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Currently, there is a lack of knowledge of how complex metal oxide nanomaterials, like LiCoO2 (LCO) nanosheets, interact with eukaryotic green algae. Previously, LCO was reported to cause a number of physiological impacts to Raphidocelis subcapitata including endpoints related to growth, reproduction, pigment & lipid biosynthesis, and carbon biomass assimilation. Furthermore, LCO was proven to physically enter the cells, thus indicating the possibility for it to directly interact with key subcellular components. However, the mechanisms through which LCO interacts with these key subcellular components is still unknown. This study assesses the interactions of LCO at the biointerface of R. subcapitata using a novel multiplexed algal cytological imaging (MACI) assay and machine learning in order to predict its phytotoxic mechanism of action (MoA). Algal cells were exposed to varying concentrations of LCO, and their phenotypic profiles were compared to that of cells treated with reference chemicals which had already established MoAs. Hierarchical clustering and machine learning analyses indicated photosynthetic electron transport to be the most probable phytotoxic MoA of LCO. Additionally, single-cell chlorophyll fluorescence results demonstrated an increase in irreversibly oxidized photosystem II proteins. Lastly, LCO-treated cells were observed to have less nuclei/cell and less DNA content/nucleus when compared to non-treated cell controls. 

Limited data exist on how surface charge and morphology impact the effectiveness of nanoscale copper oxide (CuO) as an agricultural amendment under field conditions. This study investigated the impact of these factors on tomatoes and watermelons following foliar treatment with CuO nanosheets (NS-) or nanospikes (NP+ and NP-) exhibiting positive or negative surface charge. Results showed plant species-dependent benefits. Notably, tomatoes infected with Fusarium oxysporum had significantly reduced disease progression when treated with NS-. Watermelons benefited similarly from NP+. Although disease suppression was significant and trends indicated increased yield, the yield effects weren't statistically significant. However, several nanoscale treatments significantly enhanced the fruit's nutritional value, and this nano-enabled biofortification was a function of particle charge and morphology. Negatively charged nanospikes significantly increased the Fe content of healthy watermelon and tomato (20–28 %) and Ca in healthy tomato (66 %), compared to their positively charged counterpart. Negatively charged nanospikes also outperformed negatively charged nanosheets, leading to significant increases in the content of S and Mg in infected watermelon (37–38 %), Fe in healthy watermelon (58 %), and Ca (42 %) in healthy tomato. These findings highlight the potential of tuning nanoscale CuO chemistry for disease suppression and enhanced food quality under field conditions. 

Semiconductor InSe 2D nanomaterials have emerged as potential photoresponsive materials for broadly distributed photodetectors and wearable electronics technologies due to their high photoresponsivity and thermal stability. This paper addresses an environmental concern about the fate of InSe 2D nanosheets when disposed and released into the environment after use. Semiconducting materials are potentially reactive and often form environmentally damaging species, for example reactive oxygen and nitrogen species, when degraded. InSe nanosheets are prepared using a semi bottom-up approach which involves a reaction between indium and selenium precursors at elevated temperature in an oxygen-free environment to prevent oxidation. InSe nanosheets are formed as a stable intermediate with micrometer-sized lateral dimensions and a few monolayer thickness. The InSe 2D nanosheets are obtained when the reaction is stopped after 30 minutes by cooling. Keeping the reaction at elevated temperature for a longer period, for example 60 minutes leads to the formation of InSe 3D nanoparticles of about 5 nm in diameter, a thermodynamically more stable form of InSe. The paper focuses on the colloidal stabilization of InSe nanosheets in an aqueous solution that contains epigallocatechin gallate (EGCG), a natural organic matter (NOM) simulant. We show that EGCG coats the surface of the hydrophobic, water-insoluble InSe nanosheets via physisorption. The formed EGCG-coated InSe nanosheets are colloidally stable in aqueous solution. While unmodified semiconducting InSe nanosheets could produce reactive oxygen species (ROS) when illuminated, our study shows low levels of ROS generation by EGCG-coated InSe nanosheets under ambient light, which might be attributed to ROS quenching by EGCG. Growth-based viability (GBV) assays show that the colloidally stable EGCG-coated InSe nanosheets adversely impact the bacterial growth of Shewanella oneidensis MR-1, an environmentally relevant Gram-negative bacterium in aqueous media. The impact on bacterial growth is driven by the EGCG coating of the nanosheets. In addition, live/dead assays show insignificant membrane damage of the Shewanella oneidensis MR-1 cells by InSe nanosheets, suggesting a weak association of EGCG-coated nanosheets with the cells. It is likely that the adverse impact of EGCG-coated nanosheets on bacterial growth is the result of increasing local concentration of EGCG either when adsorbed on the nanosheets when the nanosheets interact with the cells, or when desorbed from the EGCG-coated nanosheets to interact with the bacterial cells. 

