Carbon nanotubes functionalizing modifiers

Cui RJ, Huang HP, Yin ZZ, Gao D, Zhu JJ (2008) Horseradish peroxidase-functionalized gold nanoparticle label for amplified immunoanalysis based on gold nanoparticles/carbon nanotubes hybrids modified biosensor. Biosens Bioelectron 23 1666-1673... 

As discussed in sec 3, CNTs have been extensively used to develop pesticide sensors with higher sensitivity and longer stability. In this section we discuss about the design and the development of CNT based pesticide sensors. Joshi et al. reported the detection of OP compounds at a disposable biosensor with AChE-functionalized acid purified multi-wall carbon nanotubes (MCNTs) modified SPE [10]. The degree of inhibition of AChE by OP compounds was determined by measuring the electro oxidation current of the thiocholine generated by the AChE catalyzed hydrolysis of ATCh. The large surface area and electro-catalytic activity of MWCNTs lowered the over potential for thiocholine oxidation to + 0.2 Y. Further, mediators were not used in this case and enzyme immobilization was done by physical adsorption. 

Carbon nanotubes functionalized with organic residues can act as sensors, too. For example, the limit of detection of NO2 drops below 100 ppt using nanotubes modified with polyethylene imine. Strongly electron-withdrawing molecules as well can be detected this way. Sensors consisting of nanotubes may further... 

More recently, positively functionalized carbon nanotubes were modified by a covalent synthetic route with polycatiOTuc dendrimeric chains, fostering the successive decoration with a multi-metallic and polyanionic water oxidation catalyst, the Ru4(POM), with a complementary combination of covalent/non-covalent approaches (Fig. 9) [149]. 

Similar strategies for the immobilization of biomolecules are applied to the fabrication of an electrochemical biosensor for the determination of tyrosine. The enzyme tyrosinase was immobilized on the carbojyl functionalized single-walled carbon nanotubes (SWCNT) modified SPE by Apetrei and Apetrei. As previously mentioned by Perez and Fabre-gas, Apetrei confirmed that carbo>yl functionalized CNTs provide a... 

K. Yang and M. Gu, "Enhanced thermal conductivity of epoxy nanocomposites filled with hybrid filler system of triethylenetetramine-functionalized multi-walled carbon nanotube/silane-modified nano-sized silicon carbide," Composites Part A, vol. 41, pp. 215-221,2010. 

Recently, a cholesterol biosensor was developed using cholesterol oxidase function-ahzed on multiwall carbon nanotubes film—modified glassy carbon electrode (ChOx/ MWCNTs/GCE) (Li et al., 2011 Figure 3.7). The electrocatalytic behavior toward cholesterol was investigated by cyclic voltammetry. This sensor showed excellent perfor-... 

Tiwari 1, Singh M, Gupta M, Aggarwal SK (2012) Electroanalytical properties and appUcation of anthraquinone derivative-functionalized multiwalled carbon nanotubes nanowires modified glassy carbon electrode in the determination of dissolved oxygtai. Mater Res Bull 47 (7) 1697-1703. doi 10.1016/j.materresbull.2012.03.031... 

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

In another example [56] SWNT was modified with peroxytrifluoroacetic add (PTFAA). Raman spectrum of the carbon nanotubes after the FIFA A treatment shows a D-line substantially increased indicating the formation of defect sites with sp3-hybridized carbon atoms on the sidewalls due to the addition of the functional groups. The RBM bands in the region of 170-270cm-1 decreased and shifted to higher... 

Amide bond is an effective anchor to connect CNTs to substrate surfaces. Lan et al. [52] covalently assembled shortened multi-walled carbon nanotubes (s-MWNT) on polyelectrolyte films. The shortened MWNT is functionalized with acyl chloride in thionyl chloride (SOCl2) before self-assembling. The FTIR spectrum of self-assem-bled MWNT (SA-MWNT) adsorbed on a CaF2 plate modified with PEI/(PSS/PEI)2 shows two characteristic absorption peaks at 1646cm-1 (amide I bond) and 1524cm-1 (amide II bond) resulting from the amide bond formed between the polyelectrolyte films and s-MWNTs. 

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]. 

Noncovalent functional strategies to modify the outer surface of CNTs in order to preserve the sp2 network of carbon nanotubes are attractive and represent an effective alternative for sidewall functionalization. Some molecules, including small gas molecules [195], anthracene derivatives [196-198] and polymer molecules [118, 199], have been found liable to absorb to or wrap around CNTs. Nanotubes can be transferred to the aqueous phase through noncovalent functionalization of surface-active molecules such as SDS or benzylalkonium chloride for purification [200-202]. With the surfactant Triton X-100 [203], the surfaces of the CNTs were changed from hydrophobic to hydrophilic, thus allowing the hydrophilic surface of the conjugate to interact with the hydrophilic surface of biliverdin reductase to create a water-soluble complex of the immobilized enzyme [203]. 

The amine function served also as the starting point for the first covalent linkage of Pcs to single-walled carbon nanotubes (SWNTs) [94], The pipes with open-end and surface-bound acyl chloride moieties were used to prepare the Pc-SWNTs system by amide-bond formation (Fig. 14). Accordingly, statistical reaction of 4-aminophthalonitrile with 4-tcr/-bu(yIph111alonitrile in the presence of zinc ions delivered the monoamino Pc that was then employed in the conjugation with the acid chloride modified carbon nanotubes (CNTs). Here, it should also be mentioned that other functions have been applied to the covalent modification of CNTs, i.e., amide [95], ester [96,97], or click chemistry [98],... 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo-... 

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