay k_nr have been obtained through the quantum yields and lifetime, and a larger k_f and smaller k_nr were present for compound TPE-C4N, suggesting that the aggregated TPE-C4N should posses the most remarkable fluorescent property.     

Effect of a neutral water-soluble polymer on the lamellar phase of a zwitterionic surfactant system

We have studied the effect of adding a water-soluble polymers (PEG) to the lamellar phases of the ternary system tetradecyldimethylaminoxide (C14DMAO)-hexanol-water. The results of Freeze-Fracture Electron Microscopy (FFEM) and Small Angle X-ray Scattering (SAXS) experiments show that the addition of the polymer induces the spontaneous formation of highly monodisperse multilayered vesicles above a threshold polymer concentration.     

Interfacial microgels formed by oppositely charged polyelectrolytes and surfactants. Part 2. Influence of surfactant chain length and surfactant/polymer ratio

The adsorption and complexation of polystyrene sulfonate (a highly charged anionic polyelectrolyte) and a series of cationic surfactants, alkyltrimethylammonium bromide, CnTAB, n = 8-16, at the air-water interface has been studied by combining surface tension and ellipsometry measurements. We find that increasing the chain length of the surfactant from 8 to 10 carbons leads to a sharp increase in adsorption of PSS/CnTAB complexes. When the surfactant tail length is further increased to 12 and 14 carbons, surface adsorption becomes less favored than macroscopic phase separation, resulting in a partial surface depletion. Furthermore, we find that when surface tensions are plotted against surfactant/monomer molar concentration ratio, all data collapse to a single curve. This result shows that the surfactant-polymer molar ratio, s/p, is a key parameter for tuning the surface activity of the complexes formed.     

Highly sensitive fluorescent sensor for copper (II) based on amplified fluorescence quenching of a water-soluble NIR emitting conjugated polymer

We have synthesized the near-infrared water-soluble conjugated polymer poly[2,5-di(propyloxysulfonate)-1,4-phenylene-ethynylene-9,10-anthrylene (referred to as PPEASO3). Its fluorescence (at wavelengths between 650 and 800?nm following photoexcitation at 550?nm) is efficiently quenched by Cu(II) ions, while other physiologically relevant metal ions do not cause significant quenching at the same concentrations. Under optimum conditions, fluorescence intensity is inversely proportional to the concentration of Cu (II). The calibration curve displays two linear regions over the range of 0–3.2?×?10^?7 mol L^?1 and 3.2?×?10^?7 mol L^?1 to 1.0?×?10^?4 mol L^?1 of Cu(II), respectively. The long-wavelength excitation and emission can substantially reduce interferences by the autofluorescence and light scattering of biological matter under UV excitation. The method was successfully applied to the determination of Cu(II) in synthetic and tea samples.

POE chain length selectivity in the clouding of a Triton surfactant

The POE chain length distribution between the coacervate and aqueous phases of a clouded Triton X-114 solution was studied. The average chain length of the surfactant in the aqueous layer was determined by HPLC and compared to the distribution in the original (unclouded) solution. Both the clouding temperature and the equilibration time were found to govern the chain length selectivity. A slight excess of longer POE chains were encountered in the aqueous layer, thus enriching the coacervate layer with shorter, less soluble chains. Chain length selection appeared to occur when the surfactant particles were dispersed in the clouded suspension, rather than after the establishment of the aqueous and coacervate layers.     

Mechanism of oil-in-water emulsification using a water-soluble amphiphilic polymer and lipophilic surfactant

A new O/W (oil-in-water) emulsification system was developed using the amphiphilic polymer HHM-HEC (hydrophobically-hydrophilically modified hydroxyethylcellulose) and a lipophilic surfactant. HHM-HEC was used as a thickener and polymeric surfactant, and the addition of small quantities of various types of nonionic lipophilic surfactant (hydrophilic-lipophilic balance <5) decreased the droplet size of several types of oil due to a lowering of the tension at the water/oil interface. The oil droplets were held by the strong network structure of the aqueous HHM-HEC solution, preserving the O/W phase without inversion. These stable O/W emulsions were prepared without the addition of hydrophilic surfactants and thus show improved water repellency.     

