Extensive photochemical restructuring of molecule-metal surfaces under room light

The molecule-metal interface is of paramount importance for many devices and processes, and directly involved in photocatalysis, molecular electronics, nanophotonics, and molecular (bio-)sensing. Here the photostability of this interface is shown to be sensitive even to room light levels for specific molecules and metals. Optical spectroscopy is used to track photoinduced migration of gold atoms when functionalised with different thiolated molecules that form uniform monolayers on Au. Nucleation and growth of characteristic surface metal nanostructures is observed from the light-driven adatoms. By watching the spectral shifts of optical modes from nanoparticles used to precoat these surfaces, we identify processes involved in the photo-migration mechanism and the chemical groups that facilitate it. This photosensitivity of the molecule-metal interface highlights the significance of optically induced surface reconstruction. In some catalytic contexts this can enhance activity, especially utilising atomically dispersed gold. Conversely, in electronic device applications such reconstructions introduce problematic aging effects.

Correction to "Searching for the Rules of Electrochemical Nitrogen Fixation"

[This corrects the article DOI: 10.1021/acscatal.3c03951.].

Probing Degradation in Lithium Ion Batteries with On-Chip Electrochemistry Mass Spectrometry

The rapid uptake of lithium ion batteries (LIBs) for large scale electric vehicle and energy storage applications requires a deeper understanding of the degradation mechanisms. Capacity fade is due to the complex interplay between phase transitions, electrolyte decomposition and transition metal dissolution; many of these poorly understood parasitic reactions evolve gases as a side product. Here we present an on-chip electrochemistry mass spectrometry method that enables ultra-sensitive, fully quantified and time resolved detection of volatile species evolving from an operating LIB. The technique's electrochemical performance and mass transport is described by a finite element model and then experimentally used to demonstrate the variety of new insights into LIB performance. We show the versatility of the technique, including (a) observation of oxygen evolving from a LiNiMnCoO2 cathode and (b) the solid electrolyte interphase formation reaction on graphite in a variety of electrolytes, enabling the deconvolution of lithium inventory loss (c) the first direct evidence, by virtue of the improved time resolution of our technique, that carbon dioxide reduction to ethylene takes place in a lithium ion battery. The emerging insight will guide and validate battery lifetime models, as well as inform the design of longer lasting batteries.

Searching for the Rules of Electrochemical Nitrogen Fixation

Li-mediated ammonia synthesis is, thus far, the only electrochemical method for heterogeneous decentralized ammonia production. The unique selectivity of the solid electrode provides an alternative to one of the largest heterogeneous thermal catalytic processes. However, it is burdened with intrinsic energy losses, operating at a Li plating potential. In this work, we survey the periodic table to understand the fundamental features that make Li stand out. Through density functional theory calculations and experimentation on chemistries analogous to lithium (e.g., Na, Mg, Ca), we find that lithium is unique in several ways. It combines a stable nitride that readily decomposes to ammonia with an ideal solid electrolyte interphase, balancing reagents at the reactive interface. We propose descriptors based on simulated formation and binding energies of key intermediates and further on hard and soft acids and bases (HSAB principle) to generalize such features. The survey will help the community toward electrochemical systems beyond Li for nitrogen fixation.

Correction: The role of ion solvation in lithium mediated nitrogen reduction

[This corrects the article DOI: 10.1039/D2TA07686A.].

The role of ion solvation in lithium mediated nitrogen reduction

Since its verification in 2019, there have been numerous high-profile papers reporting improved efficiency of lithium-mediated electrochemical nitrogen reduction to make ammonia. However, the literature lacks any coherent investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we discover that the salt concentration has a remarkable effect on electrolyte stability: at concentrations of 0.6 M LiClO₄ and above the electrode potential is stable for at least 12 hours at an applied current density of -2 mA cm^-2 at ambient temperature and pressure. Conversely, at the lower concentrations explored in prior studies, the potential required to maintain a given N₂ reduction current increased by 8 V within a period of 1 hour under the same conditions. The behaviour is linked more coordination of the salt anion and cation with increasing salt concentration in the electrolyte observed via Raman spectroscopy. Time of flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy reveal a more inorganic, and therefore more stable, SEI layer is formed with increasing salt concentration. A drop in faradaic efficiency for nitrogen reduction is seen at concentrations higher than 0.6 M LiClO₄, which is attributed to a combination of a decrease in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by electrochemical impedance spectroscopy.

Nonaqueous Li-Mediated Nitrogen Reduction: Taking Control of Potentials

The performance of the Li-mediated ammonia synthesis has progressed dramatically since its recent reintroduction. However, fundamental understanding of this reaction is slower paced, due to the many uncontrolled variables influencing it. To address this, we developed a true nonaqueous LiFePO₄ reference electrode, providing both a redox anchor from which to measure potentials against and estimates of sources of energy efficiency loss. We demonstrate its stable electrochemical potential in operation using different N₂- and H₂-saturated electrolytes. Using this reference, we uncover the relation between partial current density and potentials. While the counter electrode potential increases linearly with current, the working electrode remains stable at lithium plating, suggesting it to be the only electrochemical step involved in this process. We also use the LiFePO₄/Li⁺ equilibrium as a tool to probe Li-ion activity changes in situ. We hope to drive the field toward more defined systems to allow a holistic understanding of this reaction.

Metal coordination in C2N-like materials towards dual atom catalysts for oxygen reduction

Single-atom catalysts, in particular the Fe-N-C family of materials, have emerged as a promising alternative to platinum group metals in fuel cells as catalysts for the oxygen reduction reaction. Numerous theoretical studies have suggested that dual atom catalysts can appreciably accelerate catalytic reactions; nevertheless, the synthesis of these materials is highly challenging owing to metal atom clustering and aggregation into nanoparticles during high temperature synthesis treatment. In this work, dual metal atom catalysts are prepared by controlled post synthetic metal-coordination in a C2N-like material. The configuration of the active sites was confirmed by means of X-ray adsorption spectroscopy and scanning transmission electron microscopy. During oxygen reduction, the catalyst exhibited an activity of 2.4 ± 0.3 A gcarbon -1 at 0.8 V versus a reversible hydrogen electrode in acidic media, comparable to the most active in the literature. This work provides a novel approach for the targeted synthesis of catalysts containing dual metal sites in electrocatalysis.

ZnO Nanomaterials and Ionic Zn Partition within Wastewater Sludge Investigated by Isotopic Labeling

The increasing commercial use of engineered zinc oxide nanomaterials necessitates a thorough understanding of their behavior following their release into wastewater. Herein, the fates of zinc oxide nanoparticles (ZnO NPs) and ionic Zn in a real primary sludge collected from a municipal wastewater system are studied via stable isotope tracing at an environmentally relevant spiking concentration of 15.2 µg g^-1. Due to rapid dissolution, nanoparticulate ZnO does not impart particle-specific effects, and the Zn ions from NP dissolution and ionic Zn display indistinguishable behavior as they partition equally between the solid, liquid, and ultrafiltrate phases of the sludge over a 4-h incubation period. This work provides important constraints on the behavior of engineered ZnO nanomaterials in primary sludge-the first barrier in a wastewater treatment plant-at low, realistic concentrations. As the calculated solid-liquid partition coefficients are significantly lower than those reported in prior studies that employ unreasonably high spiking concentrations, this work highlights the importance of using low, environmentally relevant doses of engineered nanomaterials in experiments to obtain accurate risk assessments.

