PORTLAND, Ore. A biosensor that uses nanoshells nanoscale hollow beads may provide the long-sought technology U.S. homeland security officials have sought to sense arbitrary biotoxins.
Researchers at the University of Arizona have continued the pioneering work of a colleague to create the biosensors. Made from cell membrane material with embedded ion channels, the biosensors transduce fluorescence in the presence of nearly any agent, from biotoxins to proteins to other difficult-to-sense organics, even those inside a living cell.
Because the nanoshells are so small and can work inside a living cell without disrupting normal activities, as many as 100 can monitor as many as 100 different agents.
"Thanks to the late David O'Brien, a groundbreaking chemist here, chemically and environmentally stable self-assembling lipid-polymer nanosensors are now possible. They can be used for all kinds of biosensors, from homeland security applications like remote sensing to medical diagnosis where we put them inside living cells," said University of Arizona (Tucson) chemist Craig Aspinwall.
O'Brien pioneered the use of polymerized phospholipids. Because phospholipids are the main component of living cells, the body does not reject them as foreign matter even after they have been polymerized (structurally bonded to one another) as a sensor.
"Others use plastics to make nanometer-sized beads that are doped with chemicals that fluoresce in the presence of various molecules, but they are very limited in what they can sense, whereas our hollow spheres can safely hold anything"even toxic substances," said Aspinwall.
Nonhollow plastic beads are limited in their coatings because the coating cannot affect cellular activity. Aspinwall's nanoshells, however which are based on O'Brien's organic material keep their contents intact and separate at all times. After the nanosized sensors are used, they are flushed from the body, through normal cellular metabolism, without spilling their contents.
The hollow-sphere approach also enables proteins to be recognized, something impossible for plastic beads, Aspinwall said.
The enabling technology in these hollow, self-assembling lipid-polymer spheres can be traced to the ion channels that are mixed into the lipid polymer while it is being made. Ion channels, which allow only certain molecules to pass through the channel on their way to the inside of the sphere, act to isolate the interior of the nanosensors from their environment.
Once the agent is channeled to the inside of the nanosensor, the fluorescent marker dye is activated. (The molecular-recognition element can be used to target delivery to a specific location.) The dye can then be imaged through the skin.
In effect, the ion channels form a transducer that converts the presence of a particular molecule into a signal coming from the fluorescent marker.
"With our technology, chemists can select proteins that interact with specific ions or molecules, put them inside a nanoshell membrane, then send them inside a cell to sniff out any number of specific substances," said Aspinwall.
So far, prototypes have successfully monitored oxygen. A new version that senses glucose is in the works to help fight diabetes.
The good news for homeland security is that future security-oriented versions of the nanoshells should be able to easily detect many varieties of biotoxins that have been difficult to sense until now, Aspinwall said.
"We are opening up an entirely new world of molecules that can be sensed. Almost anything that interacts with a protein is a potential target for our nanosensor," Aspinwall said.
Nanoscale self-assembled phospholipid shells can also be exposed to chemicals, radiation, dehydration and rehydration and heat as well as long terms of storage, yet remain intact.