Structure Analysis of Amyloid Aggregates at Lipid Bilayers by Supercritical Angle Raman Microscopy.

The amyloid-ß peptide is correlated with Alzheimer's disease and is assumed to cause toxicity by its interaction with the neuron membrane. A custom-made microscope objective based on the supercritical angle technique was developed by our group, which allows investigation of interfacial events by performing surface-sensitive and low-invasive spectroscopy. Applied to Raman spectroscopy, this technique was used to collect information about the structure of polypeptides that interact with a supported lipid bilayer. Notably, the conformation used by amyloid-ß(1-40) and amyloid-ß(1-42) when interacting directly with or next to the supported lipid bilayer was characterized. We observed two distinct secondary structures, α-helix and ß-sheet, which were exhibited by the peptide. These two structures were detected simultaneously. The propensity of the peptide to fold into these structures seemed dependent on both their number of amino acids and their proximity with the supported lipid bilayer. The α-helix structure was observed for amyloid-ß(1-42) fragments that were closer to the lipid bilayer. Peptides that were located further away from the bilayer favored the ß-sheet structure. Amyloid-ß(1-40) was less prone to adopt the α-helix secondary structure.

Amyloid-ß Peptide-Lipid Bilayer Interaction Investigated by Supercritical Angle Fluorescence.

The understanding of the interaction between the membrane of neurons and amyloid-ß peptides is of crucial importance to shed light on the mechanism of toxicity in Alzheimer's disease. This paper describes how supercritical angle fluorescence spectroscopy was applied to monitor in real-time the interaction between a supported lipid bilayer (SLB) and the peptide. Different forms of amyloid-ß (40 and 42 amino acids composition) were tested, and the interfacial fluorescence was measured to get information about the lipid integrity and mobility. The results show a concentration-dependent damaging process of the lipid bilayer. Prolonged interaction with the peptide up to 48 h lead to an extraction and clustering of lipid molecules from the surface and a potential disruption of the bilayer, correlated with the formation of peptide aggregates. The natural diffusion of the lipid was slightly hindered by the interaction with amyloid-ß(1-42) and closely related to the oligomerization of the peptide. The adsorption and desorption of Amyloid-ß was also characterized in terms of affinity. Amyloid-ß(1-42) exhibited a slightly higher affinity than amyloid-ß(1-40). The former was also more prone to aggregate and to adsorb on the bilayer as oligomer.

Scalable Manufacturing of Single Nanowire Devices Using Crack-Defined Shadow Mask Lithography.

Single nanowires (NWs) have a broad range of applications in nanoelectronics, nanomechanics, and nanophotonics, but, to date, no technique can produce single sub-20 nm wide NWs with electrical connections in a scalable fashion. In this work, we combine conventional optical and crack lithographies to generate single NW devices with controllable and predictable dimensions and placement and with individual electrical contacts to the NWs. We demonstrate NWs made of gold, platinum, palladium, tungsten, tin, and metal oxides. We have used conventional i-line stepper lithography with a nominal resolution of 365 nm to define crack lithography structures in a shadow mask for large-scale manufacturing of sub-20 nm wide NWs, which is a 20-fold improvement over the resolution that is possible with the utilized stepper lithography. Overall, the proposed method represents an effective approach to generate single NW devices with useful applications in electrochemistry, photonics, and gas- and biosensing.

Massively parallel fabrication of crack-defined gold break junctions featuring sub-3 nm gaps for molecular devices.

Break junctions provide tip-shaped contact electrodes that are fundamental components of nano and molecular electronics. However, the fabrication of break junctions remains notoriously time-consuming and difficult to parallelize. Here we demonstrate true parallel fabrication of gold break junctions featuring sub-3 nm gaps on the wafer-scale, by relying on a novel self-breaking mechanism based on controlled crack formation in notched bridge structures. We achieve fabrication densities as high as 7 million junctions per cm2, with fabrication yields of around 7% for obtaining crack-defined break junctions with sub-3 nm gaps of fixed gap width that exhibit electron tunneling. We also form molecular junctions using dithiol-terminated oligo(phenylene ethynylene) (OPE3) to demonstrate the feasibility of our approach for electrical probing of molecules down to liquid helium temperatures. Our technology opens a whole new range of experimental opportunities for nano and molecular electronics applications, by enabling very large-scale fabrication of solid-state break junctions.

