Selective chemical modification of silicon nitride/silicon oxide nanostructures to develop label-free biosensors

The selective introduction of functional groups on the surface of silicon nitride/silicon oxide nanostructures was studied. Chemical strategies based on organosilane, Si–H and N–H reactivities were assayed. Among these strategies, the use of glutaraldehyde to selectively immobilize biomolecules only on the silicon nitride part of the chip surface was the most effective for the covalent attachment of proteins, maintaining also their bioavailability. The biomolecule surface coverage results up to 80% and the modification is selective versus silicon oxide; the biomolecule attaching only to silicon nitride and leaving the silicon oxide area of the device unmodified. The effectiveness of our novel selective surface modification procedure is also supported by comparing experimental and numerical calculations of the optical performance of a label-free optical ring resonator based on Si3N4/SiO2 slot-waveguides.