Sensor and concentration measurement method

A sensor for detecting or quantifying a target substance contained in a liquid sample including blood, comprising:

• a working electrode;
• a counter electrode;
• a quinone compound having quinone and at least one hydrophilic substituent;
• a coenzyme-dependent enzyme dehydrogenating or oxidizing the target substance;
• and
• a reagent layer including the coenzyme-dependent enzyme and the quinone compound,
• wherein the reagent layer is disposed so as to be in direct physical contact with the working electrode and/or the counter electrode,
• the oxidation-reduction potential of the quinone compound measured using a silver/silver chloride (saturated potassium chloride) electrode as a reference electrode is less than 0, is greater than oxidation reduction potential of the coenzyme, and is smaller than oxidation reduction potential of ascorbic acid,
• the hydrophilic substituent has a benzene ring and a hydrophilic functional group added to the benzene ring,
• the coenzyme-dependent enzyme is a PQQ-dependent, an FAD-dependent, or an NAD-dependent enzyme, and
• the quinone is a phenanthrenequinone.