Developing a materials perspective of how to control the degradation and negative impact of complex metal oxides requires an integrated understanding of how these nanomaterials transform in the environment and interact with biological systems. Doping with aluminum is known to stabilize oxide materials, but has not been assessed cohesively from synthesis to environmental fate and biological impact. In the present study, the influence of aluminum doping on metal ion release from transition metal oxides was investigated by comparing aqueous transformations of lithium nickel cobalt aluminum oxide (LiNi0.82Co0.15Al0.03O2; NCA) and lithium nickel cobalt oxide (LiNi0.80Co0.20O2; NC) nanoparticles and by calculating the energetics of metal release using a density functional theory (DFT) and thermodynamics method. Two model environmental organisms were used to assess biological impact, and metal ion release was compared for NCA and NC nanoparticles incubated in their respective growth media: moderately hard reconstituted water (MHRW) for the freshwater invertebrate Daphnia magna (D. magna) and minimal growth medium for the Gram-negative bacterium Shewanella oneidensis MR-1 (S. oneidensis). The amount of metal ions released was reduced for NCA compared to NC in MHRW, which correlated to changes in the modeled energetics of release upon Al substitution in the lattice. In minimal medium, metal ion release was approximately an order of magnitude higher compared to MHRW and was similar to the stoichiometry of the bulk nanoparticles for both NCA and NC. Interpretation of the release profiles and modeling indicated that the increase in total metal ion release and the reduced influence of Al doping arises from lactate complexation of metal ions in solution. The relative biological impacts of NC and NCA exposure for both S. oneidensis and D. magna were consistent with the metal release trends observed for minimal medium and MHRW, respectively. Together, these results demonstrate how a combined experimental and computational approach provides valuable insight into the aqueous transformations and biological impacts of complex metal oxide nanoparticles. 

We use diamond nanoparticles (DNPs) wrapped in the cationic polyelectrolyte poly(allylamine) hydrochloride (PAH) and bilayers composed of either pure DOPC or a mixture of DOPC/DOPG to investigate the influence of membrane phospholipid composition and net surface charge on nanoparticle-membrane interactions and the extent of nanoparticle adhesion to supported phospholipid bilayers. Our results show that in all cases electrostatic attractions between the negatively charged bilayer and cationic PAH-DNP were responsible for the initial attachment of particles, and the lateral electrostatic repulsion between adsorbed particles on the bilayer surface determined the final extent of PAH-DNP attachment. Upon attachment, NPs attract lipids by the contact ion pairing between the ammonium groups on PAH and phosphate and glycerol groups on the lipids and acquire a lipid corona. Lipid corona formation on the PAH-DNP reduces the effective charge density of the particle and is in fact a key factor determining the final extent of NP attachment to the bilayer. Incorporation of DOPG to the bilayer leads to a decrease in efficiency and final extent of attachment compared to DOPC alone. The reduction in PAH-DNP attachment in the presence of DOPG is attributed to the adsorption of free PAH in equilibrium with bound PAH in the nanoparticle solution, thus reducing electrostatic attraction between PAH-DNPs and SLBs. This leads to an increase in hydrogen bonding interactions between lipid headgroups that limits extraction of phospholipids from the bilayer by PAH-DNP, lessening the reduction in interparticle repulsion achieved by acquisition of a lipid corona. Our results indicate that the inclusion of charged phospholipids in SLBs changes bilayer rigidity and stability and hinders the attachment of PAH-DNPs by preventing lipid extraction from the bilayer. 

