Tian A. Qiu

Gene expression as an indicator of the molecular response and toxicity in the bacterium Shewanella oneidensis and the water flea Daphnia magna exposed to functionalized gold nanoparticles

Nanoparticle (NP) physiochemical properties have been shown to be important determinants of NP interactions with biological systems. Due to both nanomaterial diversity and environmental complexity, a mechanistic understanding of how physiochemical properties affect NP/organism interactions will greatly aid in the accurate assessment and prediction of current and emerging NP-induced environmental impacts. Herein, we investigated key biological apical endpoints, such as viability, growth, and reproduction and the expression of genes associated with related molecular pathways in response to exposure to gold nanoparticles (AuNPs) functionalized with either positively charged ligands, polyallyamine hydrochloride, or negatively charged ligands, mercaptopropionic acid, in two model organisms, the bacterium Shewanella oneidensis MR-1 and the water flea Daphnia magna. By linking changes in molecular pathways to apical endpoints, potential biomarkers for functionalized AuNP impacts were identified in both organisms. Specifically, act was identified as a potential biomarker in D. magna and 16S as a potential biomarker in S. oneidensis. We also revealed that changes in molecular pathways induced by ligand–NP combination were strongly dependent upon the type of ligand on the NP surface, and the effects from their respective ligands alone might predict these effects for the ligand–NP combination, but only in some cases. Lastly, we revealed that it is possible to identify similar pathways provoked upon NP exposure across organisms. This study shows that molecular pathways will help elucidate mechanisms for NP toxicity that are predictive of adverse environmental outcomes.

Quantification of Free Polyelectrolytes Present in Colloidal Suspension, Revealing a Source of Toxic Responses for Polyelectrolyte-Wrapped Gold Nanoparticles

Polyelectrolyte (PE) wrapping of colloidal nanoparticles (NPs) is a standard method to control NP surface chemistry and charge. Because excess polyelectrolytes are usually employed in the surface modification process, it is critical to evaluate different purification strategies to obtain a clean final product and thus avoid ambiguities in the source of effects on biological systems. In this work, 4 nm diameter gold nanoparticles (AuNPs) were wrapped with 15 kDa poly(allylamine hydrochloride) (PAH), and three purification strategies were applied: (a) diafiltration or either (b) one round or (c) two rounds of centrifugation. The bacterial toxicity of each of these three PAH-AuNP samples was evaluated for the bacterium Shewanella oneidensis MR-1 and is quantitatively correlated with the amount of unbound PAH molecules in the AuNP suspensions, as judged by X-ray photoelectron spectroscopy, nuclear magnetic resonance experiments and quantification using fluorescent assay. Dialysis experiments show that, for a 15 kDa polyelectrolyte, a 50 kDa dialysis membrane is not sufficient to remove all PAH polymers. Together, these data showcase the importance of choosing a proper postsynthesis purification method for polyelectrolyte-wrapped NPs and reveal that apparent toxicity results may be due to unintended free wrapping agents such as polyelectrolytes.

Research highlights: unveiling the mechanisms underlying nanoparticle-induced ROS generation and oxidative stress

The field of nanotoxicology has a long-tested hypothesis, supported by a significant body of evidence, that nanoparticle-induced reactive oxygen species (ROS) lead to oxidative stress in biological systems. Within this paradigm, it is critical to fundamentally understand the underpinning mechanisms of nanoparticle ROS production and the corresponding oxidative stress they induce. This Highlight is focused on four recent articles on this topic. The first highlighted work investigated ROS generation from various silica nanoparticle surfaces and demonstrated that porosity and surface functionalization are key factors influencing ROS generation and nanoparticle toxicity. The second article demonstrated plasmon-mediated ROS production via hot electron production on gold nanocage surfaces under near-infrared irradiation. The third highlighted work correlated electronic properties of metal oxide nanoparticles to ROS generation, and built a quantitative linear relationship between ROS generation and antibacterial activity. Finally, the fourth study provided insights regarding protein signatures and pathways sensitive to oxidative stress in macrophage cells using a redox proteomic approach. Together, these four reports reveal mechanisms underlying nanoparticle-induced ROS generation and the resulting cellular oxidative stress.

Growth-Based Bacterial Viability Assay for Interference-Free and High-Throughput Toxicity Screening of Nanomaterials

