8 research outputs found
Fermi-Energy-Dependent Structural Deformation of Chiral Single-Wall Carbon Nanotubes
In this work, we use an extended tight-binding approach for calculating the Fermi-energy dependence of the structural deformation of chiral single-wall carbon nanotubes (SWNTs). We show that, in general, nanotube strains occur in such a way as to avoid a net charge from being accumulated on the nanotube. We also investigate the effect of the Fermi-energy-induced strains on the electronic structure of SWNTs, showing that the optical transition energies change by up to 0.5Â eV due to the induced strains and that this change is nearly independent of how the nanotube is deformed. Finally, we also consider the contribution of the electron-electron Coulomb repulsion to the total energy by using an effective regularized potential energy model. We show that the inclusion of the Coulomb repulsion leads to larger strains and smaller net charges transferred to the nanotube.National Science Foundation (U.S.) (Grant DMR-1004147
Sand fly synthetic sex-aggregation pheromone co-located with insecticide reduces the incidence of infection in the canine reservoir of visceral leishmaniasis: a stratified cluster randomised trial
The predominant sand fly vector of the intracellular parasite Leishmania infantum, that causes human and canine visceral leishmaniasis in the Americas, is Lutzomyia longipalpis. Dogs are the proven reservoir. Vector control tools to reduce transmission suited to this predominantly exophilic vector are lacking. Insecticide-impregnated dog collars protect dogs against infectious bites from sand fly vectors, and result in reductions of new infections in both dogs and humans. However, collars are costly for endemic communities, and alternative approaches are needed. Recently the bulk synthesised sex-aggregation pheromone of male Lu. longipalpis was shown to attract large numbers of conspecific females to lethal pyrethroid insecticides, indicating the potential for use in a vector control application. This study, conducted in Brazil, evaluated the efficacy of this novel lure-and-kill approach to reduce seroconversion and infection incidence with L. infantum in the canine reservoir, in addition to measuring its impact on household abundance of Lu. longipalpis. Deployed in 14 stratified clusters, the outcomes were compared to those attributed to insecticide impregnated collars fitted to dogs in another 14 clusters; each intervention was compared to 14 clusters that received placebo treatments. The beneficial effects of the lure-and-kill method were most noticeable on confirmed infection incidence and clinical parasite loads, and in reducing sand fly abundance. The overall effect of the two interventions were not statistically dissimilar, though the confidence intervals were broad. We conclude that the novel low-cost lure-and-kill approach should be added to the vector control toolbox against visceral leishmaniasis in the Americas
Microfluidic Actuation of Carbon Nanotube Fibers for Neural Recordings
Implantable devices to record and stimulate neural circuits have led to breakthroughs in neuroscience; however, technologies capable of electrical recording at the cellular level typically rely on rigid metals that poorly match the mechanical properties of soft brain tissue. As a result these electrodes often cause extensive acute and chronic injury, leading to short electrode lifetime. Recently, flexible electrodes such as Carbon Nanotube fibers (CNTf) have emerged as an attractive alternative to conventional electrodes and studies have shown that these flexible electrodes reduce neuro-inflammation and increase the quality and longevity of neural recordings. Insertion of these new compliant electrodes, however, remains challenge. The stiffening agents necessary to make the electrodes rigid enough to be inserted increases device footprint, which exacerbates brain damage during implantation. To overcome this challenge we have developed a novel technology to precisely implant and actuate high-performance, flexible carbon nanotube fiber (CNTf) microelectrodes without using a stiffening agents or shuttles. Instead, our technology uses drag forces within a microfluidic device to drive electrodes into tissue while minimizing the amount of fluid that is ejected into the tissue. In vitro experiments in brain phantoms, show that microfluidic actuated CNTf can be implanted at least 4.5 mm depth with 30 ÎĽm precision, while keeping the total volume of fluid ejected below 0.1 ÎĽL. As proof of concept, we inserted CNTfs in the small cnidarian Hydra littoralis and observed compound action potentials corresponding to contractions and in agreement with the literature. Additionally, brain slices extracted from transgenic mice were used to show that our device can be used to record spontaneous and light evoked activity from the cortex and deep brain regions such as the thalamic reticular nucleus (TRN). Overall our microfluidic actuation technology provides a platform for implanting and actuating flexible electrodes that significantly reduces damage during insertion
Single-frame 3D fluorescence microscopy with ultraminiature lensless FlatScope
