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Salmonella is a type of serious foodborne pathogenic bacterium that threatens the food safety worldwide. In this study, a fluorescence probe-based recombinase polymerase amplification analytical method (exo RPA) was developed for the sensitive and specific detection of Salmonella enterica (S. enterica). The primers and probe for this method were designed based on the iroB gene of the bacterium. The exo RPA reaction could detect as low as 102 copies of template DNA per reaction or 2.2 × 103 CFU/mL of S. enterica, and SPSS probit regression analysis indicated the limit of detection (LOD) at 95% probability of the exo RPA assay was 2.0 × 103 CFU/mL. Moreover, the exo RPA assay could successfully differentiate S. enterica from all the tested non-Salmonella strains. Importantly, this method is highly reliable; the DNA from other bacteria or food complex matrices has no obvious effect on the S. enterica exo RPA. Besides, positive signal could be obtained from the chicken or egg sample inoculated with 2.2 × 101 CFU/mL of S. enterica after 4- to 6-h enrichment at 36 °C. Therefore, this study describes a rapid test method for S. enterica, which is expected to be beneficial for monitoring trace S. enterica in real food products.

Dexamethasone has been illegally used as a growth-promoting agent to obtain an economic benefit from increased muscle development. An immunochromatographic assay was developed for the quantitative detection of dexamethasone using a probe based on upconversion luminescence nanoparticles. Lanthanide-doped upconversion nanoparticles were synthesized in a system comprising water and ethylene glycol. Various parameters, including the immunoreaction time, the structure of the coating hapten, and the type and concentration of surfactant, were optimized. Based on the optimal conditions, the assay exhibits good dynamic linear detection in the range of 0.05–5 ng/mL with an IC50 of 0.58 ng/mL. The detection limits for dexamethasone in tissue are 0.3 μg/kg. The assay worked well using a 30% methanol extraction solution, giving an average recovery of 84.5%. The assay strip can quantitate on-site using a portable upconversion luminescence reader with a cumulative analysis time of only 10 min, and its fluorescence decay after 6 months is < 25%.