Core-shell NaHoF4@TiO2 NPs: A labelling method to trace engineered nanomaterials of ubiquitous elements in the environment

Understanding the fate and behavior of nanoparticles (NPs) in the natural environment is important to assess their potential risk. Single particle inductively coupled plasma mass spectrometry (spICP-MS) allows for the detection of NPs at extremely low concentrations, but the high natural background of the constituents of many of the most widely utilized nanoscale materials makes accurate quantification of engineered particles challenging. Chemical doping, with a less naturally abundant element, is one approach to address this; however, certain materials with high natural abundance, such as TiO2 NPs, are notoriously difficult to label and differentiate from natural NPs. Using the low abundance rare earth element Ho as a marker, Ho-bearing core -TiO2 shell (NaHoF4@TiO2) NPs were designed to enable the quantification of engineered TiO2 NPs in real environmental samples. The NaHoF4@TiO2 NPs were synthesized on a large scale (gram), at relatively low temperatures, using a sacrificial Al(OH)3 template that confines the hydrolysis of TiF4 within the space surrounding the NaHoF4 NPs. The resulting NPs consist of a 60 nm NaHoF4 core and a 5 nm anatase TiO2 shell, as determined by TEM, STEM-EDX mapping, and spICPMS. The NPs exhibit excellent detectability by spICP-MS at extremely low concentrations (down to 1 × 10−3 ng/L) even in complex natural environments with high Ti background

Bioaccumulation and Toxicity of CuO Nanoparticles by a Freshwater Invertebrate after Waterborne and Dietborne Exposures

The incidental ingestion of engineered nanoparticles (NPs) can be an important route of uptake for aquatic organisms. Yet, knowledge of dietary bioavailability and toxicity of NPs is scarce. Here we used isotopically modified copper oxide (⁶⁵CuO) NPs to characterize the processes governing their bioaccumulation in a freshwater snail after waterborne and dietborne exposures. <i>Lymnaea stagnalis</i> efficiently accumulated ⁶⁵Cu after aqueous and dietary exposures to ⁶⁵CuO NPs. Cu assimilation efficiency and feeding rates averaged 83% and 0.61 g g^–1 d^–1 at low exposure concentrations (<100 nmol g^–1), and declined by nearly 50% above this concentration. We estimated that 80–90% of the bioaccumulated ⁶⁵Cu concentration in <i>L. stagnalis</i> originated from the ⁶⁵CuO NPs, suggesting that dissolution had a negligible influence on Cu uptake from the NPs under our experimental conditions. The physiological loss of ⁶⁵Cu incorporated into tissues after exposures to ⁶⁵CuO NPs was rapid over the first days of depuration and not detectable thereafter. As a result, large Cu body concentrations are expected in <i>L. stagnalis</i> after exposure to CuO NPs. To the degree that there is a link between bioaccumulation and toxicity, dietborne exposures to CuO NPs are likely to elicit adverse effects more readily than waterborne exposures

Time-resolved toxicity study reveals the dynamic interactions between uncoated silver nanoparticles and bacteria

<p>It is still unclear whether the toxicity of silver nanoparticles (AgNPs) can be attributed solely to the release of Ag⁺ or whether dissolved and nanoparticulate Ag act in parallel; this is due to the difficulty in distinguishing Ag⁺- from AgNP-effects. Also, AgNPs undergo changes during toxicity tests. This is the first study to investigate the influence of AgNP dissolution over time on viable counts at high time resolution and low cell density, avoiding the apparently reduced toxicity at higher cell densities identified in our study. Uncapped AgNPs were synthesized to avoid any interference from surface coatings. The transformations of AgNPs during storage were reduced. Lowering the concentration of AgNPs reduced their aggregation in Davis minimal medium (DMM). Also, AgNPs dissolved more slowly in DMM than in water. The minimum inhibitory concentrations (MICs) of Ag⁺ and AgNPs increased with cell density according to a power law, suggesting that binding to cells decreased effective concentrations. However, AgNPs acted as a reservoir of Ag, releasing new Ag⁺ to maintain the Ag stress. The toxicity of AgNPs was dominated by dissolved Ag. Combining controlled conditions, high time-resolution and low cell density, we could demonstrate different roles of ionic and nano Ag in bacterial death caused by AgNPs.</p

Serum proteins that bind to nano-SiO₂ particles.

<p>Nano-SiO₂ particles were incubated with fetal bovine serum under the same conditions as those used to treat A549 cells. The nanoparticles were recovered and bound proteins identified by proteomics as described in Materials and Methods. The table lists the main proteins identified in each row (the 4 with the highest Sf scores; minimum score of 3.0) and the rows in which they were present. Underlined symbols indicate the row where the highest protein coverage was found. The MW equivalent to the centre of each row is indicated. The experiment was performed twice and also repeated in the presence of A549 cells. A similar result was found on each occasion, i.e. all proteins identified were bovine in origin and none could be attributed to a human source (i.e. A549 cells). MS details supporting the identification of the proteins are provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0072363#pone.0072363.s003" target="_blank">Table S2</a>.</p

Elucidation of Toxicity Pathways in Lung Epithelial Cells Induced by Silicon Dioxide Nanoparticles

