Mechanistic Study of Amphiphilic-Assisted Self-Assembled Cadmium Sulfide Quantum Dots into 3D Superstructures

Self-assembling of nanoparticles into complex superstructures is very challenging, which usually depends on postorganizing techniques or pre-existing templates such as polypeptide chains or DNA or external stimulus. Such self-assembled processes typically lead to close-packed structures. Here, it has been demonstrated that under carefully template-free reaction conditions CdS quantum dots (QDs) could be synthesized and simultaneously self-assembled into complex superstructures without compromising individual QD properties. The superstructures of CdS QDs attained by the chemical-based method demonstrate Stokes-shifted photoluminescence (PL) from trap states. Remarkably, the PL decay of superstructures exhibits a single-exponential feature. This behavior is unusual for the synthesized superstructures, indicating that the trap states are restricted to a narrow range. The growth mechanism of these superstructures is explained through the formation of liquid crystal phases (LCPs) with the help of a small-angle X-ray scattering (SAXS) analysis.

Spherical Silver Nanocrystals Arranged in a Metastable Square Pattern

The present article demonstrates the development of two-dimensional (2D) assembly of spherical nanocrystals (NCs) in the square arrangement through the delicate balance between repulsive ligand interactions and attractive van der Waals interactions of NCs, respectively, instead of the otherwise stable hexagonal arrangement. The experimental packing efficiency values matched quite well with the theoretically calculated square arrangement patterns. The above fact indicates that the formation of the 2D square arrangement of silver NCs can be explained by introducing the concept of softness to NCs in the hard sphere model.

Exciton Dynamics in Colloidal CdS Quantum Dots with Intense and Stokes Shifted Photoluminescence in a Single Decay Channel

CdS quantum dots (QDs), synthesized by a sol-gel method, exhibit significantly Stokes shifted bright photoluminescence (PL), predominantly from the trap states. Surprisingly, the PL decay at the emission maximum is single-exponential. This is an unusual observation for as-prepared QDs and indicates a narrow distribution in the nature of trap states. A closer look reveals an additional fast component for the decays at shorter emission wavelengths, presumably due to the band edge emission, which remains elusive in the steady-state spectra. Indeed, a significantly narrower and blue-shifted emission band is observed in the decay-associated spectra. The contribution of this component to the steady-state PL intensity is shown to be overwhelmed by that of the significantly stronger trap emission. Exciton dynamics in the quantum dots is elucidated using transient absorption spectra, in which the stimulated emission is observed even at low pump power.

Voltage Stimulated Anion Binding of Metalloporphyrin-induced Crystalline 2D Nanoflakes

Voltage-stimulated redox-active materials have received significant attention in the field of organic electronics and sensor technology. Such stimuli-responsive materials trigger the formation of crystalline nanostructures and facilitate the design of efficient smart devices hitherto unknown. Herein, we report that free-base and metallo-tetratolylporphyrin-linked ferrocene derivatives (H₂ TTP-Fc and ZnTTP-Fc) undergo distinct proton/anion binding mechanism in CHCl₃ during bulk electrolysis at applied voltage of 1.4 V to give [H₄ TTP-Fc]⁺ Cl^- and H⁺ [(Cl)ZnTTP-Fc]^- followed by nanospheres and crystalline 2D nanoflakes formation, confirmed by SEM and TEM images, by methanol vapor diffusion (MVD) approach. Moreover, X-ray diffraction analysis suggest that protonated H₂ TTP-Fc aggregates exhibit amorphous nature, whereas H⁺ [(Cl)ZnTTP-Fc]^- depict crystalline nature from layer-by-layer arrangement of nanoflakes assisted by π-π stacking and ion-dipole interactions.

Cutting edge: editing of recycling class II:peptide complexes by HLA-DM

HLA-DM catalyzes the exchange and selection of ligands for MHC class II molecules within mature endosomal/lysosomal compartments. Here, evidence is provided that DM edits peptides in early endosomes, thus influencing presentation via recycling class II molecules. Maximal class II-restricted presentation of an albumin-derived peptide, dependent on endocytosis and recycling class II molecules, was observed in cells lacking HLA-DM. DM editing of this epitope was observed in early endocytic compartments as shown using inhibitors of early to late endosomal transport. Editing was tempered by coexpression of HLA-DO, suggesting that DM:DO ratio may be important in guiding epitope editing in early endosomal compartments. Thus, HLA-DM appears to interact with, and edit epitopes displayed by, recycling class II molecules.

