Patent ID: 7838301

Claim:
An assay method of assay in utilizing attenuated total reflection, in which a sensor unit is used and includes a thin film, having a sensing surface for immobilizing ligand thereon, and a transparent dielectric medium overlaid with said thin film, wherein illuminating light is applied to an interface defined between said thin film and said dielectric medium by satisfying a total reflection condition, and intensity of said illuminating light reflected by said interface is detected to acquire an assay signal representing an attenuation angle of said illuminating light, so as to measure reaction of binding between said ligand and analyte introduced on said sensing surface, said assay method comprising steps of: after measuring said reaction of said binding, washing said sensing surface by introducing washing fluid thereon; according to said assay signal in said washing, checking a regenerated state of said sensing surface; determining whether said sensing surface is regenerated to an initial state prior to said reaction of said binding or not; and ending up said washing if it is determined in said determining step that said sensing surface has been regenerated to said initial state, wherein in said checking step, a first assay signal representing said regenerated state of said sensing surface is compared with an initial assay signal representing said initial state of said sensing surface prior to said reaction of said binding; and if a level of said first assay signal reaches a level of said initial assay signal, it is determined that said sensing surface has been regenerated to said initial state in said determining step, and wherein if it is determined that said sensing surface has not been regenerated to said initial state in said determining step said, washing continues with only liquid buffer in a first state where the level of said first assay signal is not higher than a predetermined value, and wherein said washing continues with liquid buffer and a regenerant in a second state where the level of said first assay signal is higher than said predetermined value.