"Research related to carbon nanotube-based devices can be benefited tremendously by simple fluorescence microscopy solutions, which can be used to visualize and manipulate carbon-nanotubes," Mihri Ozkan told nanotechweb.org. "Fluorescence microscopy is advantageous over cumbersome high-resolution electron and atomic force microscopies in terms of simplicity, cost and ability to be performed in solution state."
The team used CdSe-ZnS core-shell nanocrystals functionalized with mercaptoacetic acid to label nanotubes in a solution of the anionic surfactant sodium-dodecyl-sulphonate. The nanocrystals attached to the sidewalls of the nanotubes and the scientists believe this was due to electrostatic interaction between surfactant micelles on the carbon nanotubes and zinc ions in the shell of the nanocrystals.
The nanocrystals fluoresced, enabling imaging of the nanotubes in an optical microscope. As the nanotubes were smaller than the resolution of the optical system, their apparent widths were the same size as the resolution limit - roughly 500 nm.
"For the first time, ropes and different cluster sizes of single-walled carbon nanotubes were identified fluorescently," said Ozkan. "By virtue of the surfactant interface, the nanocrystal emission remained stable and was not quenched by pi-stacking of nanotubes."
Ozkan and colleagues believe that, as well as providing a simple and inexpensive technique for visualizing and manipulating carbon nanotubes in solution, the technique could also help scientists develop a better understanding of nanotube alignment processes.
Now the scientists plan to micromanipulate nanotubes under the fluorescence microscope and "investigate the dependence of this labelling procedure on the branching nature of ligands passivating the nanocrystals".
The researchers reported their work in Nano Letters.