Higher Dispersion Efficacy of Functionalized Carbon Nanotubes in Chemical and Biological Environments

Abstract

Aqueous dispersions of functionalized carbon nanotubes (CNTs) are now widely used for biomedical applications. Their stability in different in vitro or in vivo environments, however, depends on a wide range of parameters, such as pH and salt concentrations of the surrounding medium, and length, aspect ratio, surface charge, and functionalization of the applied CNTs. Although many of these aspects have been investigated separately, no study is available in the literature to date, which examines these parameters simultaneously. Therefore, we have chosen five types of carbon nanotubes, varying in their dimensions and surface properties, for a multidimensional analysis of dispersion stability in salt solutions of differing pH and concentrations. Furthermore, we examine the dispersion stability of oxidized CNTs in biological fluids, such as cellular growth media and human plasma, and their toxicity toward cancer cells. To enhance dispersibility and biocompatibility, the influence of different functionalization schemes is studied. The results of our investigations indicate that both CNT dimensions and surface functionalization have a significant influence on their dispersion and in vitro behavior. In particular, factors such as a short aspect ratio, presence of oxidation debris and serum proteins, low salt concentration, and an appropriate pH are shown to improve the dispersion stability. Furthermore, covalent surface functionalization with amine-terminated polyethylene glycol (PEG) is demonstrated to stabilize CNT dispersions in various media and to reduce deleterious effects on cultured cells. These findings provide crucial data for the development of biofunctionalization protocols, for example, for future cancer theranostics, and optimizing the stability of functionalized CNTs in varied biological environments.

Design of double-walled carbon nanotubes for biomedical applications

“…was observed, possibly due to inhibition of cell proliferation or decreased cell adhesion [17]. Overall, this indicates that oxDWNT-RNA does not have a deleterious effect on cells during their passage, although long-term effects remain to be investigated.…”

Characterization of alkali activated geopolymer mortar doped with MWCNT

“…With this reaction the MWCNTs work as a kind of template during hydration. The increase in CSH-phases attributed to the effect of the NaOH alkaline solution during processing as discussed in [27].…”

“…The increase related to individual MWCNTs which spread throughout the geopolymer matrix with a uniform density. The good dispersion of MWCNTs was also attributed to the effect of the NaOH alkaline solution during processing as discussed [27] and hydrophilic groups (-COOH) in carboxylate based superplasticizer forming covalence-modified CNTs to improve interfacial interactions in composites, in which the -COOH groups form strong coordinate bonds with Ca 2+ ions in matrix, thus enhancing the formation of three dimensional geopolymer in addition to CSH [56,59]. Furthermore, the addition of CNTs fines pore size distribution and decreases the porosity (or nanoporosity) of composites by filling the gaps (or pores) between the hydration products such as C-S-H gel geopolymer composite.…”

“…The first one is the effect of sodium hydroxide (NaOH) on the dispersion of MWCNTs within the geopolymeric matrix. Previous studies have shown that NaOH acts as a surfactant and removes the oxidation debris from the surface of CNTs and consequently allowing them to de-bundle and form well-dispersed nanotubes within the matrix [27]. The other is the effect of NaOH on the electrical conductivity of the geopolymer.…”

Tailored Degree of Functionalization and Length Preservation of Multiwalled Carbon Nanotubes by an Optimized Acid Treatment Process

“…For instance, highly functionalized and short MWCNTs with narrow length distribution are preferable for bio-related applications. 19,37 MWCNTs with a substantial functionalization and a higher preservation of its aspect ratio are desirable for polymeric composites. 5,38 In the present work, we statistically evaluated the advantages of an acid treatment process of MWCNTs with integration of ultrasound, moderate heating and mechanical stirring.…”