Biomedical subjects

Robert S McLean

Publications and source records attributed to Robert S McLean.

4 recordsLinked to original sources

PubMed2006

Racemic single-walled carbon nanotubes exhibit circular dichroism when wrapped with DNA.

We have found that racemic mixtures of chiral single-walled nanotubes (SWNTs) wrapped with d(GT)20 DNA oligomer exhibit circular dichroism (CD). We attribute the CD signal to induced CD arising from the coupling of transition moments of the SWNTs and the DNA. Although the nanotube mixture appears to contain both enantiomers in equal amounts, DNA-SWNT transition moment interaction is more constructive for one SWNT enantiomer over the other, resulting in an overall CD signal.

Circular Dichroism↗

PubMed2006

Controlled two-dimensional pattern of spontaneously aligned carbon nanotubes.

We report a simple solution process to form controlled patterns of aligned single-walled carbon nanotubes on solid substrates. The essential step of the process is to deposit a dilute solution of DNA-wrapped carbon nanotubes (DNA-CNTs) on a SiO(2) surface covered with a thin hydrophobic layer. This leads to deposition of fully aligned CNTs. The alignment pattern can be controlled by metal electrodes in the deposition region and can be quantitatively modeled by the behavior of a quasi-two-dimensional DNA-CNT nematic phase near the solution/SiO(2) interface. These results point to the possibility of rational design and economical fabrication of CNT alignment patterns on solid substrates.

Crystallization↗

PubMed2003

Structure-based carbon nanotube sorting by sequence-dependent DNA assembly.

Wrapping of carbon nanotubes (CNTs) by single-stranded DNA (ssDNA) was found to be sequence-dependent. A systematic search of the ssDNA library selected a sequence d(GT)n, n = 10 to 45 that self-assembles into a helical structure around individual nanotubes in such a way that the electrostatics of the DNA-CNT hybrid depends on tube diameter and electronic properties, enabling nanotube separation by anion exchange chromatography. Optical absorption and Raman spectroscopy show that early fractions are enriched in the smaller diameter and metallic tubes, whereas late fractions are enriched in the larger diameter and semiconducting tubes.

Anions↗

PubMed2003

DNA-assisted dispersion and separation of carbon nanotubes.

Carbon nanotubes are man-made one-dimensional carbon crystals with different diameters and chiralities. Owing to their superb mechanical and electrical properties, many potential applications have been proposed for them. However, polydispersity and poor solubility in both aqueous and non-aqueous solution impose a considerable challenge for their separation and assembly, which is required for many applications. Here we report our finding of DNA-assisted dispersion and separation of carbon nanotubes. Bundled single-walled carbon nanotubes are effectively dispersed in water by their sonication in the presence of single-stranded DNA (ssDNA). Optical absorption and fluorescence spectroscopy and atomic force microscopy measurements provide evidence for individually dispersed carbon nanotubes. Molecular modelling suggests that ssDNA can bind to carbon nanotubes through pi-stacking, resulting in helical wrapping to the surface. The binding free energy of ssDNA to carbon nanotubes rivals that of two nanotubes for each other. We also demonstrate that DNA-coated carbon nanotubes can be separated into fractions with different electronic structures by ion-exchange chromatography. This finding links one of the central molecules in biology to a technologically very important nanomaterial, and opens the door to carbon-nanotube-based applications in biotechnology.

Biotechnology↗