Device That Is Ready for Slime Time

Would you drop your computer into a bucket of saltwater and slime?

The corrosive effects of such a mixture would make your prized bit of electronics decline in value even faster than it did when you walked out the store with it safely tucked in your arms.

That’s a pity, because the best way to analyze some materials and processes in saltwater marshes, and even in deep ocean trenches, is through electronics.

If somebody could just figure out how to build a microelectronic device that would separate and measure components in salty gunk without becoming destroyed, it could open vast new windows on everything from corrosion of offshore oil rigs to fouling on boat hulls to how chemical and biological processes modify the world hidden by the sea.

Enter George W. Luther III, an oceanographer with the University of Delaware.

Luther (https://www.luther@udel.edu) and some of his colleagues have created a tiny microelectrode that is about the size of a human hair, thus enabling them to analyze mud and slime on a near-microscopic level.

Nobody had ever done it before, Luther says, because “no one was dumb enough to stick these things in the mud.”

For years scientists have used small collecting devices, covered with a membrane, to suck sediments and chemicals out of the muck for examination. But a different device had to be used for each type of sediment. Luther recognized that it would be far more useful if several elements could be studied simultaneously in their natural setting because that would shed light on various interactions.

He believed that could best be done through electronics.

Luther and a graduate student, Paul Brendel, built a tiny electrode by pouring a dab of gold into a small glass tube and sealing the end. The sensor’s tip is only 25 microns wide, about the size of a human hair.

When the probe is inserted into mud or slime, it detects various voltages, Luther says. He was interested in studying five chemicals that play a crucial role in organic decay--oxygen, iron, manganese, hydrogen sulfide and iodide.

“If something is present, we get an [electric] current,” he says. “And that current is directly proportional to the concentration. And each species occurs at a specific voltage, so we can distinguish oxygen from iron and so forth.

“So with one electrode, we can get measurements of at least five major species that we want to look at.”

And just as important, the device is so small that it can detect millions of variations within a small sample. It is portable and could be embedded in deep-sea sediments by robotic submersibles, Luther says.

News of Luther’s work, sponsored by the Sea Grant College Program, has spread like wildfire through the oceanographic community. Scientists from all over the world have visited his lab.

Robert C. Aller, professor of marine sciences at the State University of New York at Stony Brook, who has reviewed Luther’s work, believes the electrode is a very useful tool.

The ability to simultaneously examine a variety of biological and chemical elements in ocean sediments “represents a significant analytical advance,” Aller says.

The device has already produced some surprises.

Scientists thought, for example, that sea-floor sediments would be clearly stratified.

“At one layer, you would expect to find oxygen, and manganese at the next layer, and then iron, and so forth,” Luther says. “It should be distributed nice and neatly.”

But when the probe was inserted, Luther found a much higher level of mixing than had been expected.

So he began looking at tiny worm burrows in the mud.

“And you find, jeez, on one side I see oxygen, and on the other I don’t,” Luther says. “The organisms that are living in the sediment are actually modifying the chemistry for their purposes.

“In a worm burrow, the worm is not just going to be living there. He’s going to be moving in and out. We can actually see that every time he made a move, the oxygen concentration would increase.”

The probe allowed Luther “to see how organisms affect their own environment,” a crucial element in chemical decomposition.

He sees that as a possible aid in the effort to develop microorganisms that can be used to degrade contaminants, such as oil, in polluted areas.

“We can actually follow the changes, the rate of decomposition,” he says. The next step is to analyze “biofilms,” the thin layers of slime that form on such things as boat hulls. The probe is so small that it can isolate the components of these very shallow films.

Perhaps some day, Luther says, it may help folks find out how to keep that stuff off the family canoe.

*

Lee Dye can be reached via e-mail at leedye@compuserve.com