Patent ID: 8465938

Claim:
An immunoassay method comprising steps of: reacting an analyte with a first complex comprising a biotin-labeled Cypridina luciferase, a polyvalent avidin substance and an antibody capable of recognizing the analyte, to form a second complex, and contacting a luciferin with the second complex and measuring a luminescence, wherein: a biotin of the biotin-labeled Cypridina luciferase is bound at a position corresponding to a lysine residue K180 and/or K203 of SEQ ID NO: 1 via a polyethylene glycol moiety represented by formula —(CH 2 CH 2 O) n — wherein n is an integer of 2 to 50, or is bound via a sugar chain with a hydrazide linkage; the biotin-labeled Cypridina luciferase is labeled with 2 to 5 biotins; and the polyvalent avidin substance is selected from the group consisting of avidin, streptavidin and NeutrAvidin.