Rapid Chemical Screening of Microplastics and Nanoplastics by Thermal Desorption and Pyrolysis Mass Spectrometry with Unsupervised Fuzzy Clustering.

The transport and chemical identification of microplastics and nanoplastics (MNPs) are critical to the concerns over plastic accumulation in the environment. Chemically and physically transient MNP species present unique challenges for isolation and analysis due to many factors such as their size, color, surface properties, morphology, and potential for chemical change. These factors contribute to the eventual environmental and toxicological impact of MNPs. As analytical methods and instrumentation continue to be developed for this application, analytical test materials will play an important role. Here, a direct mass spectrometry screening method was developed to rapidly characterize manufactured and weathered MNPs, complementing lengthy pyrolysis-gas chromatography-mass spectrometry analysis. The chromatography-free measurements took advantage of Kendrick mass defect analysis, in-source collision-induced dissociation, and advancements in machine learning approaches for the data analysis of complex mass spectra. In this study, we applied Gaussian mixture models and fuzzy c-means clustering for the unsupervised analysis of MNP sample spectra, incorporating clustering stability and information criterion measurements to determine latent dimensionality. These models provided insight into the composition of mixed and weathered MNP samples. The multiparametric data acquisition and machine learning approach presented improved confidence in polymer identification and differentiation.

Parallel Multiparameter Study of PEI-Functionalized Gold Nanoparticle Synthesis for Biomedical Applications: Part 2. Elucidating the Role of Surface Chemistry and Polymer Structure in Performance.

Elucidating the polyethyleneimine (PEI) chemistry to predictively and reproducibly synthesize gold nanoparticle (AuNP)-PEI conjugates with desired properties has been elusive despite evaluation in numerous studies and reported enhanced properties. The lack of reproducible methods to control the core size and stability has led to contradictory results for performance and safety; thus, advancement of the conjugate platform for commercial use has likely been hindered. Recently, we reported a robust, reproducible method for synthesizing PEI-functionalized AuNPs (Au-PEIs), providing an opportunity to investigate structure-function relationships and to further investigate synthesis parameters affecting performance, where only materials stable in biological media are candidates for use. The properties of Au-PEIs prepared by the optimized reduction of HAuCl4 using four different structural variants of PEI changed significantly with the PEI molar mass and backbone form (branched or linear). In the present study using our previously reported synthesis procedure, comprehensive analysis of properties such as size distribution, surface plasmon resonance (SPR), morphological state, surface functionality, and the shelf life has been systematically evaluated to elucidate the role of surface chemistry and reactive groups involved in conjugation, as a function of conjugate size and morphology. Being important for commercial adoption, the chemistry was related to the observed colloidal stability of the product in relevant media, including exposure to physiological variables such as salt, pH, proteins, and thermal changes. Overall, this work advances progress toward smart design of engineered nanoscale drug delivery systems and devices by providing unreported details of contributions affecting formation, stability, and fate.

Surface Modification of Cisplatin-Complexed Gold Nanoparticles and Its Influence on Colloidal Stability, Drug Loading, and Drug Release.

Cisplatin-complexed gold nanoparticles (PtII-AuNP) provide a promising strategy for chemo-radiation-based anticancer drugs. Effective design of such platforms necessitates reliable assessment of surface engineering on a quantitative basis and its influence on drug payload, stability, and release. In this paper, poly(ethylene glycol) (PEG)-stabilized PtII-AuNP was synthesized as a model antitumor drug platform, where PtII is attached via a carboxyl-terminated dendron ligand. Surface modification by PEG and its influence on drug loading, colloidal stability, and drug release were assessed. Complexation with PtII significantly degrades colloidal stability of the conjugate; however, PEGylation provides substantial improvement of stability in conjunction with an insignificant trade-off in drug loading capacity compared with the non-PEGylated control (<20% decrease in loading capacity). In this context, the effect of varying PEG concentration and molar mass was investigated. On a quantitative basis, the extent of PEGylation was characterized and its influence on dispersion stability and drug load was examined using electrospray differential mobility analysis (ES-DMA) hyphenated with inductively coupled plasma mass spectrometry (ICP-MS) and compared with attenuated total reflectance-FTIR. Using ES-DMA-ICP-MS, AuNP conjugates were size-classified based on their electrical mobility, while PtII loading was simultaneously quantified by determination of Pt mass. Colloidal stability was quantitatively evaluated in biologically relevant media. Finally, the pH-dependent PtII release performance was evaluated. We observed 9% and 16% PtII release at drug loadings of 0.5 and 1.9 PtII/nm2, respectively. The relative molar mass of PEG had no significant influence on PtII uptake or release performance, while PEGylation substantially improved the colloidal stability of the conjugate. Notably, the PtII release over 10 days (examined at 0.5 PtII/nm2 drug loading) remained constant for non-PEGylated, 1K-PEGylated, and 5K-PEGylated conjugates.

