CNTs functionalization

CNTs can be functionalized with protein via non-covalent bond (Li et al., 2005 Kim et al., 2003 Mitchell et al., 2002). For example, (beta-lactamase I, that can be immobilized inside or outside CNTs, doesn t change enzyme s activity (Vinuesa and Goodnow, 2002). Taq enzyme can attach to the outside of CNT, and doesn t change its activity (Cui et al., 2004). Peptide with Histidine and Tryptophan can have selective affinity for CNT(Guo et al., 1998). Monoclonal antibody can attach to SWNTs. Protein-modified CNTs can be used to improve its biocompatibility and biomolecular recognition capabilities (Um et al., 2006). For example, CNTs functionalized with PEG and Triton X-100 can prevent nonspecific binding of protein and CNTs. Biotin moiety is attached to the PEG chains Streptavidin can bind specifically with biotin-CNT (Shim et al., 2002). 

On the other hand, noncovalent adsorption leaves CNTs electronic and optical properties almost intact, as the type of modification is through van der Waals, 7T-7T stacking, H-bonding and electrostatic interactions, that do not determine any pyramidalization process. Such benefit is traded off by a decreased stability of CNT-functionalized systems, as a consequence of the weaker interactions. 

Figure 3.9 Schematic representation of the typical noncovalent CNT functionalizations and the hybrid approach by using pyrene linkers. The figure also shows transmission electron images of SWNT modified with streptavidin labeled with 10 nm gold nanoparticles that were covalently coupled to pyrene linkers that were stacked on...

SW CNT functionalized with DNA showed a 10 times more effective penetration and expression of genes in vitro, in comparison with molecular DNA. Other charged macromolecules such as polypeptides and liposomes, can provide more effective transport, but they can cause destabilization of the cellular membrane exhibiting a cytotoxic effect. Whereas, using nanotubes for gene delivery has not caused any cytotoxic effects. 

The oxidative introduction of carboxylic functions to nanotubes provides a large number of CNT-functional exploitations and permits covalent functionalization by the formation of amide and ester linkages and other carboxyl derivatives [24]. Bifunctional molecules (diamines, diols, etc.) are often utilized as linkers. More illustrative examples are nanotubes decorated with amino-functionalized dendrimers, nucleic acids, enzymes, etc., and the formation of bioconjugates of CNTs [96]. 

As said before, another way of CNT functionalization is by polymer macroradicals using methods of ultrasonic sonochemistry. The macroradicals are generated by the degradation effect of ultrasonic waves applied onto polymer solutions, e.g. those prepared of poly(methyl... 

Deeper insight into CNT functionalities when used as a dopant for polymer solar cells and polymer light-emitting diodes (PLEDs) was presented by Xu et al. [329]. While the PLED gained from rather low CNT doping levels of about 0.02%, the solar cell performance increased further up to 0.2 wt %. The improved EQE of the OLED was explained by a better charge carrier injection from the electrode, whereas for the solar cell exciton dissociation is facilitated by the nanotubes [329]. 

Aryl Diazonium-Based Chemistry. The modification of carbon surfaces by reactive aryl diazonium salts has currently been widely applied to the sidewall CNT functionalization [Fignre 8.2(b)] [28-33]. This reaction proceeds via the aryl radical generated npon one electron rednction of the diazonium salt, and it was first performed nsing electrochemical rednction [42-47]. Recently, it was shown that diazoninm fnnctionalization can also be achieved chemically, and can occur at the sidewalls as well as end-cap fnnctionalization [28-33]. 

Fig. 6 Concept of a CNT functionalized with a plasma polymer coating, luminescent QDs, and loaded with anticancer drugs. The functionalized CNTs can be used as biomarkers and drug carriers...

Further interesting works on CNTs functionalized with polymeric chains and extensively characterized by means of Raman spectroscopy have been published previously. ... 

Figure 9.4 Surface properties and size influencing the pathways of CNT internalization. Inserted panel Nanotube bundles (CNT)., functionalized with (macro)molecules (f) with the aid of sonication (US) and/or temperature (T), are dispersed in single nanotubes f-CNT this f-CNT can lead to the formation of supramolecular structure p f-CNT. (al) (CNT). interact with cell membrane and are internalized via phagocytosis (bl) f-CNT enter the cells by diffusion (b2) nanotube dispersion is not stable and nanotubes cluster in solution (nanotube clusters enter the cell by phagocytosis) (cl) p f-CNT enters the cell by ligand-receptor (1) binding (c2) p f-CNT cluster on cell membrane and enter by receptor-mediated endocytosis. CNT Carbon nanotube f-CNT Functionalized CNT.

Taking advantage of the steady increasing techniques for CNT functionalization [7], several routes were explored to attach redox molecules onto SWCNTs. Ferrocene was also attached to MWCNTs by, amide coupling, 7c-stacking interactions [8], aryldiazonium reduction [8] or 1,3 dipolar cycloaddition of azomethyne ylides [9] in order to establish electrical communication between the enzyme and the electrode (Fig. 3.5). 

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