Acid resistant functionalised magnetic nanoparticles for radionuclide and heavy metal adsorption

Coating superparamagnetic iron oxide NPs with SiO₂ has been established in order to confer stability in acidic media. Acid stability tests were carried out between pH 1 and pH 7 to determine the effectiveness of the SiO₂ passivating layer to protect the magnetic Fe₃O₄ core. Transmission Electron Microscopy (TEM) and zeta potential measurements have shown that uncoated Fe₃O₄ NPs exhibit rapid agglomeration and dissolution when exposed to acidic media, moving from a zeta potential of - 26 mV to a zeta potential of + 3 mV. In contrast, the SiO₂ coating of the Fe₃O₄ NPs shows a very high degree of stability for over 14 months and the zeta potential of these NPs remained at ∼- 39 mV throughout the acid exposure and they showed no loss in magnetisaton. Due to the use of these NPs as a potential tool for heavy metal extraction, the stability of the surface functionalisation (in this case a phosphate complex) was also assessed. With a constant zeta potential of ∼ - 29 mV for PO_x-SiO₂@Fe₃O₄ NP complex, the phosphate functionality was shown to be highly stable in the acidic conditions simulating the environment of certain nuclear wastes. ATR-FTIR was conducted after acid exposure confirming that the phosphate complex on the surface of the NPs remained present. Finally, preliminary sorption experiments were carried out with Pb(II), where the NP complexes shown complete removal of the heavy metals at pH 3 and pH 5.

Contamination of domestic groundwater systems by verotoxigenic escherichia coli (VTEC), 2003-2019: A global scoping review

Verocytotoxin-producing E. coli (VTEC) are important agents of diarrhoeal disease in humans globally. As a noted waterborne disease, emphasis has been given to the study VTEC in surface waters, readily susceptible to microbial contamination. Conversely, the status of VTEC in potable groundwater sources, generally regarded as a "safe" drinking-water supply remains largely understudied. As such, this investigation presents the first scoping review seeking to determine the global prevalence of VTEC in groundwater supply sources intended for human consumption. Twenty-three peer-reviewed studies were identified and included for data extraction. Groundwater sample and supply detection rates (estimated 0.6 and 1.3%, respectively) indicate VTEC is infrequently present in domestic groundwater sources. However, where generic (fecal indicator) E. coli are present, the VTEC to E. coli ratio was found to be 9.9%, representing a latent health concern for groundwater consumers. Geographically, extracted data indicates higher VTEC detection rates in urban (5.4%) and peri‑urban (4.9%) environments than in rural areas (0.9%); however, this finding is confounded by the predominance of research studies in lower income regions. Climate trends indicate local environments classified as 'temperate' (14/554; 2.5%) and 'cold' (8/392; 2%) accounted for a majority of supply sources with VTEC present, with similar detection rates encountered among supplies sampled during periods typically characterized by 'high' precipitation (15/649; 2.3%). Proposed prevalence figures may find application in preventive risk-based catchment and groundwater quality management including development of Quantitative Microbial Risk Assessments (QMRA). Notwithstanding, to an extent, a large geographical disparity in available investigations, lack of standardized reporting, and bias in source selection, restrict the transferability of research findings. Overall, the mechanisms responsible for VTEC transport and ingress into groundwater supplies remain ambiguous, representing a critical knowledge gap, and denoting a distinctive lack of integration between hydrogeological and public health research. Key recommendations and guidelines are provided for prospective studies directed at increasingly integrative and multi-disciplinary research.

Approaches to treating tuberculosis by encapsulating metal ions and anti-mycobacterial drugs utilizing nano- and microparticle technologies

Tuberculosis (TB) is caused by a bacterial infection that affects a number of human organs, primarily the lungs, but also the liver, spleen, and spine, causing key symptoms of fever, fatigue, and persistent cough, and if not treated properly, can be fatal. Every year, 10 million individuals become ill with active TB resulting with a mortality approximating 1.5 million. Current treatment guidelines recommend oral administration of a combination of first-line anti-TB drugs for at least 6 months. While efficacious under optimum conditions, 'Directly Observed Therapy Short-course' (DOTS) is not without problems. The long treatment time and poor pharmacokinetics, alongside drug side effects lead to poor patient compliance and has accelerated the emergence of multi-drug resistant (MDR) organisms. All this, combined with the limited number of newly discovered TB drugs to treat MDR-TB and shorten standard therapy time, has highlighted the need for new targeted drug delivery systems. In this respect, there has been recent focus on micro- and nano-particle technologies to prepare organic or/and metal particles loaded with TB drugs to enhance their efficacy by targeted delivery via the inhaled route. In this review, we provide a brief overview of the current epidemiology of TB, and risk factors for progression of latent stage tuberculosis (LTBI) to the active TB. We identify current TB treatment regimens, newly discovered TB drugs, and identify studies that have used micro- or nano-particles technologies to design a reliable inhalation drug delivery system to treat TB more effectively.

Cryptosporidium spp. in groundwater supplies intended for human consumption - A descriptive review of global prevalence, risk factors and knowledge gaps

Cryptosporidiosis is one of the leading causes of diarrhoeal illness and mortality induced by protozoan pathogens worldwide. As a largely waterborne disease, emphasis has been given to the study of Cryptosporidium spp. in surface waters, readily susceptible to pathogenic contamination. Conversely, the status of Cryptosporidium in potable groundwater sources, generally regarded as a pristine and "safe" drinking-water supply owing to (sub)-soil protection, remains largely unknown. As such, this investigation presents the first literature review aimed to ascertain the global prevalence of Cryptosporidium in groundwater supply sources intended for human consumption. Thirty-seven peer-reviewed studies were identified and included in the review. Groundwater sample and supply detection rates (estimated 10-20%) indicate Cryptosporidium is frequently present in domestic groundwater sources, representing a latent health concern for groundwater consumers. Specifically, sample (10.4%) and source (19.1%) detection rates deriving from comprehensive "temporal" investigations are put forward as representative of a contamination 'baseline' for Cryptosporidium in 'domestic' groundwater supplies. Proposed 'baseline' prevalence figures are largely applicable in preventive risk-based catchment and groundwater quality management including the formulation of Quantitative Microbial Risk Assessment (QMRA). Notwithstanding, a large geographical disparity in available investigations and lack of standardized reporting restrict the transferability of research findings. Overall, the mechanisms responsible for Cryptosporidium transport and ingress into groundwater supplies remain ambiguous, representing a critical knowledge gap, and denoting a distinctive lack of integration between groundwater and public-health sub-disciplines among investigations. Key recommendations and guidelines are provided for prospective studies directed at more integrative and multi-disciplinary research.

