Research
Si-NW sensors

Research experience
2010-2014 Ph.D., University of Basel, Switzerland [link to PhD]
2015-1016 Postdoctoral researcher at Yale university in the group of Mark Reed

Publications

  1. Label-Free FimH Protein Interaction Analysis using Silicon Nanoribbon BioFETs
    Mathias Wipf, Ralph L. Stoop, Giulio Navarra, Said Rabbani, Beat Ernst, Kristine Bedner, Christian Schoenenberger, and Michel Calame.
    ACS Sensors, 2016 [DOI] [Abstract]

    The detection of biomarkers at very low concentration and low cost is increasingly important for clinical diagnosis. Moreover, monitoring affinities for receptor-antagonist interactions by time-resolved measurements is crucial for drug discovery and development. Biosensors based on ion-sensitive field-effect transistors (BioFETs) are promising candidates for being integrated into CMOS structures and cost-effective production. The detection of DNA and proteins with silicon nanowires has been successfully demonstrated using high affinity systems such as the biotin–streptavidin interaction. Here, we show the time-resolved label-free detection of the interaction of the bacterial FimH lectin with an immobilized mannose ligand on gold-coated silicon nanoribbon BioFETs. By comparing our results with a commercial state of the art surface plasmon resonance system, additional surface effects become visible when using this charge based detection method. Furthermore, we demonstrate the effect of sensor area on signal-to-noise ratio and estimate the theoretical limit of detection.

  2. Implementing Silicon Nanoribbon Field-Effect Transistors as Arrays for Multiple Ion Detection
    Ralph L. Stoop, Mathias Wipf, Steffen Mueller, Kristine Bedner, Iain A. Wright, Colin J. Martin, Edwin C. Constable, Axel Fanget, Christian Schoenenberger, and Michel Calame.
    Biosensors, 6 (2), 21, 2016 [DOI] [Abstract]

    Ionic gradients play a crucial role in the physiology of the human body, ranging from metabolism in cells to muscle contractions or brain activities. To monitor these ions, inexpensive, label-free chemical sensing devices are needed. Field-effect transistors (FETs) based on silicon (Si) nanowires or nanoribbons (NRs) have a great potential as future biochemical sensors as they allow for the integration in microscopic devices at low production costs. Integrating NRs in dense arrays on a single chip expands the field of applications to implantable electrodes or multifunctional chemical sensing platforms. Ideally, such a platform is capable of detecting numerous species in a complex analyte. Here, we demonstrate the basis for simultaneous sodium and fluoride ion detection with a single sensor chip consisting of arrays of gold-coated SiNR FETs. A microfluidic system with individual channels allows modifying the NR surfaces with self-assembled monolayers of two types of ion receptors sensitive to sodium and fluoride ions. The functionalization procedure results in a differential setup having active fluoride- and sodium-sensitive NRs together with bare gold control NRs on the same chip. Comparing functionalized NRs with control NRs allows the compensation of non-specific contributions from changes in the background electrolyte concentration and reveals the response to the targeted species.

  3. Competing Surface Reactions Limiting the Performance of Ion-Sensitive Field-Effect Transistors
    Ralph L. Stoop, Mathias Wipf, Steffen Mueller, Kristine Bedner, Iain A. Wright, Colin J. Martin, Edwin C. Constable, Wangyang Fu, Alexey Tarasov, Michel Calame, and Christian Schönenberger.
    Sensors and Actuators B, 220, 500-507, 2015 [DOI]
  4. Sensing with Advanced Computing Technology: Fin Field Effect Transistors with High-K Gate Stack on Bulk Silicon
    Sara Rigante, Paolo Scarbolo, Mathias Wipf, Ralph L. Stoop, Kristine Bedner, Elizabeth Buitrago, Antonios Bazigos, Didier Bouvet, Michel Calame, Christian Schönenberger, and Adrian M. Ionescu.
    ACS Nano, 9 (5), 4872-4881, 2015 [DOI]
  5. Sensor system including silicon nanowire ion sensitive FET arrays and CMOS readout
    Paolo Livi, Amir Shadmani, Mathias Wipf, Ralph L. Stoop, Joerg Rothe, Yihui Chen, Michel Calame, Christian Schoenenberger, and Andreas Hierlemann.
    Sensors and Actuators B: Chemical, 204, 568-577, 2014 [DOI]
  6. Investigation of the dominant 1/f Noise Source in Silicon Nanowire Sensors
    K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, R. Stoop, S. Rigante, J. Brunner, W. Fu, C. David, M. Calame, J. Gobrecht, and C. Schoenenberger.
    Sensors and Actuators B, 191, 270-275, 2014 [DOI]
  7. pH- Response of Silicon Nanowire Sensors: Impact of Nanowire Width and Gate Oxide
    K. Bedner, V. A. Guzenko, A. Tarasov, M. Wipf, R. L. Stoop, D. Just, S. Rigante, W. Fu, R. A. and Minamisawa, C. David, M. Calame, J. Gobrecht, and C. Schoenenberger.
    Sensors and Materials, 25 (8), 567-576, 2013 [DOI]
  8. High mobility graphene ion-sensitive field-effect transistors by noncovalent functionalization
    W. Fu, C. Nef, A. Tarasov, M. Wipf, R. Stoop, O. Knopfmacher, M. Weiss, M. Calame, and C. Schoenenberger.
    Nanoscale, 5, 12104-12110, 2013 [DOI]
  9. Potassium sensing with membrane-coated silicon nanowire field-effect transistors.
    M. Wipf, R. L. Stoop, A. Tarasov, K. Bedner, W. Fu, M. Calame, and C. Schönenberger. , Proceeding of the 17th IEEE International Conference on Solid-State Sensors, Actuators & Microsystems (Transducers & Eurosensors XXVII), Barcelona, Spain, 16-20 June 2013, pages 1182-1185, 2013. [DOI]
  10. Selective Sodium Sensing with Gold-Coated Silicon Nanowire Field-Effect Transistors in a Differential Setup
    Mathias Wipf, Ralph L. Stoop, Alexey Tarasov, Kristine Bedner, Wangyang Fu, Iain A. Wright, Colin J. Martin, Edwin C. Constable, Michel Calame, and Christian Schoenenberger.
    ACS Nano, 7 (7), 5978-5983, 2013 [DOI]
  11. Understanding the Electrolyte Background for Biochemical Sensing with Ion-Sensitive Field-Effect Transistors
    A. Tarasov, M. Wipf, K. Bedner, J. Kurtz, Wangyang Fu, Vitaliy A. Guzenko, Oren Knopfmacher, Ralph L. Stoop, Michel Calame, and Christian Schoenenberger.
    ACS Nano, 6 (10), 9291-9298, 2012 [DOI]
  12. A True Reference Nanosensor Realized with Silicon Nanowires
    A. Tarasov, M. Wipf, K. Bedner, J. Kurtz, Wangyang Fu, Vitaliy A. Guzenko, Oren Knopfmacher, Ralph L. Stoop, Michel Calame, and Christian Schoenenberger.
    Langmuir, 28 (25), 9899-9905, 2012 [DOI] [Abstract]

