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 π–π 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.

A millimeter-sized tubular motor for mobile biosensing of H2O2 in environmental and relevant clinical samples is reported. The concept relies on the self-propelled motion by the Marangoni effect, where the asymmetric release of SDS surfactant induces fluid convection and rapid dispersion of horseradish peroxidase (HRP) enzyme into the sample solution. This efficient movement together with the continuous release of fresh enzyme leads to greatly accelerated enzymatic reaction processes without the need of external stirring or chemical and physical attachment of the enzyme as in common classical biosensing approaches. In this strategy, the use of a single millimeter-sized tubular motor during 120 s allows the reliable and accurate quantification of hydrogen peroxide in a set of different matrices such as tap and mineral waters, urine, plasma, and tumor cell cultures treated with antineoplasic Cisplatin without any previous sample preparation. Furthermore, detection can be performed electrochemically, optically, and via visual detection, which makes this approach a clear candidate as a point-of-care analytical tool.

Magnetic reduced graphene oxide/nickel/platinum nanoparticles (rGO/Ni/PtNPs) micromotors for mycotoxin analysis in food samples were developed for food-safety diagnosis. While the utilization of self-propelled micromotors in bioassays has led to a fundamentally new approach, mainly due to the greatly enhanced target-receptor contacts owing to their continuous movement around the sample and the associated mixing effect, herein the magnetic properties of rGO/Ni/PtNPs micromotors for mycotoxin analysis are additionally explored. The micromotor-based strategy for targeted mycotoxin biosensing focused on the accurate control of micromotor-based operations: 1) on-the-move capture of free aptamers by exploiting the adsorption (outer rGO layer) and catalytic (inner PtNPs layer) properties and 2) micromotor stopped flow in just 2 min by exploiting the magnetic properties (intermediate Ni layer). This strategy allowed fumonisin B1 determination with high sensitivity (limit of detection: 0.70 ng mL ) and excellent accuracy (error: 0.05 % in certified reference material and quantitative recoveries of 104±4 % in beer) even in the presence of concurrent ochratoxin A (105-108±8 % in wines). These results confirm the developed approach as an innovative and reliable analytical tool for food-safety monitoring, and confirm the role of micromotors as a new paradigm in analytical chemistry.

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