Aqueous synthesis of CdTe quantum dot as biological fluorescent probe for monitoring methyl parathion by fluoro-immunosensor

Bioconjugation of quantum dots (QDs) provide high resolution in biological fluorescent labelling as a result of physical and optical properties of QDs. This intrinsic property of QDs can be made use of for sensitive detection of target analytes including food and environmental monitoring. In this investigation, we report the bioconjugation of thiol stabilized CdTe QD for the sensitive detection of methyl parathion (MP) at picogram level. The specificity in the analysis was attributed by highly specific competitive immunological reactions between free MP and CdTe QD bioconjugated MP (MP-BSA-CdTe) for immobilized anti-MP IgY antibodies in a simple flow injection system. We also report the possible resonance energy transfer phenomenon as a result of nanobiomolecular interaction obtained through the bioconjugation of CdTe QD with protein bovine serum albumin (BSA). This has resulted in a significant change in the photo-absorption of CdTe QD, which can be made use for future nanosensor development

Interplay of force constants in the lattice dynamics of disordered alloys : An ab-initio study

A reliable prediction of interatomic force constants in disordered alloys is an outstanding problem. This is due to the need for a proper treatment of multisite (atleast pair) correlation within a random environment. The situation becomes even more challenging for systems with large difference in atomic size and mass. We propose a systematic density functional theory (DFT) based study to predict the ab-initio force constants in random alloys. The method is based on a marriage between special quasirandom structures (SQS) and the augmented space recursion (ASR) to calculate phonon spectra, density of states (DOS) etc. bcc TaW and fcc NiPt alloys are considered as the two distinct test cases. Ta-Ta (W-W) bond distance in the alloy is predicted to be smaller (larger) than those in pure Ta (W), which, in turn, yields stiffer (softer) force constants for Ta (W). Pt-Pt force constants in the alloy, however, are predicted to be softer compared to Ni-Ni, due to a large bond distance of the former. Our calculated force constants, phonon spectra and DOS are compared with experiments and other theoretical results, wherever available. Correct trend of present results for the two alloys pave a path for further future studies in more complex alloy systems

Thermal conductivity and diffusion-mediated localization in Fe_{1-x}Cr_{x} Alloys

We apply a new Kubo-Greenwood type formula combined with a generalized Feynman diagram- matic technique to report a first principles calculation of the thermal transport properties of disordered Fe_{1-x}Cr_{x} alloys. The diagrammatic approach simplifies the inclusion of disorder-induced scattering effects on the two particle correlation functions and hence renormalizes the heat current operator to calculate configuration averaged lattice thermal conductivity and diffusivity. The thermal conductivity K(T) in the present case shows an approximate quadratic T-dependence in the low temperature regime (T < 20 K), which subsequently rises smoothly to a T-independent saturated value at high T . A numerical estimate of mobility edge from the thermal diffusivity data yields the fraction of localized states. It is concluded that the complex disorder scattering processes, in force-constant dominated disorder alloys such as Fe-Cr, tend to localize the vibrational modes quite significantly.Comment: 5 pages, 5 figure

Pitting studies of plain carbon steel in chloride containing borate buffer solution

Passivation is the process of temporary or permanent halt in degradation or corrosion rate of a metal due to the formation of different types of surface layers or films that protects the underlying metal. Pitting corrosion is the breakdown of the surface film due to presence of aggressive ions such as chloride ions. The breakdown of the passivity film is characterized by breakdown potential (Vc) which is dependent on the pH of the solution, concentration of the aggressive ions and the potential sweep rate. This study used the Point Defect Model to characterize the breakdown potential with respect to varying pH and concentration. The pH of the solution was kept a constant at 10.4. The breakdown potential is found to decrease with increasing chloride concentration and decrease with increasing pH. The cumulative distribution of the breakdown potential was found to be in well agreement with the experimentally obtained data. Optical micrographs showed stable and Meta stable pitting. The parameters from point defect model was found to be in well agreement with the experimental data

E. coli-quantum dot bioconjugates as whole-cell fluorescent reporters for probing cellular damage

A quantum dot (QD) conjugated whole-cell E. coli biosensor (E. coli–QD bioconjugates) was developed as a new molecular tool for probing cellular damage. The E. coli–QD bioconjugates were viable and exhibited fluorescence emission at 585 nm. Scanning electron microscopy (SEM) analysis of E. coli–QD bioconjugates revealed that the QDs were immobilized on the cell-surfaces and the fluorescence emission from QDs present on cell-surfaces was visualized by confocal microscopic examination. The E. coli–QD bioconjugates were employed as whole-cell fluorescent reporters that were designed to function as fluorescence switches that turn-off when cellular damage occurs. In this study, multi-walled carbon nanotubes (CNTs) were utilized as a model nanomaterial to probe cellular damage. Fluorescence spectra were recorded after the exposure of E. coli–QD bioconjugates with CNTs. We observed a strong correlation between fluorescence emission spectra, SEM and confocal microscopic analysis demonstrating that CNTs induced a dose and exposure time-dependent cellular toxicity. This toxicity mainly occurred by the physical interaction and cellular trafficking mechanisms that led to the collapse of the cellular structure and thus loss of fluorescence. The responses of E. coli–QD bioconjugates against CNTs were also visualized by simply exposing the cells to UV light and therefore rapid toxicity analysis and screening can be made. Our study demonstrated an easy and simple method to determine an important mechanistic perspective for the biological toxicity of chemicals or nanomaterials (NMs)