Fluorescence correlation spectroscopy (FCS) is adapted for a new procedure to detect trace amounts of <i>Escherichia coli</i> 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 × 10<sup>5</sup><i>E. coli</i> per milliliter (2.5 × 10<sup>−16</sup> 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.
© 2003 Optical Society of America
(120.4570) Instrumentation, measurement, and metrology : Optical design of instruments
(170.6280) Medical optics and biotechnology : Spectroscopy, fluorescence and luminescence
(260.2510) Physical optics : Fluorescence
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence
De-Kui Qing, M. Pinar Mengüç, Fred A. Payne, and Mary-Grace C. Danao, "Convective-Diffusion-Based Fluorescence Correlation Spectroscopy for Detection of a Trace Amount of E. coli in Water," Appl. Opt. 42, 2987-2994 (2003)