▎ 摘　　要

NOVELTY - Electrochemical biosensor/system comprises (a) a platinum wire as a counter electrode, (b) a silver chloride saturated with potassium chloride as a reference electrode, and (c) an indium tin oxide as a working electrode. USE - The electrochemical biosensor/system is useful for detecting breast cancer from serum sample (claimed). ADVANTAGE - The system: utilizes thionine dye as hybridization indicator which detects/quantifies circulating miRNA-21 for early detection of breast cancer; is economical and minimally invasive; and detects breast cancer rapidly i.e. in 30-35 minutes. DETAILED DESCRIPTION - Electrochemical biosensor/system comprises (a) a platinum wire as a counter electrode, (b) a silver chloride saturated with potassium chloride as a reference electrode, and (c) an indium tin oxide as a working electrode, where, the indium tin oxide electrode comprises gold nanoparticles and graphene oxide/thiolated-single stranded-microRNA-21/polyvinyl pyrrolidine/6-mercaptoethanol/Nafion(RTM: Sulfonated tetrafluoroethylene based fluoropolymer-copolymer) in a desired ratio to form a recognition interface. The system detects/quantifies circulating miRNA-21 for early detection of breast cancer using thionine dye as hybridization indicator, the miRNA detection/quantification is performed via differential pulse voltammetry in a hybridization buffer, the system employs thiolated-single stranded (ss)-miRNA-21 probe for binding to the gold nanoparticles and protection against degradation, the ss-miRNA-21 probe has a sequence 5'-(ThiC6)-ucaacaucagucugauaagcua-3' (SEQ ID NO: 1). The system is cost-effective and minimally invasive, and the detection of breast cancer is rapid and is performed in 30-35 minutes. An INDEPENDENT CLAIM is also included for preparing a working electrode comprising (aa) mixing 50 μ l thiolated single stranded probe (thiolated-ssmiRNA-21) and 100X (tris(2-carboxyethyl)phosphine) and equal volume of an immobilization buffer, (bb) mixing a desired ratio of gold nanoparticles and graphene oxide in a vol. ratio of 2:1 and 1% polyvinylpyrrolidine in /4 volume of nanoparticles, (cc) mixing the solution obtained from step (aa) and (bb) to obtain total volume of 500 μ l, (dd) drop casting 50 μ l mixture obtained in step (cc) on an indium tin oxide electrode and leaving in humidity chamber for 45-60 minutes at 25-30° C; and (ee) coating the casted electrode from step (dd) with a desired ratio of 6-mercaptoethanol and Nafion(RTM: Sulfonated tetrafluoroethylene based fluoropolymer-copolymer) and left at 25-30° C for drying, where, the working electrode is indium tin oxide electrode of gold nanoparticles and graphene oxide/thiolated-ss-miRNA-21/polyvinyl pyrrolidine/6-mercaptoethanol/Nafion(RTM: Sulfonated tetrafluoroethylene based fluoropolymer-copolymer) in a desired ratio to form a recognition interface.