CRISPR/Cas12a and Hybridization Chain Reaction-Coregulated Magnetic Relaxation Switching Biosensor for Sensitive Detection of Viable Salmonella in Animal-Derived Foods

We combined a CRISPR/Cas12a system with a hybridization chain reaction (HCR) to develop an ultrasensitive magnetic relaxation switching (MRS) biosensor for detecting viable Salmonella typhimurium (S. typhimurium). Magnetic nanoparticles of two sizes (30 and 1000 nm: MNP₃₀ and MNP₁₀₀₀, respectively) were coupled through HCR. The S. typhimurium gene-activated CRISPR/Cas12a system released MNP₃₀ from the MNP₁₀₀₀-HCR-MNP₃₀ complex through a trans-cleavage reaction. After magnetic separation, released MNP₃₀ was collected from the supernatant and served as a transverse relaxation time (T₂) signal probe. Quantitative detection of S. typhimurium is achieved by establishing a linear relationship between the change in T₂ and the target gene. The biosensor's limit of detection was 77 CFU/mL (LOD = 3S/M, S = 22.30, M = 0.87), and the linear range was 10²-10⁸ CFU/mL. The accuracy for detecting S. typhimurium in real samples is comparable to that of qPCR. Thus, this is a promising method for the rapid and effective detection of foodborne pathogens.