Optical Biosensor for Rapid Detection of Salmonella typhimurium Based on Porous Gold@Platinum Nanocatalysts and a 3D Fluidic Chip

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 three-dimensional (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 × 10¹ to 1.8 × 10⁷ 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.