The key requirement for any biosensor is that it only detects a very specific analyte, which may be present in a very low concentration and surrounded by many other components. To ensure that only the analyte of interest is detected, a specific bioreceptor needs to be immobilized on the surface of the transducer element. Bioreceptors can be proteins (antibodies, enzymes), nucleic acids (DNA, RNA), or other biological or biomimetic structures.
For photonic biochips, binding of analyte molecules to the waveguide causes a change in the light output of the sensor. The cladding, on the other hand, does not contribute to the sensor signal. Therefore, it is beneficial to immobilize the bioreceptor only on the waveguide and not on the cladding. This is achieved by Surfix's material-selective nanocoating process. To prevent non-specific adsorption of analytes, an anti-biofouling layer is applied to the cladding in a second surface modification step.