An ultrasensitive impedance biosensor for Salmonella detection based on rotating high gradient magnetic separation and cascade reaction signal amplification.

An impedance biosensor using rotary magnetic separation and cascade reaction was developed for rapid and ultrasensitive detection of Salmonella typhimurium. First, magnetic nanoparticles (MNPs) modified with anti-Salmonella monoclonal antibodies were injected into a capillary at the presence of a rotary high gradient magnetic field, which was rotated by a stepper motor. Then, a bacterial sample was injected into the capillary and the target bacteria were continuous-flow captured onto the MNPs. After organic-inorganic hybrid nanoflowers were prepared using manganese dioxide (MnO), glucose oxidase (GOx) and anti-Salmonella polyclonal antibodies (pAbs), they were injected to label the bacteria, resulting in the formation of MNP-bacteria-nanoflower sandwich complexes. Finally, glucose (low conductivity) was injected and oxidized by GOx on the complexes to produce HO (low conductivity) and gluconic acid (high conductivity), leading to impedance decrease. Besides, the produced HO triggered a cascade reduction of MnO into Mn, leading to further impedance decrease. The impedance changes were measured using an interdigitated microelectrode and used to determine the concentration of target bacteria. This biosensor was able to detect Salmonella ranging from 10 to 10 CFU/mL in 2 h with a low detection limit of 10 CFU/mL and a mean recovery of 100.1% for the spiked chicken samples.