Shoji Maruo

Three-dimensional microfabrication with two-photon-absorbed photopolymerization

We propose a method for three-dimensional microfabrication with photopolymerization stimulated by two-photon absorption with a pulsed infrared laser. An experimental system for the microfabrication has been developed with a Ti:sapphire laser whose oscillating wavelength and pulse width are 790 nm and 200 fs, respectively. The usefulness of the proposed method has been verified by fabrication of several kinds of microstructure by use of a resin consisting of photoinitiators, urethane acrylate monomers, and urethane acrylate oligomers.

Submicron manipulation tools driven by light in a liquid

Optically driven micromanipulators with submicron probe tips are proposed and developed by using two-photon microstereolithography. The micromanipulators are worked by maneuvering their movable component with a focused laser beam, and an actual pair of microtweezers was opened and shut precisely. We also propose an effective method of controlling movable micromachines with great freedom of movement. In this method, a dot is attached to a movable component for trapping and driving it by a single laser beam. A microneedle was induced to perform several types of motion such as rotation and translation. The optically driven micromanipulators are useful for bionanotechnology applications that require work to be done in aqueous solutions.

Two-photon-absorbed near-infrared photopolymerization for three-dimensional microfabrication

We present three-dimensional (3-D) microstructures fabricated from photopolymerizable resin with a resolution of 0.62 /spl mu/m. The method used to fabricate such small structures has been developed using a femto-second-pulsed near-infrared (IR) laser. Structures such as microcoils and microtubes are presented which demonstrate the effectiveness of our method. In this method, a two-photon absorption process is successfully utilized to confine the solidification of photopolymerizable resin to the focused spot of the laser, which is possible due to the quadratic dependence of the two-photon absorption rate on light intensity. The experimental system, experimental conditions, and related issues for this novel method of photopolymerization are also discussed.

Optically driven micropump produced by three-dimensional two-photon microfabrication

An optically driven lobed micropump was developed using three-dimensional two-photon microfabrication. The two built-in rotors, 9μm in diameter, are cooperatively driven by means of time-divided scanning of a single laser beam. It was demonstrated that a tracer particle was moved by simultaneously rotating the two rotors. The velocity of the tracer particle was proportional to the rotation speed of the rotors in the range of 0.2–0.7μm∕s. The flow rate was estimated to be sub-pL/min level. This ultralow flow rate will be useful for further integration and miniaturization of micro-total-analysis systems.

Force-controllable, optically driven micromachines fabricated by single-step two-photon microstereolithography

We have fabricated optically driven micromechanisms and demonstrated their motion under optical force. All of the movable microcomponents are directly fabricated through an assembly-free process using the high-speed scanning of a femtosecond laser focused inside a photocurable resin. Since these movable micromachines are made from photocurable resin transparent to visible and near-infrared light, they can be driven by the force of optical trapping. We demonstrate a simple, versatile method for driving movable micromachines. Part of the movable component is optically trapped by a single laser beam and manipulated according to the desired trajectory. Various types of motion, including rotation and swinging are demonstrated. In addition, the optically driven micromachines can be force-controlled to femtonewton order by adjusting the position trapped by the laser beam. We demonstrated the femtonewton order force-controllable swing motion of micromanipulators. A microturbine was rotated by circular scanning of a trapping laser beam in a liquid. Such force-controllable optically driven micromachines are promising manipulation tools for biomolecules such as DNA and protein.

Three-dimensional microfabrication by use of single-photon-absorbed polymerization

We developed a promising method to fabricate three-dimensional microstructures by using single-photon-absorbed polymerization confined to the vicinity of a tightly focused spot. This localized polymerization is based on the nonlinear response of the photopolymerizable resin to optical intensity with sufficiently low exposure. The nonlinear response was verified by measuring polymerization exotherm at different light intensities. The proposed method enables us to make even movable microstructures without any of the supporting parts or sacrificial layers normally required with conventional micromachining. In the experiment reported here, we fabricated a microgear with an external diameter of 47 μm and an attached shaft.

Optically driven micropump with a twin spiral microrotor

An optically driven micropump that employs viscous drag exerted on a spinning microrotor with left- and right-handed spiral blades on its rotational axis has been developed using two-photon microfabrication. It was demonstrated that the twin spiral microrotor provides a higher rotation speed than a single spiral microrotor. The rotation speed reached 560 rpm at a laser power of 500 mW. The twin spiral microrotor was also applied to a viscous micropump with a U-shaped microchannel. To pump fluid, the twin spiral microrotor located at the corner of the U-shaped microchannel was rotated by focusing a laser beam. The flow field inside the U-shaped microchannel was analyzed using the finite element method (FEM) based on the Navier-Stokes equation to optimize the shape of the microchannel. It was confirmed that the rotation of the twin spiral microrotor generated a unidirectional laminar flow. Finally, a tandem micropump using two twin spiral microrotors was driven by a dual optical trapping system using a spatial light modulation technique.

Femtosecond laser direct writing of metallic microstructures by photoreduction of silver nitrate in a polymer matrix

Continuous silver microstructures were produced by three-dimensional (3-D) direct laser writing using a femtosecond-pulsed laser beam with polyvinylpyrrolidone (PVP) films containing silver ions. The lines drawn by scanning a tightly focused laser beam ranged from 200 nm to 1.7 microm. Using a sample solution of high density of silver nitrate, a continuous silver line with a resistivity of 3.48 x 10(-7) ohms m was produced. Not only 3-D microstructures such as pyramidal models but also hybrid microstructures comprising polymer and silver lines were demonstrated. The 3-D direct laser writing of metallic microstructures has potential for application to 3-D electrical wiring of electronic devices and MEMS devices.

Optically driven viscous micropump using a rotating microdisk

An optically driven micropump using viscous drag exerted on a rotating disk microrotor was developed. The disk microrotor (diameter of 10μm), which has three columns as targets for the optical trap, is confined to a U-shaped microchannel. To pump fluid, the disk microrotor is rotated by a time-shared optical trapping technique. The flow field inside the U-shaped microchannel was analyzed using finite element method (FEM) based on the Navier-Stokes equation. The optimized micropump was fabricated using a two-photon microfabrication technique. The flow rate of the micropump agreed with simulation result obtained by FEM analysis.An optically driven micropump using viscous drag exerted on a rotating disk microrotor was developed. The disk microrotor (diameter of 10μm), which has three columns as targets for the optical trap, is confined to a U-shaped microchannel. To pump fluid, the disk microrotor is rotated by a time-shared optical trapping technique. The flow field inside the U-shaped microchannel was analyzed using finite element method (FEM) based on the Navier-Stokes equation. The optimized micropump was fabricated using a two-photon microfabrication technique. The flow rate of the micropump agreed with simulation result obtained by FEM analysis.

Micro concentrator with opto-sense micro reactor for biochemical IC chip family. 3D composite structure and experimental verification

The concentration process is an indispensable in various chemical operations for both detection and purification. However, little research to miniaturize it have been done so far. In this paper, the world-first micro concentrator chip using ultrafiltration membrane for biochemical micro devices is developed. The micro concentrator chip consists of ultrafiltration membrane to filter molecule and a micro reactor with optical sensor to detect progress of biochemical reaction optically. Basic performance as a concentrator and real-time monitoring in-chip protein synthesis are demonstrated successfully. Another important feature of this chip is fabrication method. The Micro Stereo Lithography (IH Process) being developed in authors laboratory enable to make the chip three dimensionally without any mask process. Both the packaging difficulty and leakage problem are eliminated completely.