Protective effect of trehalose sugar on amyloid-membrane interactions using BLM electrophysiology.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by dementia and memory loss in the elderly population. The amyloid-ß peptide (Aß) is one of the main pathogenic factors in AD and is known to cause damage to neuronal cellular membranes. There is no cure currently available for AD, and new approaches, including preventive strategies, are highly desirable. In this work, we explore the possibility of protecting neuronal membranes from amyloid-induced damage with naturally existing sugar trehalose. Trehalose has been shown to protect plant cellular membranes in extreme conditions and modify Aß misfolding. We hypothesize that trehalose can protect the neuronal membrane from amyloid toxicity. In this work, we studied the protective effect of trehalose against Aß1-42-induced damage in model lipid membranes (DPPC/POPC/cholesterol) using atomic force microscopy and black lipid membrane electrophysiology. Our results demonstrate that Aß1-42 damaged membranes and led to ionic current leakage across these membranes due to the formation of various defects and pores. The presence of trehalose reduced the ion current across membranes caused by Aß1-42 peptide damage, thus efficiently protecting the membranes. These findings suggest that the trehalose sugar can potentially be useful in protecting neuronal membranes against amyloid toxicity in AD.

Localized surface plasmon resonance and atomic force microscopy study of model lipid membranes and their interactions with amyloid and melatonin.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of amyloid plaques in the brain. The toxicity of amyloid to neuronal cell surfaces arises from interactions between small intermediate aggregates, namely amyloid oligomers, and the cell membrane. The nature of these interactions changes with age and disease progression. In our previous work, we demonstrated that both membrane composition and nanoscale structure play crucial roles in amyloid toxicity, and that membrane models mimicking healthy neuron were less affected by amyloid than model membranes mimicking AD neuronal membranes. This understanding introduces the possibility of modifying membrane properties with membrane-active molecules, such as melatonin, to protect them from amyloid-induced damage. In this study, we employed atomic force microscopy and localized surface plasmon resonance to investigate the protective effects of melatonin. We utilized synthetic lipid membranes that mimic the neuronal cellular membrane at various stages of AD and explored their interactions with amyloid-ß(1-42) in the presence of melatonin. Our findings reveal that the early diseased membrane model is particularly vulnerable to amyloid binding and subsequent damage. However, melatonin exerts its most potent protective effect on this early-stage membrane. These results suggest that melatonin could act at the membrane level to alleviate amyloid toxicity, offering the most protection during the initial stages of AD.

Kelvin probe force microscopy to study electrostatic interactions of DNA with lipid-gemini surfactant monolayers for gene delivery.

In novel gene therapy mechanisms utilising gemini surfactants, electrostatic interactions of the surfactant molecules with the DNA strands is a primary mechanism by which the two components of the delivery vehicle bind. In this work, we show for the first time direct evidence of electrostatic interactions of these compounds visualised with Kelvin probe force microscopy (KPFM) and correlated to their topography from atomic force microscopy (AFM). We construct monolayers of lipids and gemini surfactant to simulate interactions on a cellular level, using lipids commonly found in cell membranes, and allow DNA to bind to the monolayer as it is formed on a Langmuir-Blodgett trough. The difference in topography and electrical surface potential between monolayers with and without DNA is striking. In fact, KPFM reveals a strongly positive relative electrical surface potential in between where we identify a background lipid and the DNA strands, evidenced by the height profiles of the domains. Such identification is not possible without KPFM. We conclude that it is likely we are seeing cationic surfactant molecules surrounding DNA strands within a sea of background lipid.

Pseudopeptide Amyloid Aggregation Inhibitors: In Silico, Single Molecule and Cell Viability Studies.

