The prevailing conception of carbon nanotubes and particularly single-walled carbon nanotubes (SWNTs) continues to be one of perfectly crystalline wires. Here, we demonstrate a selective electrochemical method that labels point defects and makes them easily visible for quantitative analysis. High-quality SWNTs are confirmed to contain one defect per 4 mu m on average, with a distribution weighted towards areas of SWNT curvature. Although this defect density compares favourably to high-quality, silicon single-crystals, the presence of a single defect can have tremendous electronic effects in one-dimensional conductors such as SWNTs. We demonstrate a one-to-one correspondence between chemically active point defects and sites of local electronic sensitivity in SWNT circuits, confirming the expectation that individual defects may be critical to understanding and controlling variability, noise and chemical sensitivity in SWNT electronic devices. By varying the SWNT synthesis technique, we further show that the defect spacing can be varied over orders of magnitude. The ability to detect and analyze point defects, especially at very low concentrations, indicates the promise of this technique for quantitative process analysis, especially in nanoelectronics development.

Hepatoma exhibits a series of heterogeneous subpopulations in its cell surface markers, tumorigenicity, invasion and metastatic capability. We previously demonstrated that the CD133(-)/EpCAM(-) hepatoma subpopulation was more metastatic than its counterpart; however, the controlling mechanisms are unexplored. The present study aimed to delineate the significance of aberrant hedgehog (Hh) signaling in the mediation of metastases. Fluorescence-activated cell sorting-enriched CD133(-)/EpCAM(-) (double negative, DN), Huh-7 cells underwent a transwell selection for metastatic cells (transwell-selected, TS). The TS cells displayed much greater metastatic activity as evidenced by an increased invasion rate, extremely upregulated expression of matrix metalloproteinase (MMP)-1/2/9 genes compared with DN and double-positive (DP) subpopulations. In contrast to DP cells, TS cells lost E-cadherin and were all vimentin-positive as shown by immunocytochemistry. There was a transitional increase in Gli-1/2 gene expression levels from DP, DN to TS subpopulations, which was consistent with elevated Gli-1/2 or Twist-1 protein levels in the nuclear fraction. Furthermore, truncated Gli-1 (tGli-1), which transactivates molecules involved in metastasis, was detected in the highly invasive Huh-7 cell subpopulation, but not in less metastatic hepatoma cells or normal hepatocytes. The enhanced metastatic features with increased expression of MMPs as well as the presence of twist and snail genes in TS Huh-7 cells were reversed by LDE225, a potent Smoothened antagonist. In conclusion, the highly metastatic capability of a unique TS subpopulation was highly attributed to significant epithelial-mesenchymal transition, enhanced Hh activity and aberrant occurrence of a tGli-1 variant, which appears to be responsible for the highly invasive behavior.