In Situ Methods for Monitoring Silver Nanoparticle Sulfidation in Simulated Waters.

To probe the transformation pathways of metallic nanomaterials, measurement tools capable of detecting and characterizing the broad distribution of products with limited perturbation are required. Here, we demonstrate the detection of transformation products resulting from 40 kDa PVP-coated silver nanoparticles (AgNPs) reacted in aerated, sulfide-containing water and EPA moderately hard reconstituted water standard. Using single particle inductively coupled plasma mass spectrometry, silver mass preservation in primary AgNP populations during sulfidation was observed under all reaction conditions examined. Disparate sensitivities of Ag+ and AgNPs to different media were observed, limiting confidence in the measured dissolved fraction. Examination with hyphenated asymmetric flow field-flow fractionation (A4F) methods supported similar mass preservation. Using flow-cell FTIR measurements, we provide direct evidence for the preservation of PVP-coatings in the presence of Na2S and fulvic acid, which we attributed to the observed, unprecedented Ag preservation. Using A4F and X-ray scattering, sub 10 nm AgNP populations, which have gone nearly unstudied in environmental systems, were detected and characterized in all the pristine and transformed product distributions examined. Furthermore, by distinguishing Ag+ from individual AgNPs, quantification of each population becomes tractable, which is a critical measurement need for toxicity testing and predicting NP fate in engineered and natural systems.

In situ monitoring, separation, and characterization of gold nanorod transformation during seed-mediated synthesis.

The control of gold nanorod (GNR) solution-based syntheses has been hindered in part by the inability to examine and control the conversion of precursor seed populations to anisotropic materials, which have resulted in low yields of desired products and limited their commercial viability. The advantages offered by tandem separation and characterization methods utilizing asymmetric-flow field flow fractionation (A4F) are principally achieved as a result of their non-disruptive nature (minimizing artefacts), fast throughput, and in-situ analysis. With hyphenated A4F methods, resolved populations of seeds and secondary products, up to long aspect ratio rods, have been achieved and exemplify progress towards elucidating mechanistic aspects of formation and thus rational design. While there have been previously reported studies on A4F separation of GNRs, to our knowledge, this is the first published investigation of in situ GNR growth, separation, and characterization based on A4F, where its utilization in this capacity goes beyond traditional separation analysis. By using hydroquinone as the reducing agent, the conversion of the initial seed population to a distribution of products, including the GNRs, could be monitored in real time using A4F hyphenated with a diode array detector. Transmission electron microscopy confirms that the number of peaks observed during fractionation corresponds with size and shape dispersity. This proof-of-principle study introduces A4F as a technique that establishes a foundation for future mechanistic studies on the growth of GNRs from gold seeds, including conversion of the seed population to initial products, a topic highly relevant to advancing progress in nanomanufacturing.

Unexpected Changes in Functionality and Surface Coverage for Au Nanoparticle PEI Conjugates: Implications for Stability and Efficacy in Biological Systems.

