Colorimetric detection of oligonucleotides using a polydiacetylene vesicle sensor

A new system for the colorimetric detection of oligonucleotides was developed using polydiacetylene vesicles, which play the dual role of an indicator of color transition and an amplification tag. The results are of significance in understanding the mechanism of color transition of biological recognition in polydiacetylene systems and in designing new biosensors.     

A titration microcalorimeter and the vesicle of mixed surfactants

A titration microcalorimeter with the sample cells of 1 mL and 3 mL volume was constructed by combining LKB-2107 ampule microcalorimeter with an improved Thermometric titration microcalorimeter. Its sensitivity and precision were tested with the baseline noise and stability, the measurement of energy equivalent, and the linear relation of electric energy and integral area as the function of voltage (V)-time (f). Its accuracy was demonstrated by measuring the dilution enthalpy of a concentrated sucrose solution and the micelle-forming enthalpy of sodium dodecyl sulfate (SDS) in aqueous solution respectively. At the same time, the enthalpy of interaction between SDS and didodecyldimethylammonium bromide (DDAB) was measured by using the titration microcalorimeter, and the phase behavior of SDS-DDAB aqueous mixture was discussed. The microcalorimetric results show that the enthalpy of interaction between SDS and DDAB micelles is -29.53 kJ/mol, the enthalpy of formation of 1:1 SDS-DDAB salt is -125.8 kJ/mol,     

Study on the preparation and structure of positive sol composed of mixed metal hydroxide

Using precipitation method mixed metal hydroxide (MMH) positive sol was prepared. The preparation process and the properties of the sol were studied with powder XRD, TEM, particle size distribution determination system and microelectrophoresis instrument.The preparation of MMH was made as follows: Diluted ammonia water was added to the mixed solution of aluminum and magnesium chlorides which was prepared in the molar ratio of 1 1 or 1 2, or 1 3; then the pH values of the suspension at different amounts of ammonia water were measured. After that, the precipitate was aged for 5 h in the mother solution at room temperature, and washed after filtering. Finally, the filter cake was peptized at constant temperature of 333 K.The results showed that 1) preparation reaction was completed in three steps, 2) pH value was decisive factor, and 3) both the contents of magnesium and the -potential of MMH sol particles increased with pH values and finally remained constant. The mechanism of the reaction was that magnesium ions intercalated Al(OH)₃ crystal lattice, forming mixed metal hydroxide. The results also showed that positively charged MMH colloidal particle belonged to hexagonal system and three-layer superposition structure.     

Investigation of the effect of calcination temperature on HMDS-treated ordered mesoporous silica film

To reduce signal delay in ultra-large-scale integrated circuits, an intermetal dielectric with low dielectric constant is required. Ordered mesoporous silica film is appropriate for use as an intermetal dielectric due to its low dielectric constant and superior mechanical properties. To reduce the dielectric constant, an ordered mesoporous silica film prepared by a tetraethoxysilane/methyltriethoxysilane silica precursor and Brij-76 block copolymer was surface-modified by hexamethyldisilazane (HMDS) treatment. HMDS treatment substituted OH with Si(CH₃)₃ groups on the silica surface. After treatment, ordered mesoporous silica films were calcined at various calcination temperatures, and the calcination temperature to obtain optimal structural, electrical, and mechanical properties was determined to be approximately 300 °C.     

Effect of alkyl chain length on chemical sensing of polydiacetylene and polydiacetylene/ZnO nanocomposites

Polydiacetylenes (PDAs) and PDA/ZnO nanocomposites based on the monomers 10,12-pentacosadiynoic acid (PCDA), 10,12-tricosadiynoic acid (TCDA), and 10,12-docosadiynedioic acid (DCDA) monomers have been investigated for chromatic chemical sensing of a number of organic liquids. Chromatic sensitivity is associated with the interaction of the organic liquid with the PDA side chain to give rise to the strain-induced blue to red colorimetric transition. Attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy demonstrated that in the PDA/ZnO nanocomposites, the PDA side chains form chelates with ZnO. The chromatic properties of PDAs and PDA/ZnO composites in organic liquids, to certain extent, depend on the side-chain length and the number of carboxylic head groups. Pure PDAs and PDA/ZnO nanocomposites in different organic liquids studied by Raman spectroscopy show that the chromatic selectivity of PDAs for certain organic liquids with respect to the blue to red phase transition is closely related to the side-chain structure of the PDAs. Moreover, the interactions are stronger with those PDAs where the blue to red transition is irreversible. Density functional theory (DFT) simulations show that the chromatic sensitivity of the PDAs toward a particular organic correlates with the C–C bond torsion angle of the PDA backbone.     

