Order vs. Disorder: Cholesterol and Omega-3 Phospholipids Determine Biomembrane Organization

Lipid structural diversity strongly affects biomembrane chemico-physical and structural properties in addition to membrane-associated events. At high concentrations, cholesterol increases membrane order and rigidity, while polyunsaturated lipids are reported to increase disorder and flexibility. How these different tendencies balance in composite bilayers is still controversial. In this study, electron paramagnetic resonance spectroscopy, small angle neutron scattering, and neutron reflectivity were used to investigate the structural properties of cholesterol-containing lipid bilayers in the fluid state with increasing amounts of polyunsaturated omega-3 lipids. Either the hybrid 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine or the symmetric 1,2-docosahexaenoyl-sn-glycero-3-phosphocholine were added to the mixture of the naturally abundant 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine and cholesterol. Our results indicate that the hybrid and the symmetric omega-3 phospholipids affect the microscopic organization of lipid bilayers differently. Cholesterol does not segregate from polyunsaturated phospholipids and, through interactions with them, is able to suppress the formation of non-lamellar structures induced by the symmetric polyunsaturated lipid. However, this order/disorder balance leads to a bilayer whose structural organization cannot be ascribed to either a liquid ordered or to a canonical liquid disordered phase, in that it displays a very loose packing of the intermediate segments of lipid chains.     

Niobium microelectrodes for submicron particle confinement

By the superposition of niobium, titanium and gold layers have been fabricated electrodes for submicron particles confinement by dielectrophoresis forces. Electron beam lithography allowed us to define the critical geometries of the electrodes in the submicron range. The niobium layer improves also the mechanical strength of the electrodes and their robustness against the galvanic corrosion making them suitable for the confinement of particles and viruses immersed in a physiological solution.     

SAR optimization in a phased array radiofrequency hyperthermiasystem

RF deep hyperthermia systems make use of phased arrays of applicators in order to heat tumors selectively while maintaining healthy tissue at normal temperatures. A new method for the array synthesis is proposed based on the identification of targets to be heated (tumors) and targets to be prevented from excess electromagnetic radiation. The best array feed for each target is found from the solution of the eigenvector problem for a positive definite Hermitian matrix defined for that target. The optimal feed in a global sense then results from a trade-off of the best feeds of individual targets enforced through minimization of an objective function aimed at weighting the distances of the globally optimal feed from the feed vectors optimized for each target separately. An application to the heating of a pelvis is provided as an example     

Synthesis,Surface Properties,and Self-Aggregation Behavior of a Branched N,N-Dimethylalkylamine Oxide Surfactant

Amine-oxide surfactants have emerged as highly stable, nontoxic, and cost-effective constituents of detergent formulations, specifically as wetting agents and foam boosters. With the aim of enhancing their functional behavior, a new member of this family, N,N-dimethyl-2-propylheptan-1-amine oxide, bearing a branched alkyl tail (C₁₀DAO-branched) was synthesized and purified using a simple and easily scalable strategy starting from 2-propylheptan-1-ol. 2D-nuclear magnetic resonance (NMR) and mass spectrometry confirm the obtainment of the desired product in high yield and purity. The protonation behavior of the branched surfactant is not affected by alkyl tail branching, as shown by potentiometric titrations. In contrast, surface activity and aggregation behavior of C₁₀DAO-branched is dramatically different from that of the linear analog N,N-dimethyldecyl-1-amine oxide (C₁₀DAO-linear), in that it occupies a higher area at the solution interface and aggregates at much higher concentration, forming larger aggregates, as detected using tensiometry and dynamic light scattering (DLS), respectively. Aggregation behavior of C₁₀DAO-branched is less sensitive to pH variations. Foaming tests show that C₁₀DAO-branched is a more effective foam booster than its linear analog, in both acidic and basic solutions. The experimental results indicate that the branched surfactant can be used in applications that require enhanced and pH-independent surface activity and foamability.     

