Convective-Diffusion-Based Fluorescence Correlation Spectroscopy for Detection of a Trace Amount of E. coli in Water

Fluorescence correlation spectroscopy (FCS) is adapted for a new procedure to detect trace amounts of Escherichia coli in water. The present concept is based on convective diffusion rather than Brownian diffusion and employs confocal microscopy as in traditional FCS. With this system it is possible to detect concentrations as small as 1.5 x 10^5 E. coli per milliliter (2.5 x 10^-16 M). This concentration corresponds to an ~1.0-nM level of Rhodamine 6G dyes. A detailed analysis of the optical system is presented, and further improvements for the procedure are discussed.