Publications

Full list of publications

Cryo-electron Tomography Provides Novel Insights into Nuclear Pore Architecture: Implications for Nucleocytoplasmic Transport
Daniel Stoffler, Bernhard Feja, Birthe Fahrenkrog, Jochen Walz, Dieter Typke and Ueli Aebi
Journal of Molecular Biology, Volume 328, Issue 1, 119-130
To go beyond the current structural consensus model of the nuclear pore complex (NPC), we performed cryo-electron tomography of fully native NPCs from Xenopus oocyte nuclear envelopes (NEs). The cytoplasmic face of the NPC revealed distinct anchoring sites for the cytoplasmic filaments, whereas the nuclear face was topped with a massive distal ring positioned above the central pore with indications of the anchoring sites for the nuclear basket filaments and putative intranuclear filaments. The rather "spongy" central framework of the NPC was perforated by an elaborate channel and void system, ...
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Full-length Rat Amylin Forms Fibrils Following Substitution of Single Residues from Human Amylin
Janelle Green, Claire Goldsbury, Thierry Mini, Shabir Sunderji, Peter Frey, Joerg Kistler, Garth Cooper, and Ueli Aebi
Journal of Molecular Biology 326 (2003), 1147-1156
Pancreatic amyloid deposits, composed of the 37 amino acid residue peptide amylin, represent an integral part of type 2 diabetes mellitus pathology. Human amylin (hA) forms fibrils in vitro and is toxic to cultured pancreatic islet -cells. In contrast, rat amylin (rA) which differs from hA by only six amino acid residues in the central region of the peptide, residues 18-29, does not form fibrils and is not cytotoxic. To elucidate the role of individual residues in fibril formation, we have generated a series of full-length rA variants and examined their ability to form fibrils in vitro. Single ...
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Development of an Arthroscopic Atomic Force Microscope
M. Stolz, R. Imer, U. Staufer, and U. Aebi
Bioworld 4, 2-5
Nanotechnology is on the verge of clinical applications. Scientists of the Universities of Basel and Neuchâtel describe the development of an atomic force microscope for the use in arthroscopy. ...
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Symmetrically arranged quartz tuning fork with soft cantilever for intermittent contact mode atomic force microscopy
T. Akiyama, U. Staufer, N. F. de Rooij, P. Frederix and A. Engel
Review of Scientific Instruments, Vol. 74, No. 1
A self-sensing and -actuating probe for dynamic mode atomic force microscopy (AFM) based on a commercial quartz tuning fork and a microfabricated cantilever is presented. The U-shaped cantilever, exhibiting a sharp tip, is combined with the tuning fork in a symmetrical arrangement, such that each of the two legs of the cantilever is fixed to one of the prongs of the tuning fork. The tuning fork is used as an oscillatory force sensor. ...
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Atomic-force microscopy: Rhodopsin dimers in native disc membranes
Dimitrios Fotiadis, Yan Liang, Slawomir Filipek, David A. Saperstein, Andreas Engel, Krzystof Palczewski
Nature Vol. 421, 9. January 2003
In vertebrate retinal photoreceptors, the rod outer-segment disc membranes contain densely packed rhodopsin molecules for optimal light absorption and subsequent amplification by the visual signalling cascade, but how these photon receptors are organized with respect to each other is not known. Here we use infrared-laser atomic-force microscopy to reveal the native arrangement of rhodopsin, which forms paracrystalline arrays of dimers in mouse disc membranes. ...
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Organization of the G Protein-coupled Receptors Rhodopsin and Opsin in Native Membranes
Yan Liang, Dimitrios Fotiadis, Sawomir Filipek, David A. Saperstein, Krzysztof Palczewski and Andreas Engel
J. Biol. Chem., Vol. 278, Issue 24, 21655-21662, June 13, 2003
We have determined by atomic force microscopy (AFM) the organization of rhodopsin in native membranes obtained from wild-type mouse photoreceptors and opsin isolated from photoreceptors of Rpe65-/- mutant mice that do not produce the chromophore 11-cis-retinal.. ...
