Sensor and concentration measurement method

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

• introducing the liquid sample into the sensor;
• applying a voltage corresponding to a range of an oxidation-reduction potential of the quinone compound between the working electrode and the counter electrode;
• measuring a current that flows between the working electrode and the counter electrode when a voltage is applied;
• and
• detecting or quantifying a target substance contained in the liquid sample based on the measurement,
• wherein the reagent layer is disposed so as to be in direct physical contact with at least one of the working electrode and the counter electrode,
• the quinone compound has a hydrophilic functional group,
• the coenzyme-dependent enzyme is a PQQ-dependent, an FAD-dependent, or an NAD-dependent enzyme,
• the quinone is a phenanthrenequinone, and
• the oxidation-reduction potential of the phenanthrenequinone based on potential of a silver/silver chloride (saturated potassium chloride) electrode as the reference electrode is less than 0 volts, greater than oxidation reduction potential of the coenzyme, and smaller than oxidation reduction potential of ascorbic acid.