AFM Measurements of Long, Isolated Single-Walled Carbon Nanotubes Wrapped with Peptide V. Zorbas 1 , A. Ortiz-Acevedo 1 , A. B. Dalton 2 , G. R. Dieckmann 1, 2 , R. K. Draper 1, 2, 3 , R. H. Baughman 1, 2 , I. H. Musselman 1, 2* 1. Department of Chemistry, University of Texas at Dallas, Richardson, TX 75083 2. NanoTech Institute, University of Texas at Dallas, Richardson, TX 75083 3. Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, TX 75083 Due to their extraordinary electrical and mechanical properties, single-walled carbon nanotubes (SWNTs) are promising candidates for various applications ranging from nanoscale electronic devices to biomedical sensors. Two common challenges for effectively exploiting the remarkable properties of SWNTs are first to isolate intact individual nanotubes from the raw material, and second to assemble these isolated SWNTs into useful structures. We have previously shown that a synthesized 29-residue peptide, termed nano-1, effectively dispersed SWNTs in aqueous solution [1]. Nano-1 folds into an amphiphilic α-helix, in which apolar residues occupy one face of the helix, and more polar residues form the other face. The hydrophobic face of the helix was designed to noncovalently interact with the graphite surface of the SWNTs, and the hydrophilic face was designed to promote self-assembly through peptide-peptide interactions. With sub-nanometer lateral and vertical resolution, atomic force microscopy (AFM) can be used to measure accurately the lengths and diameters of SWNTs under the assumption that they have circular cross-sections. TappingMode AFM images were acquired under ambient conditions using a Digital Instruments, Inc. Nanoscope III Multimode Scanning Probe Microscope. The AFM was calibrated using a NanoDevices Inc. standard consisting of lines with 2 µm pitch and 20 nm height, dimensions similar to those of SWNTs. The height calibration was verified using hydrofluoric acid- etched pits in muscovite mica, where 2 nm and 1 nm steps are observed along the long axis and short axis, respectively [2]. Prior to conducting quantitative height measurements, we examined the effect of applied force on apparent diameter of peptide-wrapped SWNTs. Silicon tip/cantilever assemblies with a range of force constants (0.9 to 40 N m -1 ) were tested on a nano-1/SWNT sample. A decrease in apparent height with increasing applied force was observed for the higher force constant cantilevers. Cantilevers having force constants of 0.9 and 3 N m -1 demonstrated minimal vertical sample compression with increasing applied force (Fig. 1). In this study, we present AFM evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using nano-1 and a specific sonication and centrifugation procedure. Long, individual peptide-wrapped SWNTs were observed with an average length of 1.2 ± 1.1 µm and an average diameter of 2.4 ± 1.3 nm. Long SWNTs were not present in sodium dodecyl sulfate (SDS)/SWNT and peptide control samples (Fig. 2). Peptide- assisted assembly of SWNT structures, specifically in the form of Y-, X-, and closed ring or O- junctions, were observed in the AFM images. Therefore, we have investigated the possibility of peptide-assisted end-to-end assembly in creating the long SWNTs. Beyond the anticipated biocompatibility benefits of peptide-wrapped SWNTs, amphiphilic peptides offer the advantage of exceptional dispersion capability, as well as an aptitude to form higher-ordered structures on the SWNT surface through peptide-peptide interactions. 138 Microsc Microanal 10(Suppl 2), 2004 DOI: 10.1017/S1431927604881625 Copyright 2004 Microscopy Society of America