Detection of antibody-antigen reaction by silicon nitride slot-ring biosensors using protein G

• The PSA with the sensitivity of ~1×10−8 g/ml has been achieved by using SiN biosensor.

Biosensors using ring resonators with silicon nitride (SiN) slot waveguides have been fabricated. The temperature coefficient of the resonance wavelength of the SiN resonator is 0.006 nm/°C, which is one order of magnitude smaller than that of Si. The sensitivity of the biosensor has been improved by using slot waveguide together with Si-binding protein (designated as Si-tag), which bonds to SiN or SiO2 surface, as an anchoring molecule to immobilize bioreceptors on the SiN rings in an oriented manner. Furthermore, the protein G, which strongly bonds to many kinds of mammalian antibodies only by mixing the antibody solution, is used to efficiently immobilize the antigen on the sensor surface. By means of these devises the sensitivity of the biosensor has been improved by factor of 10–100 compared with that of normal Si ring resonator sensors without slot. Then the detection of prostate specific antigen (PSA) with the sensitivity of ~1×10−8 g/ml, which is the concentration of strongly suspicious for the prostate cancer, has been achieved.