Immunomagnetic separation was coupled with quantum dot (QD) labeling for the rapid, selective and sensitive detection of Escherichia coli in water samples. The target bacteria were recovered from the solution by antibody-coated paramagnetic beads, and sandwich complexes were formed by using secondary antibodies labeled with QDs. The fluorescence intensities, as a result of the capturing of different concentrations of bacteria, were measured, and a linear correlation (R-2 = 0.976) was obtained between log E. coli concentration (x) and the intensity (y) with a regression model of y = 26.9x + 41.1 in a working range of 8.9 x 10(1) and 1.9 x 10(6) cfu/mL. The selectivity of the developed sensor was examined with Enterobacter aerogenes and Enterobacter dissolvens, which did not produce any significant response. The ability of the immunoassay to detect E. coli in real water samples was investigated and the results were compared with the experimental results from plate-counting methods. A good agreement was observed between the QD-enhanced detection and plate counting.