Bhupendra Chudasama

Antibacterial activity of silver: the role of hydrodynamic particle size at nanoscale.

Silver shows the highest antimicrobial activities amongst all metals. It is better than many first line antibiotics. The antimicrobial properties of silver can be tuned by altering its physical and surface properties. Researchers have demonstrated enhancement in the antibacterial properties of silver with decreasing particle size from bulk to nano. In the present article, we study the effect of particle size of silver at nanoscale on their antimicrobial properties. Two samples of silver nanoparticles (SNPs) of same physical size (≈8 nm) but different hydrodynamic size (59 and 83 nm) are prepared by chemical reduction of AgNO3 with oleylamine followed by phase transfer with triblock copolymer Pluronic F-127. Their antimicrobial properties are investigated by microdilution method against clinically important strains of gram positive (S. aureus and B. megaterium) and gram negative (P. vulgaris and S. sonnei) bacteria. Nearly 38-50% enhancement in the antibacterial action of SNPs was observed when their hydrodynamic size was reduced to 59 nm from 83 nm. It has been observed that the antibacterial action of SNPs was governed by their hydrodynamic size and not by their crystallite and physical size. The phenomenological model was also proposed which makes an attempt to explain the microscopic mechanism responsible for the size dependent antibacterial activities of silver.

Field induced rotational viscosity of ferrofluid : Effect of capillary size and magnetic field direction

In the present investigation we report the effect of capillary diameter and the direction of applied magnetic field on the rotational viscosity of water and kerosene based ferrofluids. We found that changes in the field induced rotational viscosity are larger in the case of water based magnetic fluid than that of kerosene based fluid. The field induced rotational viscosity is found to be inversely proportional to the capillary diameter and it falls exponentially as a function of the angle between the direction of field and vorticity of flow. Magnetophoretic mobility and hydrodynamic volume fraction of nanomagnetic particles are determined for above cases.

A growth kinetic study of ultrafine monodispersed silver nanoparticles

In this article we report the growth kinetics of ultrafine monodispersed silver nanoparticles prepared via thermal reduction of silver nitrate with oleylamine. Effect of nucleation and growth temperature and time on the quality and quantity of silver nanoparticles was monitored in terms of product yield, crystal phase, morphology, aggregation, particle size and size distribution. To understand the effect of kinetic parameters, purified silver nanoparticles were characterized by UV-visible, FTIR and photon correlation spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetry (TG). Irrespective of the kinetic conditions, oleylamine always reduces AgNO3 into spherical Ag nanoparticles with simple cubic structure. The nanoparticle yield is highest for 21 mM oleylamine. Its size decreases with increasing oleylamine concentration and levels off at 3.5 nm with a polydispersity of 0.12. When concentration of oleylamine is <15 mM, agglomerated silver nanoparticles resulted while they self-assembled into hexagonal close pack structure when oleylamine is ≥15 mM. Nucleation at 200 °C for 30 min and growth at 150 °C for 4 h are the optimum processing parameters for highest nanoparticle yield (60%), lowest particle size (3.5 nm) and polydispersity index (0.12) with no or very little agglomeration.

Combined and individual doxorubicin/vancomycin drug loading, release kinetics and apatite formation for the CaO–CuO–P2O5–SiO2–B2O3 mesoporous glasses

The novel mesoporous glass series based on (25 − x)CaO–xCuO–10P2O5–5B2O3–60SiO2 (x = 2.5, 5, 7.5, 10) has been prepared using the sol–gel technique. The pore size of the prepared mesoporous bioactive glasses (MBG) lies between 6.1 and 9.1 nm, whereas the surface area varies from 281 to 418 m2 g−1. The pH variation, zeta potential, Fourier transform infra-red (FTIR) spectroscopy and simulated body fluid (SBF) studies indicated the in vitro bioactivity of all the MBGs. The MBGs were loaded with the anticancerous and antibacterial drugs, doxorubicin and vancomycin, respectively. The increasing copper content predominantly influenced the bioactive properties as well as the drug loading and release kinetics of the doxorubicin and vancomycin drugs. In addition to the individual loading of drugs in the MBG, both the drugs were also loaded together in the MBG to investigate the effect of combined loading on the release capability of the MBGs.

Experimental investigation of magnetically induced unusual emission of light from a ferrodispersion

An unusual emission of light is observed when a coherent light beam is passed through a mixture of a magnetorheological suspension and a ferrofluid that is subjected to a critical magnetic field. When first the incident light is removed and then the field is switched off, a flash of light is observed. In this Letter certain characteristics of this unusual emission are reported. Our findings suggest that a part of the incident light energy is magnetically trapped within the medium. Upon removal of the field, the same is released. Several physical phenomena that may give rise to such emission are discussed. The magnetically tunable emission will be useful to develop photonic devices.

Influence of antibiotic adsorption on biocidal activities of silver nanoparticles.