Neurodegeneration in Alzheimer's disease (AD) is defined by pathology featuring amyloid-ß (Aß) deposition in the brain. Aß monomers themselves are generally considered to be nontoxic, but misfold into ß-sheets and aggregate to form neurotoxic oligomers. One suggested strategy to treat AD is to prevent the formation of toxic oligomers. The SG inhibitors are a class of pseudopeptides designed and optimized using molecular dynamics (MD) simulations for affinity to Aß and experimentally validated for their ability to inhibit amyloid-amyloid binding using single molecule force spectroscopy (SMFS). In this work, we provide a review of our previous MD and SMFS studies of these inhibitors and present new cell viability studies that demonstrate their neuroprotective effects against Aß(1-42) oligomers using mouse hippocampal-derived HT22 cells. Two of the tested SG inhibitors, predicted to bind Aß in anti-parallel orientation, demonstrated neuroprotection against Aß(1-42). A third inhibitor, predicted to bind parallel to Aß, was not neuroprotective. Myristoylation of SG inhibitors, intended to enhance delivery across the blood-brain barrier (BBB), resulted in cytotoxicity. This is the first use of HT22 cells for the study of peptide aggregation inhibitors. Overall, this work will inform the future development of peptide aggregation inhibitors against Aß toxicity.

Melatonin Alters Fluid Phase Coexistence in POPC/DPPC/Cholesterol Membranes.

The structure and biophysical properties of lipid membranes are important for cellular functions in health and disease. In Alzheimer's disease, the neuronal membrane is a target for toxic amyloid-ß (Aß). Melatonin is an important pineal gland hormone that has been shown to protect against Aß toxicity in cellular and animal studies, but the molecular mechanism of this protection is not fully understood. Melatonin is a small membrane-active molecule that has been shown to interact with model lipid membranes and alter the membrane biophysical properties, such as membrane molecular order and dynamics. This effect of melatonin has been previously studied in simple model bilayers with one or two lipid components. To make it more relevant to neuronal membranes, we used a more complex ternary lipid mixture as our membrane model. In this study, we used 2H-NMR to investigate the effect of melatonin on the phase behavior of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and cholesterol lipid membranes. We used deuterium-labeled POPC-d31 and DPPC-d62,separately to probe the changes in hydrocarbon chain order as a function of temperature and melatonin concentration. We find that POPC/DPPC/cholesterol at molar proportions of 3:3:2 is close to liquid-disordered/liquid-ordered phase separation and that melatonin can induce phase separation in these ternary mixtures by preferentially incorporating into the disordered phase and increasing its level of disorder. At 5 mol% melatonin, we observed phase separation in samples with POPC-d31, but not with DPPC-d62, whereas at 10 mol% melatonin, phase separation was observed in both samples with either POPC-d31 or DPPC-d62. These results indicate that melatonin can have a strong effect on membrane structure and physical properties, which may provide some clues to understanding how melatonin protects against Aß, and that choice of chain perdeuteration is an important consideration from a technical point of view.

Deciphering Melatonin-Stabilized Phase Separation in Phospholipid Bilayers.

Lipid bilayers are fundamental building blocks of cell membranes, which contain the machinery needed to perform a range of biological functions, including cell-cell recognition, signal transduction, receptor trafficking, viral budding, and cell fusion. Importantly, many of these functions are thought to take place in the laterally phase-separated regions of the membrane, commonly known as lipid rafts. Here, we provide experimental evidence for the "stabilizing" effect of melatonin, a naturally occurring hormone produced by the brain's pineal gland, on phase-separated model membranes mimicking the outer leaflet of plasma membranes. Specifically, we show that melatonin stabilizes the liquid-ordered/liquid-disordered phase coexistence over an extended range of temperatures. The melatonin-mediated stabilization effect is observed in both nanometer- and micrometer-sized liposomes using small angle neutron scattering (SANS), confocal fluorescence microscopy, and differential scanning calorimetry. To experimentally detect nanoscopic domains in 50 nm diameter phospholipid vesicles, we developed a model using the Landau-Brazovskii approach that may serve as a platform for detecting the existence of nanoscopic lateral heterogeneities in soft matter and biological materials with spherical and planar geometries.