Cationic polyethylenimine conjugated gold nanoparticles (AuNP-PEI) are a widely studied vector for drug delivery and an effective probe for interrogating NP-cell interactions. However, an inconsistent body of literature currently exists regarding the reproducibility of physicochemical properties, colloidal stability, and efficacy for these species. To address this gap, we systematically examined the preparation, stability, and formation mechanism of PEI conjugates produced from citrate-capped AuNPs. We considered the dependence on relative molar mass, Mr, backbone conformation, and material source. The conjugation mechanism of Au-PEI was probed using attenuated total reflectance FTIR and X-ray photoelectron spectroscopy, revealing distinct fates for citrate when interacting with different PEI species. The differences in residual citrate, PEI properties, and sample preparation resulted in distinct products with differentiated stability. Overall, branched PEI (25 kDa) conjugates exhibited the greatest colloidal stability in all media tested. By contrast, linear PEI (25 kDa) induced agglomeration. Colloidal stability of the products was also observed to correlate with displaced citrate, which supports a glaring knowledge gap that has emerged regarding the role of this commonly used carboxylate species as a "place holder" for conjugation with ligands of broad functionalities. We observed an unexpected and previously unreported conversion of amine functional groups to quaternary ammonium species for 10 kDa branched conjugates. Results suggest that the AuNP surface catalyzes this conversion. The product is known to manifest distinct processes and uptake in biological systems compared to amines and may lead to unintentional toxicological consequences or decreased efficacy as delivery vectors. Overall, comprehensive physicochemical characterization (tandem spectroscopy methods combined with physical measurements) of the conjugation process provides a methodology for elucidating the contributing factors of colloidal stability and chemical functionality that likely influence the previously reported variations in conjugate properties and biological response models.

Stability-Enhanced Cisplatin Gold Nanoparticles As Therapeutic Anticancer Agents.

Using dendron chemistry, we developed stability enhanced, carboxylate surface modified (negatively charged dendron) AuNPs (Au-NCD). Since the carboxylate surface of Au-NCD is optimal for complexation with cisplatin (Pt) moieties, we further synthesized Pt loaded Au-NCD (Au-NCD/Pt) to serve as potential therapeutic anticancer agents. The size distribution, zeta potential and surface plasmon resonance of both Au-NCDs and Au-NCD/Pt were characterized via dynamic light scattering, scanning transmission electron microscopy and ultraviolet-visible spectrophotometry. Surface chemistry, Pt uptake, and Pt release were evaluated using inductively coupled plasma-mass spectrometry and X-ray photoelectron spectroscopy. Colloidal stability in physiological media over a wide pH range (1 to 13) and shelf-life stability (up to 6 months) were also assessed. Finally, the cytotoxicity of both Au-NCD and Au-NCD/Pt to Chinese hamster ovary cells (CHO K1; as a normal cell line) and to human lung epithelial cells (A549; as a cancer cell line) were evaluated. The results of these physicochemical and functional cytotoxicity studies with Au-NCD/Pt demonstrated that the particles exhibited superlative colloidal stability, cisplatin uptake and in vitro anticancer activity despite low amounts of Pt release from the conjugate.

Temperature-programmed electrospray-differential mobility analysis for characterization of ligated nanoparticles in complex media.

An electrospray-differential mobility analyzer (ES-DMA) was operated with an aerosol flow-mode, temperature-programmed approach to enhance its ability to characterize the particle size distributions (PSDs) of nanoscale particles (NPs) in the presence of adsorbed and free ligands. Titanium dioxide NPs (TiO2-NPs) stabilized by citric acid (CA) or bovine serum albumin (BSA) were utilized as representative systems. Transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry were used to provide visual information and elemental-based PSDs, respectively. Results show that the interference resulting from electrospray-dried nonvolatile salt residual nanoscale particles (S-NPs) could be effectively reduced using the thermal treatment process: PSDs were accurately measured at temperatures above 200 °C for CA-stabilized TiO2-NPs and above 400 °C for BSA-stabilized TiO2-NPs. Moreover, TEM confirmed the volumetric shrinkage of S-NPs due to thermal treatment and also showed that the primary structure of TiO2-NPs was relatively stable over the temperature range studied (i.e., below 700 °C). Conversely, the shape factor for TiO2-NPs decreased after treatment above 500 °C, possibly due to a change in the secondary (aggregate) structure. S-NPs from BSA-stabilized TiO2-NPs exhibited higher global activation energies toward induced volumetric shrinkage than those of CA-stabilized TiO2-NPs, suggesting that activation energy is dependent on ligand size. This prototype study demonstrates the efficacy of using ES-DMA coupled with thermal treatment for characterizing the physical state of NPs, even in a complex medium (e.g., containing plasma proteins) and in the presence of particle agglomerates induced by interaction with binding ligands.

Predictive gold nanocluster formation controlled by metal-ligand complexes.

