A voltammetric hybridization assay for microRNA-21 using carboxylated graphene oxide decorated with gold-platinum bimetallic nanoparticles

An electrochemical hybridization assay is described for the determination of microRNA-21. Fluorine tin oxide (FTO) sheets were coated with carboxylated graphene oxide followed by deposition of gold-platinum bimetallic nanoparticles by using chronoamperometry at a potential of -0.2V for 350s. The capture probe was immobilized on the surface of the modified FTO sheets by biotin-avidin interaction. On exposure to microRNA-21, hybridization occurs, and that can be detected at a relatively low working potential of 0.25V by using ferri/ferro-cyanide as an electrochemical probe. The various modifications of the FTO sheets were characterized by means of FE-SEM, FT-IR, contact angle studies and electrochemical techniques. The effects of pH value, EDC-NHS activation time, concentration of capture probe and incubation time were optimized. The sensor has a wide linear response that extends from 1 fM to 1M of microRNA-21, and the detection limit is 1 fM. The sensor is stable for about 15days (by retaining 90% of its initial activity) and can be reused for about 3 times (85% of initial activity) after regeneration with 50mM NaOH solution. The sensor was applied to the analysis of spiked human serum and gave recoveries between 90 and 111%.