Influence of diameter and chirality of single-walled carbon nanotubes on their fate and effects in the aquatic environment

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0933484SalehSingle-walled carbon nanotubes (SWNTs) have emerged as high-performance nanomaterials with numerous applications, including electronic, optical, medical, and structural composite technologies. Because of their anticipated role in large-scale industrial production, there is little doubt that SWNTs will ultimately find their way into our aquatic environment. The unusual physicochemical characteristics of SWNTs compared to other nanoparticles -- particularly their very large aspect ratio and complex colloidal behavior (e.g. aggregation) in aqueous solutions -- preclude meaningful theoretical predictions of their colloidal stability and transport behavior. Furthermore, there is a complete lack of fundamental studies on the effects of SWNT structural properties (e.g. diameter and electronic structure) on their fate, transport and biological interactions in aquatic systems. Consequently, there exist no reliable methods to predict the fate and implications of SWNTs in natural aquatic environments based on measurable physical properties of these nanomaterials. The purpose of this proposal is to fundamentally understand the effect of structural properties of SWNTs on their fate and biological behavior in the natural aquatic environment. The study design involves systematic evaluation of aggregation, deposition, organic compound sorption, and uptake/toxicity in fish (Japanese medaka) for semiconductive SWNTs for a range of electronic structures (with consequent variation in diameter and chirality). These studies will be fully novel, as there are no fundamental studies reported in the literature examining the effect of basic structural properties on environmental fate and implications of SWNTs. The research proposed will address the following aims. (1) Fractionation of semiconductive SWNTs by diameter/chirality using density gradient ultracentrifugation; (2) examination of aggregation and deposition kinetics of diameter/chirality-sorted SWNT fractions as a function of organic matter concentration and ionic strength using state-of-the-art dynamic light scattering, quartz crystal microbalance, and conventional column-flow transport experiments; (3) determination of the effect of SWNT diameter/chirality on organic contaminant adsorption using common headspace-partitioning methods; and (4) assessment of the uptake, bio-distribution, and toxic effects of diameter/chirality-sorted SWNTs in Japanese medaka fish after waterborne- or dietary exposure using near-IR fluorescence spectroscopy and microscopy. The proposed research will fill a critical gap in the scientific literature by providing a systematic understanding of the effects of structural properties on SWNT fate, transport and biological behavior. Results of this study may lead to structure-property relations for SWNTs in aquatic environments, allowing a priori predictions of their fate, transport and effects and therefore meets the definition set forth by the NSF for transformative research. The expected research outcomes and benefits include implementation of techniques to systematically separate chiral SWNTs; a complete understanding of the effects of electronic structure on colloidal stability, deposition, and sorptive properties; role of SWNT electronic structure on biological uptake and toxic effects; and finally an increased knowledge-base on the influence of surface structure on the behavior and effects of nanomaterials in the aquatic environment. This increase in basic scientific understanding will ultimately lead to structure-activity relationships from which we may build strategies to assess risks of nanomaterials in the ambient environment, as is currently possible for molecular environmental contaminants. The proposed activity will generate critical knowledge to better understand the environmental implication of a commercially important class of nanomaterial. The majority of requested funds are directed toward the training of doctoral students in an emerging and interdisciplinary research topic. This research will lead to discovery and understanding through teaching and exploration. It provides for student education, mentoring, and research in a novel and highly relevant area that is of immediate and critical importance to our society. This project has potential to involve minority students through student exchange activities with two minority institutions. Dissemination of the research results is planned through conference presentations and peer-reviewed publications.