Specific Coordination between Zr-MOF and Phosphate-Terminated DNA Coupled with Strand Displacement for the Construction of Reusable and Ultrasensitive Aptasensor.

Electrochemical aptasensors involved in chemical labeling are often single-use and sensitivity-limited because the probes are commonly single-point labeled and irreversible. In this work, the specific coordination between Zr4+ and phosphate group (-PO43-) was employed to construct a new aptasensor that is highly sensitive and reusable, using Ochratoxin A (OTA) as the test model. The OTA binding aptamer (OBA) was hybridized with the thiolated supporting sequence (TSS) immobilized on the surface of a gold electrode. The UiO-66 with a formula of [Zr6O4(OH)4(BDC)6], one of the class of Zr metal-organic frameworks (MOFs), was then particularly grafted on the terminal of OBA through the specific coordination between Zr4+ and 5'-PO43-, i.e., the Zr-O-P coordination bond. Similarly, as much as the 5'-PO43- and 3'-methylene blue dual-labeled sequences (DLS) were further assembled on UiO-66 due to the large surface area of MOF and rich active sites of Zr4+. Owing to the specific coordination for signal amplification, the developed aptasensor shows greatly enhanced sensitivity. A wide detection range from 0.1 fM to 2.0 μM and an ultralow detection limit of 0.079 fM (S/N = 3) for OTA were obtained. Additionally, the TSS can rehybridize with a new OBA to regenerate the aptasensor but without complicated pretreatments, enabling a aptasensor that is readily reusable for OTA detection. The aptasensor was successfully applied for OTA detection in the red wine samples, demonstrating a promising prospect for food safety monitoring.