Graphene-based Electrochemical Biosensor for Impedimetric Detection of miRNAs as Potential Cancer Biomarkers

MicroRNAs (miRNAs) have shown great potential to be used as biomarkers for the screening and clinical diagnosis of cancer. In this study, an electrochemical biosensor based on graphene-modified glassy carbon electrode was developed for the detection of miRNA-21, a well-known biomarker for the early stage of prostate cancer. A novel molecular tethering agent was used for immobilization of single-stranded probe DNA onto the electrode surface. Different parameters related to biosensor fabrication and experimental conditions were optimized to obtain the highest biosensor response. Electrochemical impedance spectroscopy was employed to achieve a sensitive and label-free detection method for miRNA-21 through measuring the change in charge-transfer resistance (R _ct ) before and after hybridization. Under the optimal conditions, the biosensor showed a linear impedimetric response between ΔR _ct and logarithm of miRNA-21 concentration ranging from 10 ⁻¹⁴ to 10 ⁻⁸ M with a correlation coefficient of 0.972 and a detection limit of 3 fM. The selectivity of the biosensor was examined against non-complementary miRNA-141. The biosensor showed acceptable reproducibility, regeneration ability and stability as well as remarkable response (recoveries 90%–116%) in real plasma samples. The results indicated that the proposed biosensor could be used as a promising alternative to conventional methods in early clinical and point-of-care cancer diagnosis.