Effects of Hydrophobic Gold Nanoparticles on Structure and Fluidity of SOPC Lipid Membranes

Gold nanoparticles (AuNPs) are promising candidates in various biomedical applications such as sensors, imaging, and cancer therapy. Understanding the influence of AuNPs on lipid membranes is important to assure their safety in the biological environment and to improve their scope in nanomedicine. In this regard, the present study aimed to analyze the effects of different concentrations (0.5, 1, and 2 wt.%) of dodecanethiol functionalized hydrophobic AuNPs on the structure and fluidity of zwitterionic 1-stearoyl-2-oleoyl-sn-glycerol-3-phosphocholine (SOPC) lipid bilayer membranes using Fourier-transform infrared (FTIR) spectroscopy and fluorescent spectroscopy. The size of AuNPs was found to be 2.2 ± 1.1 nm using transmission electron microscopy. FTIR results have shown that the AuNPs induced a slight shift in methylene stretching bands, while the band positions of carbonyl and phosphate group stretching were unaffected. Temperature-dependent fluorescent anisotropy measurements showed that the incorporation of AuNPs up to 2 wt.% did not affect the lipid order in membranes. Overall, these results indicate that the hydrophobic AuNPs in the studied concentration did not cause any significant alterations in the structure and membrane fluidity, which suggests the suitability of these particles to form liposome-AuNP hybrids for diverse biomedical applications including drug delivery and therapy.

The ability of carbon nanoparticles to increase transmembrane current of cations coincides with impaired synaptic neurotransmission

Here, carbon nanodots synthesized from β-alanine (Ala-CDs) and detonation nanodiamonds (NDs) were assessed using (1) radiolabeled excitatory neurotransmitters L-[¹⁴C]glutamate, D-[2,3³H]aspartate, and inhibitory ones [³H]GABA, [³H]glycine for registration of their extracellular concentrations in rat cortex nerve terminals; (2) the fluorescent ratiometric probe NR12S and pH-sensitive probe acridine orange for registration of the membrane lipid order and synaptic vesicle acidification, respectively; (3) suspended bilayer lipid membrane (BLM) to monitor changes in transmembrane current. In nerve terminals, Ala-CDs and NDs increased the extracellular concentrations of neurotransmitters and decreased acidification of synaptic vesicles, whereas have not changed sufficiently the lipid order of membrane. Both nanoparticles, Ala-CDs and NDs, were capable of increasing the conductance of the BLM by inducing stable potential-dependent cation-selective pores. Introduction of divalent cations, Zn²⁺ or Cd²⁺ on the particles` application side (cis-side) increased the rate of Ala-CDs pore-formation in the BLM. The application of positive potential (+100 mV) to the cis-chamber with Ala-CDs or NDs also activated the insertion as compared with the negative potential (-100 mV). The Ala-CD pores exhibited a wide-range distribution of conductances between 10 and 60 pS and consecutive increase in conductance of each major peak by ~10 pS, which suggest the clustering of the same basic ion-conductive structure. NDs also formed ion-conductive pores ranging from 6 pS to 60 pS with the major peak of conductance at ~12 pS in cholesterol-containing membrane. Observed Ala-CDs and NDs-induced increase in transmembrane current coincides with disturbance of excitatory and inhibitory neurotransmitter transport in nerve terminals.

Polymer Coating and Lipid Phases Regulate Semiconductor Nanorods' Interaction with Neuronal Membranes: A Modeling Approach

