Filming nanotubes inside living animals
A team of researchers at Rice University has filmed carbon nanotubes inside living animals. They've used a custom-built microscope and a technique called near-infrared fluorescent imaging to detect DNA-sized nanotubes inside living fruit flies. But more importantly, they've compared a group of fruit fly larvae fed with a yeast paste that contained carbon nanotubes with a control group fed normally. And they found no significant differences between the two groups. Does this mean that nanoparticles are innocuous, especially for humans? Only time will tell.
This research project has been led by Bruce Weisman, professor of chemistry, and Kathleen Beckingham, professor of biochemistry and cell biology. You can see above one image showing one of the results of this project, the fluorescent glow of carbon nanotubes in live fruit fly (Credit: Rice University). This image is a screen capture extracted from a a 3-second video posted on YouTube by the research team.
How did the researchers conduct their experiments? "In the study, fruit fly larvae were raised on a yeast paste that contained carbon nanotubes. The flies were fed this food from the time they hatched throughout their initial feeding phase of 4-5 days. Fruit flies are ravenous eaters during this period and gain weight continuously until they are about 200 times heavier than hatchlings. Then they become pupae. As pupae, they do not eat or grow. They mature inside pupal cases and emerge as adult flies."
And here is how Beckingham commented the results. "Developmentally, the first few days of a fruit fly's life are critical. We provided larval flies with a steady diet of food that contained carbon nanotubes and checked their weight just after they emerged from their pupal cases. We found no significant differences in the adult weight of nanotube-fed flies when compared to control groups that were not fed carbon nanotubes." The nanotube-fed larvae also survived to adulthood just as well as the control group.
Now, how did they visualize the results? "Using a custom-built microscope, the team aimed a red laser beam into the fruit flies. This excited a fluorescent glow from the carbon nanotubes, as they emitted near-infrared light of specific wavelengths. The researchers were able to use a special camera to view the glowing nanotubes inside living flies. Videos constructed from these images clearly showed peristaltic movements in the digestive system."
The major result of this experiment is that carbon nanotubes don't stay inside the fruit flies. "The team estimates that only about one in 100 million nanotubes passed through the gut wall and became incorporated into the flies' organs."
This research work has been published in Nano Letters under the name "Single-Walled Carbon Nanotubes in the Intact Organism: Near-IR Imaging and Biocompatibility Studies in Drosophila" (Volume 7, Number 9, Pages 2650-2654, September 2007). Here is the abstract. "The ability of near-infrared fluorescence imaging to detect single-walled carbon nanotubes (SWNTs) in organisms and biological tissues has been explored using Drosophila melanogaster (fruit flies). Drosophila larvae were raised on food containing ~10 ppm of disaggregated SWNTs. Their viability and growth were not reduced by nanotube ingestion. Near-IR nanotube fluorescence was imaged from intact living larvae, and individual nanotubes in dissected tissue specimens were imaged, structurally identified, and counted to estimate a biodistribution."
Sources: Rice University news release, via EurekAlert!, September 24, 2007; and various websites
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