Target-responsive ratiometric fluorescent aptasensor for OTA based on energy transfer between [Ru.sub.3].sup.2+ and silica quantum dots

A ratiometric fluorescent aptasensor based on energy transfer between [Ru(bpy).sub.3].sup.2+ and silica quantum dots (silica QDs) for assaying OTA was fabricated. The aptamer for OTA was used as the gate to shield the fluorescent reagent [Ru(bpy).sub.3].sup.2+ into mesoporous silica nanoparticle (MSN). In the presence of OTA, the constrained [Ru(bpy).sub.3].sup.2+ was released from MSN due to a target-induced aptamer conformational change. The released [Ru(bpy).sub.3].sup.2+ adsorbed onto the negatively charged silica QDs through electrostatic interaction. This creates appearance of fluorescence from [Ru(bpy).sub.3].sup.2+ at 625 nm and decrease of the fluorescence from silica QDs at 442 nm owing to the energy transfer. The value of FL.sub.625nm/FL.sub.442nm was in proportion to the concentration of OTA in the range 0.5~100 ng mL.sup.-1 with a LOD of 0.08 ng mL.sup.-1. Practical applicability of this method was validated by the determination of OTA in flour samples.