Optically Driven Micromanipulation Tools Fabricated by Two-photon Microstereolithography
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Optically Driven Micromanipulation Tools Fabricated by Two-photon Microstereolithography Shoji Maruo, Koji Ikuta and Hayato Korogi Department of Micro System Engineering, Graduate School of Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan ABSTRACT Light-driven micromanipulators have been developed by two-photon microstereolithography. The manipulators are driven and controlled by optical trapping. The torque of micromanipulator was successfully controlled on the order of femto-newton by adjusting the focal position of the trapped laser beam. Nanotweezers and a nanoneedle with probe tip of diameter 250 nm were fabricated and driven in a liquid. Such remote-controlled manipulation tools provide a unique and effective handling method of biological samples such as living cell, protein and DNA. INTRODUCTION Manipulation techniques at micro and nanometer scale are crucial for progress in biotechnology as well as nanoscale science and technology. Recently several types of nanomanipulators such as carbon nanotube nanotweezers and micromachined nanotweezers have been developed for grabbing or probing nanoscale objects [1-3]. However, since most of these tweezers are based on electrostatic force, they are not ideal for aqueous solution work such as manipulation of cells, microbes and single molecules. In this paper, we report promising types of nanomanipulators suitable for aqueous solution work. Our manipulators were fabricated by using an assembly-free process based on two-photon microstereolithography that was previously developed by us [4-6]. We have developed several types of microstereolithography [7-9]. The two-photon process is suitable for making nanomanipulators owing to the submicron resolution. The manipulators are driven by optical trapping based on radiation pressure from a tightly focused laser beam. Since optical trapping enables remote manipulation of microobjects in biological fluid environments, the manipulators are especially suited for the application in biotechnology unlike electrostatic types. TWO-PHOTON MICROSTEREOLITHOGRAPHY Two-photon microstereolithography uses a pulsed near-infrared (IR) laser as a light source, though conventional methods use an ultraviolet (UV) laser as a light source. The rate of two-photon absorption is proportional to the squared intensity of light, so that near-IR light is strongly absorbed only at the focal point within the photopolymer [10, 11]. The quadratic dependence of two-photon-absorption assists to confine the solidification in submicron volume. This virtue of the two-photon process allows the fabrication of three-dimensional (3D) structures by scanning a focus inside the photopolymer. Fig. 1 shows our fabrication system. A Ti: sapphire laser is used to generate the two-photon absorption. The beam from the laser is introduced into the galvano-scanner system, and then it is focused with an objective lens (N.A.: 1.3). The beam scans laterally while the stage that supports the photopolymer is scanned vertically, thereby moving the poin
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