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Marvellous things in marvellous rings: energy spectrum, spins and persistent currents
T. Ihn, A. Fuhrer, T. Heinzel, K. Ensslin, W. Wegscheider and M. Bichler
Physica E 16, 83 (2003)
Magnetotransport experiments on a semiconductor quantum ring in the Coulomb blockade regime are described. The measurements allow to extract the discrete energy levels of a realistic ring, which are found to agree well with theoretical expectations. The interaction effects important for our ring structure are analysed in detail. The experimentally observed charging energy can be quantitatively understood within the Hartree approximation including a strong screening contribution due to the top gate. The strong screening effect is the reason for the frequent occurrence of spin-pairs in the addit ...
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Electrical control of spin precession in semiconductor quantum wells
G. Salis, Y. Katoa, K. Ensslin, D. C. Driscoll, A. C. Gossard and D. D. Awschaloma
Physica E 16, 99 (2003)
Electrical tuning of coherent electron spin dynamics is demonstrated in a specially designed AlxGa1-xAs quantum well in which the Al concentration x is parabolically varied across the structure. Application of an electric bias leads to a continuous displacement of an unperturbed wave function into regions with different Al concentration. Using time-resolved optical techniques, we directly observe gate-voltage mediated tunability of electron spin precession over a 13 GHz frequency range at low temperatures and at a fixed magnetic field of 6 T. Such control of spin coherence persists up to room ...
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Amphiphilic Dendrimers: Novel Self-Assembling Vectors for Efficient Gene Delivery.
Derk Joester, Myriam Losson, Raphaël Pugin, Harry Heinzelmann, Elke Walter, Hans P. Merkle, François Diederich
Angew. Chem. Int. Ed. 2003, 42, No. 13, 1486-1490
Nonviral gene delivery remains an outstanding challenge to the scientific community. Fifteen years of interdisciplinary effort since the introduction of cationic amphiphiles for DNA and RNA transfection by Felgner at al. compare to millions of years of evolutionary optimization to the competing viral vectors. While actual progress has been moderate, some key issues for efficient delivery have been identified. Biocompatibility, charge/receptor-mediated uptake, tissue-specific targeting, endosomal espape, nuclear tropism, and vector unpacking all contribute to the canon of requirements... ...
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Acetylenic scaffolding on solid support: poly(triacetylene)- derived oligomers by Sonogashira and Cadiot–Chodkiewicz-type cross-coupling reactions
Nils F. Utesch and François Diederich
Org. Biomol. Chem., 2003, 1 (2), 237 - 239
We report the first synthesis of poly(triacetylene)-derived oligomers by Pd(0)-catalysed Sonogashira and Cadiot–Chodkiewicz-type cross-coupling reactions on solid support. Oligo(phenylene triacetylene)s, members of a new class of linearly -conjugated oligomers with all-carbon backbones, feature very high fluorescence intensities. ...
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Structures of Annealed Decanethiol Self-Assembled Monolayers on Au(111): an Ultrahigh Vacuum Scanning Tunneling Microscopy Study
Yile Qian, G. Yang, J. Yu, T. A. Jung, and G. Liu
Langmuir, 19 (15), 6056 -6065, 2003
While the structures of self-assembled monolayers (SAMs) of alkanethiols on Au(111) are extensively studied and well-known, new structures and complex phase behavior have been progressively discovered when coverage of these layers falls below saturation. Structures and phase transitions of annealed decanethiol monolayers on Au(111) surfaces were systematically investigated using scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. Rich structures were revealed as a result of annealing in UHV. At temperatures below 345 K, no significant changes in coverage were observed, ...
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Label-free protein assay based on a nanomechanical cantilever array
Y. Arntz, J. D. Seelig, H. P. Lang, J. Zhang, P. Hunziker, J. P. Ramseyer, E. Meyer, M. Hegner and Ch. Gerber
Nanotechnology 14 (2003) 86-90
We demonstrate continuous label-free detection of two cardiac biomarker proteins (creatin kinase and myoglobin) using an array of microfabricated cantilevers functionalized with covalently anchored anti-creatin kinase and anti-myoglobin antibodies. ...
