Joseph T. Buchman

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: 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.

Influence of nickel manganese cobalt oxide nanoparticle composition on toxicity toward Shewanella oneidensis MR-1: redesigning for reduced biological impact

Lithium nickel manganese cobalt oxide (LixNiyMnzCo1−y−zO2, 0 < x, y, z < 1, also known as NMC) is a class of cathode materials used in lithium ion batteries. Despite the increasing use of NMC in nanoparticle form for next-generation energy storage applications, the potential environmental impact of released nanoscale NMC is not well characterized. Previously, we showed that the released nickel and cobalt ions from nanoscale Li1/3Ni1/3Mn1/3Co1/3O2 were largely responsible for impacting the growth and survival of the Gram-negative bacterium Shewanella oneidensis MR-1 (M. N. Hang et al., Chem. Mater., 2016, 28, 1092). Here, we show the first steps toward material redesign of NMC to mitigate its biological impact and to determine how the chemical composition of NMC can significantly alter the biological impact on S. oneidensis. We first synthesized NMC with various stoichiometries, with an aim to reduce the Ni and Co content: Li0.68Ni0.31Mn0.39Co0.30O2, Li0.61Ni0.23Mn0.55Co0.22O2, and Li0.52Ni0.14Mn0.72Co0.14O2. Then, S. oneidensis were exposed to 5 mg L−1 of these NMC formulations, and the impact on bacterial oxygen consumption was analyzed. Measurements of the NMC composition, by X-ray photoelectron spectroscopy, and composition of the nanoparticle suspension aqueous phase, by inductively coupled plasma-optical emission spectroscopy, showed the release of Li, Ni, Mn, and Co ions. Bacterial inhibition due to redesigned NMC exposure can be ascribed largely to the impact of ionic metal species released from the NMC, most notably Ni and Co. Tuning the NMC stoichiometry to have increased Mn at the expense of Ni and Co showed lowered, but not completely mitigated, biological impact. This study reveals that the chemical composition of NMC nanomaterials is an important parameter to consider in sustainable material design and usage.

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.

Size dependent oxidative stress response of the gut of Daphnia magna to functionalized nanodiamond particles

ABSTRACT Nanodiamonds are a type of engineered nanomaterial with high surface area that is highly tunable and are being proposed for use as a material for medical imaging or drug delivery to composites. With their potential for widespread use they may potentially be released into the aquatic environment as are many chemicals used for these purposes. It is generally thought that nanodiamonds are innocuous, but toxicity may occur due to surface functionalization. This study investigated the potential oxidative stress and antioxidant response of enterocytes in a freshwater invertebrate, Daphnia magna, a common aquatic invertebrate for ecotoxicological studies, in response to two types of functionalized nanodiamonds (polyallylamine and oxidized). We also examined how the size of the nanomaterial may influence toxicity by testing two different sizes (5 nm and 15 nm) of nanodiamonds with the same functionalization. Adults of Daphnia magna were exposed to three concentrations of each of the nanodiamonds for 24 h. We found that both 5 and 15 nm polyallylamine nanodiamond and oxidized nanodiamond induced the production of reactive oxygen species in tissues. The smaller 5 nm nanodiamond induced a significant change in the expression of heat shock protein 70 and glutathione‐S‐transferase. This may suggest that daphnids mounted an antioxidant response to the oxidative effects of 5 nm nanodiamonds but not the comparative 15 nm nanodiamonds with either surface chemistry. Outcomes of this study reveal that functionalized nanodiamond may cause oxidative stress and may potentially initiate lipid peroxidation of enterocyte cell membranes in freshwater organisms, but the impact of the exposure depends on the particle size. HighlightsWe examined the effects of 2 sizes and 2 types of functionalized diamond nanoparticles.Our results suggest a correlation between size and ROS production.5 nm DNPs instigate expression of hsp70 and oxidized DNPs cause greater stress than PAH‐ND particles.

