Nanocatalyst-triggered cascade immunoassay: Multi-model immunochromatography assay for sensitive detection of Salmonella typhimurium

The Salmonella-caused food safety problem is a potentially serious threat to public health and economic development, which stresses an urgent need for effective strategies to control the spread of food-borne pathogenic bacteria. In this work, a nanocatalyst-triggered cascade immunoassay (NTCI) combined with colorimetric-catalytic-photothermal multi-model signals has been developed for the detection of Salmonella typhimurium (S. Typhimurium). PtNiCo@TA trimetallic nanoflower was employed as the signal label of the NTCI, due to its excellent peroxidase-mimicking properties, colorimetric performance, biocompatibility, and stability. Here, the multi-model NTCI consists of three parts: (i) colorimetric immunochromatography assay (ICA) with a double antibody sandwich system, (ii) catalytic amplification system triggered by 3, 3′, 5, 5′ -tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2), and (iii) photothermal analysis achieved by the near-infrared (NIR) laser-driven photothermal properties of oxidized TMB (oxTMB). Based on this multi-model cascade reaction, both specific qualitative and quantitative analyses of pathogenic bacteria are realized. The limit of detection (LOD) of multi-model NTCI is 500 cfu·mL−1, which is 20-fold more sensitive than that of the colorimetric analysis alone. Moreover, the NTCI system shows preeminent applicability and flexibility for S. Typhimurium detection in milk samples. Therefore, this work suggests an innovative direction for the design of nanocatalyst-triggered photothermal multi-model immunoassays in the detection of food-borne pathogens.