Michele Giocondo

The Pleurotus ostreatus hydrophobin Vmh2 and its interaction with glucans

Hydrophobins are small self-assembling proteins produced by fungi. A class I hydrophobin secreted by the basidiomycete fungus Pleurotus ostreatus was purified and identified. The pure protein is not water soluble, whereas complexes formed between the protein and glycans, produced in culture broth containing amylose, are soluble in water. Glycan structure matched to cyclic structures of alpha-(1-4) linked glucose containing from six to 16 monomers (cyclodextrins). Moreover, it was verified that not only pure cyclodextrins but also a linear oligosaccharide and even the simple glucose monomer are able to solubilize the hydrophobin in water. The aqueous solution of the protein-in the presence of the cyclic glucans-showed propensity to self-assembly, and conformational changes towards beta structure were observed on vortexing the solution. On the other hand, the pure protein dissolved in less polar solvent (60% ethanol) is not prone to self assembly, and no conformational change was observed. When the pure protein was deposited on a hydrophobic surface, it formed a very stable biofilm whose thickness was about 3 nm, whereas the biofilm was not detected on a hydrophilic surface. When the water-soluble protein-in the presence of the cyclic glucans-was used, thicker (up to 10-fold) biofilms were obtained on either hydrophilic or hydrophobic surfaces.

Fast bistable nematic display with grey scale

We present a novel principle for a fast bistable nematic display with intrinsic grey scale. The geometry of a single pixel is the usual hybrid texture in between two conductive flat plates. The device is written by creating surface walls when an electric field is applied, above the thresholds to achieve both the planar anchoring breaking and an electro-hydrodynamic flow. Erasing is obtained by simply breaking the anchoring in absence of vortices. The distorted regions around surface walls depolarize the incident light. As the surface defect density can be modulated, a grey scale is achieved.

BISTABLE NEMATIC AZIMUTHAL ALIGNMENT INDUCED BY ANCHORING COMPETITION

We present a novel method to obtain bistable azimuthal anchoring conditions for nematic liquid crystals. The fine control of the anchoring strengths of two independent planar surface anchoring attractors, perpendicular to each other, induces controlled surface transitions that give bistability. The independent anchoring sources are obtained by means of a composite surface made with a film of photopolymer on an anisotropic SiO layer. A phenomenological model, based on anchoring competition between the two orienting layers, is developed to describe the surface bistability.

Langmuir−Blodgett Film of Hydrophobin Protein from Pleurotus ostreatus at the Air−Water Interface

We present results concerning the formation of Langmuir-Blodgett (LB) films of a class I hydrophobin from Pleurotus ostreatus at the air-water interface, and their structure as Langmuir-Blodgett (LB) films when deposited on silicon substrates. LB films of the hydrophobin were investigated by atomic force microscopy (AFM). We observed that the compressed film at the air-water interface exhibits a molecular depletion even at low surface pressure. In order to estimate the surface molecular concentration, we fit the experimental isotherm with Volmers equation describing the equation of state for molecular monolayers. We found that about (1)/ 10 of the molecules contribute to the surface film formation. When transferred on silicon substrates, compact and uniform monomolecular layers about 2.5 nm thick, comparable to a typical molecular size, were observed. The monolayers coexist with protein aggregates, under the typical rodlet form with a uniform thickness of about 5.0 nm. The observed rodlets appear to be a hydrophilic bilayer and can then be responsible for the surface molecular depletion.

Optical characterization of liquid crystals by combined ellipsometry and half-leaky-guided-mode spectroscopy in the visible-near infrared range

In this paper, we present our results for the anisotropic refractive index measurements of commonly used liquid crystal (LC) materials (E7 and 5CB) in the whole visible–near infrared range. In order to achieve a high accuracy in the obtained values, we have employed a combination of two techniques, namely, Mueller matrix spectroscopic ellipsometry in transmission and half-leaky-guided-mode (HLGM). Measurements with the HLGM technique are usually performed at a single wavelength. In order to obtain a spectroscopic measurement based on the HLGM technique in a wide wavelength range, we modified our commercial VASE® ellipsometer. In particular, we designed a sample holder by means of which measurements in guiding structures are also possible. Thus, we take advantage of the wide-spectrum light, emitted from a standard Xe lamp of the ellipsometer, also in the HLGM setup. The complementary and in-one-setup utilization of both techniques has allowed us to overcome most of the problems previously encountered in ap...