Research highlights: examining the effect of shape on nanoparticle interactions with organisms

There are many variables that influence the toxicity of nanoparticles to organisms, such as nanoparticle size, shape, core composition, and ligand chemistry, composition, and coverage. Assessing the unique effects elicited by each of these parameters has been challenging as they impact each other. It is therefore difficult to change one parameter while keeping all other parameters constant. Here, we highlight three articles in which investigators carefully controlled as many confounding factors as possible while assessing the impacts of nanoparticle shape on their interactions with organisms. One study revealed shape-dependent effects of silver nanoparticles on the annual ryegrass, Lolium multiflorum. Another study identified shape-dependent effects of lanthanide-doped NaYF4 nanoparticles on nanoparticle association with a model cell membrane and on the cellular uptake and toxicity in selected cell lines. Finally, we highlight a study that used a coarse grain computational approach to effectively keep other parameters constant while determining the effect of shape on nanoparticle endocytosis.

Quaternary Amine-Terminated Quantum Dots Induce Structural Changes to Supported Lipid Bilayers

The cytoplasmic membrane represents an essential barrier between the cytoplasm and the environment external to cells. Interaction with nanomaterials can alter the integrity of the cytoplasmic membrane through the formation of holes and membrane thinning, which can ultimately lead to adverse biological impacts. Here we use supported lipid bilayers as experimental models for the cytoplasmic membrane to investigate the impact of quantum dots functionalized with the cationic polymer poly(diallyldimethylammonium chloride) (PDDA) on membrane structure. Using a quartz crystal microbalance with dissipation monitoring we show that the positively charged quantum dots attach to and induce structural rearrangement to zwitterionic bilayers in solely the liquid-disordered phase and in those containing phase-segregated liquid-ordered domains. Real-time atomic force microscopy imaging revealed that PDDA-coated quantum dots and, to a lesser extent, PDDA itself induced the disappearance of liquid-ordered domains. We hypothesize this effect is due to an increase in energy per unit area caused by collisions between PDDA-coated quantum dots at the membrane surface. This increase in free energy per area exceeds the approximate free-energy change associated with membrane mixing between the liquid-ordered and liquid-disordered phases and results in the destabilization of membrane domains.

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).

Stabilization of Silver and Gold Nanoparticles: Preservation and Improvement of Plasmonic Functionalities

Noble metal nanoparticles have been extensively studied to understand and apply their plasmonic responses, upon coupling with electromagnetic radiation, to research areas such as sensing, photocatalysis, electronics, and biomedicine. The plasmonic properties of metal nanoparticles can change significantly with changes in particle size, shape, composition, and arrangement. Thus, stabilization of the fabricated nanoparticles is crucial for preservation of the desired plasmonic behavior. Because plasmonic nanoparticles find application in diverse fields, a variety of different stabilization strategies have been developed. Often, stabilizers also function to enhance or improve the plasmonic properties of the nanoparticles. This review provides a representative overview of how gold and silver nanoparticles, the most frequently used materials in current plasmonic applications, are stabilized in different application platforms and how the stabilizing agents improve their plasmonic properties at the same time. Specifically, this review focuses on the roles and effects of stabilizing agents such as surfactants, silica, biomolecules, polymers, and metal shells in colloidal nanoparticle suspensions. Stability strategies for other types of plasmonic nanomaterials, lithographic plasmonic nanoparticle arrays, are discussed as well.

Optically Detected Magnetic Resonance for Selective Imaging of Diamond Nanoparticles

While there is great interest in understanding the fate and transport of nanomaterials in the environment and in biological systems, the detection of nanomaterials in complex matrices by fluorescence methods is complicated by photodegradation, blinking, and the presence of natural organic material and other fluorescent background signals that hamper detection of fluorescent nanomaterials of interest. Optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond nanoparticles provides a pathway toward background-free fluorescence measurements, as the application of a resonant microwave field can selectively modulate the intensity from NV centers in nanodiamonds of various diameters in complex materials systems using on-resonance and off-resonance microwave fields. This work represents the first investigation showing how nanoparticle diameter impacts the NV center lifetime and thereby directly impacts the accessible contrast and signal-to-noise ratio when using ODMR to achieve background-free imaging of NV-nanodiamonds in the presence of interfering fluorophores. These results provide new insights that will guide the choice of optimum nanoparticle size and methodology for background-free imaging and sensing applications, while also providing a model system to explore the fate and transport of nanomaterials in the environment.