In 2D FCS, a perturbation is introduced into the molecular system. Temporal responses of the system to the perturbation are monitored at many wavelengths and the time correlation function between wavelengths is evaluated. Based on the differences in relaxation rates of different fluorescent species, 2D FCS significantly enhances the spectral resolution and can facilitate structural and kinetic studies of individual species. The relaxation rates could be rates of translational or rotational diffusion, fluorescence decay rates, or rates of chemical reactions, depending on the nature of the external perturbation. With the enhanced spectral resolution, 2D FCS provides a method for simultaneous characterization of multiple species in environmental and biomedical samples.
Early diagnosis is the key to improved treatment of cancers.
Optical spectroscopy provides a promising alternative to histopathology, the standard method of cancer diagnosis in clinics. Optical methods are noninvasive, inexpensive, and the diagnosis can be in situ , without time delay. To be a successful technique for cancer diagnosis, an optical method is required to provide high contrast between healthy and adenomatous tissue and short measurement time. By combining both spectral and temporal information of the tissue fluorescence, 2D FCS provides a high contrast between samples, forming the basis for cancer diagnosis. Fast collection of two-dimensional fluorescence spectra of tissue is facilitated by frequency domain measurements.