Optical choline sensor based on a water-soluble fluorescent conjugated polymer and an enzyme-coupled assay

We report on a simple and sensitive water-soluble fluorescent conjugated polymer for use in a choline biosensor. Choline is oxidized by the enzyme choline oxidase (ChOx), and the hydrogen peroxide (H₂O₂) formed is used to oxidize catechol via catalysis by horseradish peroxidase. The product of oxidation acts as a quencher of the photoluminescence of a fluorescent conjugated polymer. The ratio of the fluorescence intensity of the system in the presence and absence of the choline, respectively, serves as the analytical information. It is proportional to the concentration of choline in the 0.1 μM to 20 μM concentration range. The detection limit for choline is 50 nM. The biosensor was successfully applied to the determination of choline in milk samples with satisfactory reproducibility and accuracy. This is the first biosensor where a ChOx/HRP enzyme-coupled assay is used in combination with a water-soluble conjugated polymer for the fluorescent detection of choline. In our opinion, it provides a common platform for further development of enzymatic biosensors based on fluorescent conjugated polymers.

Amphiphilic polymer gel electrolytes. II. Influence of the ethylene oxide side‐chain length on the gel properties

Amphiphilic polymers consisting of copolymethacrylates carrying about 26 wt % ethylene oxide [(EO)_n] side chains of different lengths were used as matrices in gel electrolytes. The gel electrolytes were composed of 30 wt % copolymer and 70 wt % 1 M LiPF₆ in a mixture of ethylene carbonate and γ‐butyrolactone (2/1 w/w). The coordination of lithium ions by the (EO)_n side chains in competition with the solvent was studied by Raman spectroscopy. A significantly stronger lithium coordination was observed when the gel electrolyte was based on a copolymer carrying (EO)₉ units in comparison with copolymers having (EO)₁, (EO)₂, and (EO)₄ units. Despite the observed stronger lithium coordination by (EO)₉ units in the gel, the ion conductivity was not significantly lower with respect to the gels based on the other copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1519–1524, 2001     

Influence of a surfactant and electrolytes on adsorbed polymer layers

Solvent relaxation NMR and small-angle neutron scattering have been used to characterize adsorbed poly(ethylene oxide) (PEO) layers on silica at a range of surfactant and electrolyte concentrations. Below the critical aggregation concentration (cac), the results suggest that sodium dodecyl sulfate (SDS) interacts relatively weakly, perhaps analogously to a simple salt reducing the solvency of PEO. This is evidenced by a decrease in the adsorbed layer thickness combined with an increase in the bound fraction, although the total adsorbed amount is not greatly affected. The layer thickness goes through a minimum at the cac, after which further SDS addition results in the formation of PEO/SDS aggregates that repel each other and, hence, tend to desorb. The adsorbed amount therefore decreases, from 0.7 mg m(-2) initially to 0.2 mg m(-2) with 32 mM SDS. The aggregates that remain adsorbed also repel, and hence, there is an increase in the layer thickness and the persistence length, while the bound fraction is reduced. In comparison, the effects of electrolyte at the ionic strength studied are relatively minimal. There is, however, evidence that the repulsions between adsorbed PEO/SDS aggregates are partially screened, allowing them to approach each other more readily. This leads to a contraction of the adsorbed layer when the SDS concentration is sufficiently high.     

Influence of bifurcation position and length of side chains on the structure of isoindigo-based conjugated polymer thin films

We chose a series of isoindigo-based conjugated polymer(ⅡDDT,ⅡDDT-C3 and ⅡDDT-C4) with different length of side chains and bifurcation positions to investigate the relationship between the degree of alignment and the length of side chains and bifurcation positions.We found that the dichroic ratio was increased from 2.37 to 5.23 when the side chain was longer and the bifurcation position was away from the backbone.The π-π stacking distance was decreased from 3.67 A to 3.61 A when the bifurcation position was away from the backbone because of its smaller hindrance and the d-spacing of the(100)was increased from 20.06 A to 25.21 A when the side chain was longer.All the polymers were adopted an edge-on orientation with the backbone paralleled with the long axis of fibers.The weak interaction of side-chain in ⅡDDT-C4 was beneficial for the molecules being rearranged in parallel during the contact line receding and the strong n-n interaction could accelerate the interchain assembly of the parallel molecules through π-π interaction to form aligned fibers.     

