Rapid and selective detection of Bacillus cereus in food using cDNA-based up-conversion fluorescence spectrum copy and aptamer modified magnetic separation.

A sensitive luminescent bioassay for the detection of Bacillus cereus (B. cereus), a common bacterium, harmful to human health, was established based on up-conversion fluorescence and magnetic separation technology. Herein, aptamers (Apt) are modified on the surface of magnetic nanoparticles (MNPs) to form Apt-MNPs capture probes. The aptamer complementary strands (cDNA) are connected to upconversion nanoparticles (UCNPs) to form UCNPs-cDNA signal probes. In the absence of analyte, the UCNPs-cDNA-Apt-MNPs complex will be formed due to the specific binding between the aptamer and the complementary strand. In the presence of B. cereus, the amount of free UCNPs-cDNA increased in the system, which ultimately increased the fluorescence intensity of the solution. Hence, when the UCNPs-cDNA-Apt-MNPs system was excited by a 980 nm near-infrared light, a decrease in the fluorescence of the complex was observed at 548 nm due to the detachment of UCNPs-cDNA. Therefore, based on this principle, the calibration curve is constructed between the concentration of the analyte (B. cereus) and the fluorescence intensity. The results show that the method has a good quantitative ability for B. cereus in the range of 49-49 × 106 cfu/mL under the optimal conditions with a detection limit of 22 cfu/mL. Moreover, the proposed detection method also exhibits a high degree of specificity. The spiked recovery rate of the actual sample was in the range of 90.54%-111.28%, with good relative standard deviation values (2.12%-3.13%), indicating that the method has good reproducibility and stability. This study demonstrates that the constructed method can be used successfully for the rapid detection of B. cereus in food.