Role of Iron Speciation in Oxidation and Deposition at the Hexadecane-Iron Interface

Interactions between iron surfaces and hydrocarbons are the basis for a wide range of materials synthesis processes and novel applications, including sensing. However, in diesel engines these interactions can lead to deposit formation that reduces performance, lowers efficiency, and increases emissions. Here, we present a global study to understand deposition at iron-hexadecane interfaces. We use a combination of spectroscopy, microscopy, and mass spectrometry to investigate surface reactions, bulk chemistry, and deposition processes. A dynamic equilibrium between the oxidation products, both at the surface and in solution, determines the deposition at the surface. Considering the solution and the surface in parallel, we find that the iron speciation affects the morphology, composition, and quantity of the deposit at the surface, as well as the oxidation of hexadecane. Fe(II) and Fe(III) both promote the decomposition of peroxides-intermediates in the oxidation of hexadecane-but through noncatalytic and catalytic mechanisms, respectively. In contrast, Fe(0) is proposed to initiate hexadecane autoxidation during its oxidation to Fe(III). We find that in all cases, the surfaces exclusively contain Fe(III) following heat treatment with hexadecane. Upon subsequent exposure at room temperature, Fe(III) species are found to promote oxidation; this finding is particularly concerning for hybrid vehicles where longer time periods are expected between engine operation. Our work provides a foundation for the development of strategies that disrupt the role of iron in the degradation of hexadecane to ultimately reduce oxidation and deposition in diesel engines.

Geometry-induced protein reorientation on the spikes of plasmonic gold nanostars

Functionalized gold nanostars (AuStrs) are remarkable candidates for drug delivery, photothermal therapy and imaging due to their large surface area to volume ratio and plasmonic properties. In this study, we address the challenge of achieving therapeutically controlled dosing using these high aspect ratio nanoparticle vectors by tailoring the nanostar loading area and protein conformation. We synthesized a library of different Au nanostars with varied geometries for potential biomedical applications. The Au nanostars were subsequently coated with different amounts of transferrin (Tf) and a novel depletion method was devised to measure the amount of Tf bound to the surface of the nanostructures. This methodology allowed us to show that coating thickness could be controllably varied and moulded onto the nanoparticle's high index features, whilst simultaneously preserving the key properties of the particle. The orientation of the Tf was measured on nanostars and spheres using transmission electron microscopy by negatively staining the Tf. The Tf was conformal on the nanostars, and protein packing efficiency increased on the AuStrs by 14-fold due to a geometry-induced protein reorientation at the nanoparticle surface. Interestingly, the reorientation of the transferrin observed at the AuStrs spikes did not occur at the AuStrs tips thus highlighting surface energy effects associated with surface curvature.

Spatially Resolved Dissolution and Speciation Changes of ZnO Nanorods during Short-Term in Situ Incubation in a Simulated Wastewater Environment

Zinc oxide engineered nanomaterials (ZnO ENMs) are used in a variety of applications worldwide due to their optoelectronic and antibacterial properties with potential contaminant risk to the environment following their disposal. One of the main potential pathways for ZnO nanomaterials to reach the environment is via urban wastewater treatment plants. So far there is no technique that can provide spatiotemporal nanoscale information about the rates and mechanisms by which the individual nanoparticles transform. Fundamental knowledge of how the surface chemistry of individual particles change, and the heterogeneity of transformations within the system, will reveal the critical physicochemical properties determining environmental damage and deactivation. We applied a methodology based on spatially resolved in situ X-ray fluorescence microscopy (XFM), allowing observation of real-time dissolution and morphological and chemical evolution of synthetic template-grown ZnO nanorods (∼725 nm length, ∼140 nm diameter). Core-shell ZnO-ZnS nanostructures were formed rapidly within 1 h, and significant amounts of ZnS species were generated, with a corresponding depletion of ZnO after 3 h. Diffuse nanoparticles of ZnS, Zn₃(PO₄)₂, and Zn adsorbed to Fe-oxyhydroxides were also imaged in some nonsterically impeded regions after 3 h. The formation of diffuse nanoparticles was affected by ongoing ZnO dissolution (quantified by inductively coupled plasma mass spectrometry) and the humic acid content in the simulated sludge. Complementary ex situ X-ray absorption spectroscopy and scanning electron microscopy confirmed a significant decrease in the ZnO contribution over time. Application of time-resolved XFM enables predictions about the rates at which ZnO nanomaterials transform during their first stages of the wastewater treatment process.

Label-Free Time-of-Flight Secondary Ion Mass Spectrometry Imaging of Sulfur-Producing Enzymes inside Microglia Cells following Exposure to Silver Nanowires

There are no methods sensitive enough to detect enzymes within cells, without the use of analyte labeling. Here we show that it is possible to detect protein ion signals of three different H₂S-synthesizing enzymes inside microglia after pretreatment with silver nanowires (AgNW) using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Protein fragment ions, including the fragment of amino acid (C₄H₈N⁺ = 70 amu), fragments of the sulfur-producing cystathionine-containing enzymes, and the Ag⁺ ion signal could be detected without the use of any labels; the cells were mapped using the C₄H₈N⁺ amino acid fragment. Scanning electron microscopy imaging and energy-dispersive X-ray chemical analysis showed that the AgNWs were inside the same cells imaged by TOF-SIMS and transformed chemically into crystalline Ag₂S within cells in which the sulfur-producing proteins were detected. The presence of these sulfur-producing cystathionine-containing enzymes within the cells was confirmed by Western blots and confocal microscopy images of fluorescently labeled antibodies against the sulfur-producing enzymes. Label-free TOF-SIMS is very promising for the label-free identification of H₂S-contributing enzymes and their cellular localization in biological systems. The technique could in the future be used to identify which of these enzymes are most contributory.