Effect of Varying Concentrations of Docosahexaenoic Acid on Amyloid Beta (1⁻42) Aggregation: An Atomic Force Microscopy Study.

Healthcare has advanced significantly, bringing with it longer life expectancies and a growing population of elders who suffer from dementia, specifically Alzheimer's disease (AD). The amyloid beta (Aß) peptide has been implicated in the cause of AD, where the peptides undergo a conformational change and form neurotoxic amyloid oligomers which cause neuronal cell death. While AD has no cure, preventative measures are being designed to either slow down or stop the progression of this neurodegenerative disease. One of these measures involves dietary supplements with polyunsaturated fatty acids such as docosahexaenoic acid (DHA). This omega-3 fatty acid is a key component of brain development and has been suggested to reduce the progression of cognitive decline. However, different studies have yielded different results as to whether DHA has positive, negative, or no effects on Aß fibril formation. We believe that these discrepancies can be explained with varying concentrations of DHA. Here, we test the inhibitory effect of different concentrations of DHA on amyloid fibril formation using atomic force microscopy. Our results show that DHA has a strong inhibitory effect on Aß1⁻42 fibril formation at lower concentrations (50% reduction in fibril length) than higher concentrations above its critical micelle concentration (70% increase in fibril length and three times the length of those at lower concentrations). We provide evidence that various concentrations of DHA can play a role in the inhibitory effects of amyloid fibril formation in vitro and help explain the discrepancies observed in previous studies.

Atomic force microscopy to study molecular mechanisms of amyloid fibril formation and toxicity in Alzheimer's disease.

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by dementia and memory loss for which no cure or effective prevention is currently available. Neurodegeneration in AD is linked to formation of amyloid plaques found in brain tissues of Alzheimer's patients during post-mortem examination. Amyloid plaques are composed of amyloid fibrils and small oligomers - insoluble protein aggregates. Although amyloid plaques are found on the neuronal cell surfaces, the mechanism of amyloid toxicity is still not well understood. Currently, it is believed that the cytotoxicity is a result of the nonspecific interaction of small soluble amyloid oligomers (rather than longer fibrils) with the plasma membrane. In recent years, nanotechnology has contributed significantly to understanding the structure and function of lipid membranes and to the study of the molecular mechanisms of membrane-associated diseases. We review the current state of research, including applications of the latest nanotechnology approaches, on the interaction of lipid membranes with the amyloid-ß (Aß) peptide in relation to amyloid toxicity. We discuss the interactions of Aß with model lipid membranes with a focus to demonstrate that composition, charge and phase of the lipid membrane, as well as lipid domains and rafts, affect the binding of Aß to the membrane and contribute to toxicity. Understanding the role of the lipid membrane in AD at the nanoscale and molecular level will contribute to the understanding of the molecular mechanism of amyloid toxicity and may aid into the development of novel preventive strategies to combat AD.

Melatonin directly interacts with cholesterol and alleviates cholesterol effects in dipalmitoylphosphatidylcholine monolayers.

Melatonin is a pineal hormone that has been shown to have protective effects in several diseases that are associated with cholesterol dysregulation, including cardiovascular disease, Alzheimer's disease, and certain types of cancers. Cholesterol is a major membrane constituent with both a structural and functional influence. It is also known that melatonin readily partitions into cellular membranes. We investigated the effects of melatonin and cholesterol on the structure and physical properties of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer as a simple membrane model using the Langmuir-Blodgett (L-B) monolayer technique and molecular dynamics (MD) simulations. We report that melatonin increases the area per lipid and elastic compressibility of the DPPC monolayer in a concentration dependent manner, while cholesterol has the opposite effect. When both melatonin and cholesterol were present in the monolayer, the compression isotherms showed normalization of the area per molecule towards that of the pure DPPC monolayer, thus indicating that melatonin counteracts and alleviates cholesterol's effects. Atomistic MD simulations of melatonin enriched DPPC systems correlate with our experimental findings and illustrate the structural effects of both cholesterol and melatonin. Our results suggest that melatonin is able to lessen the influence of cholesterol through two different mechanisms. Firstly, we have shown that melatonin has a fluidizing effect on monolayers comprising only lipid molecules. Secondly, we also observe that melatonin interacts directly with cholesterol. Our findings suggest a direct nonspecific interaction of melatonin may be a mechanism involved in reducing cholesterol associated membrane effects, thus suggesting the existence of a new mechanism of melatonin's action. This may have important biological relevance in addition to the well-known anti-oxidative and receptor binding effects.

