47 research outputs found
Natural channel protein inserts and functions in a completely artificial, solid-supported bilayer membrane
Reconstitution of membrane proteins in artificial membrane systems creates a platform for exploring their potential for pharmacological or biotechnological applications. Previously, we demonstrated amphiphilic block copolymers as promising building blocks for artificial membranes with long-term stability and tailorable structural parameters. However, the insertion of membrane proteins has not previously been realized in a large-area, stable, and solid-supported artificial membrane. Here, we show the first, preliminary model of a channel membrane protein that is functionally incorporated in a completely artificial polymer, tethered, solid-supported bilayer membrane (TSSBM). Unprecedented ionic transport characteristics that differ from previous results on protein insertion into planar, free-standing membranes, are identified. Our findings mark a change in understanding protein insertion and ion flow within natural channel proteins when inserted in an artificial TSSBM, thus holding great potential for numerous applications such as drug screening, trace analyzing, and biosensing
Large-scale BN tunnel barriers for graphene spintronics
We have fabricated graphene spin-valve devices utilizing scalable materials
made from chemical vapor deposition (CVD). Both the spin-transporting graphene
and the tunnel barrier material are CVD-grown. The tunnel barrier is realized
by h-BN, used either as a monolayer or bilayer and placed over the graphene.
Spin transport experiments were performed using ferromagnetic contacts
deposited onto the barrier. We find that spin injection is still greatly
suppressed in devices with a monolayer tunneling barrier due to resistance
mismatch. This is, however, not the case for devices with bilayer barriers. For
those devices, a spin relaxation time of 260 ps intrinsic to the CVD graphene
material is deduced. This time scale is comparable to those reported for
exfoliated graphene, suggesting that this CVD approach is promising for
spintronic applications which require scalable materials.Comment: 13 pages, 3 figure
Self-optimizing Feature Generation via Categorical Hashing Representation and Hierarchical Reinforcement Crossing
Feature generation aims to generate new and meaningful features to create a
discriminative representation space.A generated feature is meaningful when the
generated feature is from a feature pair with inherent feature interaction. In
the real world, experienced data scientists can identify potentially useful
feature-feature interactions, and generate meaningful dimensions from an
exponentially large search space, in an optimal crossing form over an optimal
generation path. But, machines have limited human-like abilities.We generalize
such learning tasks as self-optimizing feature generation. Self-optimizing
feature generation imposes several under-addressed challenges on existing
systems: meaningful, robust, and efficient generation. To tackle these
challenges, we propose a principled and generic representation-crossing
framework to solve self-optimizing feature generation.To achieve hashing
representation, we propose a three-step approach: feature discretization,
feature hashing, and descriptive summarization. To achieve reinforcement
crossing, we develop a hierarchical reinforcement feature crossing approach.We
present extensive experimental results to demonstrate the effectiveness and
efficiency of the proposed method. The code is available at
https://github.com/yingwangyang/HRC_feature_cross.git
Aqueous Noncovalent Functionalization and Controlled Near-Surface Carbon Doping of Multiwalled Boron Nitride Nanotubes
Recognition of dipole-induced electric field in 2D materials for surface-enhanced Raman scattering
The application of two-dimensional (2D) materials, including metallic graphene, semiconducting transition metal dichalcogenides, and insulating hexagonal boron nitride (h-BN) for surface-enhancement Raman spectroscopy has attracted extensive research interest. This article provides a critical overview of the recent developments in surface-enhanced Raman spectroscopy using 2D materials. By re-examining the relationship between the lattice structure and Raman enhancement characteristics, including vibration selectivity and thickness dependence, we highlight the important role of dipoles in the chemical enhancement of 2D materials
Anatomical study of simple landmarks for guiding the quick access to humeral circumflex arteries
