Publications

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The directed, head-to-tail self-assembly of microtubule filaments may be generalized in the context of Janus colloidal rods. Specifically, their assembly at the tens of micron-length scale involves a careful balance between long-range electrostatic repulsion and short-range attractive forces. Here we show that the addition of counterion salts increases the rate of directed assembly by screening the electrostatic forces and enhancing the effectiveness of short-range interactions at the microtubule ends.

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Biomolecular motors are a unique class of intracellular proteins that are fundamental to a considerable number of physiological functions such as DNA replication, organelle trafficking, and cell division. The efficient transformation of chemical energy into useful work by these proteins provides strong motivation for their utilization as nanoscale actuators in ex vivo, meso- and macro-scale hybrid systems. Biomolecular motors involved in cytoskeletal transport are quite attractive models within this context due to their ability to direct the transport of nano-/micro-scale objects at rates significantly greater than diffusion, and in the absence of bulk fluid flow. As in living organisms, biomolecular motors involved in cytoskeletal transport (i.e., kinesin, dynein, and myosin) function outside of their native environment to dissipatively self-assemble biological, biomimetic, and hybrid nanostructures that exhibit nonequilibrium behaviors such as self-healing. These systems also provide nanofluidic transport function in hybrid nanodevices where target analytes are actively captured, sorted, and transported for autonomous sensing and analytical applications. Moving forward, the implementation of biomolecular motors will continue to enable a wide range of unique functionalities that are presently limited to living systems, and support the development of nanoscale systems for addressing critical engineering challenges. © 2013 Wiley Periodicals, Inc.

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Engineered nanomaterials (ENMs) are increasingly being used in commercial products, particularly in the biomedical, cosmetic, and clothing industries. For example, pants and shirts are routinely manufactured with silver nanoparticles to render them 'wrinkle-free.' Despite the growing applications, the associated environmental health and safety (EHS) impacts are completely unknown. The significance of this problem became pervasive within the general public when Prince Charles authored an article in 2004 warning of the potential social, ethical, health, and environmental issues connected to nanotechnology. The EHS concerns, however, continued to receive relatively little consideration from federal agencies as compared with large investments in basic nanoscience R&D. The mounting literature regarding the toxicology of ENMs (e.g., the ability of inhaled nanoparticles to cross the blood-brain barrier; Kwon et al., 2008, J. Occup. Health 50, 1) has spurred a recent realization within the NNI and other federal agencies that the EHS impacts related to nanotechnology must be addressed now. In our study we proposed to address critical aspects of this problem by developing primary correlations between nanoparticle properties and their effects on cell health and toxicity. A critical challenge embodied within this problem arises from the ability to synthesize nanoparticles with a wide array of physical properties (e.g., size, shape, composition, surface chemistry, etc.), which in turn creates an immense, multidimensional problem in assessing toxicological effects. In this work we first investigated varying sizes of quantum dots (Qdots) and their ability to cross cell membranes based on their aspect ratio utilizing hyperspectral confocal fluorescence microscopy. We then studied toxicity of epithelial cell lines that were exposed to different sized gold and silver nanoparticles using advanced imaging techniques, biochemical analyses, and optical and mass spectrometry methods. Finally we evaluated a new assay to measure transglutaminase (TG) activity; a potential marker for cell toxicity.

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