A microfluidic signal-off biosensor for rapid and sensitive detection of Salmonella using magnetic separation and enzymatic catalysis

Abstract

The key to prevent and control the spread of foodborne diseases is rapid screening and early warning of pathogenic bacteria in foods. In this study, a microfluidic biosensor using magnetic nanoparticles (MNPs) and catalases was developed for rapid and sensitive detection of Salmonella typhimurium. First, the MNPs modified with anti-Salmonella monoclonal antibodies were used to separate and enrich target bacteria from sample background to form magnetic bacteria, which were reacted with polystyrene microspheres (PSs) modified with anti-Salmonella polyclonal antibodies and catalases to form enzymatic bacteria. Then, the enzymatic bacteria were injected into the capillary in microfluidic chip and captured by high gradient magnetic field. After washing to remove unbound PSs, hydrogen peroxide was finally injected and catalyzed by the catalases on enzymatic bacteria to produce oxygen gap in the capillary, leading to electrical signal-off. The change of electrical voltage was found to have a good linear relationship with the concentration of target bacteria from 3.7 × 101 to 3.7 × 106 CFU/mL. The proposed biosensor was able to detect Salmonella as low as 33 CFU/mL within 2 h, and could be further combined with microfluidics to develop a lab-on-a-chip system for in-field detection of foodborne bacteria to ensure food safety.