Properties of mixed lipid monolayers assembled on hydrophobic surfaces through vesicle adsorption

Supported lipid films are becoming increasingly important tools for the study of membrane protein function because of the availability of high-sensitivity surface analytical and patterning techniques. In this study, we have characterized the physical chemical properties of lipid films assembled on hydrophobic surfaces through the spontaneous adsorption of large unilamellar lipid vesicles composed of dioleoylphosphatidylglycerol (DOPG) and dioleoylphosphatidylcholine (DOPC). The density of the lipid films was measured with surface plasmon resonance spectroscopy as the lipid composition of the vesicles and ionic concentration were varied. As expected, monolayer films were formed, but the density of the monolayers was found to be weakly dependent on the lipid composition of the vesicles and strongly dependent on the ionic concentration of the solution in contact with the monolayer. Atomic force microscopy (AFM) images of the lipid films indicate that they are composed of a homogeneous monolayer. Surface force measurements were used to determine the surface charge and DOPG density of the monolayers. The DOPG content of the films was found to be weakly dependent on the DOPG composition of the vesicles and strongly dependent on the salt concentration of the environment. A model has been developed to describe the behavior of the lipid composition of the films in terms of the hydrophobic, electrostatic, and steric forces acting on the lipid monolayer on the hydrophobic surface.     

Influences of the concentration and the molar ratio of mixed surfactants on the performance of vesicle pseudostationary phase

In our previous work, it was found that the vesicles were formed spontaneously by mixing octyltriethylammonium bromide (C₈NE₃Br) with sodium dodecyl benzene sulfonate (SDBS), and the vesicles have been developed as a pseudostationary phase (PSP) in EKC. In the present work, the effects of the concentration and the molar ratio of cationic to anionic surfactant on the vesicle properties and the performances of vesicle PSP in EKC have been investigated. The aggregates at all mixing ratio were negatively charged regardless of which surfactant surplus. As C₈NE₃Br proportion increased, the microviscosity of the vesicle became larger. With the increase in the total surfactant concentration, the migration time window broadened at the molar ratio of C₈NE₃Br to SDBS of 3:7. Unexpectedly, the window became narrowed at molar ratio of 5:5 and 6:4. However, the methylene selectivity of vesicle PSP at all above‐mentioned molar ratios enhanced as the total surfactant concentration increased, no matter whether the migration time window enlarged or narrowed. It implied that the vesicle PSP at molar ratio of 5:5 and 6:4 made it possible to obtain a better separation in a shorter time. When the total surfactant concentration was fixed at 20 mM, the methylene selectivity of the vesicle PSP of molar ratio of 5:5 was comparable to that of 3:7, but the migration time shortened by a half.     

Water-solubilisation and bio-conjugation of a red-emitting BODIPY marker

The synthesis and preliminary bio-conjugation studies of a novel water-soluble red-emitting di-styryl BODIPY dye are disclosed. Aggregation behaviour of this compound under physiological conditions was suppressed by specific introduction of a di-sulfonated peptide-based linker at the meso phenyl substituent, sultonated styryl arms and short polyethyleneglycol chains at the boron center. Thus, a good quantum yield of 22% in PBS for this red-emitting BODIPY was obtained. Introduction of an activated ester function enabled successful bio-conjugation to monoclonal antibodies and proteins.     

Size effect of polydiacetylene vesicles functionalized with glycolipids on their colorimetric detection ability

In this paper, the size effect of the polydiacetylene vesicles functionalized with glycolipids on their colorimetric detection ability has been studied. Polydiacetylene vesicles in which were incorporated glycolipids acted as a model system for the affinochromatic property. Visible color changes from blue to red could be observed to the naked eye owing to Con A binding to the sugar moiety and be detected quantitatively by the visible absorption spectrum. In the experiment, small and uniform vesicles were obtained after extrusion through membranes with different pore sizes. The morphology and mean size distribution of the extruded vesicles were studied by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. Our work shows that the smaller the vesicles are, the stronger is the effect, making the detection of Con A easier. The results may apply to the sensitivity enhancement of polydiacetylene biosensors for the recognition of other biomolecules.     

