Poor solubility of single-walled and multiwalled carbon nanotubes (NTs) in water and organic solvents presents a considerable challenge for their purification and applications. Macromolecules can be convenient solubilizing agents for NTs and a structural element of composite materials for them. Several block copolymers with different chemical functionalities of the side groups were tested for the preparation of aqueous NT dispersions. Poly(N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co-4-vinylpyridine) was found to form exceptionally stable NT dispersions. It is suggested that the efficiency of macromolecular dispersion agents for NT solubilization correlates with the topological and electronic similarity of polymer-NT and NT-NT interactions in the nanotube bundles. Raman spectroscopy and atomic force and transmission electron microcopies data indicate that the polycations are wrapped around NTs forming a uniform coating 1.0-1.5 nm thick. The ability to wind around the NT originates in the hydrophobic attraction of the polymer backbone to the graphene surface and topological matching. Tetraalkylammonium functional groups in the side chains of the macromolecule create a cloud of positive charge around NTs, which makes them hydrophilic. The prepared dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for electronic materials and sensing. Positive charge on their surface is particularly important for biological and biomedical applications because it strengthens interactions with negatively charged cell membranes. A high degree of spontaneous bundle separation afforded by the polymer coating can also be beneficial for NT sorting.

Single-walled carbon nanotubes (SWNTs) have a set of unique mechanical and electrical properties that has stimulated tremendous interest in them. Significant efforts have been directed towards utilizing these materials as building blocks of composites for a variety of technological contexts, such as nanoelectronic devices, [1][2][3][4][5][6] sensors, [7][8][9][10][11][12] and field emission electron displays and lighting elements. [13,14] We strongly believe that one of the most prolific areas of their applications will be in biomedicine, where compact, strong, and high-performance devices can be engineered. These devices will exploit the properties of SWNTs and will compete with existing products. The novel technologies of diagnostics and therapeutics can be based on SWNT composites and individual tubes. Along these lines, SWNTs have been demonstrated as potential sensing materials of biological systems, [15][16][17][18][19] which are typically considered for the use in ex vivo modality. The potential use of SWNT-based structures for the purpose of healing neurological and brain-related injuries represents one of the major scientific and practical interests. The high mechanical strength and electrical properties possessed by SWNTs makes these materials perfect candidates for various prosthetic devices, including bone and joint repair. It is important to realize, however, that successful utilization of SWNT-based devices in biomedicine is hinged on the ability of such materials to interface with living cells, support their growth, and at the same time preserve their viability. [20][21][22][23][24] These factors are not well understood for any SWNT structures, which limits the development of in vivo, that is, implantable devices from such materials. The actual processes and techniques used for the preparation of macroscopic objects from SWNTs will play a significant role in determining cellular effects of SWNT composites. Substrates prepared from multi-walled carbon nanotubes (MWNTs) as well as SWNTs have been reported to be biocompatible platforms for neuronal growth and differentiation. [25][26][27] The use of carbon nanofiber composites as devices for neural-and bone-tissue-implant integration has also been described.[28] Molecular engineering of any SWNT-based composite should have a great effect on how the material performs during long-term contact with tissue. The layer-by-layer (LBL) approach to prepare SWNT structures can be particularly useful in this respect because it allows one to exert control over the structure of the SWNT/polymer systems from angstrom to nanometer and micrometer scale, which is necessity for the engineering of the cell/SWNT interface. [29] Recently, we demonstrated that SWNT LBL films can support the growth, viability, and differentiation of neuronal NG108-15 neuroblastoma/glioma hybrid cells. [30] The first example of free-standing SWNT/polymer thin-film membranes that can be mechanically compatible with tissues and can be used as implants and repair devices for neurological-or bra...

6-mercaptopurine and its riboside derivatives are some of the most widely utilized anti-leukemic and anti-inflammatory drugs. Their short biological half-life and severe side effects limit their use. A new delivery method for these drugs based on 4-5 nm gold nanoparticles can potentially resolve these issues. We have found substantial enhancement of the antiproliferative effect against K-562 leukemia cells of Au nanoparticles bearing 6-mercaptopurine-9-beta-d-ribofuranoside compared to the same drug in typically administered free form. The improvement was attributed to enhanced intracellular transport followed by the subsequent release in lysosomes. Enhanced activity and nanoparticle carriers will make possible the reduction of the overall concentration of the drug, renal clearance, and, thus, side effects. The nanoparticles with mercaptopurine also showed excellent stability over 1 year without loss of inhibitory activity.