BackgroundZnO nanoparticles (grown in the template of folic acid) are biologically useful, luminescent material. It can be used for multifunctional purposes, e.g., as biosensor, bioimaging, targeted drug delivery and as growth promoting medicine.MethodsSol–gel chemical method was used to develop the uniform ZnO nanoparticles, in a folic acid template at room temperature and pH ~ 7.5. Agglomeration of the particles was prevented due to surface charge density of folic acid in the medium. ZnO nanoparticle was further characterized by different physical methods.ResultsNanocrystalline, wurtzite ZnO particles thus prepared show interesting structural as well as band gap properties due to capping with folic acid.ConclusionsA rapid, easy and chemical preparative method for the growth of ZnO nanoparticles with important surface physical properties is discussed. Emphatically, after capping with folic acid, its photoluminescence properties are in the visible region. Therefore, the same can be used for monitoring local environmental properties of biosystems.

Microstructural studies of silica gel powder were carried out using positron annihilation lifetime spectroscopy (PALS) in conjunction with transmission electron microscopy (TEM). It is argued that the two distinct longlived components found (labeled by τ 3 and τ 4 ) may be ascribed to ortho positronium annihilation in microcavities within the grains and intergranular mesoscopic pores, respectively. In the latter type of void, a significant fraction decays via the three-photon mode. A simple physical picture of positronium annihilation in the larger pores is put forward, while the situation vis-a `-vis the smaller cavities is shown to be well described by a modification of the currently prevailing model for the pick-off process. The simple parametrization finally arrived at provides a sharpening of the use of the positron as a useful probe for microstructural study of porous substances. It is emphasized that two different positron annihilation mechanisms prevail in the microcavities and mesopores.

The characteristics of positronium (Ps) annihilation in molecular substances (ranging from organic liquids to molecular solids), manifested through the observed lifetimes (τp) for the ‘pick-off’ process and values of angular correlation (θ1/2) of decay gammas, can be shown to be simply related to the size (radius R) of the cavity which the Ps creates in a liquid or finds in a molecular solid. The measured τp and θ1/2 are in turn calculable from the wavefunction describing the Ps centre-of-mass motion, which is determined from the average potential experienced by it in the confining cavity. Thus the height of this repulsive barrier (U0) at the wall of this vacant region corresponding to different materials (with varying R) can be obtained by fitting experimental observations, namely τp and θ1/2. The model we use is an improved version of the usual spherical well description of the cavity (where we take the walls to be diffuse). It is found that the values of U0 and R, taking into account all available and relevant data for different molecular substances, fall on a universal curve. We attempt to explain the reason behind this ‘universality’ by relating the potential to the Ps work-function in materials. Finally, the fit provides us with a very convenient linear relationship between the size (R) of the cavity and the pick-off lifetime (τp).

Bioactive nanomaterials, namely, gallium oxyhydroxide GaO(OH), also surface-conjugated GaO(OH) with a giant sugar molecule β-cyclodextrin (CD), have been prepared through a simple wet chemical route such that the same could be suitably used in biomedical diagnostics as well as therapeutic applications. Several physical methods were used for their characterization: powder X-ray diffraction pattern of GaO(OH) NPs for their grain size determination, optical spectroscopic absorption (UV-vis and FT-IR), and fluorescence properties of these NPs to ascertain surface conjugation and also their wide band-gap properties. Besides these, morphological properties of these NPs were studied by transmission electron microscopic (TEM) investigation, justifying the elemental constitution through energy dispersive X-ray analysis (EDX). Further, biological cellular uptake of these nanoparticles have been demonstrated on cancerous HeLa cells and reported with total fetal effect after 72 h, with CD templated GaO(OH) nanoparticles, a fact that has not been reported so far.

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The bubble model conventionally used to fit the observed characteristics of the pick-off component of ortho-positronium decay in liquids is subjected, in the present study, to a critical assessment. It is demonstrated that in its usual form (namely that of a bubble with a sharp boundary) the model is untenable, when confronted conjointly with experimental data on the lifetime and angular correlation of the decay gammas. A modified version of the model that is relatively free from such shortcomings is presented.

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