Label-free detection of biological analytes in real-time is highly desirable in health care. One possibility for realization is the use of silicon nanowire-based field effect transistors. They represent a new and promising class of electrically based sensors, but to obtain highly specific and sensitive Bio-FETs, the selection of the receptor molecules and their attachment to the surface of the sensor are crucial.
In our project, aptamers and peptides were chosen as receptors. They are expected to be small enough to be able to propagate the binding signal to the transducer and to be stable under varying conditions. For the examplary attachment of aptamers, we used a well-known DNA sequence for the detection of thrombin. To obtain peptides as specific receptor molecules, we employed the biopanning affinity selection technique. A phage-display library of randomized 12-mer peptides fused to the coat protein pIII of the filamentous phage M13 was screened to enrich phages binding to selected bioanalytes.
For the successful immobilization of these receptor molecules, silicon surfaces were functionalized with organosilanes. These silanes provide different reactive end groups, such as amino groups. By using spacer molecules the layer thickness and surface properties were varied and the biological receptors were covalently bound to the modified surfaces.
The combination of these identification and immobilization techniques will enable a nanowire-based biosensing of relevant disease markers.