Endocytic recycling is required for the presentation of an exogenous peptide via MHC class II molecules

Exogenous antigenic peptides captured and presented in the context of major histocompatibility (MHC) class II molecules on APC, have been employed as potent vaccine reagents capable of activating cellular immune responses. Binding and presentation of select peptide via surface class II molecules has been reported. Here, a role for endocytosis and early endosomes in the presentation of exogenous peptides via MHC class II molecules is described. T cell recognition of a 14 amino acid human serum albumin-derived peptide in the context of HLA-DR4 was observed only with metabolically active APC. The delayed kinetics and temperature dependence of functional peptide presentation via APC, were consistent with a requirement for peptide internalization to early endosomal compartments prior to T cell recognition. Ablating endocytosis by exposing cells to inhibitors of ATP production completely blocked the display of functional peptide:class II complexes on the surface of the APC. Presentation of the peptide was also found to be sensitive to primaquine, a drug that perturbs the recycling of transport vesicles containing endocytic receptors and mature class II complexes. Functional presentation of the endocytosed peptide was dependent upon these mature class II complexes, as inhibitor studies ruled out a requirement for newly synthesized class II molecules. N-terminal processing of the endocytosed peptide was observed upon trafficking through endosomal compartments and linked to the formation of functional peptide:class II complexes. These findings establish a novel mechanism for regulating class II-restricted peptide presentation via the endocytic pathway.

Biosensors in immunology: the story so far

In conclusion, biosensors are versatile tools with a range of applications. With a thorough knowledge of possible artefacts and limitations, it possible to perform assays that were heretofore not practicable in immunology.

Peak expiratory flow rate of carpet weaving children

OBJECTIVE

To assess the adverse influence of carpet weaving on lung functions and the nurtritional status of children employed in such factories.

DESIGN

Comparison of the peak expiratory flow rate (PEFR) of the study group with controls of similar socio-economic status and correlate it with anthropometric values.

SETTING

Field study.

SUBJECTS

One hundred and ten boys, 6-15 years of age engaged in 23 carpet weaving factories of Jaipur city.

OUTCOME MEASURES

Linear regression analysis using age, height and weight as independent variables and PEFR as the dependent variable.

RESULTS

PEFR of carpet weaving children were significantly lower (p < 0.05) than controls for all except 6-7 years group. The height, weight and chest circumference of these children were also lower (p < 0.05). PEFR did not show significant difference when children were grouped according to their height.

CONCLUSIONS

Children working in carpet weaving factories are shorter and lighter compared to normal school going children. As a consequence of the growth retardation, their PEFR values were also lower as compared to normal children.

Health status of carpet weaving children

A cross-sectional study was undertaken to determine the health status of children engaged in carpet weaving factories of Jaipur City. Two hundred and ninety school going boys of similar socio-economic status served as controls. A higher prevalence of signs of nutritional deficiencies was observed in carpet weaving children. Analysis of the presenting complaints and the illness suffered in the past six months also revealed a significantly higher morbidity in these children. A statistically significant difference was also observed in anthropometric measurements of the two groups.

Terasaki-ELISA for murine IgE. III. Determination of concentration and functional affinity by sequential equilibrium binding analysis

A simple Terasaki tray-based ELISA technique with a fluorescent detecting system has been used to determine the affinity of murine IgE antibodies. The system was shown to be sensitive enough to measure affinities in the range of 10(-6)-10(-10) M as well as detect IgE antibodies down to a limit of 0.1 ng/ml. The results, expressed as arbitrary fluorescence units (AFU), were compared with those obtained using equilibrium dialysis for several DNP-specific IgE monoclonal antibodies of known affinities yielding KD values. The relationship between KAFU and KD established a conversion factor which could then be used to compute KD from KAFU, provided the detection system remained identical. Based on the equations proposed, an alternative method for the quantitation of murine IgE is described which is independent of the affinity of IgE for the coated antigen.

Terasaki-ELISA for murine IgE antibodies. II. Quantitation of absolute concentration of antigen-specific and total IgE

A Terasaki tray-based ELISA system was developed for the quantitative measurement of antigen-specific and total IgE antibodies in 5 microliter samples of mouse serum dilutions. The assay was based upon non-competitive binding of mouse IgE antibodies between the immobilized appropriate antigen or capture antibodies and the detecting rabbit antibodies. A conjugate of protein A-labelled beta-galactosidase and the fluorigenic substrate methylumbelliferyl-beta-D-galactoside were used as a detecting system. The resulted fluorescence could be measured rapidly and automatically using an inverted micro-fluorimeter. These measurements were automatically transformed into absolute concentrations by a microprocessor-based program using a four-parameter logistic function and an absolute IgE standard. The assay was shown to have a detection limit of 0.04 ng/ml and a range of linearity of 0.04-20 ng/ml, which is sufficient to measure IgE concentrations in mouse serum.