Paper-based colorimetric detection of pathogenic bacteria in food through magnetic separation and enzyme-mediated signal amplification on paper disc

Highlights: • Paper-based colorimetric sensor was developed for the detection of E. coli O157:H7. • Detection sensitivity was greatly enhanced by enzyme-mediated signal amplification. • Excellent signal to noise ratio was achieved by engineering the surface chemistry of magnetic beads. • Readily applicable to real food (sausage) with exceptionally low LOD of ∼30 CFU/mL. Herein, we report a colorimetric sensing system for the detection of highly virulent bacteria, Escherichia coli O157:H7, in sausage by utilizing magnetic separation and enzyme-mediated signal amplification on paper disc. For magnetic separation, Poly-l-lysine coated starch magnetic particles (PLL@SMPs) were synthesized and utilized for the separation and concentration of the bacteria in sample suspension. Horseradish peroxidase-conjugated antibody (HRP-Antibody) and 3,3′,5,5′- tetramethylbenzidine (TMB) were employed for the specific signal amplification in the presence of target bacteria. The synthesized PLL@SMPs showed an excellent capture efficiency (>90%) for the pathogenic bacteria in large volume sample suspension. The intrinsic problems associated with the non-specific binding of sensing components that lead to the high background signal and low sensitivity in colorimetric detection was successfully resolved by employing hyaluronic acid as a blocking agent. The effective separation and concentration of target bacteria by PLL@SMPs and target-specific signal amplification with exceptionally high signal to noise ratio enabled the detection of target bacteria with a detection limit in the single digit regime. The sensing system proposed in this study was successfully used for the detection of the target pathogenic bacteria, E. coli O157:H7, in sausage sample with the limit of detection (LOD) as low as 30.8 CFU/mL with 95% probability. The simple nature of paper-based detection system with a great sensitivity and specificity would provide an effective means of evaluating the safety of food and environmental samples.