Fabrication of the functional 3-D micromesh structures coated with TiO<inf>2</inf> particles and biocatalyst

Abstract

This paper presents the fabrication method of the functional 3-D micromesh structures coated with TiO2 particles and biocatalyst for high efficient microreactors. The micromesh structures are useful as a micro reaction space because of their large surface area. The TiO2-fixed SU-8 micromesh structures were formed by coating the SU-8/TiO2 mixture on the surface of the SU-8 micromeshes (Fig.l(a)). The biocatalyst-immobilized micromeshes were also formed by coating the biocatalyst/polymer mixture using UV irradiation through the concentric circle patterns ( Fig. 1(b)).Fixation of TiO2 particles Previously, the fabrication method of 3-D micromesh structures and their microfluidic applications were reported'2. In addition, catalytic functions are promoted to the SU-8 micromeshes. At first, we fabricated the micromesh structures by simply using TiO2-contained SU-8. However, the mesh structures were not obtained because UV light could not pass through the TiO2/SU-8 layer due to its large amount of TiO2 particles, as shown in Fig.2. In this case, TiO2 concentration in SU-8 was 0.67%. In order to achieve high efficient microreactors, TiO2 mixed ratio should be larger the better. Coating method of high TiO2 concentrated SU-8 film on the micromesh structures is requested. Fig.3 shows the fabrication process of the TiO2 particle-fixed micromeshes. After the fabrication of micromeshes ( Fig.3(a)), TiO2-contained SU-8 was spin-coated and baked under low temperature (Fig.3(b)). Without UV exposure, this layer was removed with SU-8 developper. Thin TiO2/SU-8 film was remained on the micromesh surface (Fig.3(c)). Cr layer was etched to remove the residual TiO2/SU-8 film on the glass substrate (Fig.3(d)). Additional UV irradiation and hard-baking were performed to achieve strong adhesion between TiO2/SU-8 film and SU-8 micromeshes (Fig.3(e)). Fig.4 shows SEM micrographs of the fabricated TiO2-fixed micromesh structures. TiO2 was coated only on the surface of micromeshes (Fig.4). The TiO2 mixed ratio was dramatically improved from 0.67% to 5.63%. Immobilization of biocatalyst (enzyme)Considering biocatalyst, high temperature process, such as soft/hard baking of photoresist, should be eliminated to avoid denaturing of enzymes. In this work, enzymes were entrapped in cross-linked photopolymer3 of AWP (Azide-unit Pendant Water-soluble Photopolymer) to immobilize the enzyme on the surface of micromeshes. Fig.5 shows the fabrication process of the enzyme-immobilized micromeshes. We utilized Si/Cr double layered concentric circle patterns to cover each inclined micropillars of the mesh with AWP/Enzyme mixture. First, the Si/Cr concentric patterns were formed ( Fig.5 (a)). After the fabrication of the SU-8 micromeshes (Fig.5 (b)), Cr layer was removed to appear the Si openings (Fig.5 (c)). Then, AWP/Enzyme mixture was spin-coated and UV light was exposed through the Si openings from backside (Fig.5 (d)). Finally, AWP/Enzyme layer was developed using D.I. water. As a result, the enzyme-immobilized micromeshes were obtained (Fig.5(e)). Fig....