Chapter 6 Fourier Imaging Correlation Spectroscopy for Cellular Structure–Function

Abstract

Experiments that optically probe the dynamics of intracellular species, including the center-of-mass displacements and internal conformational transitions of biological macromolecules, have the potential to study mechanisms of biochemical processes in living cells. This chapter reviews Fourier imaging correlation spectroscopy (FICS), a novel phase-selective approach to fluorescence fluctuation spectroscopy that measures the collective coordinate fluctuations from a large population of fluorescent species (N approximately 10(6)). In FICS experiments, a spatially modulated optical grating excites a fluorescently labeled sample. Phase-synchronous detection of the fluorescence, with respect to the phase of the exciting optical grating, can be used to monitor the fluctuations of partially averaged spatial coordinates. From these data are constructed two-point space-time correlation functions and probability distributions. FICS achieves a unique balance between signal-to-noise and signal information content. It represents a route to elevate signal levels, while acquiring detailed information about molecular coordinate trajectories.