Fiber-optic assay apparatus based on phase-shift interferometry

The equipment and the method for detecting the existence of combination of the sample in the sample solution, quantity, or speed are indicated. The light source for drawing an optical beam on the optical assembly which has the 1st and 2nd reflective surfaces that estranged only the distance "d" over 50 nm, and the 1st and 2nd reflective surfaces of the above is contained in equipment, and the 1st page is formed of a sample joint molecular layer. When placing an assembly into a sample solution, the detector of equipment operates by detecting the phase shift of the light wave reflected from the 1st and 2nd reflective surfaces so that thickness change of the 1st reflective layer produced from the combination to the sample joint molecule of a sample may be detected.