Preparation and Characterization of Individual Peptide-Wrapped Single-Walled Carbon Nanotubes Vasiliki Zorbas, ² Alfonso Ortiz-Acevedo, ² Alan B. Dalton, ‡ Mario Miki Yoshida, § Gregg R. Dieckmann, ²,‡ Rockford K. Draper, ²,‡, | Ray H. Baughman, ²,‡ Miguel Jose-Yacaman, § and Inga H. Musselman* ,²,‡ Contribution from the Department of Chemistry, NanoTech Institute, and Department of Molecular and Cell Biology, The UniVersity of Texas at Dallas, 2601 North Floyd Road, Richardson, Texas, 75083-0688, and Department of Chemical Engineering, The UniVersity of Texas at Austin, 1 UniVersity Station, Austin, Texas, 78712-1062 Received February 13, 2004; E-mail: imusselm@utdallas.edu Abstract: Two challenges for effectively exploiting the remarkable properties of single-walled carbon nanotubes (SWNTs) are the isolation of intact individual nanotubes from the raw material and the assembly of these isolated SWNTs into useful structures. In this study, we present atomic force microscopy (AFM) evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using an amphiphilic R-helical peptide, termed nano-1. Transmission electron microscopy (TEM) and well-resolved absorption spectral features further corroborate nano-1’s ability to debundle SWNTs in aqueous solution. Peptide-assisted assembly of SWNT structures, specifically in the form of Y-, X-, and intraloop junctions, was observed in the AFM and TEM images. Introduction More than a decade after their discovery, 1 intense interest remains in exploiting the extraordinary electrical and mechanical properties of single-walled carbon nanotubes (SWNTs). The electrical properties of SWNTs, which range from semiconduct- ing to metallic depending on their diameter and chirality, renders SWNTs appealing for nanowires, 2-4 rectifying heterojunc- tions, 5,6 field-effect transistors, 7 and nanoscale electronic devices. 8-10 Because of their high Young’s modulus and aspect ratio, SWNTs can be used to make strong fibers. 11,12 The use of SWNTs in biological applications such as artificial muscles (actuators) 13,14 and biomedical sensors 15,16 are being evaluated. A major obstacle to realizing their potential is that SWNTs form parallel bundles as a result of intertube van der Waals interac- tions. This aggregation modifies the electronic structure of the SWNTs and complicates their dispersal, separation, and func- tionalization. 17 Since most applications will require the separation and further manipulation of SWNTs, substantial effort has been placed on developing techniques to disperse and debundle SWNTs. 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