RESEARCHERS DEVISE NANO-SCALE METHOD FOR INVESTIGATING LIVING SYSTEMS

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RESEARCHERS DEVISE NANO-SCALE METHOD FOR INVESTIGATING LIVING SYSTEMS
28 April 2002 - University of Wisconsin-Madison

By observing how tiny specks of crystal move through the layers of a biological membrane, a team of electrical and computer engineers and biologists has devised a new method for investigating living systems on the molecular level.

The discovery could lead to an entirely new level of manipulation, imaging and understanding of the inner workings of cells, according to the University of Wisconsin-Madison team led by electrical and computer engineers Dan van der Weide and Robert Blick. The work was recently published in the journal Applied Physics Letters.

The specks are known as quantum dots or inorganic semiconductor nanocrystals. Measuring in millionths of a millimeter, these dots are so small that the addition or removal of electrons changes the properties of the dot. The team, which also includes researchers Sujatha Ramachandran and George Kumar, found that by applying voltages to a solution of quantum dots and membranes similar to those of living cells, the dots would be pressed into the membranes. The dots formed rings, which in turn acted as portals in the membranes. These artificial portals or pores could enable a method of investigating living systems by means of semiconductor technology that until now could be theorized but not directly observed.

"To get a feeling of why this is important, you have to understand that each of our cell membranes has specific pores in them that regulate the flow of ions in and out," says Blick. "Through these ions, your cells will build up electric potential and communicate with other cells. This is how signal transduction is performed in your body, but it is also how chemicals react with your body. When, for example, caffeine enters a cell it stimulates the opening and closing of these ion channels. What we've found is that these quantum dots can form artificial pores that enhance the flow of ions and which we can control from the outside via voltage."

Quantum dots can be encoded with different colors, making them useful as fluorescent labels for staining cells. Their resistance to photobleaching and physical size of less than 10 nanometers are making them increasingly popular in biomedical applications ranging from intracellular tagging of molecules to applications such as tracking devices for neuronal receptors and as interfaces between nerve cells. Researchers have labeled the dots with isotopes, injected them into mice and then tracked them with tomography.

The Wisconsin engineering team set out to use optical tagging or labeling of membrane pores in order to visualize their function and simultaneously measure their current/voltage relationship.

"What we found was that quantum dots formed their own pores, which in the long run could mean that we could combine optical activity and readout with direct-current recording of cellular activity," says Blick.

Because these artificial pores elicit bursts of current in the artificial membranes, the team believes quantum dots could perform similarly in other excitable cells such as neurons and muscles, and looks forward to understanding how the dots behave in vivo in excitable cells. The researchers will look next into properties that cause the artificial pores to open and close.

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About: University of Wisconsin-Madison
In achievement and prestige, the University of Wisconsin-Madison has long been recognized as one of America’s great universities. A public, land-grant institution, UW-Madison offers a complete spectrum of liberal arts studies, professional programs and student activities. Many of its programs are hailed as world leaders in instruction, research and public service.

The university traces its roots to a clause in the Wisconsin Constitution, which decreed that the state should have a prominent public university. In 1848, Nelson Dewey, Wisconsin’s first governor, signed the act that formally created the university, and its first class, with 17 students, met in a Madison school building on February 5, 1849.

From those humble beginnings, the university has grown into a large, diverse community, with about 40,000 students enrolled each year. These students represent every state in the nation, as well as countries from around the globe, making for a truly international population.

UW-Madison is the oldest and largest campus in the University of Wisconsin System, a statewide network of 13 comprehensive universities, 13 freshman-sophomore transfer colleges and an extension service. One of two doctorate-granting universities in the system, UW-Madison’s specific mission is to provide "a learning environment in which faculty, staff and students can discover, examine critically, preserve and transmit the knowledge, wisdom and values that will help insure the survival of this and future generations and improve the quality of life for all."

The university achieves these ends through innovative programs of research, teaching and public service. Throughout its history, UW-Madison has sought to bring the power of learning into the daily lives of its students through innovations such as residential learning communities and service-learning opportunities. Students also participate freely in research, which has led to life-improving inventions from more fuel-efficient engines to cutting-edge genetic therapies.

Students, faculty and staff are motivated by a tradition known as the "Wisconsin Idea," described by UW President Charles Van Hise in 1904 as the compelling need to carry "the beneficent influence of the university ... to every home in the state." The Wisconsin Idea permeates the university’s work and helps forge close working relationships among university faculty and students and the state’s industries and government.

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