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.

Antibacterial activities of silver nanoparticles and antibiotic-adsorbed silver nanoparticles against biorecycling microbes.

Silver nanoparticles have a huge share in nanotechnology based products used in clinical and hygiene products. Silver nanoparticles leaching from these medical and domestic products will eventually enter terrestrial ecosystems and will interact with the microbes present in the land and water. These interactions could be a threat to biorecycling microbes present in the Earth's crust. The antimicrobial action towards biorecycling microbes by leached silver nanoparticles from medical waste could be many times greater compared to that of silver nanoparticles leached from other domestic products, since medical products may contain traditional antibiotics along with silver nanoparticles. In the present article, we have evaluated the antimicrobial activities of as-synthesized silver nanoparticles, antibiotics - tetracycline and kanamycin, and antibiotic-adsorbed silver nanoparticles. The antimicrobial action of silver nanoparticles with adsorbed antibiotics is 33-100% more profound against the biorecycling microbes B. subtilis and Pseudomonas compared to the antibacterial action of silver nanoparticles of the same concentration. This study indicates that there is an immediate and urgent need for well-defined protocols for environmental exposure to silver nanoparticles, as the use of silver nanoparticles in nanotechnology based products is poorly restricted.

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.