Probing of Competitive Displacement Adsorption of Casein at Oil-in-Water Interface Using Equilibrium Force Distance Measurements.

The equilibrium force distance measurement is employed for the first time to probe the competitive and displacement adsorption of casein at an oil-water (O/W) emulsion interface that was initially adsorbed with either a diblock polymer or an anionic surfactant. A significant change in the force-distance profile was observed under the competitive displacement adsorption of casein, which is further confirmed from the hydrodynamic diameter and zeta potential measurements. A decrease in the onset of repulsion and decay length are observed on competitive adsorption of smaller size casein molecules at O/W interface. With addition of casein in PVA-vac diblock polymer stabilized emulsion, the onset of repulsion decreases from 88 to 48 nm whereas the magnitude of force increases from 1 to 19 nN. The force decay length is reduced from 10.5 to 4.5 nm upon addition of casein. Our results suggest the complete replacement of adsorbed diblock polymers by casein molecules. The hydrodynamic diameter and zeta potential measurements corroborate the casein mediated polymer displacement and the competitive adsorption of casein at the O/W interface. In the case of anionic surfactant covered O/W interfaces, casein molecules weakly associate at the interface without displacing the smaller size surfactant molecules where no significant changes in the onset repulsion and force profiles are observed. These results suggest that the casein molecules are effective displacers for replacement of adsorbed macromolecules from formulations, which has several important practical applications.

Influence of Ag+ interaction on 1D droplet array spacing and the repulsive forces between stimuli-responsive nanoemulsion droplets.

This paper reports results on the effect of interaction of Ag(+) on 1D droplet array spacing and the repulsive forces between stimuli-responsive nanoemulsion droplets, stabilized with an anionic surfactant--sodium dodecyl sulfate--and a diblock polymer--poly(vinyl alcohol)-vinyl acetate. The repulsive interaction is probed by measuring the in-situ equilibrium force-distance in the presence of Ag(+) using the magnetic chaining technique. At a constant static magnetic field, emulsion droplets form 1D array that diffract visible light. A large blue-shift in the diffracted light is observed in the presence of interacting Ag(+) because of the reduction in the interdroplet spacing within the 1D array. The in-situ equilibrium force-distance measurement results show that the onset of repulsions and magnitude of repulsive forces are strongly influenced by the presence of Ag(+) in ppb levels. This suggests that the Ag(+) ions screen the surface charges through the formation of both Stern and diffuse electric double layer and produces a dramatic blue-shift in surfactant-stabilized emulsion, whereas a dramatic conformational change in the adsorbed polymer layer causes a reduction in the 1D array spacing in the diblock polymer stabilized emulsion. The force-distance results are compared with the predictions of electrical double-layer and repulsive steric forces. The droplet array shows an excellent selectivity to Ag(+) due to the strong interaction of Ag(+) with the stabilizing moieties at the oil-water interface. The possible mechanisms of interaction of Ag(+) with surfactant and polymer are discussed. The dramatic decrease in the 1D array spacing in the presence of Ag(+) may find promising practical applications in the development of optical sensors for selective detection of cations with ultrahigh sensitivity.

Microwave assisted synthesis of magnetite nanoparticles.

Magnetite nanoparticles of size ranging from 7-10 nm are prepared from aqueous solutions of Fe2+ and Fe3+ by microwave irradiation at different reaction temperatures ranging from 50 to 200 °C. The effect of reaction temperature on the structural and magnetic properties of nanoparticles is studied using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Small angle X-ray scattering (SAXS), Thermo gravimetry (TGA), Differential scanning calorimetry (DSC), Vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR) techniques. The average size of the prepared particles, obtained from SAXS, is found to vary from 11 to 15±1 nm as the reaction temperature is increased from 50 to 200 °C. The weight gain curves under an external magnetic field show slope changes at 300 and 596 °C because of the magnetite to maghemite phase transition and ferri to paramagnetic phase transitions, respectively. The ferromagnetic γ-Fe2O3 to antiferromagnetic α-Fe2O3 phase transition temperature is found to be enhanced by 154 °C for the nanoparticles prepared at 200 °C, due to an enhanced activation energy for the cubic to a more compact hexagonal transition. The increase in the phase stability of nanoparticles prepared at elevated temperature is attributed to the diffusion of Na+ in the spinel structure. These results are useful to tailor magnetic particles with enhanced thermal stability for practical applications.

Sensing of biologically important cations such as Na(+), K(+), Ca(2+), Cu(2+), and Fe(3+) using magnetic nanoemulsions.

