"Drosophila is one of biology's preeminent model organisms," said
Beckingham. "We have a wealth of knowledge about the genetic and
biochemical workings of fruit flies, and this presents us with unique
opportunities to explore the effects and fate of single-walled carbon
nanotubes in a living organism."
Weisman and Beckingham's research, which is available online, appeared
in the September issue of Nano Letters, the American Chemical
Society's journal.
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.
"Developmentally, the first few days of a fruit fly's life are
critical," Beckingham said. "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.
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.
When the researchers removed and examined tissues from the flies, they
found the near-infrared microscope allowed them to see and identify
individual nanotubes inside the tissue specimens. The highest
concentration of nanotubes was found in the dorsal vessel, which is
analogous to a main blood vessel in a mammal. Lesser concentrations
were found in the brain, ventral nerve cord, salivary glands, trachea
and fat. Based on their assays, the team estimates that only about one
in 100 million nanotubes passed through the gut wall and became
incorporated into the flies' organs.
The research was sponsored by the National Science Foundation, Rice
University's Center for Biological and Environmental Nanotechnology,
the Alliance for NanoHealth and the Welch Foundation.
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