An electrochemical biosensor for detection of copper (II) based on Fe3O4@Au magnetic nanoparticles and Cu2+-dependent DNAzyme assisted nicking endonuclease signal amplification

Abstract

Copper ion is an essential element in the human body and participates in various physiological activities in the bodies of organisms. Herein, an ultrasensitive electrochemical biosensor was developed for detection of copper ion (Cu2+) based on Fe3O4@Au magnetic nanoparticles (Fe3O4@Au MNPs) and Cu2+-dependent DNAzyme assisted nicking endonuclease signal amplification (NESA) strategy. The dsDNA is formed by hybridization reaction between DNA S2 and S1 immobilized on surface of Fe3O4@Au MNPs. Fe3O4@Au MNPs not only manifested in the construction of a magnetically controlled electrochemical response interface but also served as promising scaffolds to carry DNA. In the presence of Cu2+, DNAzyme was activated and catalyzed the cleavage of dsDNA. The left fragment of dsDNA on the Fe3O4@Au MNPs hybridized with DNA S3, initiating the polymerization reaction in the presence of DNA polymerase and dNTP, and forming a long dsDNA product with specific recognition sites for nicking endonuclease Nb.BbvCI. With the help of Nb.BbvCI, the long dsDNA product was cleaved to release the free ssDNA probe, which hybridized with Fc-labeled hairpin DNA S4 immobilized on gold electrode and resulted in decrease of electrochemical signal. Subsequently, the remaining DNA probe on Fe3O4@Au MNPs triggered next cycle of "hybridization-cleavage-dissociation" reaction and more ssDNA probe dissociated, producing a significant signal amplification. The developed Cu2+ electrochemical biosensor exhibited a reliable linear range of 1 pM to 10 μM with the detection limit of 0.4 pM (S/N = 3). Furthermore, the proposed assay platform can be easily extended to monitor other metal ions by changing the specific DNAzymes and provide the potential and promising application for environment monitoring.