Surface plasmon resonance biosensor using heterodyne interferometry

A Surface plasmon resonance (SPR) biosensor constructed with common path, heterodyne inteferometric system has been developed. The sensor ship consists of a BK7 substrate coated with gold film on which the receptor of the specific biomolecular or protein has been immobilized. The light source consisting of the s and p polarizations with heterodyne frequency of 60kHz is used to measure the phase difference between these two polarizations. Because the SPR sensor probes the changes of refractive index near the gold film (i.e. about one wave-length), the more the binding of molecules on the sensing surface results in the less sensitivity of the detection. In order to overcome this shortage, we set two quarter-wave plates before and after the SPR prism to make the sensitivity of measurement to be tunable. This sensor could detect the concentration of antibody of sheep IgG as low as several nanograms per milliliter. The results indicate that this system provides high sensitivity and is capable for detecting biomolecular interactions.