A label-free electrochemical sensor based on π-structured bipedal DNA walker-triggered hybridization chain reaction and AuPt NPs/Zr-MOF for OTA detection.

Background: Ochratoxin A (OTA) is a serious food contaminant, not easily degradable, and capable of causing irreversible damage to the human body. Therefore, it is of great practical significance to establish a sensitive and efficient OTA detection method. The electrochemical aptasensor has a broad development prospect in OTA detection with its advantages of fast response speed and low cost.

Results: Herein, a cascade signal amplification strategy based on AuPt NPs/Zr-MOF and π-structure bipedal DNA walker-triggered hybridization chain reaction (HCR) was designed for the detection of ochratoxin A (OTA). AuPt NPs/Zr-MOF was employed as the electrode modification material, providing a large number of active sites and high conductivity, achieving 1.47 times signal amplification. Interestingly, bipedal DNA walker binds to hairpin 1 (H1) to form the π-structure. Under the activation of Pb, one bipedal DNA walker can simultaneously bind and cleave two H1. It exhibits a wide walking range and high recognition efficiency. After H1 is cleaved, the trigger sequence was exposed to trigger HCR and a large amount of methylene blue was loaded on the electrode. Under the optimal conditions, the linear range of the determined OTA is 1 × 10-500 ng/mL, and the limit of detection is as low as 0.525 pg/mL.

Significance: The experimental results demonstrate that the constructed electrochemical aptasensor is a sensitive and efficient platform for OTA monitoring. The applicability in food samples was also confirmed, and the strategy was efficiently selective and reproducible for different analytes. This provides ideas for subsequent food safety testing.