Labeling of radioactive or fluorescent substances has generally been employed for conventional measurements of bonds or links such as intermolecular interactions between biomolecules, e.g., antigen-antibody reactions and intermolecular interactions between organic polymers. This labeling, however, is time-consuming, and especially labeling of proteins requires complicated procedures and causes denaturation of the proteins in some cases. RIfS (reflectometric interference spectroscopy) making use of a change in interference color of an optical film is known as a current simplified means for directly detecting bonds or links between biomolecules and organic polymers without labeling. The principle of the RIfS is disclosed in Patent Document 1 and Non Patent Document 1, for example.
RIfS will now be briefly described. RIfS employs a detector 100 shown in FIGS. 15A to 15C. With reference to FIG. 15A, the detector 100 includes a substrate 102 and an optical film 104 provided on the substrate 102. When the detector 100 is irradiated with white light, spectral intensities of the incident white light and reflected light are depicted with solid lines 106 and 108, respectively in FIG. 16. By calculating reflectance from spectral intensities of the incident white light and the reflected light thereof, reflectance spectrum 110 depicted with a solid line is obtained as shown in FIG. 17.
With reference to FIG. 15B, ligands 120 are provided on the optical film 104 in order to detect intermolecular interactions. The ligands 120 provided on the optical film 104 modify the optical thickness 112, leading to a change in light path length, and thus a change in interference wave length. This causes the peak shift of spectral intensity distribution of the reflected light. As a result, the reflection spectrum shifts from a solid line 110 to a dotted line 122 in FIG. 17. A sample solution is then poured over the detector 100, so that binding occurs between ligands 120 on the detector 100 and analytes 130 in the sample solution as depicted in FIG. 15C. The binding of the ligands 120 and the analytes 130 further modifies the optical thickness 112, and the reflection spectrum 122 shifts to the reflection spectrum 132 (a dashed line) in FIG. 17. The detection of a variation in bottom wavelength between the reflection spectra 122 and 132 enables intermolecular interactions to be determined.
FIG. 18 illustrates a temporal transition of the variation in the bottom wavelengths. The variation in the bottom wavelength by the ligand 120 can be observed at a time point 140, while the variation in the bottom wavelength by the bonds or links between the ligand 120 and the analyte 130 can be observed at a time point 142.