An efficient magnetic resonance imaging (MRI) contrast agent with a high R2 relaxivity value is achieved by controlling the shape of iron oxide to rod like morphology with a length of 30-70 nm and diameter of 4-12 nm. Fe3O4 nanorods of 70 nm length, encapsulated with polyethyleneimine show a very high R2 relaxivity value of 608 mM(-1) s(-1). The enhanced MRI contrast of nanorods is attributed to their higher surface area and anisotropic morphology. The higher surface area induces a stronger magnetic field perturbation over a larger volume more effectively for the outer sphere protons. The shape anisotropy contribution is understood by calculating the local magnetic field of nanorods and spherical nanoparticles under an applied magnetic field (3 Tesla). As compared to spherical geometry, the induced magnetic field of a rod is stronger and hence the stronger magnetic field over a large volume leads to a higher R2 relaxivity of nanorods.
The synthesis of gold nanoparticles using citrate reduction process has been revisited. A simplified room temperature approach to standard Turkevich synthesis is employed to obtain fairly monodisperse gold nanoparticles. The role of initial pH alongside the concentration ratio of reactants is explored for the size control of Au nanoparticles. The particle size distribution has been investigated using UV-vis spectroscopy and transmission electron microscope (TEM). At optimal pH of 5, gold nanoparticles obtained are highly monodisperse and spherical in shape and have narrower size distribution (sharp surface plasmon at 520 nm). For other pH conditions, particles are non-uniform and polydisperse, showing a red-shift in plasmon peak due to aggregation and large particle size distribution. The room temperature approach results in highly stable “colloidal” suspension of gold nanoparticles. The stability test through absorption spectroscopy indicates no sign of aggregation for a month. The rate of reduction of auric ionic species by citrate ions is determined via UV absorbance studies. The size of nanoparticles under various conditions is thus predicted using a theoretical model that incorporates nucleation, growth, and aggregation processes. The faster rate of reduction yields better size distribution for optimized pH and reactant concentrations. The model involves solving population balance equation for continuously evolving particle size distribution by discretization techniques. The particle sizes estimated from the simulations (13 to 25 nm) are close to the experimental ones (10 to 32 nm) and corroborate the similarity of reaction processes at 300 and 373 K (classical Turkevich reaction). Thus, substitution of experimentally measured rate of disappearance of auric ionic species into theoretical model enables us to capture the unusual experimental observations.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1576-5) contains supplementary material, which is available to authorized users.
The perfect crystalline nature along with a defect ridden surface controls the electrical and magnetic properties of ZnO nanowires. Herein, a soft chemical approach is presented to grow ZnO nanowires in powder as well as highly oriented nanowire film form. Photoluminescence measurements reveal high surface defects in as-grown nanowire and post growth annealing treatment in argon and oxygen atmosphere reduces intensity of defect emissions. Magnetic measurements illustrate the ferromagnetic nature of submicron sized zinc oxide (ZnO) nanorods arising due to singly charged oxygen vacancies. Nanowires show diamagnetic behavior when annealed at higher temperature in oxygen while argon annealing does not affect the magnetic behavior. In an analogous manner, we also investigated the effect of surface defects on electrical properties and correlated electrical conductivity with a responsible defect state
The stabilization of gold nanoparticles solution synthesized using ascorbic acid at room temperature is examined in detail. It is found that gold nanoparticles (AuNPs) synthesized using ascorbic acid have a narrow size distribution (31 ± 5, 36 ± 6, and 40 ± 5 nm) and can be readily stabilized just by adjusting the initial pH conditions of the reaction solutions. Whilst the initial pH strongly affects the stability of particles, it has no effect on the size of stabilized particles. The particles are nearly spherical having size distribution effectively in the range of 30 nm to 40 nm. Through time dependent UV-Vis spectra studies we also hypothesize the pH dependent stabilization mechanism wherein a layer of adsorbed ionic complex over AuNPs slows down the aggregation of AuNPs . The information obtained in this study can be used to design in-situ controlled nanoparticle synthesis system especially within the biological cells. Moreover, the method is green and biologically acceptable as well.
LSPR of gold nanoparticles supported over glass or silica nanoparticles modulated using simple ionic treatment.
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