Dramatically Enhanced Immunochromatographic Assay Using Cascade Signal Amplification for Ultrasensitive Detection of Escherichia coli O157:H7 in Milk

Conventional colloidal gold immunochromatographic assay (AuNP-ICA) cannot meet the requirements for rapid and sensitive detection of Escherichia coli (E. coli) O157:H7 because of its poor sensitivity. Herein, a novel two-step cascade signal amplification strategy that integrates in-situ gold growth and nanozyme-mediated catalytic deposition was proposed to enhance the detection sensitivity of conventional AuNP-ICA dramatically. The enhanced strip displayed ultrahigh sensitivity in E. coli O157:H7 detection and had a detection limit of 1.25×101 CFU/mL, which is approximately 400-fold lower than that of traditional AuNP-ICA (5×103 CFU/mL). The amplified strip had no background signal in the T line zone in the absence of E. coli O157:H7 even after one round of cascade signal amplification. The enhanced strip demonstrated excellent selectivity against E. coli O157:H7 with a negligible cross-reaction to nine other common pathogens. Intra- and inter-assays showed that the improved strip has acceptable accuracy ...