A Microfluidic Biosensor Based on Magnetic Nanoparticle Separation, Quantum Dots Labeling and MnO(2) Nanoflower Amplification for Rapid and Sensitive Detection of Salmonella Typhimurium

Screening of foodborne pathogens is an effective way to prevent microbial food poisoning. A microfluidic biosensor was developed for rapid and sensitive detection of Salmonella Typhimurium using quantum dots (QDs) as fluorescent probes for sensor readout and manganese dioxide nanoflowers (MnO(2) NFs) and as QDs nanocarriers for signal amplification. Prior to testing, amino-modified MnO(2) nanoflowers (MnO(2)-NH(2) NFs) were conjugated with carboxyl-modified QDs through EDC/NHSS method to form MnO(2)-QD NFs, and MnO(2)-QD NFs were functionalized with polyclonal antibodies (pAbs) to form MnO(2)-QD-pAb NFs. First, the mixture of target Salmonella Typhimurium cells and magnetic nanoparticles (MNPs) modified with monoclonal antibodies (mAbs) was injected with MnO(2)-QD-pAb NFs into a microfluidic chip to form MNP-bacteria-QD-MnO(2) complexes. Then, glutathione (GSH) was injected to dissolve MnO(2) on the complexes into Mn(2+), resulting in the release of QDs. Finally, fluorescent intensity of the released QDs was measured using the fluorescent detector to determine the amount of Salmonella. A linear relationship between fluorescent intensity and bacterial concentration from 1.0 × 10(2) to 1.0 × 10(7) CFU/mL was found with a low detection limit of 43 CFU/mL and mean recovery of 99.7% for Salmonella in spiked chicken meats, indicating the feasibility of this biosensor for practical applications.