M.K. Mitra

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.

Effect of Ni doping on the dielectric constant of ZnO and its frequency dependent exchange interaction

Ni doped ZnO powders were synthesized by a simple dissolution followed by precipitation using zinc acetate, nickel acetate and oxalic acid for different atomic percentages of Ni doping. Proper phase formation was confirmed by x-ray diffraction and the compositional analysis was performed by using x-ray photoelectron spectroscopic studies. The frequency dependent dielectric constant of the Ni doped ZnO samples was measured by an LCR meter, and from the dielectric constant versus frequency curve, fitted with the Cole equation, we obtained static and high frequency dielectric constants of the Ni doped ZnO samples. It was observed that both the static and high frequency dielectric constants decreased with increasing percentages of Ni doping in ZnO. A simple theoretical model based on the Penn model has been successfully developed to describe the above-mentioned variation. We have also observed the frequency dependence of the s, p–d exchange interaction and a theoretical calculation has been successfully developed to explain it.

Effect of Co doping on the static dielectric constant of ZnO nanoparticles

Co doped ZnO nanoparticles were synthesized by a simple rheological phase reaction-precursors method using zinc acetate, cobalt acetate, and oxalic acid for different atomic percentages of Co doping. X-ray diffraction studies confirmed the correct phase formation, and the composition were obtained from the x-ray photoelectron spectroscopic studies. Particle size was obtained from the small angle x-ray scattering studies. It was observed that the static dielectric constant, calculated from the shift of band gap energy, shows a gradual decrease with Co doping. A simple theoretical model was developed to explain the observed change of dielectric constant on the doping concentration. The model could successfully describe the dependence of the static dielectric constant on the doping concentration.

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.

Magnetic and dielectric properties of sol-gel derived nanoparticles of double perovskite Y2NiMnO6

Nanoparticles of Y2NiMnO6 having diameters around 20 nm were synthesized by a sol-gel method. X-ray data were analysed by Rietveld method. This showed the crystals to have monoclinic structure. X-ray photoelectron spectroscopy studies showed a ratio of Mn3+/Mn4+ equal to 0.64 to be present in the nanocrystals. A small polaron hopping conduction model was found to satisfactorily explain the electrical resistivity behaviour of the samples. The latter exhibited ferromagnetic (FM) properties with a Curie temperature around 92 K. This behaviour was ascribed to a ferromagnetic superexchange interaction between Mn4+ and Ni2+ ions. Spin glass behaviour was ruled out on the basis of ac magnetic susceptibility data. The nanocrystals exhibited a peak in the dielectric constant at a temperature 535 K indicating a ferroelectric transition. This is consistent with the recent theoretical prediction made on the basis of density functional calculations.

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.

Preparation of alumina–silica–nickel nanocomposite by in situ reduction through sol–gel route

Abstract Ceramic based composites with dispersion of nano sized metal/metal carbide particles have generated wide technological interest for their improved mechanical properties — hardness, fracture strength as well as fracture toughness, superior electrical properties and magnetic properties. In the present investigation alumina–silica gels have been prepared along with nickel chloride and dextrose distributed in the nanometric pores of the gel. The gels are prepared with different molar proportions of alumina and silica containing 5 wt% of nickel chloride and 50 wt% excess dextrose. During heat treatment at a temperature of 9008C for half an hour in nitrogen atmosphere, nickel chloride is reduced to metallic nickel by in situ generated hydrogen in the silica–alumina matrix. X-ray analyses indicate that no nickel chloride reduction is possible upto 50 mol% silica in alumina–silica matrix. Beyond this range, higher the silica content, higher is the reduction of nickel chloride. The presence of metallic nickel has been substantiated further by SAD analysis. Particle size analysis based on X-ray diffraction as well as transmission electron micrograph shows the presence of nickel particles of size ,20 nm distributed in the alumina–silica nanocomposite.

Electronic structure and optical properties of CuAlO2 under biaxial strain.

An ab initio calculation has been carried out to investigate the biaxial strain ( - 10.71% < ε < 9.13%) effect on elastic, electronic and optical properties of CuAlO(2). All the elastic constants (c(11), c(12), c(13), c(33)) except c(44) decrease (increase) during tensile (compressive) strain. The band gap is found to decrease in the presence of tensile as well as compressive strain. The relative decrease of the band gap is asymmetric with respect to the sign of the strain. Significant differences between the parallel and perpendicular components of the dielectric constant and the optical properties have been observed due to anisotropic crystal structure. It is further noticed that these properties are easily tunable by strain. Importantly, the collective oscillation of the valence electrons has been identified for light polarized perpendicular to the c-axis. From calculations, it is clear that the tensile strain can enhance the hole mobility as well as the transparency of CuAlO(2).

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.

siRNA-nanoparticle conjugate in gene silencing: A future cure to deadly diseases?

Alzheimers, cancer, acquired immune deficiency syndrome (AIDS) are considered to be some of the most deadly diseases of the 21st century on account of their severity and rapid increase in the number of affected population and with scarce cases of recovery, they still remain a troubling paradox. Specifically, with millions of cancer patients worldwide and lack of proper cure for the same, understanding the deadly disease at the molecular level and planning a therapeutic strategy in the same line is the need of the hour. Further, the potential threat of prevalence and escalation of Alzheimers and HIV (human immunodeficiency virus) infection by more than three times as of recent past, needs a medical breakthrough to arrive at a meaningful solution to tackle the present day scenario. It is evident that these diseases initiate and propagate based on certain genes and their expression which needs to be silenced by the help of small interfering RNA (siRNA) by at least 70%. For short term silencing of the protein coding genes, siRNA is the most appropriate tool. Hence, the present communication explores the possibility for treatment and cure of a plethora of deadly diseases, e.g., cancer, including Alzheimers and AIDS to some extent, emphatically at the molecular level, using the current trend of RNAi (RNA interference) delivery via a wide variety of nanoparticles.