Synthesis of Functionalized Carbon Nanotubes

Synthesis of Functionalized Carbon Nanotubes
using DNA and Gold Nanoparticles

Goo-Hwan Jeong, Satoru Suzuki and Yoshihiro Kobayashi
Material Science Laboratory

　Due to the outstanding physical, chemical and electrical properties of carbon nanotubes (CNT), a number of applications in various fields are expected. Especially, extensive researches related with CNT-functionalization using foreign atom or molecules have been performed to control electronic property of CNT because diameter- or chirality-controlled growth has not been realized yet, which is determining factor of electronic property. Here, we introduce our CNT-functionalization study for the application of CNT-based nanoelectronics or biosensor. DNA and Au nanoparticles (NP) are selected among various materials to functionalize CNT [1] owing to their specific assembling and strong coupling properties.
　Ferritin covered with protein shell and contains Fe clusters in its 6-nm diameter inner space was used to synthesize diameter-controlled single-walled carbon nanotubes (SWNTs). A Co-ferritin, Fe is replaced by Co, was also used. By controlled methane CVD experiments at 900^oC, suspended SWNTs are successfully synthesized on Si or SiO₂ pillar-structured substrates using not only ferritin but also Co-ferritin, which is the first report [2]. A scanning electron microscope (SEM) image [Fig. 1(a)] and Raman spectrum [Fig. 1(b)] of the suspended SWNTs grown using Co-ferritin catalyst are presented.
　SWNTs-functionalization was performed by covalent coupling between carboxyl and amine groups produced by acid and aminopropyltriethoxysilane (APTES) treatment, respectively. DNA/Au hybrids were made by simple mixing of thiolated-DNA and Au NP (5nm diameter). Finally, SWNTs are modified by Au NP or DNA/Au hybrids.
　Figure 2 shows SEM images obtained from SWNTs/Au [Fig. 2(a) and (b)] and SWNTs/DNA/Au hybrids [Fig. 2(c)]. The density of Au NP attached along the suspended SWNTs was controlled by changing treatment time and Au-colloid concentration. In addition, the change of Raman spectra was also observed from the SWNTs/DNA/Au hybrid [3], which implies the different electronic or optical properties are expected. These results show functionalized CNT can be developed to electronic and optical applications.
[1] M. Zheng et al., Science 302 (2003) 1545-1548.
[2] G.-H. Jeong et al., J. Am. Chem. Soc., submitted 2005.
[3] G.-H. Jeong et al., MRS 2005 Spring Meeting, San Francisco, March 2005.

Fig. 1.

Suspended SWNTs from Co-ferritin.(a) SEM image and (b) Raman result.
Fig. 2. SEM images of CNT/Au hybrids [(a),(b)] and CNT/DNA/Au hybrid (c).

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Fig. 1.	Suspended SWNTs from Co-ferritin.(a) SEM image and (b) Raman result.		Fig. 2.	SEM images of CNT/Au hybrids [(a),(b)] and CNT/DNA/Au hybrid (c).