Amrita Mandal

Surface-modified sulfur nanoparticles: an effective antifungal agent against Aspergillus niger and Fusarium oxysporum

Surface-modified sulfur nanoparticles (SNPs) of two different sizes were prepared via a modified liquid-phase precipitation method, using sodium polysulfide and ammonium polysulfide as starting material and polyethylene glycol-400 (PEG-400) as the surface stabilizing agent. Surface topology, size distribution, surface modification of SNPs with PEG-400, quantitative analysis for the presence of sulfur in nanoformulations, and thermal stability of SNPs were determined by atomic force microscopy (AFM), dynamic light scattering (DLS) plus high-resolution transmission electron microscopy (HR-TEM), fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray (EDX) spectroscopy, and thermogravimetric analysis (TGA), respectively. A simultaneous study with micron-sized sulfur (S0) and SNPs was carried out to evaluate their fungicidal efficacy against Aspergillus niger and Fusarium oxysporum in terms of radial growth, sporulation, ultrastructural modifications, and phospholipid content of the fungal strains using a modified poisoned food technique, spore-germination slide bioassay, environmental scanning electron microscopy (ESEM), and spectrometry. SNPs expressed promising inhibitory effect on fungal growth and sporulation and also significantly reduced phospholipid content.

Investigation of antimicrobial physiology of orthorhombic and monoclinic nanoallotropes of sulfur at the interface of transcriptome and metabolome

Nanosized elemental sulfur (ES) is already reported to exert superior antimicrobial efficacy than micron-sized ES, which encourages their use in drugs and therapeutics. The aim of the present study is to explore the possible route and mode of antimicrobial action of orthorhombic (α-SNPs) and monoclinic (β-SNPs) allotropes of sulfur, respectively, at their nano-dimensions. The antimicrobial efficacy of α- and β-SNPs was determined against both the conventionally ES-resistant and ES-susceptible fungi and bacteria. Both the SNPs inhibited the microbial growth, irrespective of their resistance profile to ES and caused significant deformities on the microbial cell surfaces. However, the extent of antimicrobial efficacy was found to be optimum for α-SNPs, which can be attributed to their size, shape, and surface modification. Subsequent transcript profiling, metabolite profiling, and enzymatic analyses revealed that α- and β-SNPs impaired a cluster of mitochondrial enzymes involved in cellular respiration and oxidative phosphorylation. ES and SNPs stress were found to elicit the NADPH-dependent glutathione reductase mediated ES-detoxification response in fungi and caused them to undertake the glyoxylate shunt in favor of energy conservation. A simultaneous study was also undertaken to assess the biocompatible or bio-adverse properties of SNPs in terms of their cytotoxic and genotoxic effects against the human derived lung fibroblast cell line (MRC-5). The present study hence explores the antimicrobial physiology of two novel functional materials and demonstrates their compatibility as a future putative antimicrobial drug.

Magnetodielectric effect in nickel nanosheet-Na-4 mica composites

Nickel nanosheets of thickness 0.6 nm were grown within the nanochannels of Na-4 mica template. The specimens show magnetodielectric effect at room temperature with a change of dielectric constant as a function of magnetic field, the electric field frequency varying from 100 to 700 kHz. A decrease of 5% in the value of the dielectric constant was observed up to a field of 1.2 T. This is explained by an inhomogeneous two-component composite model as theoretically proposed recently. The present approach will open up synthesis of various nanocomposites for sensor applications.

Ferromagnetic Behavior of Ultrathin Manganese Nanosheets

Ferromagnetic behavior has been observed experimentally for the first time in nanostructured manganese. Ultrathin (∼0.6-nm) manganese nanosheets were synthesized inside the two-dimensional channels...

Magnetodielectric effect in CdS nanosheets grown within Na-4 mica

CdS nanosheets of thickness 0.6 nm were grown within the interlayer spaces of Na-4 mica. Magnetization measurements carried out in the temperature range 2–300 K showed the composites to have weak ferromagnetic-like properties even at room temperature. The saturation magnetization (MS) at room temperature was found to be higher than that reported for CdS nanoparticles. The higher value of MS may be ascribed to the presence of a large number defects in the present CdS system, due to a large surface to volume ratio in the nanosheets as compared to that of CdS nanoparticles. The nanocomposites exhibited a magnetodielectric effect with a dielectric constant change of 5.3% for a magnetic field of 0.5 T. This occurred due to a combination of magnetoresistance and Maxwell-Wagner effect as delineated in the model developed by Catalan.

Nanoindentation studies on silver nanoparticles

Nanodimensional metallic silver was grown by electrodeposion technique in a semi solid polymer matrix of polyacrylamide. The whole structure looks like dendronic. The average particle diameter of the as grown metallic silver is 13 nm. Nanoindentation study of these nanoparticles shows modulus and hardness value as 103.93 GPa and 3.12 GPa respectively.

Magnetodielectric effect of CuO grown within highly ordered two dimensional mesoporous silica template SBA 15

A two component, inhomogeneous medium can produce magnetodielectric (MD) effect without any magnetoelectric coupling. Here, we have prepared an inhomogeneous material by growing CuO within two dimensional mesostructures of silica template SBA-15 by a single step method. The (CuO)x-(SBA-15)1−x nanocomposites with different weight percentages (x = 0.2, 0.35, and 0.5) were characterized by small angle x-ray diffraction study and transmission electron microscopy. Both studies confirmed the highly ordered hexagonal mesostructure for CuO(20) where 20 is the weight percentage of CuO in nanocomposite (i.e., x = 0.2). The mesostructure was destroyed on increasing the percentage of CuO incorporated. The nanocomposites exhibited magnetodielectric effect with dielectric constant change of 4.4% and 3% for CuO(20) and CuO(35), respectively, at 1.8 T magnetic field. This effect was explained on the basis of a two dimensional inhomogeneous two component composite model. No such effect occurs in CuO(50) due to total disap...

Enhanced magnetic anisotropy of nickel nanosheet prepared in Na-4 mica

Nanosheets of nickel with thickness equal to 0.6 nm have been grown within the interlayer spaces of Na-4 mica. The sheets are made up of percolative clusters of nanodisks. Magnetization characteristics indicate a superparamagnetic behavior with a blocking temperature of 428 K. The magnetic anisotropy constant as extracted from the coercivity data has been found to be higher than that of bulk nickel by two orders of magnitude. This is ascribed to a large aspect ratio of the nickel nanophase. The Bloch exponent is also found to be considerably different from that of bulk nickel because of a size effect. The Bloch equation is still found to be valid for the two dimensional structures.

Synthesis and Raman studies of wurtzite CdS nanosheets

CdS nanosheets with thickness of 0.6 nm were grown within interlayer spaces of Na-4 mica. The formation of wurtzite CdS was confirmed by X-ray diffraction and transmission electron microscopy measurements. Raman mode at 390 cm−1, corresponding to wurtzite phase, has been identified in ultrthin CdS with possible changes in the atomic sites with respect to that in the cubic phase. Resonance Raman studies, invoked by strong electron-phonon coupling, show longitudinal optical modes upto fourth order.