Heterogeneous Rate Constant for Amorphous Silica Nanoparticle Adsorption on Phospholipid Monolayers.

The interaction of amorphous silica nanoparticles with phospholipid monolayers and bilayers has received a great deal of interest in recent years and is of importance for assessing potential cellular toxicity of such species, whether natural or synthesized for the purpose of nanomedical drug delivery and other applications. This present communication studies the rate of silica nanoparticle adsorption on to phospholipid monolayers in order to extract a heterogeneous rate constant from the data. This rate constant relates to the initial rate of growth of an adsorbed layer of nanoparticles as SiO2 on a unit area of the monolayer surface from unit concentration in dispersion. Experiments were carried out using the system of dioleoyl phosphatidylcholine (DOPC) monolayers deposited on Pt/Hg electrodes in a flow cell. Additional studies were carried out on the interaction of soluble silica with these layers. Results show that the rate constant is effectively constant with respect to silica nanoparticle size. This is interpreted as indicating that the interaction of hydrated SiO2 molecular species with phospholipid polar groups is the molecular initiating event (MIE) defined as the initial interaction of the silica particle surface with the phospholipid layer surface promoting the adsorption of silica nanoparticles on DOPC. The conclusion is consistent with the observed significant interaction of soluble SiO2 with the DOPC layer and the established properties of the silica-water interface.

Impact of Ag2S NPs on soil bacterial community - A terrestrial mesocosm approach.

Soils might be a final sink for Ag2S nanoparticles (NPs). Still, there are limited data on their effects on soil bacterial communities (SBC). To bridge this gap, we investigated the effects of Ag2S NPs (10 mg kg-1 soil) on the structure and function of SBC in a terrestrial indoor mesocosm, using a multi-species design. During 28 days of exposure, the SBC function-related parameters were analysed in terms of enzymatic activity, community level physiological profile, culture of functional bacterial groups [phosphorous-solubilizing bacteria (P-SB) and heterotrophic bacteria (HB)], and SBC structure was analysed by 16S rRNA gene-targeted denaturing gradient gel electrophoresis. The SBC exposed to Ag2S NPs showed a significative decrease of functional parameters, such as ß-glucosidase activity and L-arginine consumption, and increase of the acid phosphatase activity. At the structural level, significantly lower richness and diversity were detected, but at later exposure times compared to the AgNO3 treatment, likely because of a low dissolution rate of Ag2S NPs. In fact, stronger effects were observed in soils spiked with AgNO3, in both functional and structural parameters. Changes in SBC structure seem to negatively correlate with parameters related to phosphorous (acid phosphatase activity) and carbon cycling (abundance of HB, P-SB, and ß-glucosidase activity). Our results indicate a significant effect of Ag2S NPs on SBC, specifically on parameters related to carbon and phosphorous cycling, at doses as low as 10 mg kg-1 soil. These effects were only observed after 28 days, highlighting the importance of long-term exposure experiments for slowly dissolving NPs.

Toxicity of nickel in the marine calanoid copepod Acartia tonsa: Nickel chloride versus nanoparticles.

Nickel compounds are widely used in industries and have been massively introduced in the environment in different chemical forms. Here we report the effect of two different chemical forms of nickel, NiCl2 and nickel nanoparticles (NiNPs), on the reproduction of the marine calanoid copepod Acartia tonsa. The behavior of nickel nanoparticles was analyzed with different techniques and with two protocols. In the "sonicated experiment" (SON) NiNP solution was sonicated while in the "non-sonicated experiment" (NON-SON) the solution was vigorously shaken by hand. Final nominal concentrations of 5, 10 and 50mgL(-1) and 1, 5 and 10mgL(-1) NiNPs were used for the acute and semichronic tests, respectively. Nanoparticle size did not change over time except for the highest concentration of 50mgL(-1) NiNPs, in which the diameter increased up to 843nm after 48h. The concentration of Ni dissolved in the water increased with NP concentration and was similar for SON and NON-SON solutions. Our results indicate that sonication does not modify toxicity for the copepod A. tonsa. Mean EC50 values were similar for NON-SON (20.2mgL(-1)) and SON experiments (22.14mgL(-1)) in the acute test. Similarly, no differences occurred between the two different protocols in the semichronic test, with an EC50 of 7.45mgL(-1) and 6.97mgL(-1) for NON-SON and SON experiments, respectively. Acute and semichronic tests, conducted exposing A. tonsa embryos to NiCl2 concentrations from 0.025 to 0.63mgL(-1), showed EC50 of 0.164 and 0.039mgL(-1), respectively. Overall, A. tonsa is more sensitive to NiCl2 than NiNPs with EC50 being one order of magnitude higher for NiNPs. Finally, we exposed adult copepods for 4 days to NiCl2 and NiNPs (chronic exposure) to study the effect on fecundity in terms of daily egg production and naupliar viability. Egg production is not affected by either form of nickel, whereas egg viability is significantly reduced by 0.025mgL(-1) NiCl2 and by 8.5mgL(-1) NiNPs. At NiNP concentration below the acute EC50 (17mgL(-1)) only 9% of embryos hatched after 4 days. Interestingly, the percentage of naupliar mortality (>82%) observed in the semichronic test at the nominal concentration of 10mgL(-1) NiNPs corresponding to almost 0.10mgL(-1) of dissolved Ni, was similar to that recorded at the same Ni salt concentration. Electron microscopical analyses revealed that A. tonsa adults ingest NiNPs and excrete them through fecal pellets. To the best of our knowledge, this is the first study investigating the toxicity of two different forms of Ni on the reproductive physiology of the copepod A. tonsa and showing the ability of the calanoid copepod to ingest nanoparticles from seawater.

Dipolar magnetism in ordered and disordered low-dimensional nanoparticle assemblies.

Magnetostatic (dipolar) interactions between nanoparticles promise to open new ways to design nanocrystalline magnetic materials and devices if the collective magnetic properties can be controlled at the nanoparticle level. Magnetic dipolar interactions are sufficiently strong to sustain magnetic order at ambient temperature in assemblies of closely-spaced nanoparticles with magnetic moments of ≥ 100 µ(B). Here we use electron holography with sub-particle resolution to reveal the correlation between particle arrangement and magnetic order in self-assembled 1D and quasi-2D arrangements of 15 nm cobalt nanoparticles. In the initial states, we observe dipolar ferromagnetism, antiferromagnetism and local flux closure, depending on the particle arrangement. Surprisingly, after magnetic saturation, measurements and numerical simulations show that overall ferromagnetic order exists in the present nanoparticle assemblies even when their arrangement is completely disordered. Such direct quantification of the correlation between topological and magnetic order is essential for the technological exploitation of magnetic quasi-2D nanoparticle assemblies.

What can nanotechnology do to fight cancer?

The marriage of physics, chemistry and biology at the namometric scale, nanotechnology, is a powerful technology which is predicted to have a large impacto on life sciences and particularly cancer treatment. In the following we will show some examples of applications which has already reached clinical treatments as new ideas which may positively influence the understanding, diagnosis and therapy of cancer (AU)

Colloidal nanocrystal shape and size control: the case of cobalt.

We show that a relatively simple approach for controlling the colloidal synthesis of anisotropic cadmium selenide semiconductor nanorods can be extended to the size-controlled preparation of magnetic cobalt nanorods as well as spherically shaped nanocrystals. This approach helps define a minimum feature set needed to separately control the sizes and shapes of nanocrystals. The resulting cobalt nanocrystals produce interesting two- and three-dimensional superstructures, including ribbons of nanorods.