Current high-throughput approaches evaluating toxicity of chemical agents toward bacteria typically rely on optical assays, such as luminescence and absorbance, to probe the viability of the bacteria. However, when applied to toxicity induced by nanomaterials, scattering and absorbance from the nanomaterials act as interferences that complicate quantitative analysis. Herein, we describe a bacterial viability assay that is free of optical interference from nanomaterials and can be performed in a high-throughput format on 96-well plates. In this assay, bacteria were exposed to various materials and then diluted by a large factor into fresh growth medium. The large dilution ensured minimal optical interference from the nanomaterial when reading optical density, and the residue left from the exposure mixture after dilution was confirmed not to impact the bacterial growth profile. The fractions of viable cells after exposure were allowed to grow in fresh medium to generate measurable growth curves. Bacterial viability was then quantitatively correlated to the delay of bacterial growth compared to a reference regarded as 100% viable cells; data analysis was inspired by that in quantitative polymerase chain reactions, where the delay in the amplification curve is correlated to the starting amount of the template nucleic acid. Fast and robust data analysis was achieved by developing computer algorithms carried out using R. This method was tested on four bacterial strains, including both Gram-negative and Gram-positive bacteria, showing great potential for application to all culturable bacterial strains. With the increasing diversity of engineered nanomaterials being considered for large-scale use, this high-throughput screening method will facilitate rapid screening of nanomaterial toxicity and thus inform the risk assessment of nanoparticles in a timely fashion.

Research highlights: applications of life-cycle assessment as a tool for characterizing environmental impacts of engineered nanomaterials

The upstream and downstream environmental impacts of engineered nanomaterials (ENMs) are increasingly realized, and have motivated research to advance promising applications while precluding adverse impacts. Life-cycle assessment (LCA) is a comprehensive tool that considers the entire lifetime of a material, product or process—from raw material acquisition to end-of-life—and can be used to characterize these impacts as various environmental and human health categories. The motivation for this highlight stems from the curiosity of experimentalists and theorists researching the environmental and biological impacts that could result from widespread implementation of nanotechnology. In particular, we are motivated to identify how our research on the nano–bio interface can liaise with the nano-LCA community to advance nano-LCA in a safe and sustainable manner. As such, this highlight focuses on four recent nano-LCA publications that survey across several system levels and address the topics of: (i) upstream impacts from nanoparticle synthesis, (ii) extended lifetimes through the incorporation of ENMs in paints, (iii) integration of nano-specific data into existing life-cycle models, and (iv) the establishment of a nano-specific LCA framework.

Research highlights: investigating the role of nanoparticle surface charge in nano–bio interactions

A systematic approach to predicting nanoparticle–cell interactions has become increasingly important due to the great potential that nanoparticles hold for biomedical and environmental applications. However, the quantitative description and accurate characterization of nanomaterial surface chemistry (e.g., ligand distribution and surface charge) is nontrivial due to the sheer complexity of both the nanoparticle mechanisms and the biological environments with which they interact. The authors of this highlight, including both experimental and theoretical chemists, were motivated to explore the current gap in the fundamental knowledge about nanoparticle surface charge-dependent interactions across a variety of biological systems. The highlight focuses on three recent publications that survey the effects of nanoparticle surface charge across several bio-system complexities, addressing: (i) ligand-coated gold nanoparticles traversing a lipid bilayer, (ii) silica nanoparticle uptake into human osteoblast cells, and (iii) the suborgan distribution of gold nanoparticles in mice.

Super-resolution imaging for monitoring cytoskeleton dynamics.

The cytoskeleton is a key cellular structure that is important in the control of cellular movement, structure, and sensing. To successfully image the individual cytoskeleton components, high resolution and super-resolution fluorescence imaging methods are needed. This review covers the three basic cytoskeletal elements and the relative benefits and drawbacks of fixed versus live cell imaging before moving on to recent studies using high resolution and super-resolution techniques. The techniques covered include the near-diffraction limited imaging methods of confocal microscopy and TIRF microscopy and the super-resolution fluorescence imaging methods of STORM, PALM, and STED.

Release, detection and toxicity of fragments generated during artificial accelerated weathering of CdSe/ZnS and CdSe quantum dot polymer composites

Next generation displays and lighting applications are increasingly using inorganic quantum dots (QDs) embedded in polymer matrices to impart bright and tunable emission properties. The toxicity of some heavy metals present in commercial QDs (e.g. cadmium) has, however, raised concerns about the potential for QDs embedded in polymer matrices to be released during the manufacture, use, and end-of-life phases of the material. One important potential release scenario that polymer composites can experience in the environment is photochemically induced matrix degradation. This process is not well understood at the molecular level. To study this process, the effect of an artificially accelerated weathering process on QD–polymer nanocomposites has been explored by subjecting CdSe and CdSe/ZnS QDs embedded in poly(methyl methacrylate) (PMMA) to UVC irradiation in aqueous media. Significant matrix degradation of QD–PMMA was observed along with measurable mass loss, yellowing of the nanocomposites, and a loss of QD fluorescence. While ICP-MS identified the release of ions, confocal laser scanning microscopy and dark-field hyperspectral imaging were shown to be effective analytical techniques for revealing that QD-containing polymer fragments were also released into aqueous media due to matrix degradation. Viability experiments, which were conducted with Shewanella oneidensis MR-1, showed a statistically significant decrease in bacterial viability when the bacteria were exposed to highly degraded QD-containing polymer fragments. Results from this study highlight the need to quantify not only the extent of nanoparticle release from a polymer nanocomposite but also to determine the form of the released nanoparticles (e.g. ions or polymer fragments).