    Conventional gate oxide layers (e.g., SiO2, Al2O3, or HfO2) in silicon field-effect transistors (FETs) provide highly active surfaces, which can be exploited for electronic pH sensing. Recently, great progress has been achieved in pH sensing using compact integrateable nanowire FETs. However, it has turned out to be much harder to realize a true reference electrode, which – while sensing the electrostatic potential – does not respond to the proton concentration. In this work, we demonstrate a highly effective reference sensor, a so-called reference FET, whose proton sensitivity is suppressed by as much as 2 orders of magnitude. To do so, the Al2O3 surface of a nanowire FET was passivated with a self-assembled monolayer of silanes with a long alkyl chain. We have found that a full passivation can be achieved only after an extended period of self-assembling lasting several days at 80 °C. We use this slow process to measure the number of active proton binding sites as a function of time by a quantitative comparison of the measured nonlinear pH-sensitivities to a theoretical model (site-binding model). Furthermore, we have found that a partially passivated surface can sense small changes in the number of active binding sites reaching a detection limit of ?Ns ? 170 ?m–2Hz–1/2 at 10 Hz and pH 3.

  13. Silicon-based ISFET shows negligible dependence on salt concentration at constant pH
    Oren Knopfmacher, Alexey Tarasov, Mathias Wipf, Wangyang Fu, Michel Calame, and Christian Schoenenberger.
    ChemPhysChem, 13 (5), 1157-1160, 2012 [DOI] [Abstract]

    The response of (miniaturized) ion-sensitive field-effect transistors (ISFETs) with oxide interfaces to changes in the electrolyte concentration is discussed. It is shown that FETs covered with a thin alumina layer are almost insensitive to changes in the ionic strength of the electrolyte, while being extremely pH-sensitive.

  14. Sensing with liquid-gated graphene field-effect transistors.
    Wangyang Fu, Cornelia Nef, Alexey Tarasov, Mathias Wipf, Ralph Stoop, Oren Knopfmacher, Markus Weiss, Michel Calame, and Christian Schoenenberger. In Nanotechnology (IEEE-NANO), Nanotechnology (IEEE-NANO). IEEE; IEEE Nanotechnol Council; Univ Birmingham; Inst Phys (IOP),, 2012. 12th IEEE International Conference on Nanotechnology (IEEE-NANO), Birmingham, ENGLAND, AUG 20-23, 2012 [DOI] [Abstract]

    Liquid-gated graphene field-effect transistors (GFETs) with reliable performance are developed. It is revealed that ideal defect-free graphene should be inert to electrolyte composition changes in solution, whereas a defective one responses to electrolyte composition. This finding sheds light on the large variety of pH or ion-induced gate shifts that have been published for GFETs in the recent literature. As a next step to target graphene-based (bio-) chemical sensing platform, non-covalent functionalization of graphene has to be introduced.

  15. Nernst Limit in Dual-Gated Si-Nanowire FET Sensors
    O. Knopfmacher, A. Tarasov, W. Fu, M. Wipf, B. Niesen, M. Calame, and C. Schönenberger.
    Nano Letters, 10, 2268-2274, 2010 [DOI]