Several studies have been conducted to see how carbon nanotubes interact with tissues of rabbits, mice and other animals.
However, Weisman and the study's co-author Kathleen Beckingham, professor of biochemistry and cell biology, chose the fruit fly Drosophila melanogaster to attempt the first-ever detection of nanotubes inside a living animal.
"Drosophila is one of biology's pre-eminent model organisms. 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," said Beckingham.
During the study, available in the American Chemical Society's journal Nano Letters, 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 four to five days.
The study report suggests that fruit flies are ravenous eaters during this period and gain weight continuously until they are about 200 times heavier than hatchlings. They then become pupae.
As pupae, they do not eat or grow. They mature inside pupal cases and emerge as adult flies, adds the report.
"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," Beckingham said.
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, which excited a fluorescent glow from the carbon nanotubes, as they emitted near-infrared light of specific wavelengths.
The researchers say that they 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, they add.
Upon removing and examining tissues from the flies, the researchers found that 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, while lesser concentrations were found in the brain, ventral nerve cord, salivary glands, trachea and fat.
Based on their findings, the researchers reckon that only about one in 100 million nanotubes passed through the gut wall and became incorporated into the flies' organs.