Fluorescence lifetime imaging is a useful but relatively complex technique for probing the local microenvironment of a fluorescent molecule. The method can be used to help determine biochemical makeup of body tissues or measure distances between molecules on the nanometer scale.

With a new grant of more than $675,000 from the National Science Foundation funded by the American Reinvestment and Recovery Act (ARRA), Warren Zipfel '87, Ph.D. '93, associate professor of biomedical engineering, is working to make fluorescence lifetime imaging more efficient and simpler to implement.

"I hope this will become a common mode of fluorescence imaging," Zipfel said.

The technique works by using fluorescent dyes to tag biological molecules of interest. These fluorophores absorb light from a pulsed laser, which puts them into a higher energy state, after which they emit light of a different wavelength. By measuring the "fluorescence lifetime" -- the time between the absorption of the light and the emission of the fluorescence -- scientists can gain information about the local environment the molecule resides in.

Fluorescence lifetime is commonly measured by time-correlated single photon counting (TCSPC), a method that, Zipfel says, "although is highly accurate, can be too slow for practical fluorescence imaging use."

With the new method and instrument his group is developing, Zipfel predicts that he will be able to collect images as much as 1,000 times faster than with TCSPC.

Zipfel also hopes that this new method will be useful to image the oxygen concentrations in and around tumors by using the method to image the phosphoresce lifetimes of oxygen sensitive phosphors. "Combined with confocal or multiphoton microscopy this would enable 3-D oxygen imaging in living animals -- something many researchers would find very useful," Zipfel said.

His group has already purchased a microscope and an optical bench with the new funding, and the grant will fund two of his graduate students for three years.

To date, Cornell has received 124 ARRA grants, totaling more than $99.9 million.

Graduate student Melissa Rice is a writer intern at the Cornell Chronicle.