Rapid detection of Salmonella Typhimurium using magnetic nanoparticle immunoseparation, nanocluster signal amplification and smartphone image analysis

Rapid detection of foodborne pathogens is of great significance for ensuring food safety. In this study, a portable biosensor was developed for rapid and sensitive detection of Salmonella Typhimurium using magnetic nanoparticle immunoseparation, nanocluster signal amplification and smartphone image analysis. The magnetic nanoparticles were conjugated with the monoclonal antibodies by biotin-streptavidin system for specifically capturing the target to form the magnetic bacteria. The polyclonal antibodies and glucose oxidase (GOx) were incubated with calcium chloride to synthesize the immune GOx-nanoclusters (GNCs) for reacting with the magnetic bacteria to form the nanocluster bacteria. The GNCs on the nanocluster bacteria were used to catalyze the glucose into hydrogen peroxide, which was measured using the peroxide test strip. The image of the strip was collected and analyzed using the Hue-Saturation-Lightness color space based smartphone APP for the determination of the target bacteria. This proposed biosensor was able to detect Salmonella Typhimurium with the linear range of 101–105 CFU/mL and the low detection limit of 1.6 × 101 CFU/mL. The mean recovery of Salmonella Typhimurium in the spiked chicken samples was 99.8%. This biosensor has the potential to provide a simple, portable and low-cost method for rapid and in-field detection of Salmonella Typhimurium in foods.