DNA-templated copper nanoparticles as signalling probe for electrochemical determination of microRNA-222.

An ultrasensitive electrochemical biosensor is described for the determination of microRNAs. It is based on the use of DNA-templated copper nanoparticles (Cu NPs) as signalling probe. MicroRNA-222 was selected as the model analyte. The probe was obtained from two different oligonucleotides (containing complementary bases) via hybridization chain reaction to form long DNA concatemers as template. The Cu NPs were formed by reaction of ascorbate with copper sulfate. The biosensor was fabricated as follows: (a) Capture probe (cDNA) with a thiolated group was immobilized on reduced graphene oxide modified with gold nanoparticles (rGO/Au NPs), (b) materials was placed on a glassy carbon electrode (GCE); (c) the modified electrode (cDNA/rGO/Au NPs/GCE) was sequentially hybridized with microRNA-222 and signal probe; this results in the formation of a sandwich structure of cDNA-microRNA-signal probe on surface of the modified electrode. Differential pulse voltammetry was employed to record the electrochemical response of biosensor in pH 6.0 solution. As a result, a sensitive oxidation current with a peak potential at 0.10 V (vs. SCE) was obtained corresponding to Cu NPs. The experimental conditions were optimized. Under optimal conditions, the biosensor exhibited wide linear response range (0.5 fM to 70 nM) and low limit of detection (0.03 fM; at S/N = 3). The assay possesses high selectivity and can discriminate analyte microRNA from single-base mismatched microRNA. Graphical abstractA sensitive electrochemical biosensor is described for the determination of microRNA-222 by using a dsDNA-templated Cu NPs as signalling probe. (A) represents the preparation of signal probe, and (B) represents the fabrication of electrochemical microRNA sensor.