Formulation and characterization of a biocompatible microemulsion composed of mixed surfactants: lecithin and Triton X-100

We report on the formation and characterization of a biocompatible microemulsion (ME) system composed of lecithin (L), Triton X-100 (T) as the surfactant(s), butyl lactate (BL) as the cosurfactant, and isopropyl myristate (IPM) as the oil phase and water. Detailed phase construction reveals that mixing of surfactants (L and T) produces larger single-phase ME region compared to L. In the mixed surfactant systems, a three-phase body appears which is otherwise not obtained in the single surfactant counterparts signifying the synergistic solubilization behaviour upon mixing. The maximum solubilization capacity decreases as the content of T increases in the mixture. Viscosity, conductance and adiabatic compressibility measurements of the single-phase ME systems at a constant amphiphile concentration (80 % w/w) show a linear trend with increasing water content revealing a droplet-type structure of all the studied formulations. FTIR studies in the water-in-oil (w/o) region identify the presence of three distinct types of water molecules in these systems and their relative content changes with the interfacial composition as well as the total water content in the system. Our study offers a biocompatible mixed ME system in which the physical properties do not differ much from those of the lecithin-based systems with the additional advantage of having higher solubilization capacity, low pH dependency and low viscosity, which renders its potential to be used for specific pharmaceutical applications.     

Simulations of temperature dependence of the formation of a supported lipid bilayer via vesicle adsorption

Recent experimental investigations of the kinetics of vesicle adsorption in solution on SiO2 demonstrate a thermally activated transition from adsorbed intact vesicles to a supported lipid bilayer. Our Monte Carlo simulations clarify the mechanism of this process. The model employed is an extension of the model used earlier to describe vesicle adsorption at room temperature. Specifically, it includes limitations of the adsorption rate by vesicle diffusion in the solution, and adsorption- and lipid-membrane-induced rupture of arriving and already adsorbed vesicles. Vesicles and lipid molecules, formed after rupture of vesicles, are considered immobile. With these ingredients, the model is able to quantitatively reproduce the temperature-dependent adsorption kinetics, including a higher critical surface concentration of intact vesicles for lower temperatures, and the apparent activation energy for the vesicle-to-bilayer transition E(a) approximately 5 kcal/mol.     

Temperature-dependent vesicle formation of aqueous solutions of mixed cationic and anionic surfactants

The phase behavior of aqueous solutions of mixed cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) was examined at different temperatures (20, 30, 40, and 50 degrees C). While stable vesicles were formed in a narrow composition range on the SOS-rich side at 20 degrees C, the range widened remarkably when the temperature was raised to 30 degrees C. Thus, the vesicle region extended to cover almost the entire composition range, CTAB:SOS = 0.5:9.5-5.0:5.0, at the total surfactant concentrations of 50-70 mM on the SOS-rich side. To analyze the temperature dependence of this phase behavior of the mixed surfactant system, DSC and fluorescence polarization measurements were performed on the system. The experimental findings obtained revealed that pseudo-double-tailed CTAB/SOS complex, the major component of the bimolecular membrane formed by the surfactant mixture, undergoes a gel (Lbeta)-liquid crystal (Lalpha) phase transition at about 26 degrees C. This phenomenon was interpreted as showing that the bimolecular membrane has no curvature and is rigid and easy to precipitate at temperatures below the phase transition point, whereas it has a curvature and is loose enough to disperse in the solution as vesicles at temperatures above the phase transition point. Vesicles formed by the anionic/cationic surfactant complex were then stable at temperatures above the phase transition temperature of the complex.     

Effect of temperature on the rheology of wormlike micelles in a mixed surfactant system

The formation and rheological behavior of a viscoelastic wormlike micellar solution in an aqueous solution of a mixed surfactant system of alkyl ethoxylate sulfate (AES), C(12)H(25)(OCH(2)CH(2))(3)OSO(-)(3)Na(+), and polyoxyethylene dodecyl ether, C(12)EO(3), and the unusual effect of temperature on the rheological behavior have been studied. Upon successive addition of C(12)EO(3) to the dilute micellar solution of AES, viscosity increases swiftly and reaches its peak where a viscoelastic solution with nearly Maxwellian behavior is formed. With the further addition of C(12)EO(3), viscosity decreases sharply, which is attributed to the formation of micellar joints. With increasing temperature, the extent of micellar growth increases and the viscosity maximum is achieved at a lower mixing fraction of C(12)EO(3), but the maximum viscosity attained by the system decreases. The evolution of relaxation time and network density of the viscoelastic network also suggests that with increasing temperature, enhanced micellar growth takes place, but an additional, faster relaxation mechanism becomes increasingly favorable at high concentrations of C(12)EO(3). These results can be explained in terms of the increase in free energy of hemispherical end-caps (end-cap energy) of the micelles with increasing temperature.     

