A voltammetric assay for microRNA-25 based on the use of amino-functionalized graphene quantum dots and ss- and ds-DNAs as gene probes

The authors describe a DNA based voltammetric assay for the cancer biomarker microRNA-25. A glassy carbon electrode (GCE) was modified with amino-functionalized graphene quantum dots and used as an amplifier of electrochemical signals. p-Biphenol is introduced as a new electroactive probe with a fairly low working potential of 0.3V (vs. Ag/AgCl). The stages of fabricating the electrode were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. ss-Probe DNA was immobilized on the modified GCE and then exposed to a sample containing microRNA-25. The results indicated that the electrode can distinguish complementary microRNA-25 from a single-base mismatch. The increase in the electrochemical response of PBP and the positive shift in the potential peak indicate that PBP is intercalated between two strands. Under optimized experimental conditions, the current of the electrode increases linearly with the logarithm of the microRNA-25 concentration in the range from 0.3 nM to 1.0 mu M, and the detection limit is 95.0 pM. The assay was successfully employed to the determination of microRNA-25 in spiked human plasma.