The interplay between nanoparticles (NPs) and cell membranes is extremely important with regard to using NPs in biology applications. With the aim of unraveling the dominating factors on the molecular scale, we have studied the interaction between polymer-coated semiconductor nanorods (NRs) made of cadmium selenium/cadmium sulfur and model lipid membranes. The zeta potential (ζ) of the NRs was tuned from having a negative value (-24 mV) to having a positive one (+11 mV) by changing the amine content in the polymer coating. Supported lipid bilayers (SLBs) and lipid monolayers (LMs) were used as model membranes. Lipid mixtures containing anionic or cationic lipids were employed in order to change the membrane ζ from -77 to +49 mV; lipids with saturated hydrophobic chains were used to create phase-separated gel domains. NR adsorption to the SLBs was monitored by quartz crystal microbalance with dissipation monitoring; interactions with LMs with the same lipid composition were measured by surface pressure-area isotherms. The results showed that the NRs only interact with the model membrane if the mutual Δζ is higher than 70 mV; at the air-water interface, positively charged NRs remove lipids from the anionic lipid mixtures, and the negative ones penetrate the space between the polar heads in the cationic mixtures. However, the presence of gel domains in the membrane inhibits this interaction. The results of the Derjaguin-Landau-Verwey-Overbeek model frame indicate that the interaction occurs not only due to electrostatic and van der Waals forces, but also due to steric and/or hydration forces.

Nanodarts, nanoblades, and nanospikes: Mechano-bactericidal nanostructures and where to find them

Over the past ten years, a next-generation approach to combat bacterial contamination has emerged: one which employs nanostructure geometry to deliver lethal mechanical forces causing bacterial cell death. In this review, we first discuss advances in both colloidal and topographical nanostructures shown to exhibit such "mechano-bactericidal" mechanisms of action. Next, we highlight work from pioneering research groups in this area of antibacterials. Finally, we provide suggestions for unexplored research topics that would benefit the field of mechano-bactericidal nanostructures. Traditionally, antibacterial materials are loaded with antibacterial agents with the expectation that these agents will be released in a timely fashion to reach their intended bacterial metabolic target at a sufficient concentration. Such antibacterial approaches, generally categorized as chemical-based, face design drawbacks as compounds diffuse in all directions, leach into the environment, and require replenishing. In contrast, due to their mechanisms of action, mechano-bactericidal nanostructures can benefit from sustainable opportunities. Namely, mechano-bactericidal efficacy needs not replenishing since they are not consumed metabolically, nor are they designed to release or leach compounds. For this same reason, however, their action is limited to the bacterial cells that have made direct contact with mechano-bactericidal nanostructures. As suspended colloids, mechano-bactericidal nanostructures such as carbon nanotubes and graphene nanosheets can pierce or slice bacterial membranes. Alternatively, surface topography such as mechano-bactericidal nanopillars and nanospikes can inflict critical membrane damage to microorganisms perched upon them, leading to subsequent cell lysis and death. Despite the infancy of this area of research, materials constructed from these nanostructures show remarkable antibacterial potential worthy of further investigation.

Nanoscale zero-valent iron/persulfate enhanced upflow anaerobic sludge blanket reactor for dye removal: Insight into microbial metabolism and microbial community

This study investigated the efficiency of nanoscale zero-valent iron combined with persulfate (NZVI/PS) for enhanced degradation of brilliant red X-3B in an upflow anaerobic sludge blanket (UASB) reactor, and examined the effects of NZVI/PS on anaerobic microbial communities during the treatment process. The addition of NZVI (0.5 g/L) greatly enhanced the decolourization rate of X-3B from 63.8% to 98.4%. The Biolog EcoPlate^TM technique was utilized to examine microbial metabolism in the reactor, and the Illumina MiSeq high-throughput sequencing revealed 22 phyla and 88 genera of the bacteria. The largest genera (Lactococcus) decreased from 33.03% to 7.94%, while the Akkermansia genera increased from 1.69% to 20.23% according to the abundance in the presence of 0.2 g/L NZVI during the biological treatment process. Meanwhile, three strains were isolated from the sludge in the UASB reactors and identified by 16 S rRNA analysis. The distribution of three strains was consistent with the results from the Illumina MiSeq high throughput sequencing. The X-ray photoelectron spectroscopy results indicated that Fe(0) was transformed into Fe(II)/Fe(III) during the treatment process, which are beneficial for the microorganism growth, and thus promoting their metabolic processes and microbial community.

