A Highly Sensitive Electrochemical Biosensor Based on Carbon Black and Gold Nanoparticles Modified Pencil Graphite Electrode for microRNA-21 Detection

This work aims to develop cost-effective, simple and sensitive electrochemical biosensor for detection of microRNA-21. The combination of carbon black (CB) and gold nanoparticles (AuNPs) as nanohybrid was employed for the first time as a platform for microRNA-21 biosensor fabrication. The developed biosensor is based on the immobilization of thiolated capture probe (complementary sequence of microRNA-21) labeled with methylene blue on the surface of the pencil graphite electrode modified with CB/AuNPs nanohybrid. After hybridization with the target microRNA-21, the orientation of the labeled capture probe changed which causes a decrease of the response of methylene blue oxidation. Differential pulse voltammetry was used for monitoring the methylene blue response before and after hybridization. Under the optimal conditions, the developed biosensor was characterized using differential pulse voltammetry (DPV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The detection of microRNA-21 was carried out using a DPV. A wide linear range was obtained between 2.9 fM and 0.7 mu M of microRNA-21. The calculated limit of detection was 1 fM of microRNA-21. This approach shows a good reproducibility, stability and an excellent selectivity. The proposed biosensor was used for microRNA-21 analysis in serum and a satisfactory result was obtained.