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Modeling and control of MEMS tweezers for the characteriza- tions of enzymatic reactions on DNA molecules

  • Lafitte, Nicolas
Publication Date
Apr 04, 2012
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The main objective of this Ph.D. work is to achieve biological experimentson DNA molecules with versatile silicon nanotweezers. Experiments on single moleculerely mostly on Optical Tweezers, Magnetic Tweezers or Atomic Force Spectroscopy, buthave a low throughput since preparations are done one at a time. To move towardssystematic biological or medical analysis, micro- and nano-systems (MNEMS) are theappropriate tools as they can integrate accurate molecular level engineering tools andcan be cheaply produced with highly parallel process.Design and fabrication of the silicon tweezers are made by ourselves in the lab of Pr.Hiroyuki Fujita (U. of Tokyo, Japan). DNA molecules are firstly trapped in solution bydielectrophoresis. Then biological reactions are characterized in real-time by monitoringthe mechanical resonance of the system {tweezers + DNA bundle}. The resolution of themeasurements allowed the sensing of about 30 of λ-DNA molecule stiffness (i.e. about20 mN/m). To achieve the single molecule resolution, we propose to implement a feedbackstrategy to alter the system.State feedback was developed to emulate a new system more sensitive to mechanicalstiffness parameter detection. As it remains problematic to design and fabricate newmicro mechanical device with extremely low stiffness (< 1 N/m), we propose to emulate acompliant system. By simulations it was demonstrated an enhancement of the sensitivityof about 10 when the resonant frequency of the closed-loop system is designed to be 10times lower than the tweezers resonant frequency (i.e. reducing the stiffness parameterof the system). Experimentally we demonstrated an improvement of the the sensitivityof superior to 2. However the issue is here to obtain stability, robustness with respectto disturbances and unmodeled dynamics. Before to attain the sensitivity of the singlemolecule, problematics about the model of the device or about the several dynamics ofthe device needs to be dealt in order to control and fit the improvement with the theory.

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