Shape-Dependent Surface Reactivity and Antimicrobial Activity of Nano-Cupric Oxide

Shape of engineered nanomaterials (ENMs) can be used as a design handle to achieve controlled manipulation of physicochemical properties. This tailored material property approach necessitates the establishment of relationships between specific ENM properties that result from such manipulations (e.g., surface area, reactivity, or charge) and the observed trend in behavior, from both a functional performance and hazard perspective. In this study, these structure-property-function (SPF) and structure-property-hazard (SPH) relationships are established for nano-cupric oxide (n-CuO) as a function of shape, including nanospheres and nanosheets. In addition to comparing these shapes at the nanoscale, bulk CuO is studied to compare across length scales. The results from comprehensive material characterization revealed correlations between CuO surface reactivity and bacterial toxicity with CuO nanosheets having the highest surface reactivity, electrochemical activity, and antimicrobial activity. While less active than the nanosheets, CuO nanoparticles (sphere-like shape) demonstrated enhanced reactivity compared to the bulk CuO. This is in agreement with previous studies investigating differences across length-scales. To elucidate the underlying mechanisms of action to further explain the shape-dependent behavior, kinetic models applied to the toxicity data. In addition to revealing different CuO material kinetics, trends in observed response cannot be explained by surface area alone. The compiled results contribute to further elucidate pathways toward controlled design of ENMs.

The relevance of membrane models to understand nanoparticles-cell membrane interactions

Over the past two decades, numerous types of nanoparticles (NPs) have been developed for medical applications; however only a few nanomedicines are actually available on the market. One reason is the lack of understanding and data concerning the NP fate and their behavior upon contact with biological media and cell membranes. Biomimetic membrane models are interesting tools to approach and understand NPs-cell membrane interactions. The use of these models permits one to control physical and chemical parameters and to rapidly compare membrane types and the influence of different media conditions. The interactions between NPs and cell membranes can be qualified and quantified using analytical and modeling methods. In this review, the major studies concerning NPs-cell membrane models and associated methods are described. The advantages and drawbacks for each method are compared for the different models. The key mechanisms of interactions between NPs and cell membranes are revealed using cell membrane models and are interrogated in comparison with the NP behavior in cellulo or in vivo. Investigating the interactions between NPs and cell membrane models is now proposed as an intermediate step between physicochemical characterization of NPs and biological assays.

Colorimetric detection of catalytic reactivity of nanoparticles in complex matrices

There is a need for new methodologies to quickly assess the presence and reactivity of nanoparticles (NPs) in commercial, environmental, and biological samples since current detection techniques require expensive and complex analytical instrumentation. Here, we investigate a simple and portable colorimetric detection assay that assesses the surface reactivity of NPs, which can be used to detect the presence of NPs, in complex matrices (e.g., environmental waters, serum, urine, and in dissolved organic matter) at as low as part per billion (ppb) or ng/mL concentration levels. Surface redox reactivity is a key emerging property related to potential toxicity of NPs with living cells, and is used in our assays as a key surrogate for the presence of NPs and a first tier analytical strategy toward assessing NP exposures. We detect a wide range of metal (e.g., Ag and Au) and oxide (e.g., CeO2, SiO2, VO2) NPs with a diameter range of 5 to 400 nm and multiple capping agents (tannic acid (TA), polyvinylpyrrolidone (PVP), branched polyethylenimine (BPEI), polyethylene glycol (PEG)). This method is sufficiently sensitive (ppb levels) to measure concentrations typically used in toxicological studies, and uses inexpensive, commercially available reagents.

Native silica nanoparticles are powerful membrane disruptors

Silica nanoparticles permeabilize liposomal membranes as a function of nanoparticle size, surface chemistry and biocoating as well as membrane charge.

