# All Science Fair Projects

## Science Fair Project Encyclopedia for Schools!

 Search    Browse    Forum  Coach    Links    Editor    Help    Tell-a-Friend    Encyclopedia    Dictionary

# Science Fair Project Encyclopedia

For information on any area of science that interests you,
enter a keyword (eg. scientific method, molecule, cloud, carbohydrate etc.).
Or else, you can start by choosing any of the categories below.

# Fluorescence lifetime imaging

Fluorescence lifetime imaging is a confocal microscopy technique for producing an image based on the differences in the exponential decay rate of the fluorescence from a fluorescent sample.

A fluorophore which is excited by a photon will drop to the ground state with a certain probability based on the decay rates through a number of different decay pathways. To observe fluorescence, one of these pathways must be by spontaneous emission of a photon. In the ensemble description, the fluorescence emitted will decay with time according to

F(t) = F0e - t / τ

where

$\frac{1}{\tau} = \sum_i k_i$.

In the above, t is time, τ is the fluorescence lifetime, F0 is the initial fluorescence at t = 0, and ki are the rates for each decay pathway, at least one of which must be the fluorescence decay rate kf.

Fluorescence lifetime imaging yields images with the intensity of each pixel determined by τ, which allows one to view contrast between materials with different fluorescence decay rates (even if those materials fluoresce at the exact same wavelength), and also produces images which show changes in other decay pathways, such as in FRET imaging.

## External References

03-10-2013 05:06:04