Saltatory rolling circle amplification assay coupled with photosensitization method for rapid and sensitive detection of Salmonella in food

Colorimetry has emerged as a promising option for pathogenic detection. Herein, a novel method based on saltatory rolling circle amplification (SRCA) combined with photosensitization colorimetric assay (SRCA-C) was developed for rapid and sensitive detection of Salmonella in food. The target identification and signal amplification are realized by SRCA to produce a large amount of double-stranded DNA. Subsequently, SYBR Green I as photosensitizer and 3,3',5,5"-tetramethylbenzidine (TMB) as colorimetric oxidase substrate are added to the colorimetric reaction system. The photosensitization reaction occurs under cyan LED irradiation, and TMB is oxidized to convert the double-stranded DNA signal into absorbance signal, thus realizing the detection of Salmonella. This colorimetric method benefits from convenience (label-free and no requirement of costly and complex equipment), short detection time (DNA amplification for 50 min and color development for 15 min) and high sensitivity (detected as low as 13 CFU/mL of Salmonella in pure culture). Five target strains and 10 nontarget strains were used to validate the specificity of the method. The recovery of Salmonella in the spiked milk samples ranged from 98.4% to 118.4%. Compared with the standard culture method, this method was 100% sensitivity, 98.2% specificity, and 98.3% accuracy for the detection of the real samples. Overall, this method highlights the importance for convenient, rapid, and sensitive detection of Salmonella in food.