The formation of ligand-protected gold nanoclusters during size-selective syntheses is seemingly driven by the inherent properties of the protecting ligands, but a general description of the product formation has not been presented. This study uses diphosphine-protected Au clusters as a model system to examine i) control of metal-ligand complex distributions in methanol-chloroform solutions, ii) role of solution perturbations, e.g., oxidation, and iii) nanocluster formation through reduction of characterized complex distributions. By selectively reducing complexes and monitoring cluster formation with electrospray ionization mass spectrometry and UV-vis, data show the distribution of complexes can be controlled through ligand exchange, and the reduction of specific complexes produce characteristic ligated gold clusters based on ligand class. Specifically, 1,n-bis(diphenylphosphino)n-alkane ligands, L(n), where n = 1 through 6, are classified into two distinct sets. The classes represent ligands that either form mainly [AuL(n)(2)](+) (Class I, n = 1-3) or bridged [Au(2)L(n)(2)](2+) (Class II, n = 4-6) complexes after complete ligand exchange with AuClPPh(3). Selectively reducing gold-phosphine ligand complexes allows mapping of product formation, resulting collectively in a predictive tool for ligated gold cluster production by simply monitoring the initial complex distribution prior to reduction.

Environmental implications of nanoparticle aging in the processing and fate of copper-based nanomaterials.

Copper nanomaterials are being used in a large number of commercial products because these materials exhibit unique optical, magnetic, and electronic properties. Metallic copper nanoparticles, which often have a thin surface oxide layer, can age in the ambient environment and become even more oxidized over time. These aged nanoparticles will then have different properties compared to the original nanoparticles. In this study, we have characterized three different types of copper-based nanoparticle (NP) samples designated as Cu(new) NPs, Cu(aged) NPs, and CuO NPs that differ in the level of oxidation. The solution phase behavior of these three copper-based nanoparticle samples is investigated as a function of pH and in the presence and absence of two common, complexing organic acids, citric and oxalic acid. The behavior of these three copper-based NP types shows interesting differences. In particular, Cu(aged) NPs exhibit unique chemistry including oxide phases that form and surface adsorption properties. Overall, the current study provides some insights into the impacts of nanoparticle aging and how the physicochemical characteristics and reactivity of nanomaterials can change upon aging.

Reaction network governing diphosphine-protected gold nanocluster formation from nascent cationic platforms.

We identify the reaction network governing gold monolayer protected cluster (MPC) formation during the reduction of Au(PPh(3))Cl and L(5) (L(5) = 1,5-bis(diphenylphosphino)pentane) in solutions. UV-vis spectroscopy and electrospray ionization mass spectrometry (ESI-MS) monitored the formation of ligated Au(x): 6 ≤ x ≤ 12 clusters, which comprise the reaction intermediates and final products. Initially, predominantly [Au(2)L(5)(2)](2+) complexes form through dissolution of Au(PPh(3))Cl. These complexes control the reduction and nucleation reactions that form nascent phosphine-ligated Au(8) and Au(10) ionic clusters. [Au(10)L(5)(4)](2+) is an observed growth platform for ligated Au(11) and Au(12) clusters. The data for syntheses of Au : L(5) systems evidence that the nascent reaction products (t < 3 days) are less dependent on the chosen reducing agent (borane tert-butylamine complex or NaBH(4)); instead, after reduction ceases, subsequent solution phase processing provides greater control for tuning cluster nuclearity.

Reaction mechanism governing formation of 1,3-bis(diphenylphosphino)propane-protected gold nanoclusters.

This report outlines the determination of a reaction mechanism that can be manipulated to develop directed syntheses of gold monolayer-protected clusters (MPCs) prepared by reduction of solutions containing 1,3-bis(diphenylphosphino)propane (L(3)) ligand and Au(PPh(3))Cl. Nanocluster synthesis was initiated by reduction of two-coordinate phosphine-ligated [Au(I)LL'](+) complexes (L, L' = PPh(3), L(3)), resulting in free radical complexes. The [Au(0)LL'](•) free radicals nucleated, forming a broad size distribution of ligated clusters. Timed UV-vis spectroscopy and electrospray ionization mass spectrometry monitored the ligated Au(x), 6 ≤ x ≤ 13, clusters, which comprise reaction intermediates and final products. By employing different solvents and reducing agents, reaction conditions were varied to highlight the largest portion of the reaction mechanism. We identified several solution-phase reaction classes, including dissolution of the gold precursor, reduction, continuous nucleation/core growth, ligand exchange, ion-molecule reactions, and etching of colloids and larger clusters. Simple theories can account for the reaction intermediates and final products. The initial distribution of the nucleation products contains mainly neutral clusters. However, the rate of reduction controls the amount of reaction overlap occurring in the system, allowing a clear distinction between reduction/nucleation and subsequent solution-phase processing. During solution-phase processing, the complexes undergo core etching and core growth reactions, including reactions that convert neutral clusters to cations, in a cyclic process that promotes formation of stable clusters of specific metal nuclearity. These processes comprise "size-selective" processing that can narrow a broad distribution into specific nuclearities, enabling development of tunable syntheses.

