Jan. 19, 2007 — Einstein's explanation of why tea leaves accumulate at the bottom of a stirred cup is inspiring scientists who are working on a new type of medical test kit.
Dr Leslie Yeo and his team at Australia's Monash University are developing a credit-card-sized diagnostic blood test. They're basing their design on a technique that spins the cells out of a tiny drop of blood, an essential step in many routine medical tests.
The technique is described in the latest issue of the journal Biomicrofluidics.
Yeo made the key step in his research by accident a couple of years ago, while working at the University of Notre Dame in Indiana. He was using electric fields to spray tiny drops of liquid from the tip of a needle when one drop went astray, short-circuiting the machinery.
After he turned the machine back on, he noticed that small flecks of solid material in that rogue drop were spinning around, a bit like leaves in a stirred teacup.
A little investigation revealed that the voltage across the needle was creating a wind of charged particles that was blowing at an angle across the surface of the liquid and stirring it.
Yeo studied this chance event further in cylindrical containers just 5 millimeters (0.2 inches) across. He soon found that microscopic particles in the liquid were accumulating in the center of the bottom of the cup.
"To begin with this baffled me," he said, "because I had expected the particles to spin outwards, in the same way that you're pushed toward a car door as you go around a corner."
The researcher's curiosity eventually led him to a paper Einstein published in 1926, which explains the paradox using the example of a cup of tea.
Einstein illustrated the 'tea leaf paradox' by showing that friction at the bottom of a cup suppresses that outward force and causes an opposing force that pushes the tea leaves toward the center.
Yeo says this principle could be used to spin cells out of a blood sample, allowing doctors to do blood tests without sending samples to a laboratory.
"The idea is that if you wanted to make a diagnostic kit on a credit card sized device, this would allow you to do it," he said.
Yeo says these devices could be produced cheaply with current manufacturing techniques, for less than a dollar per chip.
"We've tried it and the principle seems to work," he said. "Now we're working on making a model using similar methods as are used to make computer chips."
But other components still need to be brought together first, to extract and pump the blood and then analyze the samples once they've been separated. Yeo estimates that could take five to 10 years.