Modern biology increasingly relies on fluorescence microscopy, which is driving demand for smaller, lighter, and cheaper microscopes. However, traditional microscope architectures suffer from a fundamental trade-off: As lenses become smaller, they must either collect less light or image a smaller field of view. To break this fundamental trade-off between device size and performance, we present a new concept for three-dimensional (3D) fluorescence imaging that replaces lenses with an optimized amplitude mask placed a few hundred micrometers above the sensor and an efficient algorithm that can convert a single frame of captured sensor data into high-resolution 3D images. The result is FlatScope: perhaps the world's tiniest and lightest microscope. FlatScope is a lensless microscope that is scarcely larger than an image sensor (roughly 0.2 g in weight and less than 1 mm thick) and yet able to produce micrometer-resolution, high-frame rate, 3D fluorescence movies covering a total volume of several cubic millimeters. The ability of FlatScope to reconstruct full 3D images from a single frame of captured sensor data allows us to image 3D volumes roughly 40,000 times faster than a laser scanning confocal microscope while providing comparable resolution. We envision that this new flat fluorescence microscopy paradigm will lead to implantable endoscopes that minimize tissue damage, arrays of imagers that cover large areas, and bendable, flexible microscopes that conform to complex topographies
Fluidic Microactuation of Flexible Electrodes for Neural Recording
Soft
and conductive nanomaterials like carbon nanotubes, graphene,
and nanowire scaffolds have expanded the family of ultraflexible microelectrodes
that can bend and flex with the natural movement of the brain, reduce
the inflammatory response, and improve the stability of long-term
neural recordings. However, current methods to implant these highly
flexible electrodes rely on temporary stiffening agents that temporarily
increase the electrode size and stiffness thus aggravating neural
damage during implantation, which can lead to cell loss and glial
activation that persists even after the stiffening agents are removed
or dissolve. A method to deliver thin, ultraflexible electrodes deep
into neural tissue without increasing the stiffness or size of the
electrodes will enable minimally invasive electrical recordings from
within the brain. Here we show that specially designed microfluidic
devices can apply a tension force to ultraflexible electrodes that
prevents buckling without increasing the thickness or stiffness of
the electrode during implantation. Additionally, these “fluidic
microdrives” allow us to precisely actuate the electrode position
with micron-scale accuracy. To demonstrate the efficacy of our fluidic
microdrives, we used them to actuate highly flexible carbon nanotube
fiber (CNTf) microelectrodes for electrophysiology. We used this approach
in three proof-of-concept experiments. First, we recorded compound
action potentials in a soft model organism, the small cnidarian <i>Hydra</i>. Second, we targeted electrodes precisely to the thalamic
reticular nucleus in brain slices and recorded spontaneous and optogenetically
evoked extracellular action potentials. Finally, we inserted electrodes
more than 4 mm deep into the brain of rats and detected spontaneous
individual unit activity in both cortical and subcortical regions.
Compared to syringe injection, fluidic microdrives do not penetrate
the brain and prevent changes in intracranial pressure by diverting
fluid away from the implantation site during insertion and actuation.
Overall, the fluidic microdrive technology provides a robust new method
to implant and actuate ultraflexible neural electrodes
Fluidic Microactuation of Flexible Electrodes for Neural Recording
Soft
and conductive nanomaterials like carbon nanotubes, graphene,
and nanowire scaffolds have expanded the family of ultraflexible microelectrodes
that can bend and flex with the natural movement of the brain, reduce
the inflammatory response, and improve the stability of long-term
neural recordings. However, current methods to implant these highly
flexible electrodes rely on temporary stiffening agents that temporarily
increase the electrode size and stiffness thus aggravating neural
damage during implantation, which can lead to cell loss and glial
activation that persists even after the stiffening agents are removed
or dissolve. A method to deliver thin, ultraflexible electrodes deep
into neural tissue without increasing the stiffness or size of the
electrodes will enable minimally invasive electrical recordings from
within the brain. Here we show that specially designed microfluidic
devices can apply a tension force to ultraflexible electrodes that
prevents buckling without increasing the thickness or stiffness of
the electrode during implantation. Additionally, these “fluidic
microdrives” allow us to precisely actuate the electrode position
with micron-scale accuracy. To demonstrate the efficacy of our fluidic
microdrives, we used them to actuate highly flexible carbon nanotube
fiber (CNTf) microelectrodes for electrophysiology. We used this approach
in three proof-of-concept experiments. First, we recorded compound
action potentials in a soft model organism, the small cnidarian <i>Hydra</i>. Second, we targeted electrodes precisely to the thalamic
reticular nucleus in brain slices and recorded spontaneous and optogenetically
evoked extracellular action potentials. Finally, we inserted electrodes
more than 4 mm deep into the brain of rats and detected spontaneous
individual unit activity in both cortical and subcortical regions.
Compared to syringe injection, fluidic microdrives do not penetrate
the brain and prevent changes in intracranial pressure by diverting
fluid away from the implantation site during insertion and actuation.
Overall, the fluidic microdrive technology provides a robust new method
to implant and actuate ultraflexible neural electrodes