Douglas Magde

Douglas Magde is a physical and analytical chemist whose research includes fluorescence and chemical kinetics. His UC San Diego profile documents studies of fluorescence lifetimes and reaction processes; an important earlier contribution was the development of fluorescence correlation spectroscopy with collaborators.^[ref]

The team's 1972 experiment measured fluorescence fluctuations in an equilibrium reacting system. Molecules moving into and out of the observed region, and changes associated with binding, alter the recorded light signal. Correlating that signal with itself at later times supplies information about molecular motion and reaction rates even when the average signal remains steady. The reported system involved DNA and a fluorescent binding molecule.^[ref]

For a toy illustration, a correlation $G(\tau )=G(0)e^{-\tau /{\tau }_c}$ falls to $G(0)/e$ at lag ${\tau }_c$. Two samples can have equal mean brightness and different ${\tau }_c$, revealing different dynamics. This exponential is an explanatory model rather than the complete fitting function for the original experiment: diffusion geometry and chemical reactions determine the appropriate autocorrelation model.