An unplugged and quantitative foam based immunochromatographic assay for Escherichia coli O157:H7 using nanozymes to catalyze hydrogen peroxide decomposition reaction

Abstract Quantitative and portable detection of target without skilled personnel and equipment is an important research focus in point-of-care testing field. A cost-effective, portable and unplugged foam immunochromatographic assay (Foam-ICA) for on-site and quantitative detection of Escherichia coli O157:H7 (E. coli O157:H7) without any instrument was reported. In sample solution the detection target E. coli O157:H7 were captured and labeled by monoclonal antibody modified the gold platinum bimetallic nanoparticles (anti-E. coli O157:H7 mAb Au@Pt NP). And horse radish peroxidase (HRP) was loaded on Au@Pt NP instead of BSA to block the active site. In this way, catalytic activity of Au@Pt NP was further enhanced and the final signal was further amplified. After addition of positive sample, anti-E. coli O157:H7 mAb modified Au@Pt NP are captured in the test (T) line by antibody-antigen recognition. And then the T line zone cut and added to hydrogen peroxide (H2O2) to catalyze decomposition of H2O2 to oxygen (O2) in 96-well plates. Produced O2 gas is trapped by sodium dodecyl sulfate (SDS) forms large amount of foam, which converts the E. coli O157:H7 amount into foam height with a reaction time of 8 min at 50 °C. The linear range of Foam-ICA for detecting E. coli O157:H7 is from 1.93 × 104 to 1.93 × 108 CFU mL−1, and the limit of detection (LOD) was 1.83 × 104 CFU mL−1 (3σ). The LOD of Foam-ICA for E. coli O157:H7 can be further enhanced to 1 CFU mL−1 by pre-incubation of the samples for 8 h. Thus, the Foam-ICA may be used for quantitative and cost effective detection of target without electrical instruments.