Screening of pathogenic bacteria is a key to avoid food poisoning. The major drawbacks of existing assays for foodborne bacteria detection include long time for culture, complex DNA extraction for the polymerase chain reaction (PCR), and low sensitivity for enzyme-linked immunosorbent assay (ELISA), greatly limiting their practical applications. Here, we developed a sensitive optical biosensor based on porous gold@platinum nanocatalysts (Au@PtNCs) and a passive threedimensional (3D) micromixer for fast detection of Salmonella typhimurium. The target Salmonella cells were first separated using immunomagnetic nanoparticles and the passive 3D micromixer. Then, immune Au@PtNCs were labeled onto the target cells as signal output to catalyze hydrogen peroxide− 3,3′,5,5′-tetramethylbenzidine. Finally, the absorbance was measured at 652 nm to calculate the bacterial amount. This optical biosensor could detect Salmonella at concentrations from 1.8 × 10 1 to 1.8 × 10 7 CFU/mL in 1 h. Its detection limit was calculated to be 17 CFU/mL. Besides, this passive 3D micromixer could magnetically separate 99% of target bacteria from the sample in 10 min. This biosensor has the potential to be extended to detect other bacteria by changing the antibodies.

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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 Salmonella using manganese dioxide nanoflowers (MnO2 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 MnO2 NFs were fully mixed and sufficiently incubated in the spiral micromixer to form MNP–bacteria–MnO2 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 MnO2 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 Salmonella from 4.4 × 101 to 4.4 × 106 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.