Comparative study of lens solutions' ability to remove tear constituents.

PURPOSE: The purpose of this study was to use atomic force microscopy to compare and characterize the cleaning abilities of a hydrogen peroxide-based system (HPS) and a polyhexamethylene biguanide-containing multipurpose solution (MPS) at removing in vitro deposited tear film constituents, as well as to determine deposition patterns on various silicone hydrogel contact lenses. METHODS: Silicone hydrogel materials-balafilcon A (BA), lotrafilcon B (LB), and senofilcon A (SA)-were incubated for 1 week in an artificial tear solution (ATS) containing representative lipids, proteins, and salts from the tear film. Atomic force microscopy was used to resolve each lens before and after being cleaned overnight in HPS or MPS. Atomic force microscopy was used again to resolve HPS/MPS-cleaned lenses, which were reincubated in fresh ATS for 1 week, before and after an overnight clean in their respective cleaning solution. RESULTS: Atomic force microscopy imaging was able to characterize lens deposits with high resolution. Lenses incubated in ATS revealed distinct differences in their deposition pattern across lens materials. The surface of BA contained about 20-nm-high deposits, whereas deposit heights up to 150 nm completely occluded the surface of SA. Lotrafilcon B lenses revealed clusters of deposits up to 90 nm. The use of either lens solution left trace amounts of tear film constituents, although components from the MPS were seen adsorbed onto the surface after cleaning. Surface roughness (Ra) measurements revealed a significant difference between ATS-incubated and HPS/MPS-cleaned SA and LB lenses (p < 0.05). Ra between first incubated and HPS/MPS-cleaned reincubated SA and LB was also significant (p < 0.05). CONCLUSIONS: Unique variations in ATS deposition patterns were seen between lenses with atomic force microscopy. The application of both HPS and MPS removed most visible surface deposits.

Nanoscale Structure of Lipid-Gemini Surfactant Mixed Monolayers Resolved with AFM and KPFM Microscopy.

Drug delivery vehicles composed of lipids and gemini surfactants (GS) are promising in gene therapy. Tuning the composition and properties of the delivery vehicle is important for the efficient load and delivery of DNA fragments (genes). In this paper, we studied novel gene delivery systems composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-3-phosphocholine (DPPC), and GS of the type N,N-bis(dimethylalkyl)-α,ω-alkanediammonium dibromide at different ratios. The nanoscale properties of the mixed DOPC-DPPC-GS monolayers on the surface of the gene delivery system were studied using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We demonstrate that lipid-GS mixed monolayers result in the formation of nanoscale domains that vary in size, height, and electrical surface potential. We show that the presence of GS can impart significant changes to the domain topography and electrical surface potential compared to monolayers composed of lipids alone.

Effects of lithium isotopes on sodium/lithium co-transport and calcium efflux through the sodium/calcium/lithium exchanger in mitochondria.