Transformation of engineered nanomaterials through the prism of silver sulfidation.

Understanding the structure transformation of engineered nanomaterials (ENMs) is a grand measurement challenge, which impacts many aspects of ENMs applications, such as their efficacy, safety, and environmental consequence. To address the significant knowledge gap regarding the fundamental kinetic rate and extent of ENM transformation in the environment, we present a comprehensive and mechanistic structural investigation of the transformation, aggregation, and dissolution behavior of a polyvinylpyrrolidone-coated silver nanoparticle (AgNP) suspension upon sulfidation in moderately reduced hard water with fulvic acid and dissolved Na2S. This reaction is among the most prevalent and industrially and environmentally relevant ENMs transformation. Using ex situ transmission electron microscopy (TEM) and both in situ and ex situ synchrotron-based small angle X-ray scattering (SAXS) and X-ray diffraction (XRD), we find that sulfidation of faceted AgNPs strongly depends on the crystallographic orientation of the facets, with nanometer-scale passivation layers developed on {111} and {100} facets and continuous nucleation and growth on {110} facets. Nanobeam electron diffraction and atomic resolution imaging show Ag and Ag2S domains both possess a high degree of crystalline order, contradicting amorphous structures as previously reported. In situ SAXS/XRD allowed simultaneous determination of the morphological changes and extent of sulfidation of AgNPs. SAXS/XRD results strongly indicate sulfidation follows first-order reaction kinetics without any aggregation. Aided by their size monodispersity, for the first time, using direct, in situ morphology and atomic-structure probes whose results mutually corroborate, we unequivocally determined the sulfidation rate constant of AgNPs under an environmentally relevant condition (~0.013 min-1 for 68 nm diameter AgNPs). A rigorous analysis of the long-term sulfidation product of the AgNPs under different S/Ag ratios using ex situ SAXS/XRD clearly demonstrates that the silver mass in the original AgNP and transformed Ag/Ag2S NP is preserved. This result has important environmental implications, strongly suggesting that Ag+ ions, a known highly effective antimicrobial agent, are not leached into the solution during sulfidation of AgNPs. The combined nondestructive methodology can be extended to unfold the structure transformation pathway and kinetics in a broad range of ENM systems.

Chemical and Physical Transformations of Silver Nanomaterial Containing Textiles After Modeled Human Exposure.

The antimicrobial properties of silver nanomaterials (AgNM) have been exploited in various consumer applications, including textiles such as wound dressings. Understanding how these materials chemically transform throughout their use is necessary to predict their efficacy during use and their behavior after disposal. The aim of this work was to evaluate chemical and physical transformations to a commercial AgNM-containing wound dressing during modeled human exposure to synthetic sweat (SW) or simulated wound fluid (WF). Scanning electron microscopy with energy dispersive X-ray spectroscopy (EDS) revealed the formation of micrometer-sized structures at the wound dressing surface after SW exposure while WF resulted in a largely featureless surface. Measurements by X-ray photoelectron spectroscopy (XPS) revealed a AgCl surface (consistent with EDS) while X-ray diffraction (XRD) found a mixture of zero valent silver and AgCl suggesting the AgNM wound dressings surface formed a passivating AgCl surface layer after SW and WF exposure. For WF, XPS based findings revealed the addition of an adsorbed protein layer based on the nitrogen marker which adsorbed released silver at prolonged exposures. Silver release was evaluated by inductively coupled plasma mass spectrometry which revealed a significant released silver fraction in WF and minimal released silver in SW. Analysis suggests that the protein in WF sequestered a fraction of the released silver which continued with exposure time, suggesting additional processing at the wound dressing surface even after the initial transformation to AgCl. To evaluate the impact on antimicrobial efficacy, zone of inhibition (ZOI) testing was conducted which found no significant change after modeled human exposure compared to the pristine wound dressing. The results presented here suggest AgNM-containing wound dressings transform chemically in simulated human fluids resulting in a material with comparable antimicrobial properties with pristine wound dressings. Ultimately, knowing the resulting chemical properties of the AgNM wound dressings will allow better predictive models to be developed regarding their fate.