Frizzled-7-targeted delivery of zinc oxide nanoparticles to drug-resistant breast cancer cells

There is a need for novel strategies to treat aggressive breast cancer subtypes and overcome drug resistance. ZnO nanoparticles (NPs) have potential in cancer therapy due to their ability to potently and selectively induce cancer cell apoptosis. Here, we tested the in vitro chemotherapeutic efficacy of ZnONPs loaded via a mesoporous silica nanolayer (MSN) towards drug-sensitive breast cancer cells (MCF-7: estrogen receptor-positive, CAL51: triple-negative) and their drug-resistant counterparts (MCF-7TX, CALDOX). ZnO-MSNs were coated on to gold nanostars (AuNSs) for future imaging capabilities in the NIR-II range. Electron and confocal microscopy showed that MSN-ZnO-AuNSs accumulated close to the plasma membrane and were internalized by cells. High-resolution electron microscopy showed that MSN coating degraded outside the cells, releasing ZnONPs that interacted with cell membranes. MSN-ZnO-AuNSs efficiently reduced the viability of all cell lines, and CAL51/CALDOX cells were more susceptible than MCF7/MCF-7-TX cells. MSN-ZnO-AuNSs were then conjugated with the antibody to Frizzled-7 (FZD-7), the receptor upregulated by several breast cancer cells. We used the disulphide (S-S) linker that could be cleaved with a high concentration of glutathione normally observed within cancer cells, releasing Zn2+ into the cytoplasm. FZD-7 targeting resulted in approximately three-fold amplified toxicity of MSN-ZnO-AuNSs towards the MCF-7TX drug-resistant cell line with the highest FZD-7 expression. This study shows that ZnO-MSs are promising tools to treat triple-negative and drug-resistant breast cancers and highlights the potential clinical utility of FZD-7 for delivery of nanomedicines and imaging probes specifically to these cancer types.

Tunable Three-Dimensional Plasmonic Arrays for Large Near-Infrared Fluorescence Enhancement

Metal-enhanced fluorescence (MEF), resulting from the near-field interaction of fluorophores with metallic nanostructures, has emerged as a powerful tool for dramatically improving the performance of fluorescence-based biomedical applications. Allowing for lower autofluorescence and minimal photoinduced damage, the development of multifunctional and multiplexed MEF platforms in the near-infrared (NIR) windows is particularly desirable. Here, a low-cost fabrication method based on nanosphere lithography is applied to produce tunable three-dimensional (3D) gold (Au) nanohole-disc arrays (Au-NHDAs). The arrays consist of nanoscale glass pillars atop nanoholes in a Au thin film: the top surfaces of the pillars are Au-covered (effectively nanodiscs), and small Au nanoparticles (nanodots) are located on the sidewalls of the pillars. This 3D hole-disc (and possibly nanodot) construct is critical to the properties of the device. The versatility of our approach is illustrated through the production of uniform and highly reproducible Au-NHDAs with controlled structural properties and tunable optical features in the NIR windows. Au-NHDAs allow for a very large NIR fluorescence enhancement (more than 400 times), which is attributed to the 3D plasmonic structure of the arrays that allows strong surface plasmon polariton and localized surface plasmon resonance coupling through glass nanogaps. By considering arrays with the same resonance peak and the same nanodisc separation distance, we show that the enhancement factor varies with nanodisc diameter. Using computational electromagnetic modeling, the electric field enhancement at 790 nm was calculated to provide insights into excitation enhancement, which occurs due to an increase in the intensity of the electric field. Fluorescence lifetime measurements indicate that the total fluorescence enhancement may depend on controlling excitation enhancement and therefore the array morphology. Our findings provide important insights into the mechanism of MEF from 3D plasmonic arrays and establish a low-cost versatile approach that could pave the way for novel NIR-MEF bioapplications.

The electrochemical behaviour of magnetocaloric alloys La(Fe,Mn,Si)13Hx under magnetic field conditions

The degradation mechanism of La(Fe,Mn,Si)13Hx has been examined under conditions representative of the complex operating parameters of a refrigeration cycle. The magnetic field effects are found to be dominated by magneto-transport and are most significant when the material is in its paramagnetic state - resulting in significantly accelerated corrosion rates.

Towards multiplexed near-infrared cellular imaging using gold nanostar arrays with tunable fluorescence enhancement

Sensitive detection of disease biomarkers expressed by human cells is critical to the development of novel diagnostic and therapeutic methods. Here we report that plasmonic arrays based on gold nanostar (AuNS) monolayers enable up to 19-fold fluorescence enhancement for cellular imaging in the near-infrared (NIR) biological window, allowing the application of low quantum yield fluorophores for sensitive cellular imaging. The high fluorescence enhancement together with low autofluorescence interference in this wavelength range enable higher signal-to-noise ratio compared to other diagnostic modalities. Using AuNSs of different geometries and therefore controllable electric field enhancement, cellular imaging with tunable enhancement factors is achieved, which may be useful for the development of multicolour and multiplexed platforms for a panel of biomarkers, allowing to distinguish different subcell populations at the single cell level. Finally, the uptake of AuNSs within HeLa cells and their high biocompatibility, pave the way for novel high-performance in vitro and in vivo diagnostic platforms.

Fluorescence enhancement from single gold nanostars: towards ultra-bright emission in the first and second near-infrared biological windows

Gold nanostars (AuNSs) are promising agents for the development of high-performance diagnostic devices, by enabling metal enhanced fluorescence (MEF) in the physiological near-infrared (NIR) and second near-infrared (NIR-II) windows. The local electric field near their sharp tips and between their branches can be enhanced by several orders of magnitude, holding great promise for large fluorescence enhancements from single AuNS particles, rather than relying on interparticle coupling in nanoparticle substrates. Here, guided by electric field simulations, two different types of AuNSs with controlled morphologies and plasmonic responses in the NIR and NIR-II regions are used to investigate the mechanism of MEF from colloidal AuNSs. Fluorophore conjugation to AuNSs allows significant fluorescence enhancement of up to 30 times in the NIR window, and up to 4-fold enhancement in the NIR-II region. Together with other inherent advantages of AuNSs, including their multispike morphology offering easy access to cell membranes and their large surface area providing flexible multifunctionality, AuNS are promising for the development of in vivo imaging applications. Using time-resolved fluorescence measurements to deconvolute semi-quantitatively excitation enhancement from emission enhancement, we show that a combination of enhanced excitation and an increased radiative decay rate, both contribute to the observed large enhancement. In accordance to our electric field modelling, however, excitation enhancement is the component that varies most with particle morphology. These findings provide important insights into the mechanism of MEF from AuNSs, and can be used to further guide particle design for high contrast enhancement, enabling the development of MEF biodetection technologies.

Multimetallic Microparticles Increase the Potency of Rifampicin against Intracellular Mycobacterium tuberculosis

Mycobacterium tuberculosis ( M.tb) has the extraordinary ability to adapt to the administration of antibiotics through the development of resistance mechanisms. By rapidly exporting drugs from within the cytosol, these pathogenic bacteria diminish antibiotic potency and drive the presentation of drug-tolerant tuberculosis (TB). The membrane integrity of M.tb is pivotal in retaining these drug-resistant traits. Silver (Ag) and zinc oxide (ZnO) nanoparticles (NPs) are established antimicrobial agents that effectively compromise membrane stability, giving rise to increased bacterial permeability to antibiotics. In this work, biodegradable multimetallic microparticles (MMPs), containing Ag NPs and ZnO NPs, were developed for use in pulmonary delivery of antituberculous drugs to the endosomal system of M.tb-infected macrophages. Efficient uptake of MMPs by M.tb-infected THP1 cells was demonstrated using an in vitro macrophage infection model, with direct interaction between MMPs and M.tb visualized with the use of electron FIB-SEM tomography. The release of Ag NPs and ZnO NPs within the macrophage endosomal system increased the potency of the model antibiotic rifampicin by as much as 76%, realized through an increase in membrane disorder of intracellular M.tb. MMPs were effective at independently driving membrane destruction of extracellular bacilli located at the exterior face of THP1 macrophages. This MMP system presents as an effective drug delivery vehicle that could be used for the transport of antituberculous drugs such as rifampicin to infected alveolar macrophages, while increasing drug potency. By increasing M.tb membrane permeability, such a system may prove effectual in improving treatment of drug-susceptible TB in addition to M.tb strains considered drug-resistant.