The effects of lithium (Li) isotopes and their impact on biological processes have recently gained increased attention due to the significance of Li as a pharmacological agent and the potential that Li isotopic effects in neuroscience contexts may constitute a new example of quantum effects in biology. Previous studies have shown that the two Li isotopes, which differ in mass and nuclear spin, have unusual different effects in vivo and in vitro and, although some molecular targets for Li isotope fractionation have been proposed, it is not known whether those result in observable downstream neurophysiological effects. In this work we studied fluxes of Li+, sodium (Na+) and calcium (Ca2+) ions in the mitochondrial sodium/calcium/lithium exchanger (NCLX), the only transporter known with recognized specificity for Li+. We studied the effect of Li+ isotopes on Ca2+ efflux from heart mitochondria in comparison to natural Li+ and Na+ using Ca2+-induced fluorescence and investigated a possible Li isotope fractionation in mitochondria using inductively coupled plasma mass spectrometry (ICP-MS). Our fluorescence data indicate that Ca2+ efflux increases with higher concentrations of either Li+ or Na+. We found that the simultaneous presence of Li+ and Na+ increases Ca2+ efflux compared to Ca2+ efflux caused by the same concentration of Li+ alone. However, no differentiation in the Ca2+ efflux between the two Li+ isotopes was observed, either for Li+ alone or in mixtures of Li+ and Na+. Our ICP-MS data demonstrate that there is selectivity between Na+ and Li+ (greater Na+ than Li+ uptake) and, most interestingly, between the Li+ isotopes (greater 6Li+ than 7Li+ uptake) by the inner mitochondrial membrane. In summary, we observed no Li+ isotope differentiation for Ca2+ efflux in mitochondria via NCLX but found a Li+ isotope fractionation during Li+ uptake by mitochondria with NCLX active or blocked. Our results suggest that the transport of Li+ via NCLX is not the main pathway for Li+ isotope fractionation and that this differentiation does not affect Ca2+ efflux in mitochondria. Therefore, explaining the puzzling effects of Li+ isotopes observed in other contexts will require further investigation to identify the molecular targets for Li+ isotope differentiation.

Rapid cortisol signaling in response to acute stress involves changes in plasma membrane order in rainbow trout liver.

The activation of genomic signaling in response to stressor-mediated cortisol elevation has been studied extensively in teleosts. However, very little is known about the rapid signaling events elicited by this steroid. We tested the hypothesis that cortisol modulates key stress-related signaling pathways in response to an acute stressor in fish liver. To this end, we investigated the effect of an acute stressor on biophysical properties of plasma membrane and on stressor-related protein phosphorylation in rainbow trout (Oncorhynchus mykiss) liver. A role for cortisol in modulating the acute cellular stress response was ascertained by blocking the stressor-induced elevation of this steroid by metyrapone. The acute stressor exposure increased plasma cortisol levels and liver membrane fluidity (measured by anisotropy of 1,6-diphenyl-1,3,5-hexatriene), but these responses were abolished by metyrapone. Atomic force microscopy further confirmed biophysical alterations in liver plasma membrane in response to stress, including changes in membrane domain topography. The changes in membrane order did not correspond to any changes in membrane fatty acid components after stress, suggesting that changes in membrane structure may be associated with cortisol incorporation into the lipid bilayer. Plasma cortisol elevation poststress correlated positively with activation of intracellular stress signaling pathways, including increased phosphorylation of extracellular signal-related kinases as well as several putative PKA and PKC but not Akt substrate proteins. Together, our results indicate that stressor-induced elevation of plasma cortisol level is associated with alterations in plasma membrane fluidity and rapid activation of stress-related signaling pathways in trout liver.

Surface and tribological behaviors of the bioinspired polydopamine thin films under dry and wet conditions.

