PURPOSE: To detect a human serum in an organismic liquid optically, and to perform quantitative measurement by adding specific anionic cyanin dye to a sample.

CONSTITUTION: By adding anionic cyanin dye expressed by an equation to a sample, the human serum albumin in a humor can be optically detected and quantitatively measured rapidly and inexpensively. In the equation, n indicates 0 or 1; M+ does monovalent cation; R0 and R1 do cyano, aryl or COR (R indicates an alkoxy, alkyl, or aryl); and R2 and R8 do alkyl or cyano. R3, R5, R6, and R7 indicate H or alkyl; R4 does H, a halogen, alkyl, aryl, aryloxy, alkoxy, or NR2 (R indicates an alkyl or aryl). R9 indicates cyano, aryl, COR, CO-NAB (A indicates an alkyl, aryl, or carbamoyl and B indicates an alkyl or aryl); H does heterocyclyl; R10 indicates cyano, aryl, COR, CO-NAB, H or heterocyclyl. At least one substituent out of R0, R1, R9, R10 indicates cyane and R3-R5 indicate the components of a ring.