Portland, Ore. Experiments in the International Space Station will soon determine whether a new biosensor that uses living cells encased in a self-assembling inorganic nanocrystal can withstand the vacuum and hard radiation of space. If successful, the experiment could yield ultrasensitive biosensors as well as a new surface treatment that repels bacteria for surgical tools like catheters. It could also serve as a test bed for medical researchers trying to understand how some bacteria, such as tuberculosis, can survive long periods of dormancy within the human body.
"We have genetically engineered simple living cells, such as yeast, so that it glows fluorescent green when it encounters a harmful chemical or biotoxin," said Helen Baca, a consultant at Sandia National Laboratories. Baca performed the work for her PhD in chemical engineering at the University of New Mexico. "At Sandia, we encapsulated the living cells in nanocrystals and tested them as a biosensor."
Sandia had previously reported that it could direct the self-assembly of nanocrystals into thin films. By controlling the structure of the nanocrystals so that they self-organize to encapsulate the living cells, the researchers were able to seal them in a controlled environment that preserved their health while enabling them to work as biosensors.
"We already knew how to self-assemble the nanocrystals," said Jeff Brinker, who is both a Sandia National Laboratories fellow and an engineering professor at the University of New Mexico. "By mixing the living cells with our nanocrystals in solution, we were able to get them to form around the living cells to preserve them indefinitely."
The cells were mixed with a solution of silica and phospholipids two-sided molecules that make up cell membranes. This slurry was then spin-coated on an insulating substrate and allowed to self-assemble into a network of nanoscale compartments that encased the living cells with the aqueous solution that keeps them alive.
"We have shown that the cells can live and function as biosensors for months, which we think we can extend much further as we learn more about the process," said Baca.
The environment inside the encapsulated living cells was watertight even when they were studied in a vacuum, leading the researchers to the experiment in the International Space Station. It will gauge how hardy their encapsulation will be in protecting the cells from hard radiation, cold and the vacuum of space. If they pass the test, and are found to be alive and still functioning as a biosensor when the experiment is returned to Earth on the next shuttle mission, then the researchers expect to develop applications for the biosensor. For instance, the Defense Department is looking for a biosensor that can be carried by insects onto the battlefield.
Then, said Brinker, the "fluorescent markers [on the insects] could be read from unmanned aircraft."
R. Colin Johnson