Parallel multi-parameter study of PEI-functionalized gold nanoparticle synthesis for bio-medical applications: part 1-a critical assessment of methodology, properties, and stability.

Cationic polyethyleneimine (PEI)-conjugated gold nanoparticles (AuNPs) that are chemically and physically stable under physiological conditions are an ideal candidate for certain bio-medical applications, in particular DNA transfection. However, the issue remains in reproducibly generating uniform stable species, which can cause the inadequate characterization of the resulting product under relevant conditions and timepoints. The principal objective of the present study was to develop an optimized and reproducible synthetic route for preparing stable PEI-conjugated AuNPs (Au-PEIs). To achieve this objective, a parallel multi-parametric approach involving a total of 96 reaction studies evaluated the importance of 6 key factors: PEI molar mass, PEI structure, molar ratio of PEI/Au, concentration of reaction mixtures, reaction temperature, and reaction time. Application of optimized conditions exhibited narrow size distributions with characteristic surface plasmon resonance absorption and positive surface charge. The optimized Au-PEI product generated by this study exhibits exceptional stability under a physiological isotonic medium (phosphate-buffered saline) over 48 h and shelf-life in ambient condition without any significant change or sedimentation for at least 6 months. Furthermore, the optimized Au-PEI product was highly reproducible. Contributions from individual factors were elucidated using a broad and orthogonal characterization suite examining size and size distribution, optical absorbance, morphological transformation (agglomeration/aggregation), surface functionalities, and stability. Overall, this comprehensive multi-parametric investigation, supported by thorough characterization and rigorous testing, provides a robust foundation for the nanomedicine research community to better synthesize nanomaterials for biomedical use.

Determining surface chemical composition of silver nanoparticles during sulfidation by monitoring the ligand shell.

Evaluating the surface and core compositions of transforming nanoparticles (NP) represents a significant measurement challenge but is necessary for predicting performance in applied systems and their toxicity in natural environments. Here, we use X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to characterize both the surface and core ofpolyvinyl pyrollidone-silver nanoparticles in the presence of two Suwannee River fulvic acid (FA) standards and humic acid (HA) during sulfidation, the predominant transformation pathway in environmental systems. Only by using data from both spectroscopic methods was a clear relationship established between AgNP core composition and FA affinity established, where concomitant loss of FA was observed with Ag2S formation. Using XPS to measure AgNP surface composition, overlapping trends from XPS on FA I desorption from the AgNP surface as function of surface sulfidation were observed with FA II in the ATR-FTIR measurements. The reproducibility of the changing heterogeneous coating as a function of AgNP sulfidation provided a transferable method to determine the extent of Ag sulfidation without further need for the high resolution, high cost measurement tools that underpinned validation of the method. The relationship was not observed for HA, where a lower affinity to the AgNP surface was observed, suggesting distinct binding to the NP.

Comparing sulfidation kinetics of silver nanoparticles in simulated media using direct and indirect measurement methods.

Reported reaction kinetics of metal nanoparticles in natural and engineered systems commonly have used proxy measurements to infer chemical transformations, but extension of these methods to complex media has proven difficult. Here, we compare the sulfidation rate of AgNPs using two ion selective electrode (ISE)-based methods, which rely on either (i) direct measurement of free sulfide, or (ii) monitor the free Ag+ available in solution over time in the presence of sulfide species. Most experiments were carried out in moderately hard reconstituted water at pH 7 containing fulvic acid or humic acid, which represented a broad set of known interferences in ISE. Distinct differences in the measured rates were observed between the two proxy-based methods and details of the divergent results are discussed. The two ISE based methods were then compared to direct monitoring of AgNP chemical conversion to Ag2S using synchrotron-based in situ X-ray diffraction (XRD). Using XRD, distinct rates from both ISE-based technique were observed, which demonstrated that ISE measurements alone are inadequate to discriminate both the rate and extent of AgNP sulfidation. XRD rate data elucidated previously unidentified reaction regimes that were associated with AgNP coating (PVP and citrate acid) and NOM components, which provided new mechanistic insight into metallic NP processing. In general, the extent of Ag2S formation was inversely proportional to surface coverage of the initial AgNP. Overall, methods to determine reaction kinetics of nanomaterials in increasingly complex media and heterogeneous size distributions to improve NP-based design and performance will require similar approaches.

