Surface modification of single-walled carbon nanotubes (SWNTs) with DNA molecules has attracted much attention in recent years to increase SWNT solubility and make various SWNT-based nanobiodevices. Therefore, there is a critical need to quantify the interaction between DNA molecules and SWNT surfaces, particularly the intermediate structures during DNA adsorption. In this study, we demonstrate the ability to detect the adsorption of DNA oligomers on SWNT surfaces by fluorescence spectroscopy. Fluorescein-labelled, 30 mer, thymine oligonucleotides (F-T30) were employed as a fluorescent probe to study the interaction of DNA with SWNTs. A clear quenching effect was observed when F-T30 was adsorbed onto SWNT surfaces. Using this method, the amount of DNA adsorbed onto the SWNT surfaces was measured under different sonication conditions to correlate absorption efficiency with sonication strength and duration. When a bath-type sonicator was used, mild adsorption of F-T30 on SWNT surfaces was observed. Furthermore, a two-step adsorption was observed in this condition. In contrast, we observed rapid adsorption of F-T30 to SWNT surfaces at the higher sonication amplitude (60% maximal) using a probe-type sonicator, while only slight adsorption of DNA molecules was observed at the lower amplitude (20% maximal). Our data revealed that the quenching effect can be used to evaluate DNA adsorption onto SWNT surfaces. In addition, atomic force microscopy (AFM) and photoacoustic spectroscopy (PAS) were conducted to provide complementary information on the DNA-SWNT nanoconjugates.

Nanobioconjugates using carbon nanotubes (CNTs) are attractive and promising hybrid materials. Various biological applications using the CNT nanobioconjugates, for example, drug delivery systems and nanobiosensors, have been proposed by many authors. Scanning techniques such as scanning electron microscopy (SEM) and scanning probe microscopy (SPM) have advantages to characterize the CNT nanobioconjugates under various conditions, for example, isolated conjugates, conjugates in thin films, and conjugates in living cells. In this review article, almost 300 papers are categorized based on types of CNT applications, and various scanning data are introduced to illuminate merits of scanning techniques.

charged molecules and can allow sequencing (e.g. of DNA). In contrast, the binding reaction typically occurs with short, neutral polymer molecules, requires high salinity (e.g. KCl 3-4 M) and enables the high-resolution discrimination of polymer masses 1 . The aerolysin nanopore has recently been shown to strongly interact with short adenine oligonucleotides (A3-A10) and this interaction allows mass discrimination on the basis of the depth of block of ionic current induced by the binding of the analyte, 2 suggesting a binding-type interaction. Using low-noise current recording, we have indentified strong dynamics of this interaction between DC and 50 kHz and indentified short visits to deeper blocked states preceding and following the principal, mass-dependent state (pre-and post-blocks). Statistical analysis indicates that the probability of post-but not pre-blocks decreases with (1) oligomer length and (2) transmembrane voltage. We interpret this finding in terms of a combined translocation and binding interaction, probably involving several binding sites for DNA in the pore. In line with this hypothesis, longer polynucleotides (A30) showed stable and long-lasting interactions with near-complete block of current.(1) Robertson et al.

No abstract