( shown promise in such wide-ranging appl...)Nano-Probes Allow an Inside Look at Cell Nuclei

shown promise in such wide-ranging applications as solar cells, computer design, and biology. In 1998, for example, Alivisatos developed a way to fashion inorganic nanocrystals composed of cadmium selenide and cadmium sulfide into fluorescent probes suitable for the study of living cells. This technology has been licensed to the Hayward, California-based Quantum Dot Corporation for use in biological assays.

More recently, Chen and Gerion wondered if they could get even closer to the genetic action by transporting quantum dots inside cell nuclei.

"We took the tool Paul developed and applied it to a problem faced by biologists every day ?getting inside the nucleus, a desirable target because the cell's genetic information resides there," says Chen.

First, they had to breach the nuclear membrane, which has pores that are only about 20 nanometers wide. To fit through these tiny slits, Chen and Gerion used an especially compact cadmium selenide/zinc sulfide quantum dot coated with silica. Next, they stole a trick from a virus's playbook to smuggle this nanocrystal past the highly selective membrane that guards the entrance into the nucleus. In nature, a virus called SV40 is coated with a protein that binds to a cell's nuclear trafficking mechanism, a ploy that gives the virus an unhindered ride inside the nucleus. Chen and Gerion obtained a portion of this protein and attached it to the quantum dot. The result is a hybrid quantum dot, part biological molecule and part nano-sized semiconductor, that is small enough to slide through the nuclear membrane's pores and believable enough to slip past the membrane's barriers.

"We knew we could get quantum dots inside a cell, but getting them through the nuclear membrane is very difficult," says Chen. "So we learned from the virus."

So far, Chen and Gerion have been able to introduce and retain quantum dots in the nuclei of living cells for up to a week without harming the cell. In addition
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Source:Lawrence Berkeley National Laboratory

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