This work presents molecular-level investigations of how wellcharacterized silica-supported phospholipid bilayers formed from either pure DOPC or a 9:1 mixture of DOPC:DOTAP interact with positively and negatively charged 4 nm gold metal nanoparticles at pH 7.4 and NaCl concentrations ranging from 0.001 to 0.1 M. Second harmonic generation (SHG) charge screening measurements indicate the supported bilayers carry a negative interfacial potential. Resonantly enhanced SHG measurements probing electronic transitions within the gold core of the nanoparticles show the particles interact irreversibly with the supported bilayers at a range of concentrations. At 0.1 M NaCl, surface coverages for the particles functionalized with the negatively charged ligand mercaptopropionic acid (MPA) or wrapped in the cationic polyelectrolyte poly(allylamine) hydrochloride (PAH) are estimated from a joint analysis of QCM-D, XPS, AFM, and ToF-SIMS to be roughly 1 × 10 7 and 1 × 10 11 particles cm −2 , respectively. Results from complementary SHG charge screening experiments point to the possibility that the surface coverage of the MPA-coated particles is more limited by interparticle Coulomb repulsion due to the charges within their hydrodynamic volumes than with the PAH-wrapped particles. Yet, SHG adsorption isotherms indicate that the interaction strength per particle is independent of ionic strength and particle coating, highlighting the importance of multivalent interactions. 1 H NMR spectra of the lipids within vesicles suspended in solution show little change upon interaction with either particle type but indicate loosening of the gold-bound PAH polymer wrapping upon attachment to the vesicles. The thermodynamic, spectroscopic, and electrostatic data presented here may serve to benchmark experimental and computational studies of nanoparticle attachment processes at the nano−bio interface.

Nickel manganese cobalt oxide (NMC) comprises a class of lithium intercalation compounds with the composition L x Ni y Mn z Co 1-y-z O 2 (0 < x,y,z < 1). These compounds are of emerging importance in nanoparticle form as cathode materials for lithium-ion batteries used in transportation and consumer electronics. To evaluate the potential environmental impact of release of this material in the environment, we synthesized NMC nanosheets and investigated their interaction with Shewanella oneidensis, a soil and sediment bacterium. Exposure to 5 mg/L NMC significantly impaired bacterial population growth and respiration. Measurements of NMC surface composition by X-ray photoelectron spectroscopy and of the composition of the suspending solution via inductively coupled plasma-optical emission spectroscopy (ICP-OES) demonstrated incongruent material dissolution and measurable release of all four metal constituents (Li, Mn, Co, and Ni) into solution. Speciation modeling and assessment of bacterial response to metal ion exposure (via cell growth and respiration measurements) established that the observed bacterial inhibition arose from the metal ions released from the NMC, with the largest effects arising from Ni(II) and Co(II) species.

For nanoparticles that have been released into the environment, the cell membrane represents an initial site of interaction with eukaryotic cells. The encounter of nanoparticles with cellular membranes may alter membrane structure and function, lead to uptake into cells, or elicit adverse biological responses.Supported lipid bilayers have proven to be valuable ex vivo models for biological membranes, allowing investigation of their mechanisms of interaction with nanoparticles with a degree of control impossible in living cells. To date, the majority of research on nanoparticle interaction with supported lipid bilayers has employed membranes composed of single or binary mixtures of phospholipids. Cellular membranes contain a wide variety of lipids and exhibit lateral organization. Ordered membrane domains enriched in specific membrane components, also referred to as lipid rafts, have not been explored with respect to their interaction with nanoparticles. Here we develop model membranes containing segregated domains differing in fluidity that are amenable to investigation by a variety of surface-sensitive analytical techniques and demonstrate that these domains influence the extent of nanoparticle attachment to model membranes. We determined conditions that allow reliable formation of bilayers containing liquid-ordered domains enriched in sphingomyelin and cholesterol and confirmed their morphology by structured illumination and atomic force microscopies. We demonstrate that the presence of liquid-ordered domains increases attachment of cationic gold nanoparticles to model membranes relative to those lacking such domains under near physiological ionic strength conditions (0.1 M NaCl) at pH 7.4. We anticipate that these results will serve as the foundation for and motivate further study of nanoparticle interaction with phasesegregated domains.Environ. Sci.: Nano This journal isThe interaction of nanoparticles with cellular membranes can be a critical determinant in eliciting adverse outcomes in organisms. Model membranes composed of single or binary phospholipid mixtures have provided insight into the interaction with nanomaterials. Cytoplasmic membranes of living organisms, however, are made up of hundreds of components laterally organized into dynamic functional domains. We have established a platform to investigate the interaction of nanoparticles with model membranes containing ordered lipid domains with a variety of surface-sensitive analytical techniques. We demonstrate that the presence of these domains influences the interaction of cationic gold nanoparticles with model membranes under high ionic strength conditions. This study highlights the need to systematically investigate the interaction of nanoparticles with important membrane components and structures.

