A novel self-cleaning electrochemical biosensor integrating copper porphyrin-derived metal-organic framework nanofilms, G-quadruplex, and DNA nanomotors for achieving cyclic detection of lead ions

A self-cleaning electrochemical biosensor based on two-dimensional Cu-porphyrin (Cu-TCPP) metal-organic framework nanofilms, novel super G-quadruplex (G4), and DNA nanomotors was developed for the cyclic detection of Pb2+ ions. The Cu-TCPP framework with inherent peroxidase activity can create an ultra-thin nanofilm that functioned as a carrier to support the metastable G4 comprising four individual DNA strands. The introduction of Pb2+ and the intercalation of hemin can help it to form stable G4-hemin DNAzymes, which exhibits strong catalytic H2O2 reduction activity, and its number will be directly related to the amount of the introduced Pb2+. Moreover, a DNA nanomotor system is introduced to achieve cyclic detection, and the addition of the fuel DNA strands enables G4 to perform a "complete-dissociation-complete" process for achieving self-cleaning of the electrode interface and the cycle detection of Pb2+. The synergistic effects of Cu-TCPP and G4-hemin DNAzymes, which exhibits efficient and catalytic H2O2 reduction, enhance the performance of the electrochemical sensing system. The linear range of this sensor to Pb2+ is 5 nM-5 μM, and the detection limit is 1.7 nM. Compared with the best system in reported studies, its linear range is five times wider and its detection limit is lower than the previously lowest one. Taking advantage of the Pb2+ stabilized G4, the proposed sensor can selectively detect Pb2+ in the presence of other metal ions. The results presented herein comprise a valuable reference for constructing DNA nanoelectronic devices and establish sensitive and cyclic detection of the target and preparing of self-cleaning electrode interfaces.