Hindawi Publishing Corporation Journal of Nanomaterials Volume 2011, Article ID 938491, 12 pages doi:10.1155/2011/938491 Research Article Characterization of Multiwalled Carbon Nanotubes Dispersing in Water and Association with Biological Effects Xuelian Cheng, 1 Jun Zhong, 2 Jie Meng, 1 Man Yang, 1 Fumin Jia, 1 Zhen Xu, 1 Hua Kong, 1 and Haiyan Xu 1 1 Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100005, China 2 Institute of Functional Nano & Soft Materials, Soochow University, Jiangsu 215123, China Correspondence should be addressed to Haiyan Xu, xuhy@pumc.edu.cn Received 24 May 2011; Accepted 23 June 2011 Academic Editor: Xing J. Liang Copyright © 2011 Xuelian Cheng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Biomedical application potentials of carbon nanotubes-based materials have been investigated intensively in recent years; however, characterization and metrology are still facing great technical challenges when the materials are intended to be used as carriers for therapeutics in aqueous solutions. Systematic characterization on the dispersing carbon nanotubes is urgently required and therefore of significance. In this paper multiwalled carbon nanotubes (MWCNTs) with different average lengths or with different oxidation degrees were dispersed in water and characterized systematically by applying UV spectroscopy, SEM, DLS, TGA, XPS, and FTIR. In particular, the characteristic absorption of the carbon nanotubes was analyzed using resolution-fitting technique to establish relations of wavelength and absorption intensity to the size distribution and surface chemistry. Results indicated that the absorption spectra of MWCNTs could reflect the variation of surface chemistry and length distribution of carbon nanotubes dispersed in water by combining with the other measurements. A vascular endothelium cell line was taken as a model to figure out association between physicochemical features and cytotoxicity of the carbon nanotubes. It was showed that the multiwalled carbon nanotubes with different oxidation degrees and similar length distribution exhibited different interaction files to the cells proliferation in a manner of time dependence and concentration dependence. 1. Introduction Carbon nanotubes have shown their promising potentials in biomedical fields including novel delivery systems for drugs or DNAs/RNAs in recent years, which have been reviewed in detail in some publications [1–6]. Meanwhile, biological safety and risks along with the application of carbon nanotubes-based materials have been seriously concerned, as related research publications are increasing constantly and the experimental data from different research groups are often different and even conflicted each other [7–12]. For example, Takagi et al. reported an incidence of mesothelioma in p53-deficient mice injected intraperitoneally with 3 mg per mouse of multiwalled carbon nanotubes [8]. On the contrary, Muller et al. reported that, several months after the injection of nanotubes, the inflammatory reaction was almost absent and limited by a fibrotic encapsulation; hence, multiwalled carbon nanotubes (MWCNTs) with or without structural defects did not induce mesothelioma in this bioassay displaying the absence of carcinogenicity of nanotubes [9]. Accumulating evidence implied that one of the important reasons that cause these conflicts is the lack of standard metrology for carbon nanotubes due to the lack of comprehensive characterization, which makes it difficult to compare data from different laboratories worldwide. Besides making comparison, the great efforts to apply carbon nanotubes into biomedical fields are requiring comprehensive characterization urgently. For molecular drugs, their physicochemical properties such as molecular weight, chemical composition, purity, solubility, and stability are usually necessary to analyze. The instrumentation to ascertain these properties have been well established, and the techniques are standardized. Techniques