Influence of carbon chain length on physical properties of 3FmHPhF homologues

ABSTRACT

Four compounds from 3FmHPhF homologous series of chiral smectogenic fluorinated compounds (m = 2, 4, 5, 6) were studied by frequency domain dielectric spectroscopy, electro-optic measurements, X-ray diffraction and differential scanning calorimetry. Values of the relaxation time and dielectric increment of relaxation processes versus temperature and bias field were determined. The temperature-dependent tilt angles, spontaneous polarisations, switching times, rotational viscosities, and average intermolecular distances and correlation lengths within smectic layers were obtained. Experimental results were supplemented by density functional theory calculations of isolated 3FmHPhF molecular geometries, and the relationship between the molecular structures and the transverse component of their dipole moments was studied for the mesogens with m = 2, 4, 5, 6, 7. The results are discussed in terms of the length of the C_mH_2m flexible carbon chain of the homologues.     

Influence of chemical structure and chain length on conducting properties of dielectric polymers in metal/polymer/metal structures

The influence of weight-average molecular mass M _w on the maximal width of a conducting layer h _max of polysterene, polymethylmethacrylate, and polyamidine films was investigated. It was shown that h _max increases in proportion to M _w ^S for all investigated polymers. It points to the fact that the h _max value is defined by the macromolecular coil size.     

Aggregation properties of diacyl lysine surfactant compounds: hydrophobic chain length and counterion effect

In this paper, we report on the study of aqueous solution and aggregation properties of diacyl Lysine surfactant salts with several surfactant counterions at a fixed hydrophobic chain length. They present a critical micellar concentration nearly independent of the counterion. The area per surfactant molecule is around 1.3 nm (2) also independent of the counterion. We have also studied the dry state crystallization of these surfactant salts. We show that small counterion systems tend to form bicontinuous cubic structures and that the increase in counterion size tends to form lamellar structures. We have compared this behavior with the dry state crystallization of the diacyl Lysine surfactants as a function of hydrophobic chain length. For long hydrophobic chains, the crystal structure is lamellar, while for intermediate, length is cubic. Among the structures studied, the one with the shortest chain length crystallizes in a hexagonal inverse phase.     

Doping properties of polydithienylmethine: a study on the correlation between polymer chain length, spectroscopy, and transport

(1S)-(+)-10-Camphorsulfonic acid-doped polydithienylmethine was prepared through an acid-catalyzed condensation reaction of alpha,alpha'-di-2-thienyl-(2,2'-bithiophene)-5,5'-dimethanol and was characterized by 1H NMR spectroscopy and size exclusion chromatography (SEC). The electronic and vibrational properties of the resulting polymer thin films vary with the loadings of the (1S)-(+)-10-camphorsulfonic acid. The dark conductivity and drift mobility, which is significantly high, of the polymer thin films were enhanced with increasing doping levels and reached maximum values of 8.0x10(-5) S.cm-1 and 3.5x10(-2) cm2.V-1.s-1, respectively, at a 7 mol % dopant loading. Higher doping levels (>7 mol %) result in nonuniform polymer thin films with degraded optical quality due to the formation of nanocrystalite and thus a decrease in conductivity and drift mobility was observed. The doped polydithienylmethine thin film also exhibited a photoconductivity response with an excitation at 457 nm and the highest photoconductivity (2x10(-4) S.cm-1) was again observed at the 7 mol % doping level. Spectroscopic investigation suggests that the enhanced transport properties can be attributed to polaronic species present. The electronic and vibrational changes which relate to such doping were characterized by electronic absorption spectroscopy, Raman spectroscopy, and FTIR spectroscopy. The changes in transport values can be directly related to the changes we see in our spectroscopic investigations.