Stoop, Ralph. Understanding silicon nanowire field-effect transistors for biochemical sensing. 2015, PhD Thesis, University of Basel, Faculty of Science.
Official URL: http://edoc.unibas.ch/diss/DissB_11832
Despite the achievements obtained in the last years, commercial products based on ISFETs are using the device as a pH sensor only. The reason for this development lies in the incomplete understanding of the complex interface between the electrolyte and the solid-state sensor as well as the difficulties related to the design of surfaces which selectively bind a targeted analyte.
In this PhD project, we address these points by studying arrays of ISFETs based on silicon nanowires (Si NWs) fabricated by a top-down lithography approach and investigate their potential as an integrable sensing platform. First we characterize the devices and analyze their pH response. We find a response to pH at the fundamental (Nernst) limit, due to the special properties of the gate oxide materials used for the devices. We further demonstrate that the sensor signal is not affected by the width of the NWs, i.e. enhanced sensing is not observed for nanoscale devices. However, we reveal that the low-frequency noise of the devices decreases for increasing NW width, an aspect which has to be considered when ultimate integration is targeted. For the specific detection of ionic species, the sensor surface needs to be modified with functional groups, which selectively bind the target analyte. Unfortunately, the high pH sensitivity of oxide surfaces greatly complicates the detection of any target analyte other than pH. To circumvent this problem, we propose the use of an additional coating with a material with minimal sensitivity to pH. We find that gold is a promising candidate easily applied for this purpose. The gold layer allows immobilizing ligands via the well-established thiol-based chemistry thereby providing a platform suitable for surface functionalization. Using the additional gold layer, we demonstrate the successful detection of different ions such as sodium, calcium and fluoride ions with a differential setup having both functionalized and control NWs on the same sample. Furthermore, we find that the residual pH response of the gold layer still influences the detection of the targeted species by affecting the effective binding constant via the surface potential. To take this effect into account, an extended site binding model is proposed. Finally, we show that SiNWs have the potential to even monitor binding kinetics of ligand-protein systems and we obtain concentration dependent signals for a clinically relevant protein.
|Advisors:||Schönenberger, Christian and Calame, Michel and Clément, Nicolas and Ingebrandt, S.|
|Faculties and Departments:||05 Faculty of Science > Departement Physik > Physik > Experimentalphysik Nanoeklektronik (Schönenberger)|
|Bibsysno:||Link to catalogue|
|Number of Pages:||1 Online-Ressource (x, 154 Seiten)|
|Last Modified:||10 Oct 2016 05:52|
|Deposited On:||10 Oct 2016 05:51|
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