A sensitive immunoassay for simultaneous detection of foodborne pathogens using MnO nanoflowers-assisted loading and release of quantum dots.

In this study, a sensitive immunoassay using immunomagnetic nanobeads (MNBs), manganese dioxide nanoflowers (MnO NFs) and quantum dots (QDs) was developed for simultaneous detection of E. coli O157: H7 and Salmonella typhimurium. MnO NFs were synthesized, functionalized and incubated with QDs to obtain QDs@MnO nanocomposites, followed by modification with antibodies (pAbs) to obtain pAb-QDs@MnO nanocomposites (QM NCs). Target bacteria were first conjugated with MNBs and QM NCs to form MNB-bacteria-QM complexes. Then, QDs were quickly released from the complexes using glutathione to reduce MnO to Mn. Finally, fluorescent intensity at characteristic wavelength was measured by optical detector to determine target bacteria. This immunoassay could simultaneously and quantitatively detect E. coli from 1.5 × 10 to 1.5 × 10 CFU/mL with detection limit of 15 CFU/mL and Salmonella from 4.0 × 10 to 4.0 × 10 CFU/mL with detection limit of 40 CFU/mL in 2 h. The mean recovery for both bacteria in spiked chicken samples was ∼96%.