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Direct Determination of the Energy Required to Operate a Single Molecule Switch
Ch. Loppacher, M. Guggisberg, O. Pfeiffer, E. Meyer, M. Bammerlin, R. Lüthi, R. Schlittler, J. K. Gimzewski, H. Tang and C. Joachim
Physical Review Letters Vol. 90, No. 6, 066107
Using a noncontact atomic-force and scanning-tunneling microscope in ultrahigh vacuum, we have measured the switching energy of a single molecule switch based on the rotation of a di-butyl-phenyl leg in a Cu-tetra-3,5 di-tertiary-butyl-phenyl porphyrin. ...
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Nanoscale Dispensing of Liquids through Cantilevered Probes
A. Meister, S. Jeney, M. Liley, T. Akiyama, U. Staufer, N. F. De Rooij, and H. Heinzelmann
MNE 2002, Lugano, Switzerland
...
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Spin-entangled currents created by a triple quantum dot
Daniel S. Saraga, and Daniel Loss
Physical Review Letters 90, 166803 (2003).
We propose a simple setup of three coupled quantum dots in the Coulomb blockade regime as a source for spatially separated currents of spin-entangled electrons. The entanglement originates from the singlet ground state of a quantum dot with an even number of electrons. To preserve the entanglement of the electron pair during its extraction to the drain leads, the electrons are transported through secondary dots. This prevents one-electron transport by energy mismatch, while joint transport is resonantly enhanced by conservation of the total two-electron energy. ...
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Noise of Spin-Polarized Currents at a Beam Splitter with Local Spin–Orbit Interaction
G. Burkard, J. C. Egues and D. Loss
Journal of Superconductivity: Incorporating Novel Magnetism, 16 (2): 237-240, April 2003
An electronic beam splitter with a local Rashba spin–orbit coupling can serve as a detector for spin-polarized currents. The spin–orbit coupling plays the role of a tunable spin rotator and can be controlled via a gate electrode on top of the conductor. We use spin-resolved scattering theory to calculate the zero-temperature current fluctuations (shot noise) for such a four-terminal device and show that the shot noise is proportional to the spin polarization of the source. Moreover, we analyze the effect of spin–orbit-induced intersubband coupling, leading to an additional spin rotation. ...
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Electron spin evolution induced by interaction with nuclei in a quantum dot
Alexander Khaetskii, Daniel Loss, and Leonid Glazman
Phys. Rev. B 67, 195329 (2003)
We study the decoherence of a single electron spin in an isolated quantum dot induced by hyperfine interaction with nuclei for times smaller than the nuclear spin relaxation time. The decay is caused by the spatial variation of the electron envelope wave function within the dot, leading to a non-uniform hyperfine coupling. We show that the usual treatment of the problem based on the Markovian approximation is impossible because the correlation time for the nuclear magnetic field seen by the electron spin is itself determined by the flip-flop processes. The decay of the electron spin correlatio ...
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Nonballistic Spin-Field-Effect Transistor
John Schliemann, J. Carlos Egues, and Daniel Loss
Physical Review Letters 90, 146801
We propose a spin-field-effect transistor based on spin-orbit coupling of both the Rashba and the Dresselhaus types. Different from earlier proposals, spin transport through our device is tolerant against spin-independent scattering processes. Hence the requirement of strictly ballistic transport can be relaxed. This follows from a unique interplay between the Dresselhaus and the Rashba coupling; these can be tuned to have equal strengths, leading to k-independent eigenspinors even in two dimensions. We discuss two-dimensional devices as well as quantum wires. In the latter, our setup presents ...
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Magnetization transport and quantized spin conductance
Florian Meier and Daniel Loss
Physical Review Letters 90, 167204
We analyze transport of magnetization in insulating systems described by a spin Hamiltonian. The magnetization current through a quasi-one-dimensional magnetic wire of finite length suspended between two bulk magnets is determined by the spin conductance which remains finite in the ballistic limit due to contact resistance. For ferromagnetic systems, magnetization transport can be viewed as transmission of magnons, and the spin conductance depends on the temperature T. For antiferromagnetic isotropic spin-1/2 chains, the spin conductance is quantized in units of order (gµB)2/h at T = 0. Magnet ...
