'U' scientists invent smallest bio-sensors for cell research

Flooding cells with toxic dyes and probing them with fiberoptic cables are not particularly safe ways to study their biochemistry.

A team of University researchers has come up with a gentler approach to study the minute changes that take place inside living cells - shooting them full of PEBBLEs, or probes encapsulated by biolistic embedding.

PEBBLEs, the smallest bio-sensors ever developed, will allow scientists to view the real-time chemical processes occurring inside a living cell.

The team's results were presented in early March at PITTCON '98, the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, and the University has applied to patent PEBBLE technology.

"PEBBLEs are much smaller than any previous biosensor," said chemistry, physics and applied physics Prof. Raoul Kopelman. "They can be put inside a cell without hurting it and without changing what's going on."

PEBBLEs were initially developed to provide information on cells exposed to neurotoxins - biological warfare agents. The research team was funded by the U.S. Defense Advanced Research Projects Agency to help develop antidotes for these agents.

But potential applications of PEBBLEs extend far beyond biological warfare testing, including cancer therapy and drug and chemical toxicity testing.

Rackham student Murphy Brasuel, a member of the research team, said he hopes PEBBLEs will not only help with toxicity testing, but will uncover new information about cell biology "to get a better understanding of locales - not only what's happening, but where it's happening."

Researchers use one of two methods to fire PEBBLEs into cells, including pico-injection and the gene gun, "which is used to put DNA into cells," said Rackham student Karen Clark, who is also involved in the project.

Although it may seem that this method could damage the cells, PEBBLEs blast harmlessly through the cell membrane because of their tiny size and then lodge in the cytoplasm of a cell.

The researchers found the mortality rates of cells shot with PEBBLEs were only slightly higher than control cells.

Once they are in the cell, PEBBLEs can detect both slight changes in cell acidity and the concentrations of oxygen, potassium and chloride ions.

"These types of ions are a good indicator of stresses in a cell," Brasuel said.

Each PEBBLE contains a dye that glows when exposed to a certain target substance. The strength of the glow indicates the concentration of the target substance. Although these target-specific dyes are harmful to the cells, "the PEBBLE has a polymer coating that protects the cell," Clark said.

Brasuel said the isolation of the dye from the cell is a key step in the PEBBLE's inability to harm the cell.

"We don't expose the cell to the dye because it's contained within the polymer matrix," Brasuel said.

03-26-98