Dual signal amplification platform based on recombinant polymerase amplification and fluorescence-enhanced nanoparticles for sensitive detection of Salmonella

Salmonella is a common foodborne pathogen, and its detection is essential for managing public food safety. Lateral flow assay (LFA) strips are well suited for the purpose as they are inexpensive and easy to use. However, the sensitive detection of low-concentration targets requires the use of signal amplification strategies. This paper presents a LFA for the ultrasensitive detection of Salmonella based on recombinase polymerase amplification (RPA) and fluorescence-enhanced composite nanospheres dSiO2@CD@SiO2 (dCDS). RPA is capable of rapid (similar to 20 min) exponential amplification of bacterial DNA and does not require complex instrumentation. Mesoporous silica (dSiO2) has a large specific surface area and radial pore size, making it an excellent structural material for internal assembly. Nanoparticles obtained by loading carbon dots (CDs) had a strong fluorescence signal and stability. We used dCDSs as reporter molecules, which captured a large number of DNA-dCDS complexes on the test line of the LFA. With double signal amplification, the RPA and dCDS-based LFA showed greatly improved sensitivity: The limits of detection for Salmonella in buffer and milk were 3.8 CFU/mL and 36 CFU/mL, respectively. This study provides an inexpensive strategy for the sensitive detection of pathogenic bacteria.