IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 18 (2007) 405706 (5pp) doi:10.1088/0957-4484/18/40/405706 A Raman probe for selective wrapping of single-walled carbon nanotubes by DNA Quan-Hong Yang 1,2,7 , Nittaya Gale 3 , Claudio J Oton 2 , Feng Li 4 , Alun Vaughan 5 , Riichiro Saito 6 , Iris S Nandhakumar 3 , Zhi-Yuan Tang 1 , Hui-Ming Cheng 4 , Tom Brown 3 and Wei H Loh 2 1 School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People’s Republic of China 2 Optoelectronics Research Centre, The University of Southampton, Southampton SO17 1BJ, UK 3 School of Chemistry, The University of Southampton, Southampton SO17 1BJ, UK 4 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 100016, People’s Republic of China 5 School of Electronics and Computer Science, The University of Southampton, Southampton SO17 1BJ, UK 6 Department of Physics, Tohoku University and CREST, JST, Sendai 980-8578, Japan E-mail: qhyangcn@tju.edu.cn Received 13 June 2007, in final form 6 August 2007 Published 20 September 2007 Online at stacks.iop.org/Nano/18/405706 Abstract In this paper, we discuss nanotube diameter selectivity in DNA wrapping of single-walled carbon nanotubes (SWNTs) under high-shear sonication and present Raman evidence for the selective wrapping. The DNA wrapping induces an upshift (an increase in wavenumber) of the radial breathing mode (RBM) bands in the Raman spectra of SWNTs, which indicates strong interaction between nanotubes and DNA. The extent of the upshift correlates well with the change in the intensity of the RBM bands upon DNA wrapping, and larger upshifts correspond to larger intensity changes. The intensity changes represent wrapping selectivity, and differ from tube to tube due to varying diameters and electronic properties. The shift of the RBM bands thus represents a practical probe for wrapping selectivity and the extent of the shifts indicates different electronic structures of core nanotubes hybridized with DNA. S Supplementary data are available from stacks.iop.org/Nano/18/405706 (Some figures in this article are in colour only in the electronic version) 1. Introduction Considerable progress has been made in the study of complexes between single-walled carbon nanotubes (SWNTs) and DNA [1–5], with the aim of developing applications in the field of detection of DNA [2, 3] and structure-based sorting of SWNTs [4, 5]. The hybridization of SWNTs with single-stranded DNA (ss-DNA) was recently achieved through noncovalent aromatic interactions between nucleobases and nanotube sidewalls [4–8]. During high-shear sonication, ss-DNA forms a stable complex with individual SWNTs 7 Author to whom any correspondence should be addressed. (SWNT–DNA hybrid) as a result of helical wrapping of the macromolecule around the SWNTs. In this process, most of bundled nanotubes are isolated into individual entities and the SWNT–DNA hybrid becomes uniformly dispersible in aqueous solutions. The ease of formation of stable SWNT– DNA hybrids has motivated intensive investigations into both the fundamental properties of such systems and their potential use in applications such as gas sensors [9], biosensors [10], liquid-crystals [11], drug delivery vehicles [12] and electronic switches [13]. However, many fundamental issues still have to be addressed before we are fully able to understand and characterize the DNA wrapping process of SWNTs. One such 0957-4484/07/405706+05$30.00 1 © 2007 IOP Publishing Ltd Printed in the UK