Understanding the origin and sensitivity of carbon dot emission will improve their utility in various applications.

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Mechanisms of corona formation around nanomaterials remain enigmatic. Here, we provide evidence for spontaneous lipid corona formation that engenders new particle properties without the need for active mixing upon attachment to stationary and suspended lipid bilayer membranes. The mechanism of lipid corona formation can be used to improve control over nano-bio interactions and to help understand why some nanomaterial-ligand combinations are detrimental to organisms but others are not. SUMMARYAlthough mixing nanoparticles with certain biological molecules can result in coronas that afford some control over how engineered nanomaterials interact with living systems, corona formation mechanisms remain enigmatic. Here, we report results from experiments and computer simulations that provide concrete lines of evidence for spontaneous lipid corona formation without active mixing upon attachment to stationary and suspended lipid bilayer membranes. Experiments show that polycation-wrapped particles disrupt the tails of zwitterionic lipids, increase bilayer fluidity, and leave the membrane with reduced z potentials. Computer simulations suggest that the contact ion pairing between the lipid head groups and the polycations' ammonium groups leads to the formation of stable, albeit fragmented, lipid bilayer coronas. The mechanistic insight regarding lipid corona formation can be used to improve control over nanobio interactions and to help understand why some nanomaterial-ligand combinations are detrimental to organisms but others are not.

Changes to nanoparticle surface charge, colloidal stability, and hydrodynamic properties induced by interaction with natural organic matter (NOM) warrant consideration in assessing the potential for these materials to adversely impact organisms in the environment. Here, we show that acquisition of a coating, or "corona", of NOM alters the hydrodynamic and electrokinetic properties of diamond nanoparticles (DNPs) functionalized with the polycation poly(allylamine HCl) in a manner that depends on the NOM-to-DNP concentration ratio. The NOM-induced changes to DNP properties alter subsequent interactions with model biological membranes and the Gram-negative bacterium Shewanella oneidensis MR-1. Suwannee River NOM induces changes to DNP hydrodynamic diameter and apparent ζ-potential in a concentration-dependent manner. At low NOM-to-DNP ratios, DNPs aggregate to a limited extent but retain a positive ζ-potential apparently due to nonuniform adsorption of NOM molecules leading to attractive electrostatic interactions between oppositely charged regions on adjacent DNP surfaces. Diamond nanoparticles at low NOM-to-DNP ratios attach to model membranes to a larger extent than in the absence of NOM (including those incorporating lipopolysaccharide, a major bacterial outer membrane component) and induce a comparable degree of membrane damage and toxicity to S. oneidensis. At higher NOM-to-DNP ratios, DNP charge is reversed, and DNP aggregates remain stable in suspension. This charge reversal eliminates DNP attachment to model membranes containing the highest LPS contents studied due to electrostatic repulsion and abolishes membrane damage to S. oneidensis. Our results demonstrate that the effects of NOM coronas on nanoparticle properties and interactions with biological surfaces can depend on the relative amounts of NOM and nanoparticles.

Engineered nanoparticles (NPs) can negatively impact biological systems through induced generation of reactive oxygen species (ROS). Overproduced ROS cause biochemical damage and hence need to be effectively buffered by a sophisticated cellular oxidative stress response system. How this complex cellular system, which consists of multiple enzymes, responds to NP-induced ROS is largely unknown. Here, we apply a single cell analysis to quantitatively evaluate 10 key ROS responsive genes simultaneously to understand how the cell prioritizes tasks and reallocates resources in response to NPinduced oxidative stress. We focus on rainbow trout gill epithelial cellsa model cell type for environmental exposureand their response to the massive generation of ROS induced by lithium cobalt oxide (LCO) NPs, which are extensively used as cathode materials in lithium ion batteries. Using multiplexed fluctuation localization imaging-based fluorescence in situ hybridization (fliFISH) in single cells, we found a shift in the expression of oxidative stress response genes with initial increase in genes targeting superoxide species, followed by increase in genes targeting peroxide and hydroxyl species. In contrast, Li + and Co 2+ , at concentrations expected to be shed from the NPs, did not induce ROS generation but showed a potent inhibition of transcription for all 10 stress response genes. Taken together, our findings suggest a "two-hit" model for LCO NP toxicity, where the intact LCO NPs induce high levels of ROS that elicit sequential engagement of stress response genes, while the released metal ions suppress the expression of these genes. Consequently, these effects synergistically drive the exposed cells to become more vulnerable to ROS stress and damage.