Functionalization of nanophotonic silicon-on-insulator biosensor chips for real-time DNA detection

Biosensors are frequently used for easy detection of biomolecules in various applications. Within the framework of the European RAPP-ID project, nanophotonic silicon-on-insulator (SOI) chips were selected as detection platform to develop a rapid point-of-care test, which can eventually be used in hospitals to potentially lower the use of antibiotics. To be able to detect a biomolecule, in this case a DNA sequence, reliable surface chemistry is of vital importance. In a first step, the chip was functionalized in order to link a DNA strand to its surface. The commercially available, bifunctional HyNic Silane was chosen as silanization agent. Via hydrazone ligation, an aldehyde-modified DNA sequence was attached to the surface. Subsequently, a complementary oligonucleotide was hybridized and detected. Hybridization was optimized by varying the formamide concentration in the hybridization buffer and by working at elevated (i.e. physiological) temperature. The last step involves hybridization of a complementary biotin-labeled sequence. In a later stage, the biotin-label will enable amplification of the observed signal using streptavidin. Detection with ring resonators has the ability to track every binding event at the surface in real-time. Each reaction step results in a change in the resonance wavelength. These wavelength shifts can then be monitored. A net positive wavelength shift in the binding curve after each step revealed that the silanization, the attachment of DNA to the SOI and the subsequent hybridization were successful