Thermodynamics of demicellization of mixed micelles composed of sodium oleate and bile salts

Isothermal titration calorimetry (ITC) was used to determine the critical micelle concentration (cmc) and the thermodynamic parameters associated with the demicellization of sodium oleate (NaO) and mixed micelles composed of the bile salt (BS) sodium cholate (NaC) or sodium deoxycholate (NaDC), respectively, and NaO at a molar ratio of 5:2. The influence of the ionic strength (pure water and 0.1 M NaCl at pH 7.5) as well as that of the temperature (10-70 degrees C) were analyzed. For NaO, two cmc's were detected, indicating a two-step aggregation process, whereas only one cmc was observed for the two BSs. A single aggregation mechanism is also evident for the demicellization of mixed micelles (BS/NaO 5:2). Increasing the ionic strength induces the well-known decrease of the cmc. The cmc shows a minimum at room temperature. The cmc(mix) of the mixed micelles was analyzed using models assuming an ideal or nonideal mixing behavior of both detergents. The thermodynamic parameters describing the enthalpy (deltaHdemic), entropy (deltaSdemic), and Gibbs energy change (deltaGdemic), as well as the change in heat capacity (deltaCp,demic) for demicellization, were obtained from one ITC experiment. From the temperature dependence of deltaHdemic, the change of the hydrophobic surface area of the detergents from the micellar into the aqueous phase was derived. In all cases, the deltaCp,demic values are positive. In addition, the temperature dependence of the size of the formed aggregates was studied by dynamic light scattering (DLS). DLS indicated two populations of aggregates in the mixed system, small primary micelles (0.5-2 nm), and larger aggregates with a hydrodynamic radius in the range of 50-150 nm.     

Photophysical and Laser Properties of Cassettes based on a BODIPY and Rhodamine Pair

This work deals with the synthesis and the photophysical and laser properties of new BODIPY‐rhodamine cassettes. These dyads differ in their rigid and conjugated spacer group (phenyl or acetylenephenyl) and in their linking positions (meta or para). The photophysical properties of these cassettes are controlled by the formation/opening of the spirolactone ring, which, in turn, switches off/on an energy‐transfer process between the chromophores. Herein, we thoroughly describe the influence of the attached spacer group, as well as the distance and orientation between the donor–acceptor pair, on the excitation energy transfer. The observed fast dynamics and efficiency suggest that the process mainly takes place “through‐bond”, although the “through‐space” mechanism also contributes to the whole process. As a result, efficient laser emission from the rhodamine is achieved upon excitation of the BODIPY, in particular for the cassette that contains an acetylenephenyl spacer group in a para disposition.     

Investigation of the blue phase in a compensable cholesteric mixed system

Pitch dependence of cholesteric blue phase stability has been investigated in a compensable mixed system of cholesteryl nonanoate/chloride. Two critical pitches above which no blue phase exists were found depending on the structure of the liquid crystal. The clearing enthalpy does not exhibit discontinuities over the whole mixing range.     

Supramolecular organization in the solid state of a novel soluble polydiacetylene

The synthesis of the monomer 1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne, its polymerization and the purification of the polymer, which is soluble in common organic solvents, are reported. Results from powder X-ray diffraction studies carried out on the red form of the polymer are discussed. The red polymer chains self-assemble into cylindrical shapes which produce hexagonal columnar mesophases with a transition from a more (Colho) to a less ordered (Colhd) structure around 85 C. The role played by the long alkyl chains in the formation of the supramolecular hexagonal mesophase is emphasized by comparing these results with those obtained from an analogous polymer with dodecyl substituents which exhibits only the Colhd structure over the whole range of temperature explored.     

Temperature-controlled vesicle aggregation in the mixed system of sodium n-dodecyl sulfate/n-dodecyltributylammonium bromide

Temperature-controlled vesicle aggregation was investigated in a catanionic surfactant system of sodium n-dodecyl sulfate/n-dodecyltributylammonium bromide. Vesicle aggregation took place as the temperature reached the critical value (Tc). Tc can be adjusted by the variations of the total surfactant concentration and the mixed molar ratio. It was also found that the temperature variation above Tc can greatly influence the vesicle aggregation rate. The vesicle aggregation process was irreversible as long as T >/= Tc, whereas the vesicle disaggregation process occurred only below Tc.     

Thermal expansion and compressibility in the chain direction of a polydiacetylene single crystal

An x-ray back-reflection rotating camera has been used to measure the lattice constant, thermal expansion, and compressibility in the polymer chain direction of a polydiacetylene, poly[bis(p-toluene sulfonate) of 2,4-hexadiyne 1,6-diol]. The thermal expansion coefficient of the polymer chain is small and positive (0.9 ± 0.2 × 10^?6 °K^?) at 300°K, but negative below about 70°K. Application of 3.43 kbar hydrostatic pressure at 299°K changed the unit cell dimension in the polymer chain direction by less than 10 ppm.