Cross-correlated Flow Analysis in Microstructures
In most of the FCS applications, diffusion is the physical parameter usedin gaining translational information about the molecules observed. The underlyingreason for this is that a change of the diffusion constant reveals a change of the molecule size, which can be coupled to chemical reactions: therefore opening the important field of chemical kinetics measurements. In all these applications, the measurements are performed in a time-spatially isotropic environment: No information about the structure of the environment and non-diffusional transport processes is needed or being used. But especially for biotechnological applications where complete reaction cascades take place on a small chip streaked with channels and chambers, these reactions and the active transport of the react ants have to be monitored. For this, flow parameters like velocity and its direction are determined via FCS on a micrometer scale. At the same time, other parameters, like diffusion or fluorescent intensity can be measured. The ability to measure flow is greatly enhanced by the so-called “two-beam FCS” where the fluorescent signals generated by two separated foci are being cross-correlated. In the following, the theory of two-beam FCS is outlined, and a typical setup and microchannel measurements are described. Finally, possible applications of the FCS and single molecule detection in microstructures will be given.
KeywordsVolume Element Focal Spot Fluorescence Correlation Spectroscopy Single Molecule Detection Fluctuation Function
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