Exposure to Silver Nanospheres Leads to Altered Respiratory Mechanics and Delayed Immune Response in an in Vivo Murine Model

Here we examine the organ level toxicology of both carbon black (CB) and silver nanoparticles (AgNP). We aim to determine metal-specific effects to respiratory function, inflammation and potential interactions with lung lining fluid (LLF). C57Bl6/J male mice were intratracheally instilled with saline (control), low (0.05 μg/g) or high (0.5 μg/g) doses of either AgNP or CB 15 nm nanospheres. Lung histology, cytology, surfactant composition and function, inflammatory gene expression, and pulmonary function were measured at 1, 3, and 7 days post-exposure. Acutely, high dose CB resulted in an inflammatory response, increased neutrophilia and cytokine production, without alteration in surfactant composition or respiratory mechanics. Low dose CB had no effect. Neither low nor high dose AgNPs resulted in an acute inflammatory response, but there was an increase in work of breathing. Three days post-exposure with CB, a persistent neutrophilia was noted. High dose AgNP resulted in an elevated number of macrophages and invasion of lymphocytes. Additionally, AgNP treated mice displayed increased expression of IL1B, IL6, CCL2, and IL10. However, there were no significant changes in respiratory mechanics. At day 7, inflammation had resolved in AgNP-treated mice, but tissue stiffness and resistance were significantly decreased, which was accompanied by an increase in surfactant protein D (SP-D) content. These data demonstrate that the presence of metal alters the response of the lung to nanoparticle exposure. AgNP-surfactant interactions may alter respiratory function and result in a delayed immune response, potentially due to modified airway epithelial cell function.

Tuneable fluorescence enhancement of nanostructured ZnO arrays with controlled morphology

We investigate a tuneable fluorescence enhancement effect for fluorescence-based biosensing with ZnO-aligned nanorod forests and nanoflower arrays with controlled morphology.

Scalable High-Affinity Stabilization of Magnetic Iron Oxide Nanostructures by a Biocompatible Antifouling Homopolymer

Iron oxide nanostructures have been widely developed for biomedical applications because of their magnetic properties and biocompatibility. In clinical applications, stabilization of these nanostructures against aggregation and nonspecific interactions is typically achieved using weakly anchored polysaccharides, with better-defined and more strongly anchored synthetic polymers not commercially adopted because of their complexity of synthesis and use. Here, we show for the first time stabilization and biocompatibilization of iron oxide nanoparticles by a synthetic homopolymer with strong surface anchoring and a history of clinical use in other applications, poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)]. For the commercially important case of spherical particles, binding of poly(MPC) to iron oxide surfaces and highly effective individualization of magnetite nanoparticles (20 nm) are demonstrated. Next-generation high-aspect-ratio nanowires (both magnetite/maghemite and core-shell iron/iron oxide) are, furthermore, stabilized by poly(MPC) coating, with the nanowire cytotoxicity at large concentrations significantly reduced. The synthesis approach exploited to incorporate functionality into the poly(MPC) chain is demonstrated by random copolymerization with an alkyne-containing monomer for click chemistry. Taking these results together, poly(MPC) homopolymers and random copolymers offer a significant improvement over current iron oxide nanoformulations, combining straightforward synthesis, strong surface anchoring, and well-defined molecular weight.

Silver Nanowire Particle Reactivity with Human Monocyte-Derived Macrophage Cells: Intracellular Availability of Silver Governs Their Cytotoxicity

Silver nanowires (AgNWs) are increasingly being used in the production of optoelectronic devices, with manufacturing processes posing a risk for occupational exposures via inhalation. Although some studies have explored the environmental effects of AgNWs, few data exist on human health effects. Alveolar macrophages are central in the clearance of inhaled fibers from the lungs, with frustrated phagocytosis often stated as a key determinant for the onset of inflammatory reactions. However, the mechanisms through which fully ingested AgNWs interact with, degrade, and transform within primary macrophages over time, and whether the reactivity of the AgNWs arises due to ionic or particulate effects, or both, are poorly understood. Here, a combination of elemental quantification, 3D tomography, analytical transmission electron microscopy (TEM), and confocal microscopy were employed to monitor the uptake, intracellular Ag⁺ availability, and processing of AgNWs of two different lengths (1 and 10 μm) inside human monocyte-derived macrophages (HMMs). Using AgNO₃ and spherical silver nanoparticles (AgNPs) as a comparison, the amount of total bioavailable/intracellular Ag highly correlated to the cytotoxicity of AgNWs. The 10 μm AgNWs were completely internalized in HMMs, with numerous lysosomal vesicles observed in close vicinity to the AgNWs. Following cellular uptake, AgNWs dissolved and transformed intracellularly, with precipitation of AgCl as well as Ag₂S. These transformation processes were likely due to AgNW degradation in the acidic environment of lysosomes, leading to the release of Ag⁺ ions that rapidly react with Cl^- and SH^- species of the cell microenvironment. Our data suggest that, in HMMs, not only frustrated phagocytosis but also the extent of intracellular uptake and dissolution of AgNWs dictates their cytotoxicity.

Inactivation, Clearance, and Functional Effects of Lung-Instilled Short and Long Silver Nanowires in Rats

There is a potential for silver nanowires (AgNWs) to be inhaled, but there is little information on their health effects and their chemical transformation inside the lungs in vivo. We studied the effects of short (S-AgNWs; 1.5 μm) and long (L-AgNWs; 10 μm) nanowires instilled into the lungs of Sprague-Dawley rats. S- and L-AgNWs were phagocytosed and degraded by macrophages; there was no frustrated phagocytosis. Interestingly, both AgNWs were internalized in alveolar epithelial cells, with precipitation of Ag₂S on their surface as secondary Ag₂S nanoparticles. Quantitative serial block face three-dimensional scanning electron microscopy showed a small, but significant, reduction of NW lengths inside alveolar epithelial cells. AgNWs were also present in the lung subpleural space where L-AgNWs exposure resulted in more Ag+ve macrophages situated within the pleura and subpleural alveoli, compared with the S-AgNWs exposure. For both AgNWs, there was lung inflammation at day 1, disappearing by day 21, but in bronchoalveolar lavage fluid (BALF), L-AgNWs caused a delayed neutrophilic and macrophagic inflammation, while S-AgNWs caused only acute transient neutrophilia. Surfactant protein D (SP-D) levels in BALF increased after S- and L-AgNWs exposure at day 7. L-AgNWs induced MIP-1α and S-AgNWs induced IL-18 at day 1. Large airway bronchial responsiveness to acetylcholine increased following L-AgNWs, but not S-AgNWs, exposure. The attenuated response to AgNW instillation may be due to silver inactivation after precipitation of Ag₂S with limited dissolution. Our findings have important consequences for the safety of silver-based technologies to human health.

