Silicon nanostructures and coplanar waveguides for biosensors

The biosensors market had a considerable development in the last decade and is expected to increase at a quick pace in the coming years. The driving force behind this important expansion is a constant need to improve the current methods for environmental monitoring and for rapid pathogen detection. Mainly destined to point-of-care devices, biosensors are spreading through home diagnostics, bio-defense, and food industry. This high demand pushes for the development of new and more precise devices. Two fundamentally different types of sensing devices were built and studied in this work. Both types of devices were engineered using conventional micro- and nano-fabrication techniques in order to allow for a quick integration with electronic circuits. The first type is based on silicon nanowires (SiNWs) and the devices function similarly to field effect transistors. The full manufacturing protocol, which results in nanowires with trapezoidal shape, is carefully described. The effect of surface modification with (3-aminopropyl)triethoxysilane (APTES), on the electrical properties of the devices, was studied. Important changes in the threshold voltage and the subthreshold slope were observed between the as-fabricated devices and the APTES-conditioned ones. Furthermore, we show that the APTES significantly improves the stability of the SiNWs compared with more conventional micro-devices. The detection of proteins was studied with these SiNWs-based sensors. The second type of devices is based on coplanar waveguides and their functioning resembles that of capacitive sensors. These devices sense the change in the dielectric properties of the surrounding media and their use for the dielectric characterization of various materials is presented first. Subsequently, we employed these devices, operating in the radio-frequency range, in conjunction with gravitational sedimentation to develop a novel colloid-based biosensing method. This technique, in which the settling of bio-functionalized polystyrene beads clusters is monitored, was applied to the detection of proteins.