Abstract
A method of dispersion of single-wall carbon nanotubes (SWNTs) in aqueous media using Congo red (CR) is proposed. Nanotubes covered with CR constitute the high capacity system that provides the possibility of binding and targeted delivery of different drugs, which can intercalate into the supramolecular, ribbon-like CR structure. The study revealed the presence of strong interactions between CR and the surface of SWNTs. The aim of the study was to explain the mechanism of this interaction. The interaction of CR and carbon nanotubes was studied using spectral analysis of the SWNT–CR complex, dynamic light scattering (DLS), differential scanning calorimetry (DSC) and microscopic methods: atomic force microscopy (AFM), transmission (TEM), scanning (SEM) and optical microscopy. The results indicate that the binding of supramolecular CR structures to the surface of the nanotubes is based on the "face to face stacking". CR molecules attached directly to the surface of the nanotubes can bind further, parallel-oriented molecules and form supramolecular and protruding structures. This explains the high CR binding capacity of carbon nanotubes. The presented system – containing SWNTs covered with CR – offers a wide range of biomedical applications.
Highlights
Carbon nanotubes (CNTs) present enormous application potential in many areas of chemistry, technology and medicine and are currently one of the most intensely studied nanomaterials
Comparison of the absorption spectra of free CR and CR bound to SWNTs shows that the binding to the carbon nanotube surface causes a significant change in the Congo red absorption spectrum (Figure 1, curves A and D)
Direct functionalization of carbon nanotubes based on their interaction with Congo red allows for their dispersion in aqueous media and creates complexes in which the supramolecular character of CR is retained
Summary
Carbon nanotubes (CNTs) present enormous application potential in many areas of chemistry, technology and medicine and are currently one of the most intensely studied nanomaterials. Pristine CNTs exist in form of bundles composed of hundreds of single tubes bound by van der Waals interactions. Most applications of carbon nanotubes require their dispersion (solubilization) which can be achieved by either covalent or noncovalent functionalization [8,13,14]. Covalent functionalization modifies CNT walls through introduction of different atoms or groups (e.g., fluoride, carboxyl, hydroxyl) to the carbon lattice. Noncovalent functionalization leaves the nanotube walls intact, but allows for separation of the bundles due to their interaction with different amphiphilic molecules that cover the hydrophobic CNT surface with hydrophilic groups [15]
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