We present a method for assembling silicon nanowires (Si-NWs) in virtually general shape patterns using only conventional microfabrication facilities. In this method, silicon nanowires were functionalized with amine groups and dispersed in deionized water. The functionalized Si-NWs exhibited positive surface charges in the suspensions, and they were selectively adsorbed and aligned onto negatively charged surface regions on solid substrates. As a proof of concepts, we demonstrated transistors based on individual Si-NWs and long networks of Si-NWs.

(−)-Epigallocatechin gallate (EGCG), the major component of green tea, has been re-evaluated with α-synuclein (αS), a pathological constituent of Parkinson’s disease, to elaborate its therapeutic value. EGCG has been demonstrated to not only induce the off-pathway ‘compact’ oligomers of αS as suggested previously, but also drastically enhance the amyloid fibril formation of αS. Considering that the EGCG-induced amyloid fibrils could be a product of on-pathway SDS-sensitive ‘transient’ oligomers, the polyphenol effect on the transient ‘active’ oligomers (AOs) was investigated. By facilitating the fibril formation and thus eliminating the toxic AOs, EGCG was shown to suppress the membrane disrupting radiating amyloid fibril formation on the surface of liposomal membranes and thus protect the cells which could be readily affected by AOs. Taken together, EGCG has been suggested to exhibit its protective effect against the αS-mediated cytotoxicity by not only producing the off-pathway ‘compact’ oligomers, but also facilitating the conversion of ‘active’ oligomers into amyloid fibrils.

Going straight: A simple and robust mechanism coherently directs nanowire growth directions by introducing a local temperature gradient as the local kinetic variable during the conventional vapor–liquid–solid (VLS) growth (see picture, scale bar=200 μm). The nanowires grow straight in the vertical direction, but possess kinks near the catalytic tips.

Functional graffiti of nanoparticles onto target surface is an important issue in the development of nanodevices. A general strategy has been introduced here to decorate chemically diverse substrates with gold nanoparticles (AuNPs) in the form of a close-packed single layer by using an omni-adhesive protein of α-synuclein (αS) as conjugated with the particles. Since the adsorption was highly sensitive to pH, the amino acid sequence of αS exposed from the conjugates and its conformationally disordered state capable of exhibiting structural plasticity are considered to be responsible for the single-layer coating over diverse surfaces. Merited by the simple solution-based adsorption procedure, the particles have been imprinted to various geometric shapes in 2-D and physically inaccessible surfaces of 3-D objects. The αS-encapsulated AuNPs to form a high-density single-layer coat has been employed in the development of nonvolatile memory, fule-cell, solar-cell, and cell-culture platform, where the outlying αS has played versatile roles such as a dielectric layer for charge retention, a sacrificial layer to expose AuNPs for chemical catalysis, a reaction center for silicification, and biointerface for cell attachment, respectively. Multiple utilizations of the αS-based hybrid NPs, therefore, could offer great versatility to fabricate a variety of NP-integrated advanced materials which would serve as an indispensable component for widespread applications of high-performance nanodevices.

Robust polydiacetylene-based colorimetric sensing material has been developed with amyloid fibrils of α-synuclein in the presence of 10,12-pentacosadiynoic acid (PCDA) by taking advantage of the specific fatty acid interaction of α-synuclein and structural regularity of the self-assembled product of amyloid fibrils. PCDA facilitated not only self-oligomerization of α-synuclein but also its fibrillation into the fibrils with increased thickness. Upon UV irradiation, the PCDA-containing amyloid fibrils (AF-PCDAs) turned blue, which then became red following heat treatment. The blue-to-red color transition was also observed with other stimuli of pH and ethanol. AF-PCDAs were demonstrated to be mechanically stable since not only the individual colors of blue and red but also their colorimetric transition were not affected by a number of sonications which readily disrupted the polydiaceylene (PDA) vesicles with the instant loss of color. Therefore, AF-PCDA can be considered to be a novel PDA-based colorimetric sensing material with high mechanical strength, which has the potential to be employed in various areas involving advanced sensing technologies.

Heavily phosphorus-doped silicon nanowires (Si NWs) show intriguing transport phenomena at low temperature. As we decrease the temperature, the resistivity of the Si NWs initially decreases, like metals, and starts to increase logarithmically below a resistivity minimum temperature (T(min)), which is accompanied by (i) a zero-bias dip in the differential conductance and (ii) anisotropic negative magnetoresistance (MR), depending on the angle between the applied magnetic field and current flow. These results are associated with the impurity band conduction and electron scattering by the localized spins at phosphorus donor states. The analysis on the MR reveals that the localized spins are coupled antiferromagnetically at low temperature via the exchange interaction.

No abstract

Amyloidogenesis of α-synuclein (αS) is considered to be a pathological phenomenon related to Parkinson’s disease (PD). As a key component to reveal the fibrillation mechanism and toxicity, we have investigated an oligomeric species of αS capable of exhibiting the unit-assembly process leading to accelerated amyloid fibril formation. These oligomers previously shown to exist in a meta-stable state with mostly disordered structure and unable to seed the fibrillation were converted to either temperature-sensitive self-associative oligomers or NaCl-induced non-fibrillating oligomeric species. Despite their transient and disordered nature, the structural information of meta-stable αS oligomers (Meta-αS-Os) was successfully evaluated with small-angle neutron scattering (SANS) technique. By fitting the neutron scattering data with polydisperse Gaussian Coil (pGC) model, Meta-αS-O was analyzed as a sphere with approximate diameter of 100 Å. Its overall shape altered drastically with subtle changes in temperature between 37 °C and 43 °C, which would be responsible for fibrillar polymorphism. Based on their bifurcating property of Meta-αS-Os leading to either on-pathway or off-pathway species, the oligomers could be suggested as a crucial intermediate responsible for the oligomeric diversification and multiple fibrillation processes. Therefore, Meta-αS-Os could be considered as a principal target to control the amyloidogenesis and its pathogenesis.