Dopamine is a "sticky" biomolecule containing the typical functional groups of mussel adhesive proteins. It can self-polymerize into a nanoscale thin film on various surfaces. We investigated the surface, adhesion, friction, and cracking properties of polydopamine (PDA) thin films for their effective transfer to functional devices and biocompatible coatings. A series of surface characterizations and mechanical tests were performed to reveal the static and dynamic properties of PDA films coated on glass, polydimethylsiloxane (PDMS), and epoxy. We found that PDA films are highly hydrated under wet conditions because of their porous membrane-like nanostructures and hydrophilic functional groups. Upon dehydration, the films form cracks when they are coated on soft substrates due to internal stresses and the large mismatch in elastic modulus. The adhesive pull-off force or the effective work of adhesion increased with the contact time, suggesting dynamic interactions at the interface. A significant decrease in friction forces in water was observed on all three material surfaces coated with PDA; thus, the film might serve as a water-based lubrication coating. We attributed the different behavior of PDA films in air and in water to its hydration effects. These research findings provide insight into the stability, mechanical, and adhesive properties of the PDA films, which are critical for their applications.

Preparation of DOPC and DPPC Supported Planar Lipid Bilayers for Atomic Force Microscopy and Atomic Force Spectroscopy.

Cell membranes are typically very complex, consisting of a multitude of different lipids and proteins. Supported lipid bilayers are widely used as model systems to study biological membranes. Atomic force microscopy and force spectroscopy techniques are nanoscale methods that are successfully used to study supported lipid bilayers. These methods, especially force spectroscopy, require the reliable preparation of supported lipid bilayers with extended coverage. The unreliability and a lack of a complete understanding of the vesicle fusion process though have held back progress in this promising field. We document here robust protocols for the formation of fluid phase DOPC and gel phase DPPC bilayers on mica. Insights into the most crucial experimental parameters and a comparison between DOPC and DPPC preparation are presented. Finally, we demonstrate force spectroscopy measurements on DOPC surfaces and measure rupture forces and bilayer depths that agree well with X-ray diffraction data. We also believe our approach to decomposing the force-distance curves into depth sub-components provides a more reliable method for characterising the depth of fluid phase lipid bilayers, particularly in comparison with typical image analysis approaches.

Search for lithium isotope effects in neuronal HT22 cells.

Lithium has been used as a treatment for bipolar disorder for over half a century, but there has thus far been no clinical differentiation made between the two naturally occurring stable isotopes (6Li and 7Li). While the natural lithium salts commonly used in treatments are composed of a mixture of these two stable isotopes (approximately 7.59% 6Li and 92.41% 7Li), some preliminary research indicates the above two stable isotopes of lithium may have differential effects on rat behaviour and neurophysiology. Here, we evaluate whether lithium isotopes may have distinct effects on HT22 neuronal cell viability, GSK-3-ß phosphorylation in HT22 cells, and GSK-3-ß kinase activity. We report no significant difference in lithium isotope toxicity on HT22 cells, nor in GSK-3-ß phosphorylation, nor in GSK-3-ß kinase activity between the two isotopes of lithium.

The Interplay Between Cholesterol and Amyloid-ß on HT22 Cell Viability, Morphology, and Receptor Tyrosine Kinase Signaling.

BACKGROUND: There is a lack of understanding in the molecular and cellular mechanisms of Alzheimer's disease that has hindered progress on therapeutic development. The focus has been on targeting toxic amyloid-ß (Aß) pathology, but these therapeutics have generally failed in clinical trials. Aß is an aggregation-prone protein that has been shown to disrupt cell membrane structure in molecular biophysics studies and interfere with membrane receptor signaling in cell and animal studies. Whether the lipid membrane or specific receptors are the primary target of attack has not been determined. OBJECTIVE: This work elucidates some of the interplay between membrane cholesterol and Aß42 on HT22 neuronal cell viability, morphology, and platelet-derived growth factor (PDGF) signaling pathways. METHODS: The effects of cholesterol depletion by methyl-ß-cyclodextrin followed by treatment with Aß and/or PDGF-AA were assessed by MTT cell viability assays, western blot, optical and AFM microscopy. RESULTS: Cell viability studies show that cholesterol depletion was mildly protective against Aß toxicity. Together cholesterol reduction and Aß42 treatment compounded the disruption of the PDGFα receptor activation. Phase contrast optical microscopy and live cell atomic force microscopy imaging revealed that cytotoxic levels of Aß42 caused morphological changes including cell membrane damage, cytoskeletal disruption, and impaired cell adhesion; cell damage was ameliorated by cellular cholesterol depletion. CONCLUSIONS: Cholesterol depletion impacted the effects of Aß42 on HT22 cell viability, morphology, and receptor tyrosine kinase signaling.

