A sensitive immunoassay for simultaneous detection of foodborne pathogens using MnO2 nanoflowers-assisted loading and release of quantum dots

• It’s the first time to combine MnO 2 NFs with QDs to amplify biological signals. • Releasing QDs from fluorescent bacteria effectively enhanced fluorescent signals. • The detection limit for E. coli and Salmonella was as low as 10 1 CFU/mL. • The mean recovery was ∼96% for E. coli and Salmonella in spiked samples. In this study, a sensitive immunoassay using immunomagnetic nanobeads (MNBs), manganese dioxide nanoflowers (MnO 2 NFs) and quantum dots (QDs) was developed for simultaneous detection of E. coli O157: H7 and Salmonella typhimurium. MnO 2 NFs were synthesized, functionalized and incubated with QDs to obtain QDs@MnO 2 nanocomposites, followed by modification with antibodies (pAbs) to obtain pAb-QDs@MnO 2 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 2 to Mn 2+ . 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 1 to 1.5 × 10 6 CFU/mL with detection limit of 15 CFU/mL and Salmonella from 4.0 × 10 1 to 4.0 × 10 6 CFU/mL with detection limit of 40 CFU/mL in 2 h. The mean recovery for both bacteria in spiked chicken samples was ∼96%.