An impedance biosensor based on magnetic nanobead net and MnO2 nanoflowers for rapid and sensitive detection of foodborne bacteria

Abstract

Screening of pathogenic bacteria in foods is an effective way to prevent foodborne diseases. In this study, an impedance biosensor was developed for rapid and sensitive detection of Salmonella typhimurium using multiple magnetic nanobead (MNB) nets in a ring channel for continuous-flow separation of target bacteria from 10 mL of sample, manganese dioxide nanoflowers (MnO₂ NFs) for efficient amplification of biological signal, and an interdigitated microelectrode for sensitive measurement of impedance change. First, the MNBs modified with capture antibodies were vortically injected from outer periphery of this ring channel to form multiple ring MNB nets at specific locations with high gradient magnetic fields. Then, the bacterial sample was continuous-flow injected, resulting in specific capture of target bacteria onto the nets, and the MnO₂ NFs modified with detection antibodies were injected to form MNB-bacteria-MnO₂ NF complexes. After the complexes were washed with deionized water to remove excessive nanoflowers and residual ions, H₂O₂ with poor conductivity was injected to reduce MnO₂ NFs to conductive Mn²⁺ at neutral medium, leading to impedance decrease. Finally, impedance change was measured using the microelectrode for quantitative determination of Salmonella. This biosensor was able to separate ~60% of Salmonella from 10 mL of bacterial sample and detect Salmonella with a linear range of 3.0 × 10¹ to 3.0 × 10⁶ CFU/mL in 1.5 h with lower detection limit of 19 CFU/mL. This biosensor might be further improved with higher sensitivity using a larger volume (100 mL or more) for routine screening of foodborne bacteria without bacterial pre-culture.

Keywords: Impedance biosensor; Large-volume magnetic separation; Magnetic nanobead net; MnO(2) nanoflowers; Salmonella detection.