Salmonellosis continues to impose a significant economic burden globally. Rapid and sensitive detection of Salmonella is crucial to preventing the outbreaks of foodborne illnesses, yet it remains a formidable challenge. Herein, a dual-functional tetrahedron multivalent aptamer assisted amplification-free CRISPR/Cas12a assay was developed for Salmonella detection. In the system, the aptamer was programmatically assembled on the tetrahedral DNA nanostructure to fabricate a multivalent aptamer (TDN-multiApt), which displayed a 3.5-fold enhanced avidity over the monovalent aptamer and possessed four CRISPR/Cas12a targeting fragments to amplify signal. Therefore, TDN-multiApt could directly activate Cas12a to achieve the second signal amplification without any nucleic acid amplification. By virtue of the synergism of high avidity and cascaded signal amplifications, the proposed method allowed the ultrasensitive detection of Salmonella as low as 7 cfu mL-1. Meanwhile, this novel platform also exhibited excellent specificity against target bacteria and performed well in the detection of various samples, indicating its potential application in real samples.
Keywords: CRISPR/Cas12a; Salmonella detection; cascade signal amplification; multivalent aptamer; tetrahedral DNA nanostructure (TDN).