How a Nanostructure's Shape Affects its Lifetime in the Environment: Comparing a Silver Nanocube to a Nanoparticle When Dispersed in Aqueous Media

Form-Dependent Toxicity of Silver Nanomaterials in Rainbow Trout Gills

The toxicity of the form of nanoparticles is presently not well understood. The purpose of this study consists in comparing the toxicity of various forms of silver nanoparticles (nAg) in juvenile rainbow trout Oncorhynchus mykiss. Juveniles were exposed to various forms of polyvinyl-coated nAg of similar size for 96 h at 15 °C. After the exposure period, the gills were isolated and analyzed for Ag uptake/distribution, oxidative stress, glucose metabolism, and genotoxicity. Higher levels of Ag were detected in gills in fish exposed to dissolved Ag followed by spherical, cubic, and prismatic nAg. Size-exclusion chromatography of gill fractions revealed that the dissolution of nAg was observed for all forms of nAg where prismatic nAg released more important levels of Ag in the protein pool as in fish exposed to dissolved Ag as well. The aggregation of nAg was more important for cubic nAg in respect of the other forms of nAg. The data revealed that lipid peroxidation was closely associated with protein aggregation and viscosity. Biomarkers revealed changes in lipid/oxidative stress and genotoxicity, which were related to the loss of protein aggregation and inflammation (NO₂ levels), respectively. In general, the observed effects were found for all forms of nAg where the effects from prismatic nAg were generally higher than for spherical and cubic nAg. The strong relationship between genotoxicity and inflammation response suggests the participation of the immune system in the observed responses of juvenile fish gills.

The Influence of Silver Nanoparticle Form on the Toxicity in Freshwater Mussels

The contribution of the form of silver nanomaterials (nAg) towards toxicity in aquatic organisms is not well understood. The purpose of this study was to examine the toxicity of various structures (sphere, cube and prism) of nAg in Dreissena bugensis mussels. Mussels were exposed to increasing concentrations of polyvinyl-coated nAg of the same size for 96 h at 15 °C. They were then analyzed for biophysical changes in the cytoplasm (viscosity, protein aggregation and lipids), neuro-activity (fractal kinetics of acetylcholinesterase (AChE)), oxidative stress (labile zinc (Zn) and lipid peroxidation) and inflammation (arachidonate cyclooxygenase). Although some decreasing effects in protein aggregation were observed, viscosity was more strongly decreased in mussels exposed to spheric and prismatic nAg. The activity of AChE was significantly decreased in the following form-dependent manner: prismatic > cubic > spheric nAg. The fractal dimension of AChE reactions was reduced by all geometries of nAg, while dissolved Ag had no effects. For nanoparticles with the same coating and relative size, spheric nAg produced more significant changes towards the fractal dimension of AChE, while prismatic nAg increased both protein aggregation and viscosity, whereas cubic nAg decreased protein aggregation in the cytoplasm. It is concluded that the geometries of nanoparticles could influence toxicity in aquatic organisms.

Current trends and challenges in analysis and characterization of engineered nanoparticles in seawater

With the increasingly wide use of engineered nanoparticles (ENPs), their release into the environment makes it important to determine in what quantitates they occur in aquatic systems and to understand their fate therein. In particular, detection and quantification of ENPs in seawater is challenging and often requires analytical methods to perform close to the feasibility confines. This review is aimed at critical analysis of current and emerging capabilities of analytical methods as have been employed for the analysis and characterization of ENPs in seawater in the last decade. An emphasis is given to the most reliable experimental strategies focused on avoiding the high-salt matrix effect and isolation and enrichment of the nanoparticulate fraction prior to analysis. Advanced analytical methodology in use basically relies on the application of elemental mass spectrometry to determine various particle-core metals and its single-particle mode to characterize the seawater-mediated transformation of ENPs, including dissolution, aggregation, etc. On the other hand, common microscopy, light scattering or X-ray based techniques are not sensitive enough to acquire the transformation information from real seawater samples. Finally, attention is pinpointed upon an acute shortcoming of the current research which is in the overwhelming majority of cases restricted to samples spiked with ENPs and often at excessive concentration levels.

An "on-off" electrochemiluminescence immunosensor for PIVKA-II detection based on the dual quenching of CeO2-Au-g-C3N4 hybrids by Ag nanocubes-VB2

Herein, we report a novel dual-quenching electrochemiluminescence (ECL) immunosensor for detecting protein induced by vitamin K absence or antagonist-II (PIVKA-II) based on ECL resonance energy transfer (ECL-RET). In this protocol, self-accelerated ECL hybrids of CeO₂ and Au nanoparticles functionalized g-C₃N₄ nanosheets (CeO₂-Au-g-C₃N₄) were prepared, which exhibited high ECL emission in the presence of S₂O₈^2- as a coreactant for "signal on" state. Concretely, CeO₂ with a reproducible redox couple of Ce³⁺ and Ce⁴⁺ could act as an efficient co-reaction accelerator to generate more oxidizing intermediate (SO₄^•-) to significantly self-promote the ECL emission of g-C₃N₄ NSs/S₂O₈^2- ECL system. Besides, Au nanoparticles not only accelerated electron transfer in the ECL process, but also provided massive active sites for biomolecules immobilization. The dual quenching labels of Ag nanocubes modified with vitamin B₂ (AgNCs-VB₂) were firstly proposed towards g-C₃N₄ NSs/S₂O₈^2- ECL system by ECL-RET, resulting in the remarkable ECL decrease for "signal off" state. Based on the sandwich immunoreaction, the "on-off" PIVKA-II ECL immunosensor gratifyingly possessed excellent detection sensitivity with the linear range of 0.4 pg mL^-1-10 ng mL^-1 and the low detection limit of 28.46 fg mL^-1 (S/N = 3). This presented strategy might provide a potential alternative tool for PIVKA-II detection in medical research and early clinical diagnostics of hepatocellular carcinoma.

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.

Governing factors affecting the impacts of silver nanoparticles on wastewater treatment

Silver nanoparticles (nanosilver or AgNPs) enter municipal wastewater from various sources, raising concerns about their potential adverse effects on wastewater treatment processes. We argue that the biological effects of silver nanoparticles at environmentally realistic concentrations (μgL^-1 or lower) on the performance of a full-scale municipal water resource recovery facility (WRRF) are minimal. Reactor configuration is a critical factor that reduces or even mutes the toxicity of silver nanoparticles towards wastewater microbes in a full-scale WRRF. Municipal sewage collection networks transform silver nanoparticles into silver(I)-complexes/precipitates with low ecotoxicity, and preliminary/primary treatment processes in front of biological treatment utilities partially remove silver nanoparticles to sludge. Microbial functional redundancy and microbial adaptability to silver nanoparticles also greatly alleviate the adverse effects of silver nanoparticles on the performance of a full-scale WRRF. Silver nanoparticles in a lab-scale bioreactor without a sewage collection system and/or a preliminary/primary treatment process, in contrast to being in a full scale system, may deteriorate the reactor performance at relatively high concentrations (e.g., mgL^-1 levels or higher). However, in many cases, silver nanoparticles have minimal impacts on lab-scale bioreactors, such as sequencing batch bioreactors (SBRs), especially when at relatively low concentrations (e.g., less than 1mgL^-1). The susceptibility of wastewater microbes to silver nanoparticles is species-specific. In general, silver nanoparticles have higher toxicity towards nitrifying bacteria than heterotrophic bacteria.