A capillary biosensor for rapid detection of Salmonella using Fe-nanocluster amplification and smart phone imaging.

Early screening of foodborne pathogenic bacteria is a key to prevent and control foodborne diseases. This study intended to develop a capillary biosensor for rapid and sensitive detection of Salmonella using the multi-column capillary for easy operation, the Fe-nanoclusters (FNCs) for signal amplification and the smart phone APP for image analysis. The multi-column capillary was successively preloaded the magnetic nanoparticle (MNP) column, the FNC column, two phosphate buffer solution with 0.05% Tween 20 (PBST) columns and the HCl column and the columns were separated by air gap. The iron spiral mixer was fabricated to accelerate the mixing, and the multi-ring magnets was developed to transfer the MNPs and their conjugates from column to column. The target bacteria were captured by the MNPs to form the magnetic bacteria and then conjugated with the FNCs to form the nanocluster bacteria. After washing with PBST, the nanocluster bacteria were transferred into the HCl column, and the iron ions were released and reacted with potassium hexacyanoferrate to form the Prussian Blue, which was finally measured and analyzed using the Hue-Saturation-Lightness color space based smartphone APP for the determination of the target bacteria. This proposed biosensor exhibited a wide linear range for detection of Salmonella typhimurium with the lower detection limit of 14 CFU/mL. The mean recovery of the target bacteria in spiked chicken samples was ~105.0%, indicating the applicability of this biosensor. The proposed biosensor had the potential for in-field detection of foodborne pathogens.