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

Introduction: 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 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. Materials & Methods: 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. (1,2) A complementary oligonucleotide was hybridized following the procedure described in (2). Hybridization was optimized by varying the hybridization buffer (25 v/v% formamide in PBS pH 7.4 or 50 v/v% formamide in PBS pH 7.4) and by working at 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. Results & Discussion: Detection with ring resonators has the ability to track every binding event at the surface in real-time. Each reaction step resulted in a change in the resonance wavelength. These wavelength shifts were then monitored. Silanization and attachment of the aldehyde-modified DNA sequence to the surface resulted in net positive shifts ranging from 100 to 200 pm and 200 to 400 pm respectively. A wavelength increase of maximum 100 pm was observed for the hybridization of complementary DNA. The binding curves of the silanization and hybridization are shown in figure 1 and 2, respectively. In conclusion, the 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. The hybridization of the biotin-labeled complementary strand and signal amplification with streptavidin are still being optimized. References [1] J. Byeon, F. T. Limpoco, R. C. Bailey, Langmuir 2010, 26, 15430 – 15435. [2] A. J. Qavi, R. C. Bailey, Angew. Chem. Int. Ed. 2010, 49, 4608 – 4611