Carbon nanotubes are nanometer-scale materials with important properties, but their use in nanofabrication will require further development of methods for controlled positioning at well-defined locations on surfaces. We have devised an approach for specifically localizing single-walled carbon nanotubes (SWNTs) onto 1-pyrenemethylamine (PMA)-decorated lambda-DNA molecules aligned on Si surfaces. PMA is used as a bridging compound because its amine group is attracted electrostatically to the negatively charged phosphate backbone of DNA, while the pyrenyl group in PMA interacts with SWNT surfaces through pi-stacking forces. From a total of 60 atomic force microscopy images obtained on three different substrates, we determined that 63% of SWNTs observed on the surfaces were anchored along DNA, and these nanotubes covered approximately 5% of the total DNA length. DNA-templated nanopositioning offers intriguing possibilities for the bottom-up assembly of materials at the nanometer scale.

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Single-walled carbon nanotubes (SWNTs) are aligned with controlled orientation on surfaces from a droplet of nanotube suspension under gas flow. The alignment of SWNTs on surfaces is dictated by the direction of gas flow. Orthogonally aligned arrays of SWNTs have also been fabricated in a two-step process. Studies of fluid motion within droplets in the flow cell indicate that alignment is likely due to the circulation of SWNTs in the suspension droplet. The gas flow alignment method offers a facile system for generating oriented nanotubes on surfaces, and this approach may find use in SWNT nanodevice fabrication.

We describe an active contour framework with accurate shape and size constraints on the vessel cross-sectional planes to produce the vessel segmentation. It starts with a multiscale vessel axis tracing in a 3D computed tomography (CT) data, followed by vessel boundary delineation on the cross-sectional planes derived from the extracted axis. The vessel boundary surface is deformed under constrained movements on the cross sections and is voxelized to produce the final vascular segmentation. The novelty of this paper lies in the accurate contour point detection of thin vessels based on the CT scanning model, in the efficient implementation of missing contour points in the problematic regions and in the active contour model with accurate shape and size constraints. The main advantage of our framework is that it avoids disconnected and incomplete segmentation of the vessels in the problematic regions that contain touching vessels (vessels in close proximity to each other), diseased portions (pathologic structure attached to a vessel), and thin vessels. It is particularly suitable for accurate segmentation of thin and low contrast vessels. Our method is evaluated and demonstrated on CT data sets from our partner site, and its results are compared with three related methods. Our method is also tested on two publicly available databases and its results are compared with the recently published method. The applicability of the proposed method to some challenging clinical problems, the segmentation of the vessels in the problematic regions, is demonstrated with good results on both quantitative and qualitative experimentations; our segmentation algorithm can delineate vessel boundaries that have level of variability similar to those obtained manually.

Polythiourethane is a promising heteroatom-containing polymeric material possessing outstanding properties such as high refractive index, biocompatibility, and good coordinating ability to heavy metal ions. However, examples of versatile polythiourethanes are relatively scarce as a result of the limited methods for their synthesis. Herein, we report an efficient non-isocyanate and catalyst-free strategy to synthesize polythiourethane from the highly alternating and regioselective copolymerization of carbonyl sulfide (COS) and 2-methyl aziridine. The copolymerization proceeded efficiently at room temperature and afforded copolymer in 95% selectivity and molecular weight of 15.2 kg/mol in 2 h. Furthermore, the reaction was efficient even at 1 atm of COS at room temperature. Remarkably, the copolymer possessed a cyclic topology, and it could be completely recycled into cyclic thiourethane by simply heating the bulk materials at 200 °C for 1.5 h. The copolymer was applied as a heavy metal absorption and recovery agent; lead ions in aqueous solution were adsorbed by the copolymer, and both were eventually separated and recovered in the form of lead compounds and cyclic thiourethanes, respectively. Hence, this study provides a sustainable and atom-economical method for synthesizing polythiourethane and a green method to recover hazardous metals with minimal waste and VOC emission.

Synthesis of cyclic, semicrystalline, and recyclable polythiourethanes was realized via the catalyst-free zwitterionic alternating copolymerization of N-alkyl aziridines with carbonyl sulfide (COS) under mild conditions. The copolymerization proceeded efficiently at room temperature and generated copolymers with fully alternating linkages in more than 99% selectivity in 5 min under solvent-free conditions. Notably, the copolymers are typical semicrystalline thermoplastics with melting temperatures up to 137 °C (n-butyl-substituted) or 170 °C (ethyl-substituted). The resulting polythiourethanes are predominantly cyclic as evidenced by 1H NMR and MALDI-TOF mass spectroscopies. Remarkably, the cyclic copolymers could be recycled into N-substituted cyclic thiourethanes in quantitative yield by heating at 250 °C for 2 h.

We report here a novel method to simultaneously detect CpG methylation and single nucleotide polymorphisms (SNPs) using denaturing high performance liquid chromatography (DHPLC). PCR products of bisulfite-modified CpG islands were separated using DHPLC. BstUI digestion and DNA sequencing were used in confirmation studies. Consistent with the BstUI digestion assay, the 294 bp PCR product of the modified hMLH1 promoter showed different retention times between the methylated cell lines (RKO and Cla, 6.7 min) and the unmethylated cell lines (PACM82 and MGC803, 6.2 min). No hMLH1 methylation was observed in 13 primary gastric carcinomas and their matched normal tissues. One hMLH1 SNP was detected in gastric cancer patients, in both cancer and normal tissues. DNA sequencing revealed that the SNP is a G-->A variation at -93 nt of the hMLH1 promoter. A two-peak chromatogram was also obtained in the 605 bp PCR product of the Cox-2 promoter of the AGS, HEK293 and MKN45 cell lines by DHPLC. Another peak corresponding to methylated CpG islands was observed on the chromatogram of the Cox-2-methylated AGS cell line after bisulfite treatment. In conclusion, methylation in homoallelic and heteroallelic CpG islands could be detected rapidly and reliably by bisulfite-DHPLC. A SNP in the target sequence could also be detected at the same time.

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