Gopes Chandra Das

Review: biofunctionalized quantum dots in biology and medicine

Quantum dot (QD) nanocrystals which have important optical properties, in particular, the wavelength of their fluorescence, depend strongly on their size. Colloidal QDs once dispersed in a solvent are quite interesting fluorescence probes for all types of labelling studies because of their reduced tendency to photo bleach. In this review, we will give an overview on how QDs have been used so far in cell biology. In particular, we will discuss the biologically relevant properties of QDs and focus on four topics: labeling of cellular structures and receptors with QDs, incorporation of QDs by living cells, tracking the path and the fate of individual cells using QD labels, and QDs as contrast agents. QDs are seen to be much better in terms of efficacy over radioisotopes in tracing medicine in vivo. They are rapidly being applied to existing and emerging technologies but here this review deals with a comprehensive compilation of the biological relevance of quantum dots. It covers important information from 1999 till 2008 with few from 1982 to 1997.

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Abstract Silicon nitride (Si3 N4) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si3 N4 nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ∼500 nm diameter and ∼0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.

Preparation of glass-nickel microcomposites byin situ reduction via sol-gel route

Gel has been prepared with nickel chloride and glucose in the starting solution followed by heat treatment at higher temperature, where glucose decomposes to carbon and water vapour, which in turn react to form hydrogenin situ to reduce nickel chloride to metallic nickel. The presence and distribution of nickel granules in the microcomposite, has been established by transmission electron microscopy, selected area diffraction and electron paramagnetic resonance analysis.

Microstructure dependent hardness and fracture behavior in liquid-phase-sintered Al2O3

Abstract The liquid-phase-sintered Al 2 O 3 (LPS) derived from commercial powders of different particle size, e.g. coarse (70–100 μm), medium (3.6–7.0 μm) and reactive ( 2 O 3 into the glassy phase. A high flexural strength was achieved with the LPS of medium powder. A high K ic-short always resulted either due to (i) the MgO/(CaO+BaO+KNaO) ratio of nearly 1 in the chemical composition of LPS, or (ii) higher modulus of elasticity to hardness ratio, or (iii) reinforcement of coarse grains (>12 μm) in the fine-grained (∼2 μm) microstructure. The crack path was predominantly intergranular at lower MgO/(CaO+BaO+KNaO) ratio ( K ic-short was observed due to precipitation of anorthite phase in the LPS with a high MgO/(CaO+BaO+KNaO) ratio. Finally the sintered density of 91–94 wt% LPS materials comprising of all powders produced a linear relationship with both the hardness and the modulus of elasticity.

Role of fabrication route and sintering on wear and mechanical properties of liquid-phase-sintered alumina

Abstract Liquid-phase-sintered Al 2 O 3 (LPS) fabricated by slip casting, tape casting, isopressing, uniaxial pressing, piston and auger extrusion showed substantial differences in wear due to differences in morphology as observed in image analyses of SEM micrographs. The abrasive wear was low in the case of uniaxial pressing and high in the case of tape casting in the ‘dry sand and rubber wheel’ test. The wear surface of the tape cast specimen exhibited extensive microcracking possibly due to orientation of Al 2 O 3 platelet (major face) parallel to the abraded surface whereas some degree of perpendicular orientation in extruded surface resulted in lower wear loss. In wet-milling wear test, the isopressed balls of a 95–97 wt% LPS derived from reactive powder (

Large magnetoelectric coupling in nanoscale BiFeO3 from direct electrical measurements

Science Foundation Ireland (SFI Principal Investigator (PI) Project No. 11/PI/1201, SFI FORME Strategic Research Cluster Award No. 07/SRC/I1172, ISCA grant (SFI: 12/ISCA/2493)); Indo-Ireland joint program (DST/INT/IRE/P-15/11); Council of Scientific and Industrial Research, India (CSIR Research Associateship)

Effect of phase separation on the fracture toughness of SiO2-B2O3-Na2O glass

Fracture toughness of glass is usually poor, due to the absence of grain boundaries and discontinuities. The compositions of the glass studied are in the phase separated region of SiO2-B2O3-Na2O system. The interface between the glass in glass separation enhances the fracture toughness. The increase in the connectivity of phase separated regions causes increase of fracture toughness from 0.98 through 1.43 to 1. 54 MPam1/2.

Isothermalin situ reduction kinetic analysis of NiCl2-containing gel

Isothermalin situ reduction kinetic study of NiCl2-containing gel was carried out. The detailed statistical as well as reduced time analysis show that contracting geometry and nucleation and growth type of mixed mechanisms are operative. The activation energy for reduction is in the range 158–193 kJ/mol. Thermal analysis on NiCl2-containing gel was carried out in the temperature range 800°C to 900°C.

Effect of powder, chemistry and morphology on the dielectric properties of liquid-phase-sintered alumina

Dielectric properties of liquid-phase-sintered alumina (LPS) ceramics prepared using commercial powders of different particle size distribution and impurities (Na2O) content were studied. So far as the particle size distribution of the commercial powder is concerned, LPS ceramics, those derived from powders of both medium (3.1–8.4 μm) and coarse (70–100 μm) grades, showed similar dielectric loss, whereas it was higher in the case of LPS derived from the reactive powders (<1 μm). While considering the impurity levels of the powders, higher Na2O content (0.57 wt.%) in the powder showed significantly higher dielectric loss compared to that of the lower Na2O content (<0.2 wt.%). Furthermore, the MgO/(CaO+BaO+KNaO) ratio in the chemical composition of the LPS within the range of 0.4–1.8 was found to influence the dielectric properties in the frequency range of 102–107 Hz. The dielectric loss in the frequency band of 102–103 Hz was found to be higher in the case of the LPS with a MgO/(CaO+BaO+KNaO) ratio of 1.6. Besides the starting powder and the chemical composition, the orientation of alumina platelets arising out of fabrication route (e.g. tape casting) was also found to have a profound influence on the dielectric properties. A higher loss was observed in the tape cast specimen.

Influence of powder, chemistry and intergranular phases on the wear resistance of liquid-phase-sintered Al2O3

Liquid-phase-sintered (LPS) Al2O3 ceramics prepared using different powders of varying particle size, i.e. medium (3.6–7.0 μm), coarse (70–100 μm) and reactive (<2.0 μm) showed a significant difference in wear resistance in different wear test environments, e.g. abrasion and erosion tests with dry silica sand, and wet-milling test with alumina grits. LPS materials derived from the reactive powders yielded a higher wear resistance that was possibly due to dissolution of a higher amount of Al2O3 into the intergranular glassy phase. The wear resistance of 88–94 wt.% LPS Al2O3 increased linearly upon increasing the MgO/(CaO+BaO+Na2O+K2O) ratio in the chemical composition (within the experimental limits) of the sintered material that was derived from the medium and coarse powders. The precipitation of anorthite on the Al2O3 grain boundary led to a lower wear resistance in 91–94 wt.% LPS Al2O3 of medium and coarse powders. Extensive plastic deformation was observed in the high-wear resistant LPS material whereas extensive microcracking was noticed in the low-wear resistant LPS material.