Nanotubes looking for corkscrews

Many researchers around the world are looking at nanotubes as vehicles to deliver drugs to very precise locations such as individual cancerous cells. Researchers at the University of Florida have found an elegant way to 'cork' these nanotubes. But a problem remains: how do you uncork these millions of nanotubes when they reach their intended destination?

Many researchers around the world are looking at nanotubes as vehicles to deliver drugs to very precise locations such as individual cancerous cells. But these nanotubes need first to be closed in order to carry these drugs. And researchers at the University of Florida have found an elegant way to 'cork' these nanotubes. The containers they've built, which have a diameter of about 80 nanometers, can contain 5 million drug molecules, meaning they can potentially become therapeutic powerful tools. But a problem remains: how do you uncork these millions of nanotubes when they reach their intended destination? Read more...

This research work has been published in the Journal of the American Chemical Society last month under the title "Corking Nano Test Tubes by Chemical Self-Assembly" (Vol. 128, No. 13, Pages 4236 - 4237, April 5, 2006). Here are two links to the abstract and to some supplementary information (PDF format, 4 pages, 1.6 MB), which includes several images. But let's start with an introduction to this drug delivery problem coming from this paper.

There is tremendous current interest in using nanoparticles to deliver biomolecules and macromolecules (e.g., drugs and DNA) to specific sites in living systems. Release of the biomedical payload from the nanoparticle can be accomplished by chemical or enzymatic degradation of the nanoparticle or of the link between the payload and the nanoparticle. We are exploring an alternative payload-release strategy that builds on our work on template-synthesized nano test tubes.
These are hollow nanotubes that are closed on one end and open on the other, and the dimensions can be controlled at will. If these nano test tubes could be filled with a payload and then the open end corked with a chemically labile cap, they might function as a universal delivery vehicle. We show here that silica nano test tubes can be covalently corked by chemical self-assembly of nanoparticles to the tubes.

You can see below "rows of tiny nano test tubes rest[ing] on a mesh in this electron microscope photo, shot in October of last year and colorized for added clarity" (Credit: University of Florida). And here is a link to a larger version.

Corked nanotubes

But how these researchers did to "cork" these nanotubes? Let's get back to the University of Florida recent news release.

The researchers applied an amino chemical group to the mouth of the tubes and an aldehyde chemical group to the corks. The two groups are complementary, so they bond with one another. Billions of nanotubes could fit on a postage stamp. So, said [University of Florida chemistry professor Charles Martin,] "we don’t put individual caps in each nanotube the way corking machines do for bottles."
Instead, the scientists immerse a small mesh that holds millions of amino-modified nanotubes, all precisely lined up in a grid pattern, into a solution imbued with millions of the corks. Brownian motion — what happens when minute particles immersed in a fluid move about randomly — takes care of the rest. The corks simply float around, then slip into the mouths of the tubes as they encounter them.

Now that the researchers have put a cork to their nano test tubes, how can they remove it when it travels inside your body and reaches its intended destination?

There’s no easy way to unlock the amino chemical group from the aldehyde chemical group. So while Martin says there are some promising possibilities, he and his colleagues have their next job cut out for them: figuring out how to uncork the tubes.

If you have an idea for solving this problem, please contact the researchers directly.

Sources: University of Florida news release, via EurekAlert!, May 10, 2006; and various web sites

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