Fe-MOFs as signal probes coupling with DNA tetrahedral nanostructures for construction of ratiometric electrochemical aptasensor.

A ratiometric electrochemical aptasensor is proposed for the detection of thrombin. In the sensor, the iron metal-organic frameworks (Fe MOFs)-labeled aptamer as signal tags was used as signal probe (SP), and the electrolyte solution [Fe(CN)6]3-/4- was utilized as an inner reference probe (IR). In the presence of thrombin, the signal of Fe-MOFs can be detected. Meanwhile, the signal of [Fe(CN)6]3-/4-IR almost remains stable. Accordingly, thrombin concentration can be monitored with the ratio response of IFe-MOFs-SP/I[Fe(CN)6]3-/4--IR. The proposed ratiometric biosensor owns a strong ability to eliminate the disturbance that arises from different DNA loading densities, environmental impact and instrumental efficiency. DNA nanotetrahedron (NTH) with three-dimensional (3D) scaffold can effectively eliminate nonspecific adsorption of DNA and protein. The accessibility of target molecules and loading amounts of signal substances could be increased because of the enhanced mechanical rigidity of well-designed 3D NTH. Thus, detection reproducibility and sensitivity can be further improved. Moreover, the biosensor only requires conjugation with one electroactive substance. The modification procedure can be greatly simplified. The biosensor owns high sensitivity with the detection limit of 59.6 fM. We expect that it will emerge as a generalized ratiometric sensor that may be useful for detecting target analytes.