<div><p>A study into the effects of amorphous nano-SiO₂ particles on A549 lung epithelial cells was undertaken using proteomics to understand the interactions that occur and the biological consequences of exposure of lung to nanoparticles. Suitable conditions for treatment, where A549 cells remained viable for the exposure period, were established by following changes in cell morphology, flow cytometry, and MTT reduction. Label-free proteomics was used to estimate the relative level of proteins from their component tryptic peptides detected by mass spectrometry. It was found that A549 cells tolerated treatment with 100 µg/ml nano-SiO₂ in the presence of 1.25% serum for at least 4 h. After this time detrimental changes in cell morphology, flow cytometry, and MTT reduction were evident. Proteomics performed after 4 h indicated changes in the expression of 47 proteins. Most of the proteins affected fell into four functional groups, indicating that the most prominent cellular changes were those that affected apoptosis regulation (<i>e.g.</i> UCP2 and calpain-12), structural reorganisation and regulation of actin cytoskeleton (<i>e.g.</i> PHACTR1), the unfolded protein response (<i>e.g.</i> HSP 90), and proteins involved in protein synthesis (<i>e.g.</i> ribosomal proteins). Treatment with just 10 µg/ml nano-SiO₂ particles in serum-free medium resulted in a rapid deterioration of the cells and in medium containing 10% serum the cells were resistant to up to 1000 µg/ml nano-SiO₂ particles, suggesting interaction of serum components with the nanoparticles. A variety of serum proteins were found which bound to nano-SiO₂ particles, the most prominent of which were albumin, apolipoprotein A-I, hemoglobin, vitronectin and fibronectin. The use of a proteomics platform, with appropriately designed experimental conditions, enabled the early biological perturbations induced by nano-SiO₂ in a model target cell system to be identified. The approach facilitates the design of more focused test systems for use in tiered evaluations of nanomaterials.</p></div

Immunoreactive levels of UCP2.

<p>Immunoblotting was performed on A549 cell homogenates following treatment with vehicle or nano-SiO₂ and developed with antibodies against (A) UCP2 or (B) actin. The relative intensity of the immunoreactive bands was determined by densitometry as described in the Materials and Methods.</p

Analysis of proteins that bind to nano-SiO₂ particles.

<p>Nano-SiO₂ particles were incubated with 1.25% serum only or 1.25% serum and A549 cells. The nanoparticles were recovered and washed by centrifugation and then bound proteins separated by SDS-PAGE which were stained with InstantBlue. For proteomic analysis the gel was cut into 11 horizontal slices based on the migration of proteins markers and the bands in the material eluted from the nanoparticles. Each slice was further divided between each of the protein lanes for analysis by proteomics as detailed in the Materials and Methods.</p

Volcano plot analysis showing the effect of nano-SiO₂ treatment on protein expression in A549 cells.

<p>For each protein detected the relative level of protein expression following treatment is depicted on the basis of both fold change and statistical difference. The main proteins of interest are those furthest from the origin, and these are indicated as open triangles.</p

MXenes: Synthesis, properties, and applications for sustainable energy and environment

MXenes, the largest and most diverse group of emerging two-dimensional materials, have potential across multiple applications. The increasing attention is driven by the fascinating tunable surface properties, and synergetic chemistry facilitated by the presence of multiple chemical bonds dominated by covalent and metallic bonds between transition metals (M) and non-metals, X (such as carbon, nitrogen, or both). Although the various available synthesis approaches offer opportunities for tuning MXenes for specific applications, their inherent environmental and toxicity risks as well as poor scale-up potential are currently hampering research and commercialization progress. Therefore, ongoing efforts are focused on developing less hazardous, scalable methodologies to limit the barriers. This review comprehensively surveys the literature from the seminal MXene paper to the present, offering insights into the factors, latest advancements, limitations, trends, and existing gaps in MXene synthesis, properties, and applications in the areas of environment and energy storage. Special emphasis is placed on the need to address environmental concerns associated with fluoride-based synthesis while an overview of safer, non-fluoride alternatives is provided. Furthermore, the most recent breakthroughs in scalable top-down dry selective etching (DSE), bottom-up solid-state direct synthesis, and structural editing protocol using chemical scissors are presented. In particular, this review critically examines the current state of knowledge and identifies key research progresses and areas that deserve intensive attention to facilitate safe and industrial-scale synthesis and application of MXenes for catalysis, environmental remediation, and energy storage. Addressing the identified gaps will accelerate the transformation of MXenes and their composites into the components of our everyday appliances.</p

Physico-chemical characteristics of the nano-SiO₂ preparation.

<p>(A) XRD analysis confirming the sample is amorphous silica. (B) FTIR spectrum indicating the presence of non-functionalised surfaces in the sample. (C) TEM image showing monodispersed particles with an average size of 25±2 nm. (D) DLS intensity weighed particle size distributions of nano-SiO₂ particles in water, cell culture medium containing 1.25% serum (in the absence of nano-SiO₂ particles), nano-SiO₂ particles in cell culture medium containing 1.25% serum immediately after dispersion (0 h) and then after incubation at 37°C for 4 h and 24 h. (E) Changes in the average particle size (estimated from DLS) of nano-SiO₂ dispersed in culture medium containing 1.25% serum at 37°C for up to 24 h.</p