Silver nanoparticles reduce brain inflammation and related neurotoxicity through induction of H2S-synthesizing enzymes

Silver nanoparticles (AgNP) are known to penetrate into the brain and cause neuronal death. However, there is a paucity in studies examining the effect of AgNP on the resident immune cells of the brain, microglia. Given microglia are implicated in neurodegenerative disorders such as Parkinson's disease (PD), it is important to examine how AgNPs affect microglial inflammation to fully assess AgNP neurotoxicity. In addition, understanding AgNP processing by microglia will allow better prediction of their long term bioreactivity. In the present study, the in vitro uptake and intracellular transformation of citrate-capped AgNPs by microglia, as well as their effects on microglial inflammation and related neurotoxicity were examined. Analytical microscopy demonstrated internalization and dissolution of AgNPs within microglia and formation of non-reactive silver sulphide (Ag2S) on the surface of AgNPs. Furthermore, AgNP-treatment up-regulated microglial expression of the hydrogen sulphide (H2S)-synthesizing enzyme cystathionine-γ-lyase (CSE). In addition, AgNPs showed significant anti-inflammatory effects, reducing lipopolysaccharide (LPS)-stimulated ROS, nitric oxide and TNFα production, which translated into reduced microglial toxicity towards dopaminergic neurons. Hence, the present results indicate that intracellular Ag2S formation, resulting from CSE-mediated H2S production in microglia, sequesters Ag+ ions released from AgNPs, significantly limiting their toxicity, concomitantly reducing microglial inflammation and related neurotoxicity.

Room-Temperature Routes Toward the Creation of Zinc Oxide Films from Molecular Precursors

The fabrication of "flexible" electronics on plastic substrates with low melting points requires the development of thin-film deposition techniques that operate at low temperatures. This is easily achieved with vacuum- or solution-processed molecular or polymeric semiconductors, but oxide materials remain a significant challenge. Here, we show that zinc oxide (ZnO) can be prepared using only room-temperature processes, with the molecular thin-film precursor zinc phthalocyanine (ZnPc), followed by UV-light treatment in vacuum to elicit degradation of the organic components and transformation of the deposited film to the oxide material. The degradation mechanism was assessed by studying the influence of the atmosphere during the reaction: it was particularly sensitive to the oxygen pressure in the chamber and optimal degradation conditions were established as 3 mbar with 40% oxygen in nitrogen. The morphology of the film remained relatively unchanged during the reaction, but a detailed analysis of its composition using both scanning transmission electron microscopy and secondary ion mass spectrometry revealed that a 40 nm thick layer containing ZnO results from the 100 nm thick precursor after complete reaction. Our methodology represents a simple route for the fabrication of oxides and multilayer structures that can be easily integrated into current molecular thin-film growth setups, without the need for a high-temperature step.

Enhancement of the upconversion photoluminescence of hexagonal phase NaYF4:Yb3+,Er3+ nanoparticles by mesoporous gold films

Efficient enhancement of photoluminescence in rare-earth activated upconversion materials is of great significance for their practical applications in various fields.

Mechanisms of Polymer-Templated Nanoparticle Synthesis: Contrasting ZnS and Au

We combine solution small-angle X-ray scattering (SAXS) and high-resolution analytical transmission electron microscopy (ATEM) to gain a full mechanistic understanding of substructure formation in nanoparticles templated by block copolymer reverse micelles, specifically poly(styrene)-block-poly(2-vinylpyridine). We report a novel substructure for micelle-templated ZnS nanoparticles, in which small crystallites (∼4 nm) exist within a larger (∼20 nm) amorphous organic-inorganic hybrid matrix. The formation of this complex structure is explained via SAXS measurements that characterize in situ for the first time the intermediate state of the metal-loaded micelle core: Zn(2+) ions are distributed throughout the micelle core, which solidifies as a unit on sulfidation. The nanoparticle size is thus determined by the radius of the metal-loaded core, rather than the quantity of available metal ions. This mechanism leads to particle size counterintuitively decreasing with increasing metal content, based on the modified interactions of the metal-complexed monomers in direct contrast to gold nanoparticles templated by the same polymer.

Effect of pulmonary surfactant on the dissolution, stability and uptake of zinc oxide nanowires by human respiratory epithelial cells

Inhaled nanoparticles (NPs) have high-deposition rates in the alveolar region of the lung but the effects of pulmonary surfactant (PS) on nanoparticle bioreactivity are unclear. Here, the impact of PS on the stability and dissolution of ZnO nanowires (ZnONWs) was investigated, and linked with their bioreactivity in vitro with human alveolar epithelial type 1-like cells (TT1). Pre-incubation of ZnONWs with Curosurf® (a natural porcine PS) decreased their dissolution at acidic pH, through the formation of a phospholipid corona. Confocal live cell microscopy confirmed that Curosurf® lowered intracellular dissolution, thus delaying the onset of cell death compared to bare ZnONWs. Despite reducing dissolution, Curosurf® significantly increased the uptake of ZnONWs within TT1 cells, ultimately increasing their toxicity after 24 h. Although serum improved ZnONW dispersion in suspension similar to Curosurf®, it had no effect on ZnONW internalization and toxicity, indicating a unique role of PS in promoting particle uptake. In the absence of PS, ZnONW length had no effect on dissolution kinetics or degree of cellular toxicity, indicating a less important role of length in determining ZnONW bioreactivity. This work provides unique findings on the effects of PS on the stability and toxicity of ZnONWs, which could be important in the study of pulmonary toxicity and epithelial-endothelial translocation of nanoparticles in general.

Pulmonary effects of inhalation of spark-generated silver nanoparticles in Brown-Norway and Sprague-Dawley rats

Background

The increasing use of silver nanoparticles (AgNPs) in consumer products is concerning. We examined the potential toxic effects when inhaled in Brown-Norway (BN) rats with a pre-inflammatory state compared to Sprague–Dawley (SD) rats.

Methods

We determined the effect of AgNPs generated from a spark generator (mass concentration: 600–800 μg/mm³; mean diameter: 13–16 nm; total lung doses: 8 [Low] and 26–28 [High] μg) inhaled by the nasal route in both rat strains. Rats were sacrificed at day 1 and day 7 after exposure and measurement of lung function.

