Alokmay Datta

Reversible buckling in monolayer of gold nanoparticles on water surface

Formation of condensed films of nanoparticles having small ratio of metal-core-diameter to organic-shell-thickness is desired for several applications in nanotechnology. We report here results of a X-ray scattering study carried out to understand structure and morphology of monolayer of such nanoparticles having gold-core and thiol-shell directly on the water surface before the monolayer undergoes a continuous transition to a bilayer. Our results demonstrate buckling of the monolayer over a large surface pressure range (1 to 15 mN/m). The buckled state exhibits reversibility on decompression and can be annealed with temperature. We also show that condensed monolayer films of nanoparticles can be formed by annealing the buckled monolayer before transferring to solid substrates.

Comparative analysis of stability and toxicity profile of three differently capped gold nanoparticles for biomedical usage

Nowadays gold nanoparticle (GNP) is increasingly being used in drug delivery and diagnostics. Here we have reported a comparative analysis of detailed stability and toxicity (in vitro and in vivo) profile of three water soluble spherical GNPs, having nearly similar size, but the surfaces of which were modified with three different capping materials aspartic acid (GNPA), trisodium citrate dihydrate (GNPC) or bovine serum albumin (GNPB). Spectral analyses on the stability of these GNPs revealed that depending on the nature of capping agents, GNPs behave differently at different environmental modalities like wide range of pH, high salt concentrations, or in solutions and buffers of biological usage. GNPB was found to be extremely stable, where capped protein molecule successfully maintained its secondary structure and helicity on the nanoparticle, whereas colloidal stability of GNPA was most susceptible to altered conditions. In vitro cytotoxicity of these nanoparticle formulations in vitro were determined by water soluble tetrazolium and lactate dehydrogenase assay in human fibroblast cell line (MRC-5) and acute oral toxicity was performed in murine model system. All the GNPs were non-toxic to MRC-5 cells. GNPC had slight hepatotoxic and nephrotoxic responses. Hepatotoxicity was also evident for GNPA treatment. Present study established that there is a correlation between capping material and stability together with toxicity of nanoparticles. GNPB was found to be most biocompatible among the three GNPs tested.

Morphology of nanostructured materials

Here we shall discuss the importance of grazing incidence X-ray scattering techniques in studying morphology of nanostructured materials confined in thin films and multilayers. In these studies, the shapes, sizes, and structures of nanostructured materials and their distribution in composites are investigated. These studies are important for understanding properties that may deviate considerably from the known bulk properties. We shall first outline basics of three X-ray scattering techniques, namely X-ray reflectivity, grazing incidence small-angle X-ray scattering, and grazing incidence diffraction, used for these studies. We shall then demonstrate the utility of these techniques using some known results.

Atomic force microscopy in biofilm study

Biofilms have been classically visualized by Scanning Electron Microscopy (SEM). The complex operating procedure of SEM restricts its use in routine practice. There is a need of newer visualizing techniques for examining surfaces of biofilms, in particular under ambient conditions. We have presented the unique advantages of atomic force microscopy (AFM) in studying surfaces of biofilms through analyses of the height images obtained on biofilms of two gram positive and one gram negative bacteria, namely Staphylococcus aureus, Nocardia brasiliensis and Pseudomonas aeruginosa, respectively. Biofilm quality of the three different bacteria, ageing effects on Nocardia spp. biofilm surface and effects of the antibiotic ciprofloxacin at different doses on Staphylococcus and Pseudomonas biofilm surfaces have been investigated under ambient conditions and distinctive features have been observed.

Study of thin film multilayers using X-ray reflectivity and scanning probe microscopy

We have presented new schemes to analyse grazing incidence specular X-ray reflectivity data to obtain structural and chemical information of thin films. Analysis of specular reflectivity data gives information along the depth of the film, whereas, analysis of non-specular data reveals the structural information across the film surface and interfaces. The schemes proposed are based on the Born approximation and the distorted wave born approximation (DWBA). Surface structural parameters such as, height-height correlation and roughness exponent of the film obtained from the analysis of X-ray reflectivity was compared with results obtained from atomic force microscopy.

Nanoparticles influence on expression of cell cycle related genes in Drosophila: a microarray-based toxicogenomics study

Relatively little is known regarding the interaction of nanoscale objects with dynamic complex biological systems. Microarray-based toxicogenomics studies may serve as a suitable technique to explore the genome wide effects of nanoparticles on any organism through a single experiment. The influence of nanoporous aluminosilicate nanoparticles (NP), citrate-capped gold NP, lipophilic silica NP, BSA-capped silver NP, and lipophilic zinc oxide NP were studied on 75 cell cycle-related genes of adult Drosophila melanogaster. Microarray experiments were conducted after the flies were fed with NP-mixed media for 15 days. Data showed that silver, zinc oxide, and alumino silicate NP predominantly perturbed cell cycle genes, whereas gold and silica NP exerted the least influence on these genes.

Interfacial profile of a Bragg Mirror

Abstract X-ray reflectivity and secondary ion mass spectrometry studies of a Bragg Mirror are presented. We find that the AlAs-on-AlGaAs interfaces are diffused due to formation of continuously varying composition of AlxGa1−xAs at the interfaces. On the other hand, the AlGaAs-on-AlAs interfaces are found to be sharp.

Anomalous dispersion X-ray reflectometry for model-independent determination of Al/C multilayer structures

Abstract Electron density profiles across the 90–270 A depth of Al/C multilayers on Ge substrates are determined from anomalous-dispersion X-ray specular reflectivity data collected at the Ge K edge and away from it. Refractive index parameters for Ge are determined by fits of reflectivity profiles observed from a Ge surface without the Al/C film at the two photon energies and used in the calculation of electron densities for single and triple Al/C bilayers deposited on Ge substrates. The layer structures are clearly resolved and the Al/C interfaces are found to be considerably broader than expected.

Convex Arrhenius behaviour in a nematic-isotropic phase transition

Convex Arrhenius behaviour, rare in transitions between equilibrium phases of pure systems, is observed in the plot of heating rate ?vs. temperature for Nematic-Isotropic (N-I) transition of liquid crystalline MBBA through Differential Scanning Calorimetry (DSC). The plot is best fit by a monomolecular growth function, using which an entropy-driven activation barrier, increasing non-linearly with temperature, is obtained. Fourier Transform Infrared (FTIR) studies of MBBA around the N-I transition temperature show increase in out-of-plane benzene ring distortions and decrease in order along the C=N-C axis, consistent with DSC results of conformational entropy-driven barrier.

Radiation-induced synthesis of self-organized assemblies of functionalized inorganic–organic hybrid nanocomposites

We demonstrate a unique single-pot synthesis of self-organized structures of CdS/dendrimer nanocomposites having long-range correlation by adopting a radiation-induced technique. The present method has been able to produce long-range chain-like networks of CdS nanoparticles of high stability within the dendrimer matrix with particle size monodispersity ∼6%, as visualized with atomic force microscopy, while individual particles are characterized by transmission electron microscopy, photoluminescence, absorption spectroscopy and dynamic light scattering. Results point to a possible mechanism of long-range self-organization from the nanometer to micrometer length scales, where the self-organization is controlled by surface functionality of the dendrimer molecule, solvent and crystal phase of the CdS nanocrystals. The present investigation opens up new potential routes to manipulate semiconductor nanocomposites for optical diagnostics and for applications that require dendrimer nanocomposites with a long-range order.