Fundamental properties of oligo double-stranded DNA/single-walled carbon nanotube nanobiohybrids.

Fundamental properties of single-walled carbon nanotubes (SWNTs) that are individually dissolved using twenty base paired-double-stranded (ds) DNA, (dA)(20)/(dT)(20), as well as single-stranded (ss) twenty-mers of oligo DNAs, adenine (dA)(20) and thymine (dT)(20), for comparison are described. In this study, unbound oligo DNAs are fully removed from the hybrid aqueous solutions using size-exclusion chromatography (SEC)-HPLC. Each SEC chromatogram of the solutions shows two separated peaks; one is the free oligo DNAs and the others are the oligo DNA/SWNT hybrids. The earlier eluent fractions (the hybrids) are separated into four size-separated fractions, and then their stability is evaluated by the re-injection of the fractions. The chromatograms of the earlier eluent fractions are almost identical to those of the original ones even after storage for one month, indicating the high stability of the dsDNA/SWNTs and ssDNA/SWNTs hybrids in water. The results free us from considering the desorption of the bound-oligo dsDNA or oligo ssDNA from their nanohybrids with the SWNTs, which is of significant advantage to the utilization of oligo DNA/SWNT nanobiohybrids in wide areas of science. We also investigated the near-IR absorption and photoluminescence (PL) spectral behaviors of the fractionated oligo DNA/SWNTs hybrids not containing corresponding free oligo DNA.