DNA SWNTs

Figure 6.4 (a) Area map of the (6,5) nanotube peak fluorescence intensity of DNA-SWNTs within... 

Figure 17 Photoluminescence of DNA-SWNT emissions (green) within murine 3T3 cells (gray) (a) before and (b) after the addition of hydroxyl radicals. The addition of H2O2 results in the net decrease in photoluminescence within the cells. (Reproduced from Ref. 61. Nature Publishing Group, 2009.)...

Another important question is whether exocytosis occurs after CNT internalization. Evidence of exocytosis of DNA-coated SWNTs in fibroblast (NIH-3T3) cells was recently presented [148]. The exocytosis rate was close to that of endocytosis after a minor temporary offset, thus keeping the accumulation of SWNTs inside the cell below the cytotoxic levels. 

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. 

FIGURE 15.23 Raman spectra of (a) ds-calf thymus DNA/PDDA/SWNTs, (b) PDDA/SWNTs, (c) oxidized SWNTs, (d) calf thymus DNA, and (e) PDDA. Inset Magnification of the Raman spectra of DNA/PDDA/SWNTs, PDDA/SWNTs, and oxidized SWNTs. (Reprinted with permission from [55]. 

CNTs can also be encapsulated with DNA molecules. As shown in Fig. 9.1, a DNA molecule could be spontaneously inserted into a SWNT in a water solution via molecular dynamics simulation (Gao et al., 2003). The van der Waals and hydrophobic forces were very key factors for the insertion process, with the former playing a more dominant role in the course of DNA entering into the hole of CNT. Experiment also confirmed that Pt-labeled DNA molecules can be encapsulated into multi-walled carbon nanotubes in water solution at 400 K and 3 Bar as shown in Fig. 9.2 (Cui et al., 2004). The CNTs filled with DNA molecules have potential in applications such as gene delivery system, and electronic sequencing, nanomotor, etc. 

Abbreviations PDT, Photodynamic therapy EPR, Enhanced permeability and retention IHF, Tetrahydrofuran UV, Ultraviolet DNA, Deoxyribonucleic acid PL, Photoluminescence SWNT, Single-walled nanotube DWNT, Double-walled nanotube MWNT, Multi-walled nanotube IV, Intravenous HSP, Heat shock protein ... 

As with fullerenes, carbon nanotubes are also hydrophobic and must be made soluble for suspension in aqueous media. Nanotubes are commonly functionalized to make them water soluble although they can also be non-covalently wrapped with polymers, polysaccharides, surfactants, and DNA to aid in solubilization (Casey et al., 2005 Kam et al., 2005 Sinani et al., 2005 Torti et al., 2007). Functionalization usually begins by formation of carboxylic acid groups on the exterior of the nanotubes by oxidative treatments such as sonication in acids, followed by secondary chemical reactions to attach functional molecules to the carboxyl groups. For example, polyethylene glycol has been attached to SWNT to aid in solubility (Zhao et al., 2005). DNA has also been added onto SWNT for efficient delivery into cells (Kam et al., 2005). 

Figure 3.11 Differential pulse voltammograms (DPVs) for guanine at bare glassy carbon, SWNT modified glassy carbon and bamboo-modified glassy carbon. DNA cone, 0.4 mgmL (b) the corresponding DPV plots observed in (a) but with background subtraction. The signal gene rated from...

Chemical and Genetic Probes—Nanotube-tipped atomic force microscopes can trace a strand of DNA and identify chemical markers that reveal DNA fine structure. A miniaturized sensor has been constructed based on coupling the electronic properties of nanotubes with the specific recognition properties of immobilized biomolecules by attaching organic molecules handles to these tubular nanostructures. In one study, the pi-electron network on the CNT is used to anchor a molecule that irreversibly adsorbs to the surface of the SWNT. The anchored molecules have a tail to which proteins, or a variety of other... 

The interaction between DNA and carbon nanotubes is stable enough to allow separation of the dispersed nanotubes into well-defined subpopulations.46 55-57 Recently, ssDNA-wrapped SWNTs were separated into multiple fractions with different length distributions, and each fraction was examined for cellular toxicity to various cell lines.55 As demonstrated experimentally, while the longer SWNTs (>200nm) were excluded by cells, the shorter ones were found to internalize into the cytoplasm,... 

The DNA-carbon nanotube interaction is a complicated and dynamic process. Many studies on this subject have been pursued through a series of techniques, including molecular dynamic simulation, microscopy, circular dichroism, and optical spectroscopy.57,58 Although the detailed mechanism is not fully understood at present, several physical factors have been proposed to be driving DNA-carbon nanotube interactions,46,59-61 such as entropy loss due to confinement of the DNA backbone, van der Waals and hydrophobic (rr-stacking) interactions, electronic interactions between DNA and carbon nanotubes, and nanotube deformation. A recent UV optical spectroscopy study of the ssDNA-SWNT system demonstrated experimentally that... 

Carbon nanotubes, especially SWNTs, with their fascinating electrical properties, dimensional proximity to biomacromolecules (e.g., DNA of 1 nm in size), and high sensitivity to surrounding environments, are ideal components in biosensors not only as electrodes for signal transmission but also as detectors for sensing biomolecules and biospecies. In terms of configuration and detection mechanism, biosensors based on carbon nanotubes may be divided into two categories electrochemical sensors and field effect transistor (FET) sensors. Since a number of recent reviews on the former have been published,6,62,63 our focus here is mostly on FET sensors. 

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