▎ 摘　　要

NOVELTY - Electrochemical biosensor comprises an electrode comprising a surface layer of tris-ruthenium bipyridine2+ complex modified graphene oxide, and at least one enzyme linked to the surface layer. USE - The electrochemical biosensor is useful for quantifying a level of a target substrate in a sample (claimed), detecting and/or quantifying bio-markers in a liquid sample using surface-modified electrodes, and determining a level of non-esterified fatty acids (NEFA) and/or BHBA in a test sample from a subject and identifying the subject as having a metabolic disease. The sample is a biological fluid from a subject. ADVANTAGE - The electrochemical biosensor is a rapid and user-friendly device for the detection and/or quantification of analytes such as enzyme substrates, does not require a reference electrode for the detection and/or quantification of a target substrate, and specialized technical operating personnel, uses a cost-effective ruthenium bipyridine complex modified graphene oxide, and is less time-consuming. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for quantifying a level of a target substrate in a sample.