Patent ID: 7450236

Claim:
A measuring apparatus comprising: a light source for emitting a light beam, a sensor unit comprising a dielectric block, a thin film layer, a sample holding portion and a reference surface for position measurement, the dielectric block being transparent to the light beam, the thin film layer being formed on the upper surface of the dielectric block and being capable of generating surface plasmons, the sample holding portion being for holding a sample on the thin film layer and the reference surface for position measurement being coplanar with the upper surface of the dielectric block, a sensor holding means which removably holds the sensor unit in a predetermined position, a light beam projecting means which causes the light beam to enter the dielectric block to impinge upon the interface between the upper surface of the dielectric block and the thin film layer at an angle of incidence so that total internal reflection conditions are satisfied at the interface, a refractive index information obtaining means which obtains refractive index information on an analyte on the thin film layer on the basis of the light beam reflected at the interface, a displacement measuring means which measures displacement of the interface by measuring vertical displacement of the reference surface from a predetermined reference position, and a position adjustment means which mechanically adjusts the vertical position of the sensor unit according to the displacement of the reference surface measured by the displacement measuring means so that the reference surface is positioned in the predetermined reference position.