All-optical integrated micro logic gate

In this paper we present a novel approach for realizing an integrated all-optical logic gate. The basic principle is based upon stimulated emission process generated in an active gain medium while special interferometric photonic wave-guiding structure allows the realization of an integrated micro scale device. The operation rate of the proposed device structure can theoretically reach tens of Tera-Hertz.     

Single-Photon Detection System for Quantum Optics Applications

We describe the design and characterization of a fiber-coupled double-channel single-photon detection system based on superconducting single-photon detectors (SSPD), and its application for quantum optics experiments on semiconductor nanostructures. When operated at 2-K temperature, the system shows 10% quantum efficiency at 1.3-mum wavelength with dark count rate below 10 counts per second and timing resolution <100 ps. The short recovery time and absence of afterpulsing leads to counting frequencies as high as 40 MHz. Moreover, the low dark count rate allows operation in continuous mode (without gating). These characteristics are very attractive-as compared to InGaAs avalanche photodiodes-for quantum optics experiments at telecommunication wavelengths. We demonstrate the use of the system in time-correlated fluorescence spectroscopy of quantum wells and in the measurement of the intensity correlation function of light emitted by semiconductor quantum dots at 1300 nm.     

Site‐Controlled Single‐Photon Emitters Fabricated by Near‐Field Illumination

Many of the most advanced applications of semiconductor quantum dots (QDs) in quantum information technology require a fine control of the QDs' position and confinement potential, which cannot be achieved with conventional growth techniques. Here, a novel and versatile approach for the fabrication of site‐controlled QDs is presented. Hydrogen incorporation in GaAsN results in the formation of N–2H and N–2H–H complexes, which neutralize all the effects of N on GaAs, including the N‐induced large reduction of the bandgap energy. Starting from a fully hydrogenated GaAs/GaAsN:H/GaAs quantum well, the N? H bonds located within the light spot generated by a scanning near‐field optical microscope tip are broken, thus obtaining site‐controlled GaAsN QDs surrounded by a barrier of GaAsN:H (laterally) and GaAs (above and below). By adjusting the laser power density and exposure time, the optical properties of the QDs can be finely controlled and optimized, tuning the quantum confinement energy over more than 100 meV and resulting in the observation of single‐photon emission from both the exciton and biexciton recombinations. This novel fabrication technique reaches a position accuracy <100 nm and it can easily be applied to the realization of more complex nanostructures.     

Controlling the Cassie-to-Wenzel Transition: an Easy Route towards the Realization of Tridimensional Arrays of Biological Objects

Nano-Micro Letters - In this paper we provide evidence that the Cassie-to-Wenzel transition, despite its detrimental effects on the wetting properties of superhydrophobic surfaces, can be exploited...     

Hydrophobically Modified Alkali Soluble Emulsion Polymers: Literature Review

In recent years, interest in the class of water-soluble polymers—hydrophobically modified alkali soluble emulsion (HASE)—has increased on a surprising scale. With respect to other associative polymers, they have several advantages in terms of cost and ease of handling and utilization. In addition, unlike the solvent-based formulations, these water-soluble systems do not contain volatile solvents and hence do not contribute to environmental problems. In solutions, HASE polymers form a transient network through molecular associations between the hydrophobic groups. Due to these hydrophobic interactions, they have been increasingly used as rheology modifiers for various applications, such as paints, cosmetics, and personal care and paper coating products. These associative polymers have an architectural richness that allows the fine tuning of several physicochemical properties, and their optimal use requires controlling polymer concentration, molecular weight, size of the hydrophobic groups, and characteristics of the polymeric backbone. We give an overview of several studies on HASE polymers reported in the literature, focusing on the molecular structure, the synthetic methodologies, and—more specifically—on the factors that affect the rheology of their aqueous mixtures. As a general rule for the optimal HASE design and formulative exploitation, we highlight that the hydrophobic hanging groups are responsible for the rheological changes in the liquid phase, while the steric hindrance of the polymeric backbone and of the hydrophobic groups causes the stiffness.