Ultrasensitive electrochemical aptasensor for ochratoxin A based on two-level cascaded signal amplification strategy

Ochratoxin A (OTA) has a number of toxic effects to both humans and animals, so developing sensitive detection method is of great importance. Herein, we describe an ultrasensitive electrochemical aptasensor for OTA based on the two-level cascaded signal amplification strategy with methylene blue (MB) as a redox indicator. In this method, capture DNA, aptamers, and reporter DNA functionalized-gold nanoparticles (GNPs) were immobilized on the electrode accordingly, where GNPs were used as the first-level signal enhancer. To receive the more sensitive response, a larger number of guanine (G)-rich DNA was bound to the GNPs' surface to provide abundant anchoring sites for MB to achieve the second-level signal amplification. By employing this novel strategy, an ~8.5 (±0.3) fold amplification in signal intensity was obtained. Afterward, OTA was added to force partial GNPs/G-rich DNA to release from the sensing interface and thus decreased the electrochemical response. An effective sensing range from 2.5pM to 2.5nM was received with an extremely low detection limit of 0.75 (±0.12) pM. This amplification strategy has the potential to be the main technology for aptamer-based electrochemical biosensor in a variety of fields.