By Roland Piquepaille
Researchers from the Lawrence Berkeley National Laboratory (LBL) have developed fluorescent and stable nano-probes which can stay inside a cell's nucleus for hours or even days. According to this LBL news release, this will help biologists to better understand nuclear processes that evolve slowly, such as DNA replication, genomic alterations, and cell cycle control. This research was partially based on previous investigations about quantum dots. Now, the researchers want to tailor their quantum dots, which emit different colors depending on their sizes, to check specific chemical reactions inside nuclei, such as how proteins help repair DNA after irradiation. Read more...Here is a short description of what the researchers achieved.
"Our work represents the first time a biologist can image long-term phenomena within the nuclei of living cells," says Fanqing Chen of Berkeley Lab's Life Sciences Division, who developed the technique with Daniele Gerion of Lawrence Livermore National Laboratory.
Their success lies in specially prepared crystalline semiconductors composed of a few hundred or thousand atoms that emit different colors of light when illuminated by a laser. Because these fluorescent probes are stable and nontoxic, they have the ability to remain in a cell's nucleus -- without harming the cell or fading out -- much longer than conventional fluorescent labels.
This could give biologists a ringside seat to nuclear processes that span several hours or days, such as DNA replication, genomic alterations, and cell cycle control. The long-lived probes may also allow researchers to track the effectiveness of disease-fighting drugs that target these processes.
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On this image showing how a nano-sized probe is entering a cell's nucleus, "a large aggregate of immobile dots is indicated with the red arrow, while the circled stars and arrows indicate dots that move." (Credit: LBL) |
The two researchers closely collaborated with Paul Alivisatos, director of the Materials Sciences Division at LBNL, who's working on quantum dots for several years now. Here are two links to previous entries about Alivisatos research, "Nano Tetrapods With Tunable 'Legs'," and "Nanotech solar cells: Portable Plastic Power."
So, Chen and Gerion thought it was possible to introduce these quantum dots inside a cell's nucleus. And they did it.
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.
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.
And what are they working on now?
In the future, they hope to tailor quantum dots to track specific chemical reactions inside nuclei, such as how proteins help repair DNA after irradiation.
They also hope to target other cellular organelles besides the nucleus, such as mitochondria and Golgi bodies. And because quantum dots emit different colors of light based on their size, they can be used to observe the transfer of material between cells.
However, with their current nano-probes, they're already able to know if "a drug has arrived where it is supposed to, and if it is having the desired impact."
The research work has been published by Nano Letters on September 9, 2004 (Volume 4, Issue 10, Pages 1827 -1832). Here is a link to the abstract of this paper named "Fluorescent CdSe/ZnS Nanocrystal-Peptide Conjugates for Long-term, Nontoxic Imaging and Nuclear Targeting in Living Cells."
Sources: Lawrence Berkeley National Laboratory news release, March 18, 2005; and various websites
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