Results

In both strains, there was an increase in neutrophils in bronchoalveolar lavage (BAL) fluid at 24 h at the high dose, with concomitant eosinophilia in BN rats. While BAL inflammatory cells were mostly normalised by Day 7, lung inflammation scores remained increased although not the tissue eosinophil scores. Total protein levels were elevated at both lung doses in both strains. There was an increase in BAL IL-1β, KC, IL-17, CCL2 and CCL3 levels in both strains at Day 1, mostly at high dose. Phospholipid levels were increased at the high dose in SD rats at Day 1 and 7, while in BN rats, this was only seen at Day 1; surfactant protein D levels decreased at day 7 at the high dose in SD rats, but was increased at Day 1 at the low dose in BN rats. There was a transient increase in central airway resistance and in tissue elastance in BN rats at Day 1 but not in SD rats. Positive silver-staining was seen particularly in lung tissue macrophages in a dose and time-dependent response in both strains, maximal by day 7. Lung silver levels were relatively higher in BN rat and present at day 7 in both strains.

Conclusions

Presence of cellular inflammation and increasing silver-positive macrophages in lungs at day 7, associated with significant levels of lung silver indicate that lung toxicity is persistent even with the absence of airway luminal inflammation at that time-point. The higher levels and persistence of lung silver in BN rats may be due to the pre-existing inflammatory state of the lungs.

Significant metal enhanced fluorescence of Ag2S quantum dots in the second near-infrared window

The amplification of light in NIR-II from Ag2S QDs via metal enhanced fluorescence (MEF) is reported for the first time. Significant fluorescence enhancement of over 100 times for Ag2S QDs deposited on Au-nanostructured arrays, paves the way for novel sensing and imaging applications based on Ag2S QDs, with improved detection sensitivity and contrast enhancement.

Pulmonary surfactant mitigates silver nanoparticle toxicity in human alveolar type-I-like epithelial cells

Accompanying increased commercial applications and production of silver nanomaterials is an increased probability of human exposure, with inhalation a key route. Nanomaterials that deposit in the pulmonary alveolar region following inhalation will interact firstly with pulmonary surfactant before they interact with the alveolar epithelium. It is therefore critical to understand the effects of human pulmonary surfactant when evaluating the inhalation toxicity of silver nanoparticles. In this study, we evaluated the toxicity of AgNPs on human alveolar type-I-like epithelial (TT1) cells in the absence and presence of Curosurf(®) (a natural pulmonary surfactant substitute), hypothesising that the pulmonary surfactant would act to modify toxicity. We demonstrated that 20nm citrate-capped AgNPs induce toxicity in human alveolar type I-like epithelial cells and, in agreement with our hypothesis, that pulmonary surfactant acts to mitigate this toxicity, possibly through reducing AgNP dissolution into cytotoxic Ag(+) ions. For example, IL-6 and IL-8 release by TT1 cells significantly increased 10.7- and 35-fold, respectively (P<0.01), 24h after treatment with 25μg/ml AgNPs. In contrast, following pre-incubation of AgNPs with Curosurf(®), this effect was almost completely abolished. We further determined that the mechanism of this toxicity is likely associated with Ag(+) ion release and lysosomal disruption, but not with increased reactive oxygen species generation. This study provides a critical understanding of the toxicity of AgNPs in target human alveolar type-I-like epithelial cells and the role of pulmonary surfactant in mitigating this toxicity. The observations reported have important implications for the manufacture and application of AgNPs, in particular for applications involving use of aerosolised AgNPs.

Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes

Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap.

Avoiding artefacts during electron microscopy of silver nanomaterials exposed to biological environments

Electron microscopy has been applied widely to study the interaction of nanomaterials with proteins, cells and tissues at nanometre scale. Biological material is most commonly embedded in thermoset resins to make it compatible with the high vacuum in the electron microscope. Room temperature sample preparation protocols developed over decades provide contrast by staining cell organelles, and aim to preserve the native cell structure. However, the effect of these complex protocols on the nanomaterials in the system is seldom considered. Any artefacts generated during sample preparation may ultimately interfere with the accurate prediction of the stability and reactivity of the nanomaterials. As a case study, we review steps in the room temperature preparation of cells exposed to silver nanomaterials (AgNMs) for transmission electron microscopy imaging and analysis. In particular, embedding and staining protocols, which can alter the physicochemical properties of AgNMs and introduce artefacts thereby leading to a misinterpretation of silver bioreactivity, are scrutinized. Recommendations are given for the application of cryogenic sample preparation protocols, which simultaneously fix both particles and diffusible ions. By being aware of the advantages and limitations of different sample preparation methods, compromises or selection of different correlative techniques can be made to draw more accurate conclusions about the data.

Direct in situ observation of ZnO nucleation and growth via transmission X-ray microscopy

The nucleation and growth of a nanostructure controls its size and morphology, and ultimately its functional properties. Hence it is crucial to investigate growth mechanisms under relevant growth conditions at the nanometer length scale. Here we image the nucleation and growth of electrodeposited ZnO nanostructures in situ, using a transmission X-ray microscope and specially designed electrochemical cell. We show that this imaging technique leads to new insights into the nucleation and growth mechanisms in electrodeposited ZnO including direct, in situ observations of instantaneous versus delayed nucleation.

Adsorption of surfactant protein D from human respiratory secretions by carbon nanotubes and polystyrene nanoparticles depends on nanomaterial surface modification and size

The alveolar respiratory unit constitutes one of the main targets of inhaled nanoparticles; the effect of engineered nanomaterials (NMs) on human health is largely unknown. Surfactant protein D (SP-D) is synthesized by alveolar type II epithelial cells and released into respiratory secretions; its main function is in immune defence, notably against inhaled microbes. SP-D also plays an important role in modulating an appropriate inflammatory response in the lung, and reduced SP-D is associated with a number of inflammatory lung diseases. Adsorption of SP-D to inhaled NMs may facilitate their removal via macrophage phagocytosis. This study addresses the hypothesis that the chemistry, size and surface modification of engineered NMs will impact on their interaction with, and adsorption of, SP-D. To this purpose, we have examined the interactions between SP-D in human lung lavage and two NMs, carbon nanotubes and polystyrene nanoparticles, with different surface functionalization. We have demonstrated that particle size, functionalization and concentration affect the adsorption of SP-D from human lung lavage. Functionalization with negatively charged groups enhanced the amount of SP-D binding. While SP-D binding would be expected to enhance macrophage phagocytosis, these results suggest that the degree of binding is markedly affected by the physicochemistry of the NM and that deposition of high levels of some nanoparticles within the alveolar unit might deplete SP-D levels and affect alveolar immune defence mechanisms.

