Staggered magnetic bead chains enhanced bacterial colorimetric biosensing

Pathogen screening is an important measure for ensuring food safety. A colorimetric biosensor was presented for Salmonella determination employing staggered magnetic bead chains for continuous-flow bacteria isolation, MnO 2 nanozymes for effective signal amplification, and smartphone for accurate catalysate analysis. First, immune magnetic beads were distributed under the staggered magnetic field to form higher magnetic bead chains to occupy more cross-section of separation channel. Then, target bacteria were injected and captured onto magnetic bead chains, followed by labeling with the immune MnO 2 nanozymes to form bead-bacteria-nanozyme complexes. Finally, H 2 O 2 -TMB substrate was catalyzed by MnO 2 nanozymes on these complexes, and color change was monitored and analyzed through smartphone to quantify target bacteria. The sensor enabled Salmonella detection as few as 60 CFU/mL in 2 h. • The staggered magnetic field could enhance the occupation of MB chains in the channel. • The MnO 2 nanoflowers were used to greatly amplify the biological signal. • The smartphone App was developed for accurate analysis of color saturation. • This biosensor could detect Salmonella as low as 60 CFU/mL within 2 h.