REVIEW ARTICLE Diameters of single-walled carbon nanotubes (SWCNTs) and related nanochemistry and nanobiology Jie MA 1 , Jian-Nong WANG 2 , Chung-Jung TSAI 3 , Ruth NUSSINOV 3,4 , Buyong MA (✉) 3 1 Shanghai Key Laboratory for Laser Processing and Materials Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 2 Shanghai Key Laboratory for Metallic Functional Materials, Key Laboratory for Advanced Civil Engineering Materials (Ministry of Education), School of Materials Science and Engineering, Tongji University, Shanghai 200092, China 3 Basic Science Program, SAIC-Frederick, Inc., Center for Cancer Research Nanobiology Program, NCI-Frederick, NIH, Frederick, MD 21702, USA 4 Sackler Institute of Molecular Medicine, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel © Higher Education Press and Springer-Verlag Berlin Heidelberg 2010 Abstract We reviewed and examined recent progresses related to the nanochemistry and nanobiology of signal- walled carbon nanotubes (SWCNTs), focusing on the diameters of SWCNTs and how the diameters affect the interactions of SWCNT with protein and DNA, which underlay more complex biological responses. The dia- meters of SWCNTs are closely related to the electronic structure and surface chemistry of SWCNTs, and subse- quently affect the interaction of SWCNTs with membrane, protein, and DNA. The surfaces of SWCNT with smaller diameters are more polar, and these with large diameters are more hydrophobic. The preference of SWCNT to interact with Trp/Phe/Met residues indicates it is possible that SWCNT may interfere with normal protein-protein interactions. SWCNT-DNA interactions often change DNA conformation. Besides the promising future of using SWCNTs as delivering nanomaterial, thermal therapy, and other biological applications, we should thoroughly examine the possible effects of carbon nanotube on interrupting normal protein-protein interac- tion network and other genetic effects at the cellular level. Keywords carbon nanotube (CNT), nanobiology, pro- tein, DNA, toxicity, cancer 1 Introduction Cancer nanotechnology presents both challenge and promise for controlling cancer cell [1,2]. Nanoparticles with the size range of 10–100 nm can be used for drug delivery, imaging, and sensing in cancer research [3]. For example, iron oxide nanoparticles can be used to distinguish normal cells from cancer breast cells [4], and magnetic nanocrystal hybrided with polymer and anti- cancer drug has been used for targeted detection and has synergistic therapeutic effects on breast cancer cell [5]. Functionalized single-walled carbon nanotube (SWCNT) can carry small interfering RNA (siRNA) into cells, illustrating a potential useful therapeutic strategy for chronic myelogenous leukemia cells [6]. On the other hand, the nanocarrier systems may induce cytotoxicity [7]. Clearly, the nanotechnology not only provided an innovative tool but also calls for deeper understanding of nanobiology and nanosystem introduced, which will enable us to fight diseases with greater power. Carbon nanotube (CNT) is one group of carbon-based nanosystems. CNTs comprise a carbon fibrous form consisting of one (single-walled carbon nanotubes – SWCNTs) to tens of coaxial tubes (multiwalled carbon nanotubes – MWCNTs) of carbon elements with adjacent graphene sheets separated by 0.334 nm, with diameters ranging from 0.4 to 50 nm. Different synthesis methods often produce different types of CNT (either multiple walled or single walled) with different diameters. SWCNT represents a unique nanosystem not only with potential applications for cancer therapy [8], but also an excellent nanosystem to test biological reaction. Structurally simple, SWCNTs with different diameters provided a delivery system with variable surface area and internal volume. The surface chemistries (with and without modification) allow various interactions with other biomolecules. The thermal effect with near infrared frequencies can be used to target specific cancer cell for photothermal therapy. Electric properties of SWCNTs can be used as biosensor [9,10]. Received September 9, 2009; accepted September 30, 2009 E-mail: mabuyong@mail.nih.gov Front. Mater. Sci. China 2010, 4(1): 17–28 DOI 10.1007/s11706-010-0001-8