The neuronal architecture of Xenopus retinal ganglion cells is sculpted by rho-family GTPases in vivo

Dendritogenesis, axonogenesis, pathfinding, and target recognition are all affected in distinct ways when Xenopus retinal ganglion cells (RGCs) are transfected with constitutively active (ca), wild-type (wt), and dominant negative (dn) Rho-family GTPases in vivo. Dendritogenesis required Rac1 and Cdc42 activity. Moreover, ca-Rac1 caused dendrite hyperproliferation. Axonogenesis, in contrast, was inhibited by ca-Rac1. This phenotype was partially rescued by the coexpression of dn cyclin-dependent kinase (Cdk5), a proposed effector of Rac1, suggesting that Rac1 activity must be regulated tightly for normal axonogenesis. Growth cone morphology was particularly sensitive to dn-RhoA and wt-Cdc42 constructs. These also caused targeting errors, such as tectal bypass, suggesting that cytoskeletal rearrangements are involved in target recognition and are transduced by these pathways

Detection and Monitoring of Microparticles Under Skin by Optical Coherence Tomography as an Approach to Continuous Glucose Sensing Using Implanted Retroreflectors

We demonstrate the feasibility of using optical coherence tomography (OCT) to image and detect 2.8 ?m diameter microparticles (stationary and moving) on a highly-reflective gold surface both in clear media and under skin in vitro. The OCT intensity signal can clearly report the microparticle count, and the OCT response to the number of microparticles shows a good linearity. The detect ability of the intensity change (2.9%�5%) caused by an individual microparticle shows the high sensitivity of monitoring multiple particles using OCT. An optical sensing method based on this feasibility study is described for continuously measuring blood sugar levels in the subcutaneous tissue, and a molecular recognition unit is designed using competitive binding to modulate the number of bound microparticles as a function of glucose concentration. With further development, an ultra-small, implantable sensor might provide high specificity and sensitivity for long-term continuous monitoring of blood glucose concentration

Helium beam shadowing for high spatial resolution patterning of antibodies on microstructured diagnostic surfaces

We have developed a technique for the high-resolution, self-aligning, and high-throughput patterning of antibody binding functionality on surfaces by selectively changing the reactivity of protein-coated surfaces in specific regions of a workpiece with a beam of energetic helium particles. The exposed areas are passivated with bovine serum albumin (BSA) and no longer bind the antigen. We demonstrate that patterns can be formed (1) by using a stencil mask with etched openings that forms a patterned exposure, or (2) by using angled exposure to cast shadows of existing raised microstructures on the surface to form self-aligned patterns. We demonstrate the efficacy of this process through the patterning of anti-lysozyme, anti-Norwalk virus, and anti-Escherichia coli antibodies and the subsequent detection of each of their targets by the enzyme-mediated formation of colored or silver deposits, and also by binding of gold nanoparticles. The process allows for the patterning of three-dimensional structures by inclining the sample relative to the beam so that the shadowed regions remain unaltered. We demonstrate that the resolution of the patterning process is of the order of hundreds of nanometers, and that the approach is well-suited for high throughput patterning

High-Throughput Top-Down Fabrication of Uniform Magnetic Particles

Ion Beam Aperture Array Lithography was applied to top-down fabrication of large dense (108–109 particles/cm2) arrays of uniform micron-scale particles at rates hundreds of times faster than electron beam lithography. In this process, a large array of helium ion beamlets is formed when a stencil mask containing an array of circular openings is illuminated by a broad beam of energetic (5–8 keV) ions, and is used to write arrays of specific repetitive patterns. A commercial 5-micrometer metal mesh was used as a stencil mask; the mesh size was adjusted by shrinking the stencil openings using conformal sputter-deposition of copper. Thermal evaporation from multiple sources was utilized to form magnetic particles of varied size and thickness, including alternating layers of gold and permalloy. Evaporation of permalloy layers in the presence of a magnetic field allowed creation of particles with uniform magnetic properties and pre-determined magnetization direction. The magnetic properties of the resulting particles were characterized by Vibrating Sample Magnetometry. Since the orientation of the particles on the substrate before release into suspension is known, the orientation-dependent magnetic properties of the particles could be determined

Fabrication and characterization of annular magnetic nanostructures

Large arrays of permalloy (Ni81Fe19) annular structures were fabricated using a self-aligned patterning process based on ion-beam proximity lithography (IBPL), where a broad beam of energetic He ions is shaped into billions of ion beamlet by a stencil mask to pattern electron beam sensitive resist. IBPL was used to form an array of circular openings in poly(methyl methacrylate) (PMMA) resist, followed by a tone reversal process to form circular pillars in an underlying polymethylglutarimide (PMGI) layer. The PMGI pillars were conformally coated with silicon oxide, which was followed by anisotropic reactive ion etch (RIE) to form silicon oxide rings, which were transferred into the underlying sputter deposited permalloy thin film by ion milling. This fabrication approach was used to make 6 x 6 mm2 arrays of rings on a constant pitch of 670 nm with the outer diameters varied between 350 nm and 450 nm with a fixed inner diameter of 150 nm. Three unique samples that were fabricated and characterized using a vibrating sample magnetometer. The measured M-H loops showed the switching from an onion to a vortex and back to an onion state and are in good agreement with micromagnetic simulations and previously published data

Magnetization reversal in patterned, (Co/Pd)(n) multilayers

In this work, the physics of magnetization reversal in patterned high anisotropy (Co/Pd)(n) magnetic multilayer arrays is investigated where the magnetic island size, pitch, recording layer thickness, and the underlying multilayer magnetic properties are varied. Magnetization reversal was studied using magneto-optical Kerr effect magnetometry and magnetic force microscopy and supported by micromagnetic modeling. It is found that magnetic island dimension and/or pitch cannot alone explain the variations in the switching behavior of the patterned arrays and the observed values of switching field distribution (SFD). It is found that the ratio of switched magnetic islands to the total number of islands for a giving reversing field depends strongly on the magnetic island geometry. Stray fields from neighboring magnetic islands result in relatively minor influence on the switching characteristics. Micromagnetic modeling was used to further understand the magnetization reversal in patterned arrays. It is found that the bit-edge imperfections such as tapering contribute significantly to the SFD. (C) 2008 American Institute of Physics