1. Introduction

The carbon nanotubes (CNTs), one of the best novel nanostructures [1] and classic objects in nanotechnology, form bundle-like structures with very complex morphologies with a high number of Van der Waals interactions, causing extremely poor solubility in water or organic solvents. Due to their exceptional combination of mechanical, thermal, chemical, and electronic properties, single-walled (SWNTs or SWCNTs) and multiwalled carbon nanotubes (MWNTs or MWCNTs) are considered as unique materials, with very promising future applications, especially in the field of nanotechnology, nanoelectronics, and composite materials. Additionally, CNTs are becoming highly attractive molecules for applications in medicinal chemistry. At present, potential biological and medical applications [2] of CNTs have been little explored, in particular for drug delivery purposes [3]. The main difficulty to integrate such materials into biological systems derives from their lack of solubility in physiological solutions. Functionalization of CNTs with the assistance of biological molecules remarkably improves the solubility of nanotubes in aqueous or organic environment and, thus, facilitates the development of novel biotechnology, biomedicine, and bioengineering. Many of these applications require an increased “solubility” of CNTs in solvents, first of all in water, especially for biological applications. This could be reached by their functionalization, which is a very actively discussed topic in contemporary literature because the planned modification of CNT properties is believed to open the road toward real nanotechnology applications [4]. It is difficult to prepare an aqueous dispersion of CNTs stable for months; their insolubility has been a limitation for the practical applications of this unique material. Proper dispersion of CNT materials is important to retaining the electronic properties of nanotubes. The redissoluble functional compound/CNT composites are needed for post-processing because CNT dispersions usually easily aggregate and therefore make additional processing very difficult.