Dielectrophoretic Micropatterning with Microparticle Monolayers Covalently Linked to Glass Surfaces Masato Suzuki, Tomoyuki Yasukawa, Yoshiaki Mase, Daisuke Oyamatsu, † Hitoshi Shiku, and Tomokazu Matsue* Graduate School of Environmental Studies, Tohoku University, 07 Aramaki-Aoba, Aoba-Ku, Sendai 980-8579, Japan Received July 27, 2004. In Final Form: September 16, 2004 Two-dimensional micropatterns of microparticles were fabricated on glass substrates with negative dielectrophoretic force, and the patterned microparticles were covalently bound on the substrate via cross- linking agents. The line and grid patterns of microparticles were prepared using the repulsive force of negative dielectrophoresis (n-DEP). The template interdigitated microband array (IDA) electrodes (width and gap 50 µm) were incorporated into the dielectrophoretic patterning cell with a fluidic channel. The microstructures on the glass substrates with amino or sulfhydryl groups were immobilized with the cross- linking agents disuccinimidyl suberate (DSS) and m-maleimidobenzoyl-N-hydroxy-succinimide ester (MBS). Diaphorase (Dp), a flavoenzyme, was selectively attached on the patterned microparticles using the maleimide groups of MBS. The enzyme activity on the patterned particles was electrochemically characterized with a scanning electrochemical microscope (SECM) in the presence of NADH and ferrocenylmethanol as a redox mediator. The SECM images proved that Dp was selectively immobilized onto the surface of microparticles to maintain its catalytic activity. Introduction Recently, there has been a great deal of interest in the well-organized surface structures consisting of micropar- ticles, since the spatial control of the particles is a critical subject in the creation of new functional materials. 1 These colloidal structures have been applied to photonic crystals, ion sensors and biosensors, 2,3 a scaffold of cell cultivation, 4,5 and microlens projection lithography. 6 Various methods have been proposed and employed for assembling micro- particles on a solid support. The evaporation process and lateral capillary force have been used for the formation of self-assembled arrays of microparticles. When the solvent evaporates slowly, the suspended particles self- assemble to form close-packed arrays due to capillary forces. 7-9 A self-assembly method for yielding ordered arrays was also demonstrated using a tapered cell. 10,11 Three-dimensional (3D) assemblies of submicrometer colloids and two-dimensional (2D) helical chains of col- loidal particles were fabricated using a silicon or polymer template substrate with periodic unevenness. 12,13 Simi- larly, 2D and 3D arrays of microparticles were constructed using elastic molds fabricated from poly(dimethylsiloxane) (PDMS). 14 Self-assembled monolayers (SAMs) patterned using the microcontact printing (µCP) method control the placement of particles on surfaces. SAMs of periodical bands with opposite charges were fabricated by stamping them with patterned PDMS on their surfaces. 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Electrophoresis 2002, 23, 2174- 2183. 11005 Langmuir 2004, 20, 11005-11011 10.1021/la048111p CCC: $27.50 © 2004 American Chemical Society Published on Web 11/03/2004