Interfacial Structure of a Liquid Crystal/Nanoparticle Nanocomposite Studied by X-ray Scattering: Indirect Evidence for the Role of Faceting of the Nanoparticles.

The interfacial structure in a liquid crystal/nanoparticle nanocomposite is dictated by the type of nanoparticle and its functionalization compound. Nanocomposites consisting of smectic liquid crystals and nanoparticles have been studied for their applications in devices such as photovoltaics and to model biological devices. With the use of a model system, this paper presents evidence of an interfacial structure close to the vicinity of the nanoparticles that is more disordered than that of the bulk liquid crystal but is still in the smectic phase, and it seems to follow the faceting of the structure the nanoparticles adopt when they coalesce or recluster after the liquid crystal is added.

Iminobiotin binding induces large fluorescent enhancements in avidin and streptavidin fluorescent conjugates and exhibits diverging pH-dependent binding affinities.

The pH-dependent binding affinity of either avidin or streptavidin for iminobiotin has been utilized in studies ranging from affinity binding chromatography to dynamic force spectroscopy. Regardless of which protein is used, the logarithmic dependence of the equilibrium dissociation constant (K(d)) on pH is assumed conserved. However a discrepancy has emerged from a number of studies which have shown the binding affinity of streptavidin for iminobiotin in solution to be unexpectedly low, with the K(d) at values usually associated with non-specific binding even at strongly basic pH levels. In this work we have utilized a Bodipy fluorescent conjugate of avidin and an Oregon Green fluorescent conjugate of streptavidin to determine the K(d) of the complexes in solution in the pH range of 7.0 to 10.7. The study was made possible by the remarkable fluorescent enhancement of the two fluorescent conjugates (greater than 10 fold) upon saturation with iminobiotin. The streptavidin-iminobiotin interaction exhibited almost no pH dependence over the range studied, with K(d) consistently on the order of 10(-5) M. In contrast, under identical experimental conditions the avidin-iminobiotin interaction exhibited the expected logarithmic dependence on pH. We discuss the possible origins for why these two closely related proteins would diverge in their binding affinities for iminobiotin as a function of pH.

Effects of magnetic nanoparticles with different surface coating on the phase transitions of octylcyanobiphenyl liquid crystal.

The impact of magnetic nanoparticles with different surface coating upon the isotropic-to-nematic and nematic-to-smectic- A phase transitions of the liquid crystal octylcyanobiphenyl is explored by means of high-resolution adiabatic scanning calorimetry. A shrinkage of the nematic range is observed, which is strongly dependent on the surface coating of the nanoparticles. The isotropic-to-nematic transition remains weakly first order while the nematic-to-smectic- A is continuous with the effective critical exponent alpha values (0.35 and 0.39, depending on the coating) between the pure octylcyanobiphenyl value of 0.31+/-0.03 and the theoretical tricritical value of 0.5.

The use of DNA molecular beacons as nanoscale temperature probes for microchip-based biosensors.

Today's biosensors and drug delivery devices are increasingly incorporating lithographically patterned circuitry that is placed within microns of the biological molecules to be detected or released. Elevated temperatures due to Joule heating from the underlying circuitry cannot only reduce device performance, but also alter the biological activity of such molecules (i.e. binding, enzymatic, folding). As a consequence, biochip design and characterization will increasingly require local measurements of the temperature and temperature gradients on the biofunctionalized surface. We have developed a technique to address this challenge based on the use of DNA molecular beacons as a nanoscale temperature probe. The surface of fused-silica chips with lithographically patterned, current-carrying gold rings have been functionalized with a layer of molecular beacons. We utilize the temperature dependence of the molecular beacons to calibrate the temperature at the center of the rings as a function of applied current from 25 to 50 degrees C. The fluorescent images of the rings reveal the extent of heating to the surrounding chip due to the applied current while resolving temperature gradients over length scales of less than 500nm. Finite element analysis and analytic calculations of the distribution of heat in the vicinity of the current-carrying rings agree well with the experimental results. Thus, molecular beacons are shown to be a viable tool for temperature calibration of micron-sized circuitry and the visualization of submicron temperature gradients.

System for continuous production of nanophase materials using a microwave-driven polyol process.

A prototype system is described for the large scale, continuous production of nanophase metals, metal oxides, and other nanophase materials using the polyol process. The polyol process employs an organic solvent such as ethylene glycol to reduce a metal oxide/metal salt at high temperature to the metal oxide or metal. The system employs a 6 kW, 2.45 GHz microwave source to rapidly heat the continuously flowing solution to a desired process temperature as it flows through a silica tube placed along the center line of a section of waveguide.