Abstract
The detection of Salmonella Typhimurium (S.typhimurium) is of great importance in food safety field.Colorimetric strategy is particularly appealing for S. typhimurium identification because of its user-friendliness and instrument-free. However, the existing colorimetric strategies still meet the challenges of low sensitivity, tedious nucleic acid extraction and expensive labeling processes. Herein, a high sensitivity and label-free colorimetric sensing strategy for S. typhimurium detection without nucleic acid extraction is constructed. Specifically, the proposed strategy is based on three-way junction (3WJ) DNA branched structure combined with nicking enzyme signal amplification (NESA). In the presence of target, cascaded signal amplification is initiated through a series of toehold-mediated strand displacement reactions (TSDRs) to recycle the trigger DNA causing formation of the numerous 3WJ DNA branched structures (3WJ-TSDRs). Then, the branches of 3WJ-TSDRs are fully utilized to hybridize with the DNAzyme signal probes to initiate NESA in the presence of Nt. BbvCI, which making every branch has a function of signal amplification. Finally, DNAzyme signal probes (green) were completely split into two fragments (colorless). The application of NESA in the branches of 3WJ-TSDRs offers a highly sensitive detection of S. typhimurium with a low limit of detection of 42 CFU mL−1. Besides, the colorimetric sensing strategy also shows strong anti-interference. The capability of the colorimetric sensing strategy in spiked samples was also investigated, showing a more intuitive results and fast detection in compare with the traditional plate counting method. With these characteristics, the proposed sensing strategy based on 3WJ-TSDRs and NESA is a promising tool for new point-of-care (POC) applications in food safety.
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