CRISPR-Cas12a-Powered Dual-Mode Biosensor for Ultrasensitive and Cross-validating Detection of Pathogenic Bacteria

Pathogenic bacteria infection severely threatens human health and causes substantial medical and financial concern. Rapid, sensitive, specific, and reliable detection of pathogenic bacteria is crucial. In the current study, a CRISPR-Cas12a-powered dual-mode biosensor was developed for ultrasensitive and cross-validating detection of pathogenic bacteria. Simply, the amplicons of Salmonella (used as a model)-specific invA sequence triggered CRISPR-Cas12a-based indiscriminate degradation of single-stranded DNAs that were supposed to link two gold nanoparticle (AuNP) probe pairs, inducing an aggregation-to-dispersion change. This generated observable color changes that became even more apparent after centrifugation. The color changes can be discerned by naked eyes and recorded using a portable colorimeter. Meanwhile, the photothermal effect of CRISPR-Cas12-powered AuNPs was explored for the first time through 808 nm near-infrared irradiation such that quantitative measurement can be carried out by recording temperatures using a thermal camera. For both modes, a limit of detection of 1 CFU/mL and a dynamic range of detection from 100 to 108 CFU/mL were obtained, which were comparable with or better than previously reported methods. Our proposed biosensor demonstrated satisfactory selectivity for Salmonella against other interfering cells. Furthermore, this biosensor proved to be capable of Salmonella detection in food samples. Regarding the real applications, the result from each mode can be used for cross-validation. Only the case having doubly confirmed positive or negative results can be assured, which rendered a more dependable biosensing conclusion. This technology not only expands the reach of the CRISPR-Cas system in biosensing but also provides a general method for bacteria sensing with desirable sensitivity, specificity, and cross-validating capacity.