Nanoparticles meet cell membranes: probing nonspecific interactions using model membranes

Nanotoxicity studies have shown that both carbon-based and inorganic engineered nanoparticles can be toxic to microorganisms. Although the pathways for cytotoxicity are diverse and dependent upon the nature of the engineered nanoparticle and the chemical environment, numerous studies have provided evidence that direct contact between nanoparticles and bacterial cell membranes is necessary for cell inactivation or damage, and may in fact be a primary mechanism for cytotoxicity. The propensities for nanoparticles to attach to and disrupt cell membranes are still not well understood due to the heterogeneous and dynamic nature of biological membranes. Model biological membranes can be employed for systematic investigations of nanoparticle-membrane interactions. In this article, current and emerging experimental approaches to identify the key parameters that control the attachment of ENPs on model membranes and the disruption of membranes by ENPs will be discussed. This critical information will help enable the "safe-by-design" production of engineered nanoparticles that are nontoxic or biocompatible, and also allow for the design of antimicrobial nanoparticles for environmental and biomedical applications.

Biomembrane disruption by silica-core nanoparticles: effect of surface functional group measured using a tethered bilayer lipid membrane

Engineered nanomaterials (ENM) have desirable properties that make them well suited for many commercial applications. However, a limited understanding of how ENM's properties influence their molecular interactions with biomembranes hampers efforts to design ENM that are both safe and effective. This paper describes the use of a tethered bilayer lipid membrane (tBLM) to characterize biomembrane disruption by functionalized silica-core nanoparticles. Electrochemical impedance spectroscopy was used to measure the time trajectory of tBLM resistance following nanoparticle exposure. Statistical analysis of parameters from an exponential resistance decay model was then used to quantify and analyze differences between the impedance profiles of nanoparticles that were unfunctionalized, amine-functionalized, or carboxyl-functionalized. All of the nanoparticles triggered a decrease in membrane resistance, indicating nanoparticle-induced disruption of the tBLM. Hierarchical clustering allowed the potency of nanoparticles for reducing tBLM resistance to be ranked in the order amine>carboxyl~bare silica. Dynamic light scattering analysis revealed that tBLM exposure triggered minor coalescence for bare and amine-functionalized silica nanoparticles but not for carboxyl-functionalized silica nanoparticles. These results indicate that the tBLM method can reproducibly characterize ENM-induced biomembrane disruption and can distinguish the BLM-disruption patterns of nanoparticles that are identical except for their surface functional groups. The method provides insight into mechanisms of molecular interaction involving biomembranes and is suitable for miniaturization and automation for high-throughput applications to help assess the health risk of nanomaterial exposure or identify ENM having a desired mode of interaction with biomembranes.

Polystyrene nanoparticle exposure induces ion-selective pores in lipid bilayers

A diverse range of molecular interactions can occur between engineered nanomaterials (ENM) and biomembranes, some of which could lead to toxic outcomes following human exposure to ENM. In this study, we adapted electrophysiology methods to investigate the ability of 20nm polystyrene nanoparticles (PNP) to induce pores in model bilayer lipid membranes (BLM) that mimic biomembranes. PNP charge was varied using PNP decorated with either positive (amidine) groups or negative (carboxyl) groups, and BLM charge was varied using dioleoyl phospholipids having cationic (ethylphosphocholine), zwitterionic (phosphocholine), or anionic (phosphatidic acid) headgroups. Both positive and negative PNP induced BLM pores for all lipid compositions studied, as evidenced by current spikes and integral conductance. Stable PNP-induced pores exhibited ion selectivity, with the highest selectivity for K(+) (PK/PCl~8.3) observed when both the PNP and lipids were negatively charged, and the highest selectivity for Cl(-) (PK/PCl~0.2) observed when both the PNP and lipids were positively charged. This trend is consistent with the finding that selectivity for an ion in channel proteins is imparted by oppositely charged functional groups within the channel's filter region. The PK/PCl value was unaffected by the voltage-ramp method, the pore conductance, or the side of the BLM to which the PNP were applied. These results demonstrate for the first time that PNP can induce ion-selective pores in BLM, and that the degree of ion selectivity is influenced synergistically by the charges of both the lipid headgroups and functional groups on the PNP.