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.