The development of electrochemical nanotechnology biosensors requires engineering of inorganic transducer surfaces for the attachment of specific biomolecules. Our research is focused on a silicon nanowire field effect transistor sensor device, capable of detecting biological analytes with target-specific receptors, here aptamers. Aptamers act as artificial antibodies and can consist of either oligonucleotides or oligopeptides. An oligopeptide against the clinically relevant target Norovirus is being developed in a phage display biopanning process within our projects and this work focuses on binding strategies for aptamer attachment to the surface and target detection.
Therefore, a model system for the electrochemical detection is selected - a ssDNA aptamer (NH₂-C6-5'-GGTTGGTGTGGTTGG-3') against human alpha-thrombin. Silicon dioxide surface functionalization with organosilanes, e.g. APTES, provides functional end groups such as amines or carboxy groups ready for receptor attachment onto the planar surface. Contact angle measurements, ellipsometry, AFM, gold nanoparticle labeling and fluorescence microscopy are utilized to study each functionalization step, the reactivity of the surfaces andthe covalent binding of the aptamer. This is demonstrated by using microcontact printing (μCP) of silanes with PDMS stamps and fluorescent labeling of aptamers to distinguish specific binding to functionalized areas from unspecific binding to bare surfaces. Finally, the biorecognition process of the aptamer with Thrombin is investigated with nonfaradaic electrochemical impedance spectroscopy (NIS).