Microfluidic Colorimetric Biosensors Based on MnO Nanozymes and Convergence-Divergence Spiral Micromixers for Rapid and Sensitive Detection of .

In-field screening of foodborne pathogens plays an important role in ensuring food safety. Thus, a microfluidic biosensor was developed for rapid and sensitive detection of using manganese dioxide nanoflowers (MnO NFs) for amplifying the biological signal, a microfluidic chip with a convergence-divergence spiral micromixer for performing automatic operations, and a smartphone app with a saturation calculation algorithm for processing the image. First, immune magnetic nanoparticles (MNPs), the sample, and immune MnO NFs were fully mixed and sufficiently incubated in the spiral micromixer to form MNP-bacteria-MnO sandwich complexes, which were magnetically captured in a separation chamber in the microfluidic chip. Then, a 3,3',5,5'-tetramethylbenzidine (TMB) substrate was injected and catalyzed by a MnO NF nanomimetic enzyme on the complexes, resulting in the production of yellow catalysate. Finally, the catalysate was transferred into a detection chamber and its image was measured and processed using the smartphone app to determine the number of bacteria. This biosensor was able to detect from 4.4 × 10 to 4.4 × 10 CFU/mL in 45 min with a detection limit of 44 CFU/mL, and has the potential to provide a promising platform for on-site detection of foodborne bacteria.