BACKGROUND: The posterior and anterior circumflex humeral artery (PCHA and ACHA) are crucial for the blood supply of humeral head. We aimed to identify simple landmarks for guiding the quick access to PCHA and ACHA, which might help to protect the arteries during the surgical management of proximal humeral fractures. METHODS: Twenty fresh cadavers were dissected to measure the distances from the origins of PCHA and ACHA to the landmarks (the acromion, the coracoid, the infraglenoid tubercle, the midclavicular line) using Vernier calipers. RESULTS: The mean distances from the origin of PCHA to the infraglenoid tubercle, the coracoid, the acromion and the midclavicular line were 27.7Â mm, 50.2Â mm, 68.4Â mm and 75.8Â mm. The mean distances from the origin of ACHA to the above landmarks were 26.9Â mm, 49.2Â mm, 67.0Â mm and 74.9Â mm. CONCLUSION: Our study provided a practical method for the intraoperative identification as well as quick access of PCHA and ACHA based on a series of anatomical measurements
Charge transport in a single molecule transistor probed by scanning tunneling microscopy
We report on the scanning tunneling microscopy/spectroscopy (STM/STS) study of cobalt phthalocyanine (CoPc) molecules deposited onto a back-gated graphene device. We observe a clear gate voltage ( V g ) dependence of the energy position of the features originating from the molecular states. Based on the analysis of the energy shifts of the molecular features upon tuning V g , we are able to determine the nature of the electronic states that lead to a gapped differential conductance. Our measurements show that capacitive couplings of comparable strengths exist between the CoPc molecule and the STM tip as well as between CoPc and graphene, thus facilitating electronic transport involving only unoccupied molecular states for both tunneling bias polarities. These findings provide novel information on the interaction between graphene and organic molecules and are of importance for further studies, which envisage the realization of single molecule transistors with non-metallic electrodes
Competing surface reactions limiting the performance of ion-sensitive field-effect transistors
© 2015 Elsevier B.V. All rights reserved.Ion-sensitive field-effect transistors based on silicon nanowires are promising candidates for the detection of chemical and biochemical species. These devices have been established as pH sensors thanks to the large number of surface hydroxyl groups at the gate dielectrics which makes them intrinsically sensitive to protons. To specifically detect species other than protons, the sensor surface needs to be modified. However, the remaining hydroxyl groups after functionalization may still limit the sensor response to the targeted species. Here, we describe the influence of competing reactions on the measured response using a general site-binding model. We investigate the key features of the model with a real sensing example based on gold-coated nanoribbons functionalized with a self-assembled monolayer of calcium-sensitive molecules. We identify the residual pH response as the key parameter limiting the sensor response. The competing effect of pH or any other relevant reaction at the sensor surface has therefore to be included to quantitatively understand the sensor response and prevent misleading interpretations
Graphene transistors are insensitive to pH changes in solution
We observe very small gate-voltage shifts in the transfer characteristic of
as-prepared graphene field-effect transistors (GFETs) when the pH of the buffer
is changed. This observation is in strong contrast to Si-based ion-sensitive
FETs. The low gate-shift of a GFET can be further reduced if the graphene
surface is covered with a hydrophobic fluorobenzene layer. If a thin Al-oxide
layer is applied instead, the opposite happens. This suggests that clean
graphene does not sense the chemical potential of protons. A GFET can therefore
be used as a reference electrode in an aqueous electrolyte. Our finding sheds
light on the large variety of pH-induced gate shifts that have been published
for GFETs in the recent literature
Rendering graphene supports hydrophilic with non-covalent aromatic functionalization for transmission electron microscopy
Amorphous carbon films have been routinely used to enhance the preparation of frozen-hydrated samples for transmission electron microscopy (TEM), either in retaining protein concentration, providing mechanical stability or dissipating sample charge. However, strong background signal from the amorphous carbon support obstructs that of the sample, and the insulating properties of thin amorphous carbon films preclude any efficiency in dispersing charge. Graphene addresses the limitations of amorphous carbon. Graphene is a crystalline material with virtually no phase or amplitude contrast and unparalleled, high electrical carrier mobility. However, the hydrophobic properties of graphene have prevented its routine application in Cryo-TEM. This Letter reports a method for rendering graphene TEM supports hydrophilic-a convenient approach maintaining graphene's structural and electrical properties based on non-covalent, aromatic functionalization. (C) 2014 AIP Publishing LLC