Self-Assembly of Hydrophobin Protein Rodlets Studied with Atomic Force Spectroscopy in Dynamic Mode

We have investigated the self-assembling properties of the class I hydrophobin Vmh2 isolated from the fungus Pleurotus ostreatus. Five different hydrophobin self assembled samples including monolayers, bilayers, and rodlets have been prepared by Langmuir technique and studied at the nanoscale. Local wettability and visco-elasticity of the different hydrophobins samples were obtained from atomic force spectroscopy experiments in dynamic mode performed at different, controlled relative humidity (RH) values. It was found that hydrophobins assembled either in rodlets or in bilayer films, display similar hydropathicity and viscoelasticity in contrast to the case of monolayers, whose hydropathicity and viscoelasticity depend on the adopted preparation method (Langmuir-Blodgett or Langmuir-Schaeffer). The comparison with monolayers properties evidences a rearrangement of the bilayers adsorbed onto solid substrates. It is shown that this rearrangement leads to the formation of a stable hydrophobic film, and that the rodlets structure consists in fragments of restructured proteins bilayers. Our results support the hypothesis that the observed variations in the viscoelastic properties could be ascribed to the localization of the large flexible loop, typical of Class I hydrophobins which appears free at the air interface for LB monolayers but not for the other samples. These findings should now serve future developments and applications of hydrophobin films beyond the archetypal monolayer.

Ellipsometric Study of Liquid Crystal Infiltrated Porous Silicon

Porous silicon (PS) based devices are nowadays under an intense and widespread investigation in the optoelectronic and sensing fields. Recently, the range of possible applications has been widened by the use of the liquid crystals (LCs), which can be infiltrated in the PS sponge-like structure. The large changes of the optical properties, as exhibited by LCs under the action of electrical or thermal fields, allow developing a new family of optical devices like tunable PS based multilayer mirrors, microcavities and optical filters. In this work, we have optically characterized the LC-PS heterogeneous composite as a guest-host system by means of the variable angle spectroscopic ellipsometry (VASE). A PS layer, 450 nm thick, has been infiltrated with the nematic LC 5CB, and the main optical parameters, anisotropic refractive indices and thickness of both materials, have been estimated below and above the isotropic transition temperature, at 27.0°C and 38.0°C respectively. We have found a clear indication that the LC molecules tend to align parallel to the direction of the pore columns.

Light manipulation of nanoparticles in arrays of topological defects

We report a strategy to assemble and manipulate nanoparticles arrays. The approach is based on the use of topological defects, namely disclination lines, created in chiral liquid crystals. The control of nanoparticle-loaded topological defects by low power light is demonstrated. Large-scale rotation, translation and deformation of quantum dots light-emitting chains is achieved by homogeneous LED illumination. Full reconfigurability and time stability make this approach attractive for future developments and applications.

High accuracy optical characterization of anisotropic liquids by merging standard techniques

The design and fabrication of active and passive hybrid photonic devices, with tunable optical properties, based on liquid crystals require a very accurate knowledge of their anisotropic refractive indices up to 100ppm in the wavelength region of interest. At this aim, the authors have integrated two standard optical techniques commonly used in liquid crystals characterization, the variable angle spectroscopic ellipsometry and the half leaky guided mode spectroscopy, exploiting their best performances and overcoming their limits. The dispersion curves of nematic liquid crystal E7 have been estimated in the 450–1700nm wavelength interval with both precision and accuracy of 10−4.

Nematic anchoring transitions on bistable SiO films driven by temperature and impurities

The influence of temperature and impurities on the surface orientation of nematic 5CB on obliquely SiO evaporated glass plates has been studied. We observe on cooling a continuous anchoring transition from the planar alignment to the tilted one. The experimental data have been interpreted by using elastic models developed by Durand and coworkers in which the surface order parameter can vary in space, close to the surface.