Fe3O4/γ-Fe2O3 nanoparticle multilayers deposited by the Langmuir-Blodgett technique for gas sensors application.

Fe3O4/γ-Fe2O3 nanoparticles (NPs) based thin films were used as active layers in solid state resistive chemical sensors. NPs were synthesized by high temperature solution phase reaction. Sensing NP monolayers (ML) were deposited by Langmuir-Blodgett (LB) techniques onto chemoresistive transduction platforms. The sensing ML were UV treated to remove NP insulating capping. Sensors surface was characterized by scanning electron microscopy (SEM). Systematic gas sensing tests in controlled atmosphere were carried out toward NO2, CO, and acetone at different concentrations and working temperatures of the sensing layers. The best sensing performance results were obtained for sensors with higher NPs coverage (10 ML), mainly for NO2 gas showing interesting selectivity toward nitrogen oxides. Electrical properties and conduction mechanisms are discussed.

Silver nanoparticle monolayer-to-bilayer transition at the air/water interface as studied by the GISAXS technique: application of a new paracrystal model.

An original diffraction model for the analysis of grazing-incidence small-angle X-ray scattering (GISAXS) from the nanoparticle Langmuir films was developed. This model relies on the concept of the 2D hexagonal paracrystal and employs the distorted-wave Born approximation that is relevant for GISAXS measurements at the air/water interface when the angle of incidence is close to the critical value. The model comprises the cases of the close-packed nanoparticle monolayer and bilayer with the AB-type layer stacking. In this way, both the lateral (along the interface) and vertical (normal to the interface) correlations of the nanoparticle positions can be analyzed. The model was applied to an in situ GISAXS study of the formation of a silver nanoparticle Langmuir film during compression at the air/water interface in the Langmuir-Blodgett trough. Spherical nanoparticles of 5.8 ± 0.6 nm diameter were employed. Different compression stages starting from the submonolayer up to the monolayer collapse via bilayer formation were analyzed in terms of the mean lateral interparticle distance, degree of paracrystal disorder, interlayer distance, vertical disorder, and layer-stacking type in the bilayer as well as the ratio between the monolayer and bilayer coverage in the final film. The model developed is applicable to any nanoparticle Langmuir film formed at the air/liquid interface to extract structural parameters on the nanoscale. The particular results obtained have direct implications on the preparation of silver plasmonic templates with "hot spots" for surface-enhanced Raman scattering.

GISAXS analysis of 3D nanoparticle assemblies--effect of vertical nanoparticle ordering.

We report on grazing-incidence small-angle x-ray scattering (GISAXS) study of 3D nanoparticle arrays prepared by two different methods from colloidal solutions-layer-by-layer Langmuir-Schaefer deposition and spontaneous self-assembling during the solvent evaporation. GISAXS results are evaluated within the distorted wave Born approximation (DWBA) considering the multiple scattering effects and employing a simplified multilayer model to reduce the computing time. In the model, particular layers are represented by nanoparticle chains where the positions of individual nanoparticles are generated following a model of cumulative disorder. The nanoparticle size dispersion is considered as well. Three model cases are distinguished-no shift between the neighboring chains (AA stacking), a shift equal to half of the mean interparticle distance (AB stacking) and random shift between the chains. The first two cases correspond to vertically correlated nanoparticle positions across different chains. A comparison of the experimental GISAXS patterns with the model cases enabled us to distinguish important differences between the 3D arrays prepared by the two methods. In particular, laterally ordered layers without vertical correlation of the nanoparticle positions were found in the nanoparticle multilayers prepared by the Langmuir-Schaefer method. On the other hand, the solvent evaporation under particular conditions produced highly ordered 3D nanoparticle assemblies where both laterally and vertically correlated nanoparticle positions were found.

Coxsackievirus infection of mice. I. Viral kinetics and histopathological changes in mice experimentally infected with coxsackieviruses B3 and B4 by oral route.

We followed the viral kinetics and histopathological changes in different organs of immunocompetent mice infected orally with coxsackieviruses B3 (CVB3) Nancy strain and B4 (CVB4) JVB strain separately. The viruses used were not adapted to mouse organs. In the acute phase of infection, the viral kinetics indicated virus replication in the heart, spleen, thymus, pancreas, and small and large intestines. This was accompanied by histopathological changes, mild infiltration of mononuclear cells and fibrosis in the heart. The necrotic changes with mononuclear infiltration and fibrosis in the myocard was observed on days 56 and 71 p.i. in the CVB4-infected animals only. In the mice infected with CVB3 and CVB4 a prolonged presence of infectious virus was shown in the spleen and small intestine; in the latter viral antigen was localized in smooth muscles of the muscular wall immunohistochemically. This is the first report on prolonged replication of coxsackieviruses (CV) in the spleen and small intestine in orally infected mice.

Coxsackievirus infection of mice. II. Viral kinetics and histopathological changes in mice experimentally infected with coxsackievirus B3 by intraperitoneal route.

The study was focused on kinetics of Coxsackievirus B3 serotype (CVB3) in different organs of Swiss albino mice following intraperitoneal (i.p.) infection. The results indicated that the virus replicated in the heart, spleen, thymus, pancreas, small and large intestines in the acute stage of the infection. Infectious virus was present in the spleen till day 35 post infection (p.i.). Histopathology of the hearts showed mild foci of infiltration of mononuclear cells in the acute stage of infection and massive inflammation of exocrine pancreas on day 5 p.i. These results, when compared to those of our previous study (Bopegamage et al., 2003), suggest that the pathogenesis of the disease may be influenced by the route of virus administration into the host.