1,720,985 research outputs found
Lipid bilayer functionalization of multiwalled carbon nanotubes
No full textIntegration of the technologically favorable mechanical and electrical properties of carbon nanotubes (CNTs) with the specific recognition properties of proteins could enable the development of novel bioelectronic, in particular biosensing, applications. The hydrophobic graphene surface of CNTs, however, is not a biological substrate and as-synthesized CNTs aggregate in aqueous solution. CNTs can be easily dispersed by non-covalent binding of surfactants like sodium dodecyl sulfate, but the use of such detergents is undesirable because they unfold proteins and degrade cell membranes. We show here that carbon nanotubes can also be dispersed by coating them with biocompatible surfactant analogs. Incubation of multiwalled CNTs with sonicated vesicles of synthetic phospholipids resulted in a stable aqueous suspension of the nanotubes, also after removal of the vesicles by centrifugation. When the vesicles were doped with a fluorescently labelled lipid, the washed CNTs could be observed by fluorescence microscopy. Additionally, atomic force microscopy indicated that the nanotubes were coated by a smooth layer, with occasional defects or transitions to a second layer. These discontinuities were consistently 4-5 nm deep, the typical thickness of a lipid bilayer. It can thus be concluded that vesicle fusion results in the formation of lipid bilayers on the surface of multiwalled CNTs. We addressed the influence of vesicle size, lipid acyl chain saturation, lipid head group charge, CNT surface modification, and CNT diameter on the efficiency of lipid coating. Significantly, it proved possible to include a fluorescently labelled transmembrane peptide in nanotube-supported bilayers, and we are currently investigating whether this can also be achieved for membrane protein
Effects of surface passivation on top-down ZnO nanowire transistors
No full textWe fabricated unpassivated and passivated zinc oxide (ZnO) nanowire field effect transistors (NWFETs) using conventional top-down method of remote plasma atomic layer deposition and anisotropic dry etch. This paper investigates the effect of Al2O3 passivation on the electrical characteristics of the ZnO NWFETs. Measured unpassivated ZnO NWFETs show a threshold voltage of 6.5 V, drain current on/off ratio of 106 and field effect mobility of 31.4 cm2/Vs. Passivated ZnO NWFETs demonstrate threshold voltage shift to −10 V, drain current on/off ratio of 104 and improvement of mobility of 35.5 cm2/Vs. The passivated device results indicate suitability for biosensing applications
Effects of surface passivation on top-down ZnO nanowire transistors
No full textWe fabricated unpassivated and passivated zinc oxide (ZnO) nanowire field effect transistors (NWFETs) using conventional top-down method of remote plasma atomic layer deposition and anisotropic dry etch. This paper investigates the effect of Al2O3 passivation on the electrical characteristics of the ZnO NWFETs. Measured unpassivated ZnO NWFETs show a threshold voltage of 6.5 V, drain current on/off ratio of 106 and field effect mobility of 31.4 cm2/V s. Passivated ZnO NWFETs demonstrate threshold voltage shift to -10 V, drain current on/off ratio of 104 and improvement of mobility of 35.5 cm2/V s. The passivated device results indicate suitability for biosensing applications
Towards on-chip on-demand microfluidic production and manipulation of droplets for chemical computing
No full textInterfacial properties of the M1 segment of the nicotinic acetylcholine receptor
No full textWe have studied the thermodynamic, surface, and structural properties of αM1 transmembrane sequence of the nicotinic acetylcholine receptor (nAChR) by using Langmuir monolayer, FT-IR spectroscopy and molecular dynamics simulation techniques in membrane-mimicking environments. M1 spontaneously incorporates into a lipid-free air–water interface, showing a favourable adsorption free energy of - 7.2 kcal/mol. A cross-sectional molecular area of 210 Å2/molecule, a surface potential of 4.2 fV/molecule and a high stability of the film were deducted from pure M1 monolayers. FT-IR experiments and molecular dynamics simulations in membrane-mimicking environments (sodium-dodecyl-sulfate and CCl4, respectively) indicate coexistence between helical and non-helical structures. Furthermore, mixed peptide–lipid monolayers and monolayer penetration experiments were performed in order to study the peptide–lipid interaction. Mixed with condensed lipids (dipalmitoyl-phosphocholine, and dipalmitoyl-phosphoglycerol), M1 shows immiscible/miscible behaviour at low/high peptide concentration, respectively. Conversely, a complete miscible peptide–lipid interface is observed with liquid-expanded lipids (palmitoyl-oleoyl-phosphocholine, and palmitoyl-oleoyl-phosphoglycerol). Peptide penetration experiments demonstrate that the M1 peptide preferentially interacts with zwitterionic phosphocholine interfaces
The Nachbac Pore: creation and characterisation of a KcsA-like sodium channel
No full textVoltage-gated sodium channels (VGSC) are integral membrane proteins responsible for the transient flux of sodium ions across cell membranes in response to changes in membrane potential. In humans as well as lower eukaryotes they are essential for homeostasis and normal functioning, and mutations in them are associated with a range of disease states. Although potassium channels, which are members of the same large family of voltage-gated channels have been well characterized, much less known about the structural features of sodium channels. For potassium ion channels, an important advance in understanding resulted from the determination of the three dimensional structure of the bacterial potassium channel KcsA, a simplified channel composed only of two transmembrane segments per subunit present in the tetrameric structure. In 2001, Ren et al found that bacteria also possess simplified versions of sodium channels, although in this case the individual subunits of all the homologues that have been identified thus far possess six transmembrane segments, which include both a pore-forming subdomain (S5-S6) and a voltage-sensing subdomain (S1-S4). Here we report on the creation of a smaller KcsA-like pore-only version of a sodium channel from the B. halodurans VGSC (pNaChBac), engineered to contain S5-S6 plus the C-terminal region of the NaChBac channel. The NaChBac pore has been expressed and purified from E. coli membranes, solubilised in detergent micelles, reconstituted into lipid vesicles and characterized for its secondary structure and thermal stability, as well as its electrophysiological properties from single-channel recordings, providing new insight into features of sodium channel structure and function
Incorporation of the mechanosensitive channel (MscL) and the amyloid Abeta[1-40] peptide by vesicle fusion into planar lipid bilayers
No full textSensors for chemical detection based on top-down fabricated polycrystalline silicon nanowires
No full textSemiconducting Silicon (Si) nanowires (NWs) have been widely investigated for their potential to function as highly sensitive and selective sensors for both chemical and biological purposes. A key point of this sensing method is to be real-time and label-free. Several interesting sensing assays have been demonstrated such as sensing of ions, proteins, DNA and viruses[1-3]. The available approaches of silicon nanowire fabrication usually use some advanced lithographic techniques i.e., deep-UV, electron-beam or nanoimprint lithography to pattern silicon nanowires on SOI wafers. Recently, spacer nanowires patterned by a conventional anisotropic dry etch were used to form transistors. While this approach has the advantage of CMOS-compatibility, these techniques are extremely expensive and accessible only to large-scale integrated circuit manufacturers. While this approach delivers a cheap route for nanowire definition, nanowire volume control across the wafer remains challenging as the nanowire sidewall region generally receives unwanted etching
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