Comparison of 20 nm silver nanoparticles synthesized with and without a gold core: Structure, dissolution in cell culture media, and biological impact on macrophages

Widespread use of silver nanoparticles raises questions of environmental and biological impact. Many synthesis approaches are used to produce pure silver and silver-shell gold-core particles optimized for specific applications. Since both nanoparticles and silver dissolved from the particles may impact the biological response, it is important to understand the physicochemical characteristics along with the biological impact of nanoparticles produced by different processes. The authors have examined the structure, dissolution, and impact of particle exposure to macrophage cells of two 20 nm silver particles synthesized in different ways, which have different internal structures. The structures were examined by electron microscopy and dissolution measured in Rosewell Park Memorial Institute media with 10% fetal bovine serum. Cytotoxicity and oxidative stress were used to measure biological impact on RAW 264.7 macrophage cells. The particles were polycrystalline, but 20 nm particles grown on gold seed particles had smaller crystallite size with many high-energy grain boundaries and defects, and an apparent higher solubility than 20 nm pure silver particles. Greater oxidative stress and cytotoxicity were observed for 20 nm particles containing the Au core than for 20 nm pure silver particles. A simple dissolution model described the time variation of particle size and dissolved silver for particle loadings larger than 9 μg/ml for the 24-h period characteristic of many in-vitro studies.

High resolution and dynamic imaging of biopersistence and bioreactivity of extra and intracellular MWNTs exposed to microglial cells

Multi-walled carbon nanotubes (MWNTs) are increasingly being developed both as neuro-therapeutic drug delivery systems to the brain and as neural scaffolds to drive tissue regeneration across lesion sites. MWNTs with different degrees of acid oxidation may have different bioreactivities and propensities to aggregate in the extracellular environment, and both individualised and aggregated MWNTs may be expected to be found in the brain. Before practical application, it is vital to understand how both aggregates and individual MWNTs will interact with local phagocytic immune cells, the microglia, and ultimately to determine their biopersistence in the brain. The processing of extra- and intracellular MWNTs (both pristine and when acid oxidised) by microglia was characterised across multiple length scales by correlating a range of dynamic, quantitative and multi-scale techniques, including: UV-vis spectroscopy, light microscopy, focussed ion beam scanning electron microscopy and transmission electron microscopy. Dynamic, live cell imaging revealed the ability of microglia to break apart and internalise micron-sized extracellular agglomerates of acid oxidised MWNTs, but not pristine MWNTs. The total amount of MWNTs internalised by, or strongly bound to, microglia was quantified as a function of time. Neither the significant uptake of oxidised MWNTs, nor the incomplete uptake of pristine MWNTs affected microglial viability, pro-inflammatory cytokine release or nitric oxide production. However, after 24 h exposure to pristine MWNTs, a significant increase in the production of reactive oxygen species was observed. Small aggregates and individualised oxidised MWNTs were present in the cytoplasm and vesicles, including within multilaminar bodies, after 72 h. Some evidence of morphological damage to oxidised MWNT structure was observed including highly disordered graphitic structures, suggesting possible biodegradation. This work demonstrates the utility of dynamic, quantitative and multi-scale techniques in understanding the different cellular processing routes of functionalised nanomaterials. This correlative approach has wide implications for assessing the biopersistence of MWNT aggregates elsewhere in the body, in particular their interaction with macrophages in the lung.

Interpreting biomarker data from the COPHES/DEMOCOPHES twin projects: Using external exposure data to understand biomarker differences among countries

In 2011 and 2012, the COPHES/DEMOCOPHES twin projects performed the first ever harmonized human biomonitoring survey in 17 European countries. In more than 1800 mother-child pairs, individual lifestyle data were collected and cadmium, cotinine and certain phthalate metabolites were measured in urine. Total mercury was determined in hair samples. While the main goal of the COPHES/DEMOCOPHES twin projects was to develop and test harmonized protocols and procedures, the goal of the current paper is to investigate whether the observed differences in biomarker values among the countries implementing DEMOCOPHES can be interpreted using information from external databases on environmental quality and lifestyle. In general, 13 countries having implemented DEMOCOPHES provided high-quality data from external sources that were relevant for interpretation purposes. However, some data were not available for reporting or were not in line with predefined specifications. Therefore, only part of the external information could be included in the statistical analyses. Nonetheless, there was a highly significant correlation between national levels of fish consumption and mercury in hair, the strength of antismoking legislation was significantly related to urinary cotinine levels, and we were able to show indications that also urinary cadmium levels were associated with environmental quality and food quality. These results again show the potential of biomonitoring data to provide added value for (the evaluation of) evidence-informed policy making.

Low-dose AgNPs reduce lung mechanical function and innate immune defense in the absence of cellular toxicity

Multiple studies have examined the direct cellular toxicity of silver nanoparticles (AgNPs). However, the lung is a complex biological system with multiple cell types and a lipid-rich surface fluid; therefore, organ level responses may not depend on direct cellular toxicity. We hypothesized that interaction with the lung lining is a critical determinant of organ level responses. Here, we have examined the effects of low dose intratracheal instillation of AgNPs (0.05 μg/g body weight) 20 and 110 nm diameter in size, and functionalized with citrate or polyvinylpyrrolidone. Both size and functionalization were significant factors in particle aggregation and lipid interaction in vitro. One day post-intratracheal instillation lung function was assessed, and bronchoalveolar lavage (BAL) and lung tissue collected. There were no signs of overt inflammation. There was no change in surfactant protein-B content in the BAL but there was loss of surfactant protein-D with polyvinylpyrrolidone (PVP)-stabilized particles. Mechanical impedance data demonstrated a significant increase in pulmonary elastance as compared to control, greatest with 110 nm PVP-stabilized particles. Seven days post-instillation of PVP-stabilized particles increased BAL cell counts, and reduced lung function was observed. These changes resolved by 21 days. Hence, AgNP-mediated alterations in the lung lining and mechanical function resolve by 21 days. Larger particles and PVP stabilization produce the largest disruptions. These studies demonstrate that low dose AgNPs elicit deficits in both mechanical and innate immune defense function, suggesting that organ level toxicity should be considered.

Static and Dynamic Microscopy of the Chemical Stability and Aggregation State of Silver Nanowires in Components of Murine Pulmonary Surfactant

The increase of production volumes of silver nanowires (AgNWs) and of consumer products incorporating them may lead to increased health risks from occupational and public exposures. There is currently limited information about the putative toxicity of AgNWs upon inhalation and incomplete understanding of the properties that control their bioreactivity. The lung lining fluid (LLF), which contains phospholipids and surfactant proteins, represents a first contact site with the respiratory system. In this work, the impact of dipalmitoylphosphatidylcholine (DPPC), Curosurf, and murine LLF on the stability of AgNWs was examined. Both the phospholipid and protein components of the LLF modified the dissolution kinetics of AgNWs, due to the formation of a lipid corona or aggregation of the AgNWs. Moreover, the hydrophilic proteins, but neither the hydrophobic surfactant proteins nor the phospholipids, induced agglomeration of the AgNWs. Finally, the generation of a secondary population of nanosilver was observed and attributed to the reduction of Ag(+) ions by the surface capping of the AgNWs. Our findings highlight that combinations of spatially resolved dynamic and static techniques are required to develop a holistic understanding of which parameters govern AgNW behavior at the point of exposure and to accurately predict their risks on human health and the environment.