The present invention provides a
redox polymer for forming an electrochemical sensor that is suitable for use in measurement over a long period (
continuous monitoring) and excellent in stability, or a
redox mediator constituting the same. The
redox mediator provided by the present invention is a
phenothiazine-based compound having a hydrophilic
moiety introduced therein, the compound being represented by the general formula (2A) or (2B). The redox
polymer provided by the present invention is a
phenothiazine-based compound bound to a
polymer, the compound being represented by the general formula (3A) or (3B). In the formulas, R9 and R10 are both substituents, or one of these moieties is a
substituent, and the other
moiety is a
hydrogen atom, R(L)1, R(L)2, and R(L)4 to R(L)8 are each independently a predetermined group or atom, (QP)1, (QP)2, and (QP)4 to (QP)B are each independently a polymeric structure derived from a
high molecular weight polymer which is present when their corresponding R(L)1, R(L)2, and R(L)4 to R(L)8 are a specific group.