Nidhi Andhariya

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.

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.