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Journal of Sensors and Sensor Systems An open-access peer-reviewed journal
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Volume 6, issue 2
J. Sens. Sens. Syst., 6, 341–350, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
J. Sens. Sens. Syst., 6, 341–350, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular research article 09 Oct 2017

Regular research article | 09 Oct 2017

Low-cost, in-liquid measuring system using a novel compact oscillation circuit and quartz-crystal microbalances (QCMs) as a versatile biosensor platform

Stefan Beißner1,*, Jan-Wilhelm Thies2,4,*, Christopher Bechthold1,*, Philipp Kuhn3, Bettina Thürmann2, Stefan Dübel3, and Andreas Dietzel2,4 Stefan Beißner et al.
  • 1Hochschule Hannover, Fakultät für Elektro- und Informationstechnik, Ricklinger Stadtweg 120, 30459 Hannover, Germany
  • 2TU Braunschweig, Institute of Microtechnology, Alte Salzdahlumer Str. 203, 38124 Braunschweig, Germany
  • 3TU Braunschweig, Institute of Biochemistry, Biotechnology and Bioinformatics, Spielmannstr. 7, 38106 Braunschweig, Germany
  • 4TU Braunschweig, Center of Pharmaceutical Engineering (PVZ), Franz-Liszt-Straße 35A, 38106 Braunschweig, Germany
  • * These authors contributed equally to this work.

Abstract. Quartz-crystal microbalances (QCMs) are commercially available mass sensors which mainly consist of a quartz resonator that oscillates at a characteristic frequency, which shifts when mass changes due to surface binding of molecules. In addition to mass changes, the viscosity of gases or liquids in contact with the sensor also shifts the resonance but also influences the quality factor (Q-factor). Typical biosensor applications demand operation in liquid environments leading to viscous damping strongly lowering Q-factors. For obtaining reliable measurements in liquid environments, excellent resonator control and signal processing are essential but standard resonator circuits like the Pierce and Colpitts oscillator fail to establish stable resonances. Here we present a low-cost, compact and robust oscillator circuit comprising of state-of-the-art commercially available surface-mount technology components which stimulates the QCMs oscillation, while it also establishes a control loop regulating the applied voltage. Thereby an increased energy dissipation by strong viscous damping in liquid solutions can be compensated and oscillations are stabilized. The presented circuit is suitable to be used in compact biosensor systems using custom-made miniaturized QCMs in microfluidic environments. As a proof of concept we used this circuit in combination with a customized microfabricated QCM in a microfluidic environment to measure the concentration of C-reactive protein (CRP) in buffer (PBS) down to concentrations as low as 5 µg mL−1.

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