Colistin-functionalised CdSe/ZnS quantum dots as fluorescent probe for the rapid detection of Escherichia coli

Intensely fluorescent, colistin-functionalised CdSe/ZnS QDs (Colis–QDs) nanoparticles, are synthesized and used as sensitive probes for the detection of Escherichia coli, a Gram-negative bacteria. Colistin molecules are attached to the terminal carboxyl of the mercaptoacetic acid-capped QDs in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) as amide bond promoters. The TEM analysis of bacteria treated with Colis–QDs conjugates showed the accumulation of Colis–QDs in the cell wall of E. coli. Under the recommended working conditions, the method provides a detection limit as few as 28 E. coli cells per mL, which is competitive which more elaborate detection systems. The simplicity of the method together with short analysis time (<15 min, without including preparation and photoactivation of the Colis–QDs conjugate) make the proposed approach useful as quick bacteria screening system.