Aptamer-Modified Graphene-Based Catalytic Micromotors: Off-On Fluorescent Detection of Ricin

An aptamer-based catalytic micromotor sensing strategy for "Off-On" real-time fluorescent detection of the ricin B toxin is described. This approach relies on self-propelled reduced graphene-oxide (rGO)/platinum (Pt) micromotors, modified with a specific ricin B aptamer tagged with a fluorescein-amidine (FAM) dye, whose fluorescence is quenched due to pi-pi interactions with the rGO surface. The continuous movement of the motor in the sample accelerates the specific binding of the ricin B toxin to the aptamer-dye conjugate and leads to real-time fluorescent "On" detection. Coupling the "Off-On" fluorescent switching properties of the aptamer modified-rGO/Pt micromotors with their inherent mixing capabilities thus leads to high speed, simplicity, and sensitivity advantages, thus addressing the limitations of current ricin detection strategies. The new micromotor strategy represents an attractive route for detecting biological threats in a variety of biodefense applications.