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Newswise If seeing is believing, C.K. Choi has a passion for clarityin a very tiny world. The assistant professor of mechanical engineering's research lies at the micro-scale, in channels no thicker than a strand of hair.

Chois first visualization breakthrough came more than 10 years ago when his team, for the first time in the world, used a confocal microscope to observe velocity fields in a micro-channel, in a space with a diameter smaller than a pin.

His next pioneering move was an innovative use of a technology Choi describes as beautiful, the Total Internal Reflection Fluorescence Microscope. He integrated this system with other optical devices to help researchers literally see in the dark, creating fluorescent images clear enough to examine nanoparticles and proteins near the surface.

Choi sought practical applications for his optical devices and found them in biomedical engineering. Researchers were using electrical measurements to analyze physiological changes of cells inside blood vessels, but needed an optical way to verify the data. He proposed using indium tin oxide (ITO), a common coating used in modern electronics. His hunch worked: the ITO biosensor offered the perfect marriage of optical transparency and electrical conductivity, allowing both electrical measurements and visual observation simultaneously.

The ITO biosensor led to other inter-disciplinary workand a lot more questions. In the human body, cells are subjected to different environments: lung cells to the flow of oxygen, heart cells to pulses of blood, brain cells to electrical charges, etc. Given these radically different environments, Choi asked himself, If I grow cells outside their normal living conditions, will they really be the same type of cells? If companies test their drugs on cells grown here [in the static environment of the lab], will their results be accurate?

He knew that he couldnt mimic all the bodys natural conditions, but he could at least create a device that allowed medical researchers to examine their cell lines under appropriate flow conditions.

Actually very low flow conditions, as is the case with lung cells. In his search for a device that could create ultra-low flows, Choi realized that neither direct current (DC) nor syringe pumps could be used: most mechanical pumps cannot produce consistent flow in micro-channels, and DC can physiologically affect the cells being studied. Exposure to DC can alter the metabolism and nutrients, especially problematic for stem cells which are highly sensitive to environmental changes.

Choi and his collaborators proposed using diodes, which are cheap, reliable components, to drive the current in their electro-osmosis diode pumping device (EOS). It worked. The EOS creates low, consistent flows in a way that does not affect cell growth and contains optical elements to visually track the fluorescent particles.

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Seeing Is Believing