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Variational study of the ν=1 quantum Hall ferromagnet in the presence of spin-orbit interaction
John Schliemann, J. Carlos Egues, and Daniel Loss
Phys. Rev. B 67, 085302
We investigate the = 1 quantum Hall ferromagnet in the presence of spin-orbit coupling of the Rashba or Dresselhaus type by means of Hartree-Fock-typed variational states. In the presence of Rashba (Dresselhaus) spin-orbit coupling the fully spin-polarized quantum Hall state is always unstable resulting in a reduction of the spin polarization if the product of the particle charge q and the effective g factor is positive (negative). In all other cases an alternative variational state with O(2) symmetry and finite in-plane spin components is lower in energy than the fully spin-polarized state fo ...
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A Datta-Das transistor with enhanced spin control
J. Carlos Egues, Guido Burkard, and Daniel Loss
Applied Physics Letters 82, 2658
We consider a two-channel spin transistor with weak spin-orbit induced interband coupling. We show that the coherent transfer of carriers between the coupled channels gives rise to an additional spin rotation. We calculate the corresponding spin-resolved current in a Datta–Das geometry and show that a weak interband mixing leads to enhanced spin control. ...
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Quantum computing with spin cluster qubits
Florian Meier, Jeremy Levy, and Daniel Loss
Phys. Rev. Lett. 90, 047901
We study the low energy states of finite spin chains with isotropic (Heisenberg) and anisotropic (XY and Ising-like) antiferromagnetic exchange interaction with uniform and nonuniform coupling constants. We show that for an odd number of sites a spin cluster qubit can be defined in terms of the ground state doublet. This qubit is remarkably insensitive to the placement and coupling anisotropy of spins within the cluster. One- and two-qubit quantum gates can be generated by magnetic fields and intercluster exchange, and leakage during quantum gate operation is small. Spin cluster qubits inherit ...
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Ambipolar field-effect transistor on as-grown single-wall carbon nanotubes
Bakir Babic, Mahdi Iqbal and Christian Schönenberger
Nanotechnology 14 (2003) 327-331
We use a simultaneous flow of ethylene and hydrogen gases to grow single-wall carbon nanotubes by chemical vapour deposition. Strong coupling to the gate is inferred from transport measurements for both metallic and semiconducting tubes. At low temperatures, our samples act as single-electron transistors where the transport mechanism is mainly governed by Coulomb blockade. The measurements reveal very rich quantized energy level spectra spanning from the valence to the conduction band. The Coulomb diamonds have similar addition energies on both sides of the semiconducting gap. Signatures of th ...
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Multiple Andreev Reflections in a Carbon Nanotube Quantum Dot
M. R. Buitelaar, W. Belzig, T. Nussbaumer, B. Babic, C. Bruder, and C. Schönenberger
Phys. Rev. Lett. 91, 057005
We report resonant multiple Andreev reflections in a multiwall carbon nanotube quantum dot coupled to superconducting leads. The position and magnitude of the subharmonic gap structure is found to depend strongly on the level positions of the single-electron states which are adjusted with a gate electrode. We discuss a theoretical model of the device and compare the calculated differential conductance with the experimental data. ...
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Quantum Shot Noise
Carlo Beenakker and Christian Schönenberger
Physics Today, Vol. 56, issue 5, page 37-42 (2003)
Fluctuations in the flow of electrons can signal the transition from particlelike to wavelike behavior and signify the nature of charge transport in mesoscopic systems. ...
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Intrinsic Thermal Vibrations of Suspended Doubly Clamped Single-Wall Carbon Nanotubes
B. Babic, J. Furer, S. Sahoo, Sh. Farhangfar, and C. Schönenberger
Nano Letters 3 (11), 1577 (2003)
We report the observation of thermally driven mechanical vibrations of suspended doubly clamped carbon nanotubes, grown by chemical vapor deposition (CVD). Several experimental procedures are used to suspend carbon nanotubes. The vibration is observed as a blurring in images taken with a scanning electron microscope. The measured vibration amplitudes are compared with a model based on linear continuum mechanics. ...
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