Scalable Manufacturing of Nanogaps.

The ability to manufacture a nanogap in between two electrodes has proven a powerful catalyst for scientific discoveries in nanoscience and molecular electronics. A wide range of bottom-up and top-down methodologies are now available to fabricate nanogaps that are less than 10 nm wide. However, most available techniques involve time-consuming serial processes that are not compatible with large-scale manufacturing of nanogap devices. The scalable manufacturing of sub-10 nm gaps remains a great technological challenge that currently hinders both experimental nanoscience and the prospects for commercial exploitation of nanogap devices. Here, available nanogap fabrication methodologies are reviewed and a detailed comparison of their merits is provided, with special focus on large-scale and reproducible manufacturing of nanogaps. The most promising approaches that could achieve a breakthrough in research and commercial applications are identified. Emerging scalable nanogap manufacturing methodologies will ultimately enable applications with high scientific and societal impact, including high-speed whole genome sequencing, electromechanical computing, and molecular electronics using nanogap electrodes.

Design and fabrication of crack-junctions.

Nanogap electrodes consist of pairs of electrically conducting tips that exhibit nanoscale gaps. They are building blocks for a variety of applications in quantum electronics, nanophotonics, plasmonics, nanopore sequencing, molecular electronics, and molecular sensing. Crack-junctions (CJs) constitute a new class of nanogap electrodes that are formed by controlled fracture of suspended bridge structures fabricated in an electrically conducting thin film under residual tensile stress. Key advantages of the CJ methodology over alternative technologies are that CJs can be fabricated with wafer-scale processes, and that the width of each individual nanogap can be precisely controlled in a range from <2 to >100 nm. While the realization of CJs has been demonstrated in initial experiments, the impact of the different design parameters on the resulting CJs has not yet been studied. Here we investigate the influence of design parameters such as the dimensions and shape of the notches, the length of the electrode-bridge and the design of the anchors, on the formation and propagation of cracks and on the resulting features of the CJs. We verify that the design criteria yields accurate prediction of crack formation in electrode-bridges featuring a beam width of 280 nm and beam lengths ranging from 1 to 1.8 µm. We further present design as well as experimental guidelines for the fabrication of CJs and propose an approach to initiate crack formation after release etching of the suspended electrode-bridge, thereby enabling the realization of CJs with pristine electrode surfaces.

Crack-Defined Electronic Nanogaps.

Achieving near-atomic-scale electronic nanogaps in a reliable and scalable manner will facilitate fundamental advances in molecular detection, plasmonics, and nanoelectronics. Here, a method is shown for realizing crack-defined nanogaps separating TiN electrodes, allowing parallel and scalable fabrication of arrays of sub-10 nm electronic nanogaps featuring individually defined gap widths.

Small biomolecule immunosensing with plasmonic optical fiber grating sensor.

This study reports on the development of a surface plasmon resonance (SPR) optical fiber biosensor based on tilted fiber Bragg grating technology for direct detection of small biomarkers of interest for lung cancer diagnosis. Since SPR principle relies on the refractive index modifications to sensitively detect mass changes at the gold coated surface, we have proposed here a comparative study in relation to the target size. Two cytokeratin 7 (CK7) samples with a molecular weight ranging from 78 kDa to 2.6 kDa, respectively CK7 full protein and CK7 peptide, have been used for label-free monitoring. This work has first consisted in the elaboration and the characterization of a robust and reproducible bioreceptor, based on antibody/antigen cross-linking. Immobilized antibodies were then utilized as binding agents to investigate the sensitivity of the biosensor towards the two CK7 antigens. Results have highlighted a very good sensitivity of the biosensor response for both samples diluted in phosphate buffer with a higher limit of detection for the larger CK7 full protein. The most groundbreaking nature of this study relies on the detection of small biomolecule CK7 peptides in buffer and in the presence of complex media such as serum, achieving a limit of detection of 0.4 nM.