When exposed to light, each kind of dye fluoresces a different range of colors, or wavelengths. However, dye molecules by their very nature are broadband. Since molecules can rotate and vibrate in many different ways, they emit a wide range of colors that often overlap with those of other dyes.

In turn, the overlap means that one DNA base will sometimes be mistaken for another when DNA sequences are read.

To address this problem, Marquette University researchers Troy Alexander and Chieu Tran designed a special pair of dyes whose colors do not overlap.

One of the dyes exhibits two-photon fluorescence: it must be excited by two photons before it releases a photon. The other exhibits ordinary one-photon fluorescence, which emits a much different, higher-wavelength set of colors than the other dye.

Tran believes it will be possible to design four dyes for DNA sequencing, in which two dyes exhibit one-photon fluorescence and the other two exhibit two-photon fluorescence.

Generating two-photon fluorescence traditionally requires expensive high-powered lasers that deliver continuous bursts of light, but Tran says that a new generation of pulsed lasers delivers peak powers that would produce two-photon fluorescence less expensively.

In other efforts to bring this technique closer to real-world sequencing applications, the Marquette team is also simplifying their system for detecting one- and two-photon fluorescence signals simultaneously. (Alexander and Tran, Applied Optics, April 20; text at this URL.)

[Contact: Chieu Tran]

08-May-2002