We report a simple approach to the ultrasensitive detection of biologically important metal ions using a magnetic nanoemulsion. The nanoemulsion used in our study was an oil-in-water emulsion droplet of average size ∼190 nm containing ferrimagnetic iron oxide nanoparticles of average size ∼10 nm. In a static magnetic field, the emulsion droplets self-assemble into a nanoarray with distinct interdroplet spacing. In the presence of cations in the solution, the nanofluid array shows a large blue shift in the diffracted Bragg peak and a visually perceivable color change due to changes in the electrical double layer upon the diffusion of cations. The colloidal force-distance measurements in the presence of cations show large variations at the onset of repulsion in the presence of cations. The sensor shows good selectivity to Na(+), K(+), Ca(2+), Cu(2+), and Fe(3+) ions and offers a rapid response compared to conventional techniques. This approach can be useful for the recognition of biologically important cations.

A sensitive micro-platelet ELISA technique for screening anti-HLA antibodies.

An enzyme-linked immunosorbant assay (ELISA) in a Terasaki plate (Micro-Platelet ELISA), using 30000 platelets per well, 2 microL primary antibody (anti HLA antiserum) and 5 microL of secondary antibody (1:2000) are described. Platelets from 30 selected HLA tissue typed cell panel individuals were used to characterize anti HLA A and B antibodies. The first half of the Terasaki tray had platelets in sequence to characterize anti HLA antibodies, while the second half contained anti HLA B antibodies. Results revealed that the HLA specificities of the sera identified by micro-platelet ELISA and microlymphocytotoxicity were concordant. Moreover, split antigens of broader specificities were identified in the Platelet ELISA technique. The advantages of micro-platelet ELISA technique were: (i) it does not require viable/frozen lymphocytes, (ii) reading is very simple and macroscopic, (iii) specificity of the serum is identified with accuracy within the same day, (iv) avoids inter-cell, inter-day variations, (v) complement is not required, (vi) requires only 1/50 volume of the reagents required by conventional ELISA in microtitre plates, and (vii) using platelets isolated from 5 mL of peripheral blood, fifteen thousand sera can be tested. This technique is, thus, very simple, cost effective, and very much suitable for any developing HLA laboratory, which is in the process of developing indigenous HLA reagents.

Sociobiology and HLA genetic polymorphism in hill tribes, the Irula of the Nilgiri hills and the Malayali of the Shevroy hills, south India.

Two endogamous tribes of Tamil Nadu, South India, the Irula of the Nilgiri hills and the Malayali of the Shevroy hills, were studied for their sociobiology and HLA polymorphism. For sociobiological studies 166 marriages in the Irula and 368 marriages in the Malayali were recorded. The number and spatial distribution of patrilineal clans and their marriageable range (number of clans from which the brides came) were studied. Eight clans in the Irula and 16 clans in the Malayali were identified. Of these the Kuppar of the Irula and the Malayan of Malayali were the largest clans, and both of them had the greatest marriageable range. The numerical strength and the resultant spatial distribution correlated well with the marriageable range. HLA-A, B, and DR polymorphism was studied on 191 Irula and 42 Malayali following standard procedures. HLA typing revealed high frequencies (> 10%) of alleles HLA-A2, A9, A11, B17, B35, B40, DR2, and DR7 in both tribes, but the Irula had elevated HLA-A10, B8, and DR8 frequencies and the Malayali had elevated HLA-A31, B7, DR4, and DR5 frequencies. Two-locus haplotypes A10-B8 and A2-B5 were identified in both tribes, but A11-B40 and A2-B53 were present only in the Irula and A33-B44 and B15-DR6 were present only in the Malayali. The sociobiology of the Irula was correlated to the HLA genetic profile. The Irula sample was stratified based on clan and HLA data; The Kuppar clan was closer to the Kalkatti, the second largest clan, than to the Pungar and the Sambar clans. Thus the numerical strength and spatial distribution of various exogamous clans, presumably a result of migration during different periods of history, is reflected in the marriageable range and thus in the genetic distance. In studying HLA or any other genetic polymorphism of an endogamous tribe or caste, one needs to consider the social structure, spatial distribution, and marriageable range.

HLA Bw57 and DR7 association with psoriasis vulgaris in south India.

Eighty-three south Indian patients with psoriasis vulgaris were studied for HLA antigen frequencies and compared with 77 controls studied simultaneously. HLA Bw57, a split of B17 was found elevated in the patients. The two sexes differed in their age-at-onset curves: females had a preponderance to early onset of the disease, while the males had late onset. Among these patients, major group 3, a Western Brachycephal Armenoid group, revealed the highest risk for B17 & Bw57 but not major group 2, a Mediterranean one.