Controlled assembly of Ag nanoparticles and carbon nanotube hybrid structures for biosensing

Here we report a chemical-free, simple, and novel method in which a part from a silver-based anode is controllably used in a straightforward manner to produce silver nanoparticles (Ag NPs) in order to fabricate a controlled assembly of Ag NPs and single walled carbon nanotube (SWCNT) hybrid structures. The attachment and distribution of Ag NPs along SWCNTs have been investigated and characterized by field emission scanning electron microscopy (FESEM). We have achieved the decoration of SWCNTs with different densities of Ag NPs by changing the deposition time, the applied voltage, and the location of carbon nanotubes with respect to the anode. At low voltage, single silver nanoparticle is successfully attached at the open ends of SWCNTs whereas at high voltage, intermediate and full coverage densities of Ag NPs are observed. As voltage is further increased, fractals of Ag NPs along SWCNTs are observed. In addition, a device based on a Ag NPs-SWNT hybrid structure is used for the label-free detection of ssDNA molecules immobilized on it. We believe that the proposed method can be used to decorate and/or assemble metal nanoparticles or fractal patterns along SWCNTs with different novel metals such as gold, silver, and copper and can be exploited in various sensitive applications for fundamental research and nanotechnology.     

Allylation of N‐Benzoylhydrazones (=N′‐Alkylidene‐Substituted Benzohydrazides) by Treatment with Allyl Bromide in the Presence of Zinc in Aqueous Ammonium Chloride Solution

N‐Benzoylhydrazones (=N′‐alkylidene‐substituted benzohydrazides) 1 are allylated efficiently by reaction with allyl bromide ( 2 ) in the presence of Zn in aqueous NH₄Cl solution. The products 3 are formed in excellent yields (85–94%) within 35–50 min (Scheme, Table).     

Ultrasonic and Volumetric Study of N–H Bond Complexes in Binary Mixtures

Experimental values of the density and ultrasonic velocity have been measured for binary mixtures of butylamine with 1-butanol and with tert-butanol at temperatures of 293.15, 303.15 and 313.15 K over the entire mole fraction range. From these data, the excess molar volumes, deviations in isentropic compressibility, excess internal pressures, and excess molar enthalpies have been calculated. All of the excess functions were fitted to Redlich-Kister polynomial relations to estimate the adjustable parameters along with the standard deviations of the fits. The variations of these excess functions with mole fraction of butylamine have been examined. The changes in these parameters with composition suggest that the interaction between butylamine and 1-butanol is strong, whereas its interaction with tert-butanol is weak. Further, the partial molar volumes and partial molar compressibilities at infinite dilution have also been evaluated since these parameters provide better insight for studying intermolecular interactions.     

Phase transitions of AlFeO3 and GaFeO3 from the chiral orthorhombic (Pna2(1)) structure to the rhombohedral (R3c) structure

AlFeO(3) and GaFeO(3), which crystallize in a chiral orthorhombic (Pna2(1)) structure, transform to a rhombohedral (R3c) structure when subjected to ball-milling. There is a distinct difference between the transformations of AlFeO(3) and GaFeO(3). AlFeO(3) first transforms to an orthorhombic P2(1)2(1)2(1) structure followed by its transformation to the R3c structure, while GaFeO(3) goes directly to the R3c structure. The transformations have been characterized by X-ray diffraction and Raman spectroscopy. Magnetic properties of Pna2(1) and the transformed phases show significant differences. It is noteworthy that partial substitution of aluminum by gallium in AlFeO(3) as in Al(0.5)Ga(0.5)FeO(3) eliminates the intermediate P2(1)2(1)2(1) phase, causing direct transformation of the Pna2(1) structure to the R3c structure. All of the transformations are thermodynamically first-order associated with significant changes in volume. We have used first-principles simulations to determine the pressure-dependent properties of AlFeO(3) and GaFeO(3) in orthorhombic and corundum structures and have estimated the critical pressures for the structural phase transition between the two structures. On the basis of this information, we also comment on the differences in the behavior of AlFeO(3) and GaFeO(3) under ball-milling.     

Multiple dynamical time-scales in networks with hierarchically nested modular organization

Many natural and engineered complex networks have intricate mesoscopic organization, e.g., the clustering of the constituent nodes into several communities or modules. Often, such modularity is manifested at several different hierarchical levels, where the clusters defined at one level appear as elementary entities at the next higher level. Using a simple model of a hierarchical modular network, we show that such a topological structure gives rise to characteristic time-scale separation between dynamics occurring at different levels of the hierarchy. This generalizes our earlier result for simple modular networks, where fast intramodular and slow intermodular processes were clearly distinguished. Investigating the process of synchronization of oscillators in a hierarchical modular network, we show the existence of as many distinct time-scales as there are hierarchical levels in the system. This suggests a possible functional role of such mesoscopic organization principle in natural systems, viz., in the dynamical separation of events occurring at different spatial scales.     

Application of wavelet filtering techniques to Lau interferometric fringe analysis for measurement of small tilt angles

This communication presents the results of investigation undertaken towards testing the viability of wavelet filtering techniques in analyzing the Lau interferometric fringes. Towards this, the applicability of Haar, Daubechies and Symlet wavelet based filtering schemes have been tested. Of these schemes, the Symlet based filtering scheme gives the best results in terms of improved signal to noise ratio. This scheme is then used to analyze Lau interferograms recorded in the experimental arrangement for tilt angle measurement. The processed interferograms yield improved accuracy and precision of measurement.     

Ultrastructure of the human retina in aging and various pathological states

Vision is hampered in aging and diseases, such as age-related macular degeneration, retinitis pigmentosa, diabetic retinopathy and glaucoma. This review collates the fine structural alterations of the human retina in aging and various pathological situations and their links to the disease pathogenesis. It transpires that most changes occur at the level of the retinal pigment epithelium -Bruch's membrane and the photoreceptor layer, causing visual problems to the sufferers. These changes include loss of normal, essential features of these cells and their gradual disappearance. It is important to understand in depth the selective vulnerability of this retinal region to alterations in aging and diseases. Evidence indicates that some of these changes may be mediated by the effects of oxidative stress, inflammation, and chronic light exposure. There are changes also in the inner retinal layers, wherein hypertension, auto-immunity, hypoxia and ischemia could play significant roles in disease pathogenesis. Results of extensive research utilizing animal models have broadened our idea about photoreceptor pathology. However, equivalent knowledge on various changes in aging human retina and in dystrophies that affect the macula is not complete. Since cone photoreceptor and ganglion cell death are a potential problem, it is imperative to know about the basic facts on how they are affected and the mechanisms involved in their death. Thus, prevention of cone and ganglion cell loss should be the target of choice. This review also highlights the significant role played by electron microscopy in understanding such ultrastructural changes and future strategies utilizing it and other techniques to fill some of the existing lacunae and advance our knowledge.