Hybrids of DNA and carbon nanotubes (DNA-CNT hybrids) are one of several candidates for nanobiodevices. Hybrids of single-stranded DNA (ssDNA) and single-walled carbon nanotubes (SWNT) have attracted particular interest and have been intensively studied by many research groups. Structural models of ssDNA-SWNT hybrids have been also proposed based on experimental observations; however, several structural and functional characteristics of ssDNA-SWNT remain unknown. For example, although mixtures of ssDNA and SWNT are sonicated to achieve hybridization, the effects of sonication on the biological functions of ssDNA-SWNT are not well understood. Further, hybrids of double-stranded DNA (dsDNA) and SWNT have not been well studied.
In this study, we examined functions of ssDNA and dsDNA molecules adhered on SWNT surfaces. We used single-stranded binding (SSB) proteins to verify hybrid formation, as SSB distinguish ssDNA from dsDNA: binding of the SSB proteins to ssDNA-SWNT hybrids rather than dsDNA-SWNT hybrids guarantees the biological functions of ssDNA and dsDNA molecules on SWNT surfaces.
ssDNA-SWNT hybrids and dsDNA-SWNT hybrids were reacted with SSB proteins under various mixing ratios. We optimized an agarose gel electrophoresis procedure to monitor the locations of DNA, SWNT, and SSB proteins. Electrophoresis clearly indicated selective binding of SSB proteins only to ssDNA-SWNT hybrids. Limited binding to dsDNA-SWNT was observed only at very high concentrations of SSB. Atomic force microscopy also supported this conclusion. Our results provide support for the biological application of DNA-CNT hybrids.