Rapid detection of bacteria based on homogenous immunoassay using chitosan modified quantum dots

Abstract In this study, a fast and sensitive sandwich assay has been developed with the combination of immunomagnetic separation (IMS) and fluorescence techniques to enumerate Escherichia coli ( E.coli ). Iron oxide core gold shell (Fe 3 O 4 @Au) magnetic nanoparticles were prepared and modified with biotinylated antibodies specific to E.coli . Fluorescence labels have been constructed by preparing chitosan coated CdTe quantum dots (CdTe QDs) with a diameter of 3 ± 1 nm. The amounts of magnetic nanoparticles and CdTe QDs are optimized to get the best sensitivity. The calibration graph fluorescence intensity versus E.coli concentration was linear in the range of 10 2 –10 8  cfu mL −1 with a coefficient of determination (R 2 ) of 0.9905. The limit of detection (LOD) and limit of quantification (LOQ) values are calculated as 30 and 100 cfu mL −1 , respectively. Selectivity of the method is examined by applying the same procedure to bacteria, namely Enterobacter aerogenes ( E. aerogenes ), Enterobacter dissolvens ( E. dissolvens ), Staphylococcus aureus ( S. aureus ) and Pseudomonas aeruginosa ( P. aeruginosa ), and no interference has been observed. The applicability of the developed method has also been examined in spiked urine samples. As a result, it was found that, this novel method is sensitive to target E.coli and a rapid method with a total analysis time less than 120 min.