DNAzyme catalytic beacons-based a label-free biosensor for copper using electrochemical impedance spectroscopy

Abstract

In this study, we developed a novel selective method for copper quantification based on gold nanoclusters (GNCs) and DNAzyme. The GNCs were used as the sensing interface to immobilize with the DNAzyme capturing Cu²⁺ ions. The DNAzyme could be activated to cleave the substrate strand into two DNA fragments in the presence of Cu²⁺, and produce changes in the interfacial properties of the electrode. The difference in the interfacial electron-transfer resistance was probed in the presence of the reversible redox couple, Fe(CN)₆^3−/4−, as a marker using electrochemical impedance spectroscopy (EIS). A Randles equivalent circuit was employed to evaluate the EIS results. The charge transfer resistance (R_CT) of the Fe(CN)₆^3−/4− redox indicator decreased remarkably after hybridization with Cu²⁺. The difference in R_CT values before and after hybridization with Cu²⁺ showed a linear relationship with the concentration of Cu²⁺ in a range of 0.1–400 nM, with a detection limit of 0.0725 nM (S/N = 3). Furthermore, with the application of Cu²⁺ dependent DNAzyme, the proposed sensing system exhibited high selectivity. This biosensor demonstrated promising potential for Cu²⁺ detection in real samples.