Excessive use of antibiotics has posed two major challenges in public healthcare. One of them is associated with the development of multi-drug resistance while the other one is linked to side effects. In the present investigation, the authors report an innovative approach to tackle the challenges of multi-drug resistance and acute toxicity of antibiotics by using antibiotics adsorbed metal nanoparticles. Monodisperse silver nanoparticles (SNPs) have been synthesised by two-step process. In the first step, SNPs were prepared by chemical reduction of AgNO3 with oleylamine and in the second step, oleylamine capped SNPs were phase-transferred into an aqueous medium by ligand exchange. Antibiotics - tetracycline and kanamycin were further adsorbed on the surface of SNPs. Antibacterial activities of SNPs and antibiotic adsorbed SNPs have been investigated on gram-positive (Staphylococcus aureus, Bacillus megaterium, Bacillus subtilis), and gram-negative (Proteus vulgaris, Shigella sonnei, Pseudomonas fluorescens) bacterial strains. Synergistic effect of SNPs on antibacterial activities of tetracycline and kanamycin has been observed. Biocidal activity of tetracycline is improved by 0-346% when adsorbed on SNPs; while for kanamycin, the improvement is 110-289%. This synergistic effect of SNPs on biocidal activities of antibiotics may be helpful in reducing their effective dosages.

Optical absorption in gel grown cadmium tartrate single crystals

Single crystals of cadmium tartrate pentahydrate (CTP) have been grown by the famous gel technique. The slow and controlled reaction between Cd 2+ and (C4H4O6) 2- ions in silica hydrogel results in formation of the insoluble product, CdC4H4O6.5H2O. Optical absorption spectra have been recorded in the range 200 to 2500 nm. Fundamental absorption edge for electronic transition has been analyzed. The direct allowed transition is found to be present in the region of relatively higher photon energy. Analysis of the segments of D 1/2 versus hQ graph has been made to separate individual contribution of phonons. The phonons involved in the indirect transition are found to correspond to 335 and 420 cm -1 . Scattering of charge carriers in the lattice is found due to acoustic phonons.

Single step synthesis of pluronic stabilized IR responsive gold nanoplates

A single-step seed-mediated synthesis is employed to produce biocompatible infrared (IR) responsive gold nanoplates (Au-NPs) by using a biocompatible tri-block copolymer, pluronic F-127. Pluronic F-127 acts as a reducing, stabilizing and shape directing agent. Its hydrophobic polypropylene oxide (PPO) unit, preferentially binds to the {111} planes of FCC Au nuclei, inhibiting the growth on {111} crystallographic planes and promotes anisotropic growth along the {110} facets. Well faceted hexagonal, triangular and truncated triangular plates are obtained whose size ranges from 46 nm to 108 nm. These gold nanoplates exhibit strong surface plasmon resonance corresponding to in-plane quadruple vibrations which are tunable from 810 nm to 900 nm in the near-infrared (NIR) region. Aging effect of gold nanoplates are also monitored in terms of their plasmonic properties over a period of several weeks as synthesized nanoplates when preserved in pluronic F-127 demonstrate impressive stability over a period of several weeks. Tunable absorption of biocompatible gold nanoplates in the NIR region opens up new possibilities in the field of cancer diagnostics and therapeutics. The aging effect on the plasmon bands of Au-NPs is also monitored for several weeks when preserved in pluronic solvent.

Augmenting the catalytic performance of spinel nanoferrites (CoFe2O4 and NiFe2O4) via incorporation of Al into the lattice

Spinel nanoferrites have emerged as outstanding catalysts for a variety of organic transformations and reactions. Spinel nanoferrites also possess the complementary benefit of facile and complete external magnet-aided recovery. Further improvement in the catalytic performance of spinel nanoferrites is currently a vibrant area of research. In this context, in the present investigation, Al has been incorporated into the lattice of spinel nanoferrites. Owing to its octahedral site preference, Al could actively participate in the reaction mechanism as octahedral sites are exposed upon the surface and catalytic activity is predominantly related to the metal ions present in these sites. Al content has varied from x = 0.2 to x = 1.0 when incorporated into the lattice of CoFe2O4 and NiFe2O4 as CoAlxFe2−xO4 and NiAlxFe2−xO4, respectively. Catalytic activity has been evaluated for the reduction of nitrophenols in the presence of NaBH4 as the reducing agent. The catalytic activity has been found to increase with increasing Al content up to x = 0.6, before decreasing with further increase in Al content. The effect of increasing Al content on the catalytic performance is thought to be related to synergistic interactions among the metal ions present in the surface-exposed octahedral sites.

Study of seed aging in seed-mediated synthesis of IR responsive gold nanorods

Gold nanorods (GNRs) are one of the potential candidates for Plasmonic Photothermal Therapy (PPTT). In this article we report the synthesis of IR responsive GNRs by seed mediated method and investigated the role of seed aging on the synthesis of GNRs. The Longitudinal surface plasmon resonance (LSPR) band blue shifts while transverse surface plasmon resonance (TSPR) band does not show any considerable drift with seed aging. A fresh seed solution is essential for the synthesis of IR responsive GNRs. No gold nanorods are formed when seed solution is aged for 72 h.