Lithium isotopes differentially modify mitochondrial amorphous calcium phosphate cluster size distribution and calcium capacity.

Lithium is commonly prescribed as a mood stabilizer in a variety of mental health conditions, yet its molecular mode of action is incompletely understood. Many cellular events associated with lithium appear tied to mitochondrial function. Further, recent evidence suggests that lithium bioactivities are isotope specific. Here we focus on lithium effects related to mitochondrial calcium handling. Lithium protected against calcium-induced permeability transition and decreased the calcium capacity of liver mitochondria at a clinically relevant concentration. In contrast, brain mitochondrial calcium capacity was increased by lithium. Surprisingly, 7Li acted more potently than 6Li on calcium capacity, yet 6Li was more effective at delaying permeability transition. The size distribution of amorphous calcium phosphate colloids formed in vitro was differentially affected by lithium isotopes, providing a mechanistic basis for the observed isotope specific effects on mitochondrial calcium handling. This work highlights a need to better understand how mitochondrial calcium stores are structurally regulated and provides key considerations for future formulations of lithium-based therapeutics.

Nanoscale electrostatic domains in cholesterol-laden lipid membranes create a target for amyloid binding.

Amyloid fibrils are associated with multiple neurodegenerative disorders, such as Alzheimer's disease. Although biological membranes are involved in fibril plaque formation, the role of lipid membrane composition in fibril formation and toxicity is not well understood. We investigated the effect of cholesterol on the interaction of model lipid membranes with amyloid-ß peptide (Aß). With atomic force microscopy we demonstrated that binding of Aß (1-42) to DOPC bilayer, enriched with 20% cholesterol, resulted in an intriguing formation of small nonuniform islands loaded with Aß. We attribute this effect to the presence of nanoscale electrostatic domains induced by cholesterol in DOPC bilayers. Using frequency-modulated Kelvin probe force microscopy we were able to resolve these nanoscale electrostatic domains in DOPC monolayers. These findings directly affect our understanding of how the presence of cholesterol may induce targeted binding of amyloid deposits to biomembranes. We postulate that this nonhomogeneous electrostatic effect of cholesterol has a fundamental nature and may be present in other lipid membranes and monolayers.

Direct glass-to-glass bonding obtained via simplified ammonia-based low-temperature procedure resists high shear stress and powerful CW fiber laser irradiation.

Direct glass-to-glass bonding is important for high-technology components in optics, microfluidics, and micro-electromechanical systems applications. We studied direct bonding of 1 mm thick soda-lime float glass substrates. The process is based on the classic RCA-1 cleaning procedure from the semiconductor industry modified with an ammonium hydroxide rinse, followed by a thermal treatment under unidirectional pressure without the need for a dedicated drying step. RCA-1 uses a solution of ammonium hydroxide and hydrogen peroxide to clean contaminants off the surface of silicon and enable subsequent bonding. Bond quality was evaluated using destructive shear testing. Strong bonds (≈7.81 MPa on average) were achieved using unidirectional pressure of approximately 0.88 MPa and bonding temperatures between 160 °C and 300 °C applied for 30 min. Surface roughness and chemistry was characterized before and after cleaning. The optical robustness of the bonds was tested and shown to be capable of surviving high powered continuous wave (CW) fiber laser irradiation of at least 375 W focused for 2 s without delamination. Melting of the substrate was observed at higher powers and longer exposure times.