Nanotechnology and Neuroscience

Self-Propagating, Molecular-Level Polymorphism in Alzheimer's ß-Amyloid Fibrils
Science, Vol 307, Issue 5707, 262-265 , 14 January 2005
ABSTRACT: Amyloid fibrils commonly exhibit multiple distinct morphologies in electron microscope and atomic force microscope images, often within a single image field. By using electron microscopy and solid-state nuclear magnetic resonance measurements on fibrils formed by the 40-residue ß-amyloid peptide of Alzheimer's disease (Aß1–40), we show that different fibril morphologies have different underlying molecular structures, that the predominant structure can be controlled by subtle variations in fibril growth conditions, and that both morphology and molecular structure are self-propagating when fibrils grow from preformed seeds. Different Aß1–40 fibril morphologies also have significantly different toxicities in neuronal cell cultures. These results have implications for the mechanism of amyloid formation, the phenomenon of strains in prion diseases, the role of amyloid fibrils in amyloid diseases, and the development of amyloid-based nano-materials.

Nanoscale velocity–drag force relationship in thin liquid layers measured by atomic force microscopy
Applied Physics Letters -- October 25, 2004 -- Volume 85, Issue 17, pp. 3881-3883
ABSTRACT: The relationship between velocity and drag force acting on a nanoprobe has been measured with an atomic force microscope (AFM). A special nanoprobe "whisker" was partially submerged in thin layers of glycerol–water mixtures and moved by using the AFM in scanning mode. The viscous drag force-caused torsion of the cantilever probe was recorded as a function of scanning speed and submersion depth. A linear drag force–velocity function was determined for cylindrical bodies with diameters of the order of 50 nm. The experimental results were supported by calculations for the torsional force exerted on an AFM probe dragged through a viscous medium. The viscosity was calculated for each experiment assuming no slip conditions and was in agreement with the macroscopically determined values. With some refinements, this offers a possible means of determining viscosity in thin liquid layers.

Integrated multiple patch-clamp array chip via lateral cell trapping junctions
Applied Physics Letters -- March 15, 2004 -- Volume 84, Issue 11, pp. 1973-1975
ABSTRACT: We present an integrated multiple patch-clamp array chip by utilizing lateral cell trapping junctions. The intersectional design of a microfluidic network provides multiple cell addressing and manipulation sites for efficient electrophysiological measurements at a number of patch sites. The patch pores consist of openings in the sidewall of a main fluidic channel, and a membrane patch is drawn into a smaller horizontal channel. This device geometry not only minimizes capacitive coupling between the cell reservoir and the patch channel, but also allows simultaneous optical and electrical measurements of ion channel proteins. Evidence of the hydrodynamic placement of mammalian cells at the patch sites as well as measurements of patch sealing resistance is presented. Device fabrication is based on micromolding of polydimethylsiloxane, thus allowing inexpensive mass production of disposable high-throughput biochips.

Nanotubular Highways for Intercellular Organelle Transport
Science -- February 13, 2004 -- Volume 303, Issue 5660, pp. 1007-1010
ABSTRACT: Cell-to-cell communication is a crucial prerequisite for the development and maintenance of multicellular organisms. To date, diverse mechanisms of intercellular exchange of information have been documented, including chemical synapses, gap junctions, and plasmodesmata. Here, we describe highly sensitive nanotubular structures formed de novo between cells that create complex networks. These structures facilitate the selective transfer of membrane vesicles and organelles but seem to impede the flow of small molecules. Accordingly, we propose a novel biological principle of cell-to-cell interaction based on membrane continuity and intercellular transfer of organelles.

Nanotechnology for neuronal ion channels
Journal of Neurology Neurosurgery and Psychiatry 2003;74:1466-1475
ABSTRACT: Ion channels provide the basis for the regulation of electrical excitability in the central and peripheral nervous systems. This review deals with the techniques that make the study of structure and function of single channel molecules in living cells possible. These are the patch clamp technique, which was derived from the conventional voltage clamp method and is currently being developed for automated and high throughput measurements; and fluorescence and nano-techniques, which were originally applied to non-biological surfaces and are only recently being used to study cell membranes and their proteins, especially in combination with the patch clamp technique. The characterisation of the membrane channels by techniques that resolve their morphological and physical properties and dynamics in space and time in the nano range is termed nanoscopy.

Botulinum toxin type B micromechanosensor
PNAS November 11, 2003 vol. 100 no. 23 13621-13625
ABSTRACT: Botulinum neurotoxin (BoNT) types A, B, E, and F are toxic to humans; early and rapid detection is essential for adequate medical treatment. Presently available tests for detection of BoNTs, although sensitive, require hours to days. We report a BoNT-B sensor whose properties allow detection of BoNT-B within minutes. The technique relies on the detection of an agarose bead detachment from the tip of a micromachined cantilever resulting from BoNT-B action on its substratum, the synaptic protein synaptobrevin 2, attached to the beads. The mechanical resonance frequency of the cantilever is monitored for the detection. To suspend the bead off the cantilever we use synaptobrevin's molecular interaction with another synaptic protein, syntaxin 1A, that was deposited onto the cantilever tip. Additionally, this bead detachment technique is general and can be used in any displacement reaction, such as in receptor-ligand pairs, where the introduction of one chemical leads to the displacement of another. The technique is of broad interest and will find uses outside toxicology.

Simultaneous imaging of ionic conductivity and morphology of a microfluidic system
Journal of Applied Physics -- June 15, 2003 -- Volume 93, Issue 12, pp. 10134-10136
ABSTRACT: We present a method for nanoscale simultaneous measurements of the conductivity and morphology of microfluidic systems. While device morphology is imaged by atomic force microscopy (AFM), the AFM tip is used as an electrode probe to measure the conductivity through a buffer in the fluidic channels to a reference electrode. Connectivity to a reference electrode can be probed simultaneously at a large number of test points along micro- and nanofluidic channels without the requirement of external fluidic connections. Since the placement of microelectrodes is essential to a number of microfluidic applications, this technique allows for the AFM tip to be used as a rapid prototyping tool.

Nanomechanics of Microtubules
Phys. Rev. Lett. 89, 248101 (2002)
ABSTRACT: We have determined the mechanical anisotropy of a single microtubule by simultaneously measuring the Young's and the shear moduli in vitro. This was achieved by elastically deforming the microtubule deposited on a substrate tailored by electron-beam lithography with a tip of an atomic force microscope. The shear modulus is 2 orders of magnitude lower than the Young's, giving rise to a length-dependent flexural rigidity of microtubules. The temperature dependence of the microtubule's bending stiffness in the (5–40) °C range shows a strong variation upon cooling coming from the increasing interaction between the protofilaments.

RGM is a repulsive guidance molecule for retinal axons
Nature -- September 26, 2002 -- Volume 419, Issue 6905, pp. 392-395
ABSTRACT: Axons rely on guidance cues to reach remote targets during nervous system development. A well-studied model system for axon guidance is the retinotectal projection. The retina can be divided into halves; the nasal half, next to the nose, and the temporal half. A subset of retinal axons, those from the temporal half, is guided by repulsive cues expressed in a graded fashion in the optic tectum, part of the midbrain. Here we report the cloning and functional characterization of a membrane-associated glycoprotein, which we call RGM (repulsive guidance molecule). This molecule shares no sequence homology with known guidance cues, and its messenger RNA is distributed in a gradient with increasing concentration from the anterior to posterior pole of the embryonic tectum. Recombinant RGM at low nanomolar concentration induces collapse of temporal but not of nasal growth cones and guides temporal retinal axons in vitro, demonstrating its repulsive and axon-specific guiding activity.