High-valent metal oxides such as LiCoO2 and related materials are of increasing environmental concern due to the large-scale use in lithium-ion batteries and potential for metal ion release into aqueous systems. A key aspect of the environmental chemistry of these materials is the potential role redox chemistry plays in their transformations as well as their influence on the surrounding environment (i.e., biomolecules, organisms etc.). In recent work, we showed that LiCoO2(a common lithium-ion battery cathode material) oxidizes nicotinamide adenine dinucleotide (NADH), an essential molecule for electron transport, and enhances Co release from LiCoO2. In the present work, we investigated the mechanism of interaction by examining the role of the ribose, phosphate, adenosine, and the nicotinamide components of NADH in the transformation of LiCoO2 nanoparticles. To build an understanding of the interaction mechanism, we used fluorescence spectroscopy to measure the changes in redox state and inductively coupled plasma-mass spectrometry (ICP-MS) to measure the changes in dissolved Co. Our results reveal the importance of surface binding, via the phosphate functionality, in initiating the redox transformation of both the LiCoO2 and the NADH. Observations from X-ray photoelectron spectroscopy (XPS) data show that molecules containing phosphate were bound to the surface of the nanoparticles and those without that functionality were not. We further established the generality of the results with LiCoO2 by examining other high-valent transition metal oxides. This surface binding effect has implications for understanding how other phosphorylated species can be transformed directly in the presence of high-valent metal oxide nanomaterials. 

Use of complex metal oxide nanoparticles has drastically risen in recent years, especially due to their utility in electric vehicle batteries. However, use of these materials has outpaced our understanding of how they might affect environmental organisms, which they could encounter through release during manufacture, use, and disposal. In particular, little is known about the effects of chronic exposure to complex metal oxide nanoparticles. Here, we have focused on an environmentally-relevant bacterial species, Shewanella oneidensis, which is ubiquitous in nature and responsible for bioremediation of heavy metals, and assessed the toxic effects of nanoscale lithiated nickel manganese cobalt oxide (NMC), which is an emerging battery cathode material for electronic devices. We previously reported that chronic exposure of S. oneidensis to NMC results in the emergence of an adaptive phenotype where the bacteria are able to tolerate otherwise lethal concentrations of NMC. In the present study, we aim to investigate the role of reactive oxygen species (ROS) and changes in phenotype of the NMC-adapted bacterial population. We found that NMC-exposed bacteria possess ROS-containing membrane vesicles, as well as an increased propensity to generate random DNA mutations and harbor other DNA damage. Thus, our data indicate substantial genetic-level variation in bacteria that results from chronic exposure to toxic complex metal oxide nanomaterials. 

Supported lipid bilayers are often used as model systems for studying interactions of biological membranes with protein or nanoparticles. A supported lipid bilayer is a phospholipid bilayer built on a solid substrate. The latter is typically made of silica or a metal oxide due to the ease of its formation and range of compatible measurement techniques. Recently, a solvent-assisted method involving supported lipid bilayer formation has allowed the extension of compatible substrate materials to include noble metals such as gold. Here, we examine the influence of substrate composition (SiO2 vs Au) on the interactions between anionic ligand-coated Au nanoparticles or cytochrome c and zwitterionic supported lipid bilayers using quartz crystal microbalance with dissipation monitoring. We find that anionic nanoparticles and cytochrome c have higher adsorption to bilayers formed on Au relative to those on SiO2 substrates. We examine the substrate-dependence of nanoparticle adsorption with DLVO theory and all-atom simulations, and find that the stronger attractive van der Waals and weaker repulsive electrostatic forces between anionic nanoparticles and Au substrates vs anionic nanoparticles and SiO2 substrates could be responsible for the change in adsorption observed. Our results also indicate that the underlying substrate material influences the degree to which nanoscale analytes interact with supported lipid bilayers; therefore, interpretation of the supported lipid bilayer model system should be conducted with understanding of support properties. 

A classical model in the framework of the INTERFACE force field has been developed for treating the LiCoO$_2$ (LCO) (001)/water interface. In comparison to {\em ab initio} molecular dynamics (MD) simulations based on density functional theory, MD simulations using the classical model lead to generally reliable descriptions of interfacial properties, such as the density distribution of water molecules. Water molecules in close contact with the LCO surface form a strongly adsorbed layer, which leads to a free energy barrier for the absorption of polar or charged molecules to the LCO surface. Moreover, due to the strong hydrogen bonding interactions with the LCO surface, the first water layer forms an interface that exhibits hydrophobic characters, leading to favorable adsorption of non-polar molecules to the interface. Therefore, despite its highly polar nature, the LCO (001) surface binds not only polar/charged but also non-polar solutes. As an application, the model is used to analyze the adsorption of reduced nicotinamide adenine dinucleotide (NADH) and its molecular components to the LCO (001) surface in water. The results suggests that recently observed redox activity of NADH at the LCO/water interface was due to the co-operativity between the ribose component, which drives binding to the LCO surface, and the nicotinamide moiety, which undergoes oxidation.