Biopolymer Functionalized CNTs

Badaire et al. reported the formation of liquid crystalline phase of CNTs by noncovalent functionalization with single strand DNA in water [74]. The nonco-valent functionalization in water is simpler and does not affect the intrinsic properties of the CNTs. They observed that a nematic-isotropic coexistence is observed for nanombes concentrations between 2 and 4 wt%. Above 4 wt%, the system forms a single nematic phase of unmodified and freely dispersed nanotubes. They investigated the boundaries of the phase diagram with respect to the aspect ratios of the nanombes determined by dynamic depolarized light scattering. Poulin et al. uniformly aligned the nematic aqueous suspensions of nanombes in 

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Attaching chemical functionalities to CNTs can improve their solubility and allow for their manipulation and processability [24]. The chemical functionalization can tailor the interactions of nanotubes with solvents, polymers and biopolymer matrices. Modified tubes may have physical or mechanical properties different from those of the original nanotubes and thus allow tuning of the chemistry and physics of carbon nanotubes. Chemical functionalization can be performed selectively, the metallic SWCNTs reacting faster than semiconducting tubes [25]. 

Since the report of carbon nanotubes (CNT) in 1991, much attention has been focused on their unique electrical and mechanical properties. The integration of bioactive molecules (enzymes, proteins, antigens, antibodies, DNA, etc.) with CNT enables the use of the hybrid systems as biosensor devices (enzyme electrodes, immunosensors, or DNA sensors), but the hydrophobicity of the CNT limits their application in biology. Thus, the functionalization of CNT with biopolymers promises to be one of the most successful methods to improve the hydrophilicity of CNT. These biopolymers can bring a hydrophilic surface of the CNT for covalent, absorptive, or ionic bindings with bioactive molecules. 

Biopolymers have also been used to wrap CNTs in efforts to functionalize them for aqueous dispersion. Chitosan, poly(L-lactide) [93], and cellulose [94] are some of the polymers that are commonly employed. Chitosan in particular has been the subject of considerable research because of the ease with which it is functionalized. For instance, enzyme attachment has been used to produce robust chemical sensors for glucose [95,96]. Layered arrangement of chitosan/CNT composite produced a low-power requirement electrochemical actuator with superior mechanical properties and repeatability [97]. 

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