Mannose-coated CdS quantum dots (Man-QDs) were prepared in a facile aqueous, one-pot process that exploits the self-assembly of thiolated mannose in the presence of CdS under reducing conditions. The resulting not, vert, similar15 nm diameter nanoparticles produce an intense, broad luminescence emission centred at 550 nm. These Man-QDs induce luminescent aggregates of Escherichia coli which can be used to detect bacteria in cell suspensions containing as few as 104 E. coli per mL. The aggregation process is dependent on the E. coli cell surface FimH mannose-specific lectin. The recognition and subsequent detection of the E. coli using the Man-QD has been shown to be specific as aggregation does not occur either with an E. coli strain defective in the FimH lectin or with galactose-coated QDs.