Magnetic relaxation switch and fluorescence dual-mode biosensor for rapid and sensitive detection of ricin B toxin in edible oil and tap water

The ultrasensitive and rapid detection of ricin B toxin (RTB) is essential for food safety and environmental monitoring. Herein, a dual-mode magnetic relaxation switch (MRS) and fluorescence (FL) biosensing strategy was developed to efficiently detect RTB using fluorescent magnetic nanoparticles (MNP300@SiO2(FITC)). Meanwhile, the as-prepared composite MNP300@SiO2(FITC) exhibited superior biocompatibility and increased FL readout and was coupled with aptamer (Apt) to form a captured probe. Magnetic nanoparticles, 30 nm in diameter (MNP30), were coupled to a Blocker to form a paired probe to compete with RTB for Apt binding. The presence of the RTB triggered the dual-mode detection switch, thus, weakening the magnetic and fluorescent signals. Compared with the single-mode detection method, the Δ T2 and Δ FL intensity here exhibited an excellent linear relationship with logarithm of RTB concentrations at 0.001-500 ng/mL and 0.005-500 ng/mL, and obtained ultrahigh sensitivities of 0.8 pg/mL and 3 pg/mL, respectively. In addition, the dual-mode biosensor gained satisfactory spiked recoveries and relative standard deviations for quantitative detection of spiked RTB in edible oil and tap water samples. To our knowledge, this is the first study to describe the accurate quantification of RTB using a sensitive MRS-FL biosensor. We anticipate that this strategy will provide novel avenues for the development of dual-mode sensing assays.