Silicon Nanotweezers With Subnanometer Resolution for the Micromanipulation of Biomolecules

We describe electrostatically actuated silicon nanotweezers which are intended for the manipulation and characterization of filamentary molecules. The microelectromechanical system consists of a pair of opposing tips whose distance can be accurately adjusted by means of an integrated differential capacitive sensor. The fabrication process is based on silicon-on-insulator technology and combines KOH wet anisotropic etching and deep reactive ion etching of silicon to form sharp nanotips and high aspect ratio microstructures, respectively. In the designed prototype, the initial gap between the tips was around 20 mum. The device showed a maximum displacement of about 2.5 mum, and we could achieve a resolution better than 0.2 nm (in static mode). We measured a resonant frequency of 2.5 kHz and a quality factor (Q factor) of 50 in air. The instrument was used to perform static and dynamic mechanical manipulations on DNA molecules, and we could distinctly observe the viscoelastic behavior of DNA bundles from these experiments.