Inhalation exposure study of titanium dioxide nanoparticles with a primary particle size of 2 to 5 nm.

BACKGROUND: Nanotechnology offers great promise in many industrial applications. However, little is known about the health effects of manufactured nanoparticles, the building blocks of nanomaterials. OBJECTIVES: Titanium dioxide (TiO(2)) nanoparticles with a primary size of 2-5 nm have not been studied previously in inhalation exposure models and represent some of the smallest manufactured nanoparticles. The purpose of this study was to assess the toxicity of these nanoparticles using a murine model of lung inflammation and injury. MATERIALS AND METHODS: The properties of TiO(2) nanoparticles as well as the characteristics of aerosols of these particles were evaluated. Mice were exposed to TiO(2) nanoparticles in a whole-body exposure chamber acutely (4 hr) or subacutely (4 hr/day for 10 days). Toxicity in exposed mice was assessed by enumeration of total and differential cells, determination of total protein, lactate dehydrogenase (LDH) activity and inflammatory cytokines in bronchoalveolar lavage (BAL) fluid. Lungs were also evaluated for histopathologic changes RESULTS: Mice exposed acutely to 0.77 or 7.22 mg/m(3) nanoparticles demonstrated minimal lung toxicity or inflammation. Mice exposed subacutely (8.88 mg/m(3)) and necropsied immediately and at week 1 or 2 postexposure had higher counts of total cells and alveolar macrophages in the BAL fluid compared with sentinels. However, mice recovered by week 3 postexposure. Other indicators were negative. CONCLUSIONS: Mice subacutely exposed to 2-5 nm TiO(2) nanoparticles showed a significant but moderate inflammatory response among animals at week 0, 1, or 2 after exposure that resolved by week 3 postexposure.

Research highlights: engineering nanomaterial-based technologies for environmental applications.

Nanomaterials are currently of interest for water treatment and remediation applications because they can exhibit high adsorption capacities and high reactivity to degrade or transform contaminants. Research is ongoing to further increase the adsorption capacity of the nanomaterials and to engineer nanomaterial-based treatment systems for contaminant removal. Here, we highlight three articles that advance this field by devising and testing approaches to improve the design of nanomaterials as well as their implementation in water treatment applications. One study demonstrates a method for non-covalent surface functionalization to produce silica and magnetite nanoparticles exhibiting thiol ligands for heavy metal removal. In another study, the surface coating chemistry of manganese oxide nanoparticles is optimized to enhance their uranyl sorption capacity. Finally, we highlight research that evaluates the overall implementation of magnetite nanoparticles for removal of hexavalent chromium (Cr(vi)) from water, including the production of the nanoparticles, their efficiency in removing (Cr(vi)) in a reactor, and the recovery of the used NPs in a magnetic separation system.

Research highlights: improved understanding of ecological impacts resulting from nanomaterial-based in situ remediation.

Nanomaterials are currently being used for in situ remediation of soils and groundwater. However, the continued use of currently implemented nanomaterials and the systematic development of more effective and ecologically benign materials require a more complete understanding of their ecological impact, which should include the transport through the subsurface, acute, chronic and long term effects of exposure, and the role of nanomaterial characteristics (e.g., composition, surface coating). In the current highlight, three articles that examine different aspects of nanoscale zero-valent iron (nZVI) transport, reactivity or exposure to model organisms are summarily reported, which advance the development of more sustainable remediation approaches. The first study examines the role of a model biofilm on the transport of different Pd-doped nZVI species through granulated media, and also the associated nanomaterial toxicity to the forming and sessile bacteria. The second study examines the multigenerational reproductive impacts of C. elegans resulting from nZVI exposure. Lastly, the resulting products of nZVI reactivity with U(vi) species at environmentally relevant molar ratios are examined, and a thorough analysis of the resulting products are reported, which provide valuable data for predicting the consequential role nZVI remediation will have on the ecosystem at and near contaminated sites.