Investigating the transport and colloidal behavior of Fe3O4 nanoparticles in aqueous and porous media under varying solution chemistry parameters.

The possible adverse effects of engineered iron oxide nanoparticles, especially magnetite (Fe3O4 NP), on human health and the environment, have raised concerns about their transport and behavior in soil and water systems. Accumulating these NPs in the environment can substantially affect soil and water quality and the well-being of aquatic and terrestrial organisms. Therefore, it is essential to examine the factors that affect Fe3O4 NP transportation and behavior in soil and water systems to determine their possible environmental fate. In this work, experiments were conducted in aqueous and porous media using an environmentally relevant range of pH (5, 7, 9), ionic strength (IS) (10, 50, 100 mM), and humic acid (HA) (0.1, 1, 10 mg L-1) concentrations. Fe3O4 NPs exhibited severe colloidal instability at pH 7 (⁓ = pHPZC) and showed an improvement in apparent colloidal stability at pH 5 and 9 in aquatic and terrestrial environments. HA in the background solutions promoted the overall transport of Fe3O4 NPs by enhancing the colloidal stability. The increased ionic strength in aqueous media hindered the transport by electron double-layer compression and electrostatic repulsion; however, in porous media, the transport was hindered by ionic compression. Furthermore, the transport behavior of Fe3O4 NPs was investigated in different natural waters such as rivers, lakes, taps, and groundwater. The interaction energy pattern in aquatic systems was estimated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This study showed the effects of various physical-chemical conditions on Fe3O4 NP transport in aqueous and porous (sand) media.

Bio-based nanoemulsion formulation, characterization and antibacterial activity against food-borne pathogens.

The current study deals with the formulation and characterization of bio-based oil in water nanoemulsion and its potential antibacterial activity. A typical v/v% of eucalyptus oil (16.66%), Tween 80 (16.66%), and water (68.68%) was prepared by ultrasonication method. The mean droplet size was 17.1 nm as confirmed by dynamic light scattering. Different concentrations of the formulation ranging from undiluted to 10-, 100-, and 1000-fold dilutions were used to check the antibacterial activity in three different microorganisms, namely, Bacillus cereus, Staphylococcus aureus (Gram-positive), and Escherichia coli (Gram-negative). All three species showed a 100% bactericidal at the 10-fold dilution of the nanoemulsion formulation in the following order: B. cereus at 0th min, S. aureus at 15 min and E. coli at 1 h, respectively. A 10-fold dilution of the nanoemulsion showed that, the cytoplasmic content leakage from the bacterial species was high for S. aureus when compared to B. cereus and E. coli as determined by UV-Vis spectroscopic method. Fluorescence microscopic technique further confirmed this study.

Biosynthesis of silver nanoparticles using actinobacterium Streptomyces albogriseolus and its antibacterial activity.

An eco-friendly approach to the synthesis of silver nanoparticles (AgNPs) by extracellular components of Streptomyces albogriseolus has been reported. The isolated actinobacteria were genotypically identified by 16S rRNA sequencing analysis, and the morphology was observed by high-resolution scanning electron microscopy. The preliminary characterization of synthesized nanoparticles was carried out using ultraviolet-visible spectrophotometer. The maximum absorption spectra were found to be 409 nm at the 48th hour of incubation. The yield of AgNPs was found to be 72.64% as quantified by an atomic absorption spectrophotometer. The average size of AgNPs determined by the dynamic light scattering technique was 16.25 ± 1.6 nm. The results from transmission electron microscopy and X-ray diffraction confirmed the formation of spherical shaped and crystalline AgNPs. The interaction of protein with AgNPs was confirmed by Fourier transform infrared spectroscopy analysis. The biosynthesized AgNPs inhibited the growth of food pathogens (Bacillus cereus, Escherichia coli, and Staphylococcus aureus). Hence, the synthesis of AgNPs by S. albogriseolus could be employed as a probable antimicrobial agent to eliminate pathogenic microorganisms. This approach employed for the synthesis of nanoparticles paves a path for new biomaterial interfaces, which could be applied in different biomedical fields.