Electrochemical/visual dual-readout aptasensor for Ochratoxin A detection integrated into a miniaturized paper-based analytical device.

Development of portable, sensitive and reliable devices for Ochratoxin A (OTA) detection is highly demanded, especially for resource-limited regions. Herein, a novel paper-based analytical device (PAD) is designed through wax printing and screen-printed technologies, which integrates sample flowing, electrode modification, cleaning and electrochemical (EC)/colorimetric signal output. To greatly enhance the detection sensitivity, we synthesized a chitosan functionalized MoS-Au@Pt (Ch-MoS-Au@Pt) via electrostatic self-assembly, and used it to immobilize the label aptamer (apta) for signal regulation and amplification. Concretely, with the addition of analytes, the Ch-MoS-Au@Pt-apta could be combined on the sensing interface by specific biorecognition and catalyzed reduction of HO, resulting in a remarkable EC response. Meanwhile, the released hydroxyl radicals (·OH) flowed to the visualization zone and promoted the oxidation of 3,3',5,5'-tetramethylbenzidine for colorimetric detection. Consequently, the dual-mode PAD achieved acceptable prediction and accurate analysis in the range of 0.1-200 ng mL and 1 × 10-200 ng mL by matching the visual and EC signal intensity, respectively. Compared with traditional single-mode sensor for OTA, the proposed dual-mode aptasensor featuring independent signal conversion and readout, not only avoided the false-positive signal associated with detection condition and operation, but also enlarged the detection ranges and improved the sensitivity. Furthermore, the consistency of EC/colorimetric assay was validated in real OTA samples. Overall, this work provided a portable, cost-effective, sensitive and visualized aptasensor platform, which could be extended to various other mycotoxins in the field of food safety.