Rapid and automatic Salmonella typhimurium detection integrating continuous-flow magnetic separation and dynamic impedance measurement

Screening of pathogenic bacteria is an essential measure for ensuring food safety. A fast, sensitive and automatic platform for Salmonella determination was presented employing continuous-flow magnetic isolation, enzymatic impedance amplification and smartphone data analysis. First, magnetic nanoparticles coupling with polyclonal antibody, polystyrene spheres coupling with monoclonal antibody and glucose oxidase, and bacterial sample were simultaneously immitted into reaction chamber, and actively mixed for formation of MNP-Salmonella-PS complexes in the microfluidic chip. After the MNP-Salmonella-PS complexes were continuous-flow caught in separation channel using the enhanced magnetic field and successively washed for removing redundant immune PSs and remanent ions, glucose with high impedance was then pumped and catalyzed into hydrogen peroxide and gluconic acid. Finally, impedance change of catalysate was dynamically measured with the on-chip PCB electrode and analyzed by the self-developed smartphone to quantify target bacteria. The microfluidic platform was able to quantitatively detect Salmonella from 1.3 x 102 to 1.3 x 106 CFU/mL in 1.5 h with a detection limit of 53 CFU/mL. The recovery of Salmonella in spiked chicken meats ranged from 88.2% to 112.0%, verifying its good practical applicability. This platform is featured with fast detection, high sensitivity and simple operation, and promising for in-field Salmonella screening.