A Microfluidic Biosensor Based on Magnetic Nanoparticle Separation, Quantum Dots Labeling and MnO₂ Nanoflower...

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 (MnO₂ NFs) and as QDs nanocarriers for signal amplification. Prior to testing, amino-modified MnO₂ nanoflowers (MnO₂-NH₂ NFs) were conjugated with carboxyl-modified QDs through EDC/NHSS method to form MnO₂-QD NFs, and MnO₂-QD NFs were functionalized with polyclonal antibodies (pAbs) to form MnO₂-QD-pAb NFs. First, the mixture of target Salmonella Typhimurium cells and magnetic nanoparticles (MNPs) modified with monoclonal antibodies (mAbs) was injected with MnO₂-QD-pAb NFs into a microfluidic chip to form MNP-bacteria-QD-MnO₂ complexes. Then, glutathione (GSH) was injected to dissolve MnO₂ on the complexes into Mn²⁺, 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 × 10² to 1.0 × 10⁷ 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.