Simple route for the detection of Escherichia coli using quantum dots

We have demonstrated a simple route for the detection of Escherichia coli using well plates with quantum dot (QD) fluorescent labels. The genetically engineered E. coli strain DH5 alpha, containing green fluorescent protein (GFP), was used as the model system. Two approaches were employed in the detection of E. coll. In the first method, E. coli were specifically adhered onto a streptavidin-coated 96 well plate using biotin-labeled antibodies. In the second approach, E. coli were nonspecifically adsorbed onto the surfaces of 96 well plates without the use of antibodies. Whereas the fluorescence signal from GFP was not correlated with the number of E. coli cells, a linear titer dependence was found from the QD-labeled E. coll. The linear dependence of the antibody-immobilized E. coli persisted up to high ( > 10(6) cfu/mL) concentrations of E. coll. However, an exponential increase in the fluorescence intensity was found due to nonspecifically bound E. coli, and the signal intensity was much higher than that of antibody-immobilized E. coll.