Sensors and Actuators B 153 (2011) 468–473 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Short communication Electrorotation chip consisting of three-dimensional interdigitated array electrodes Kosuke Ino a , Atsuko Ishida a , Kumi Y. Inoue a , Masato Suzuki a , Masahiro Koide a,b , Tomoyuki Yasukawa c , Hitoshi Shiku a , Tomokazu Matsue a,∗ a Graduate School of Environmental Studies, Tohoku University, 6-6-11-604, Aramaki-Aoba, Aoba, Sendai 980-8579, Japan b Environmental Chemistry Division and Research Center for Environmental Risk, National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba 305-8506, Japan c Graduate School of Material Science, University of Hyogo, 3-2-1 Kouto, Kamigori, Ako, Hyogo 678-1297, Japan article info Article history: Received 28 August 2010 Received in revised form 26 October 2010 Accepted 3 November 2010 Available online 16 November 2010 Keywords: Electrorotation IDA electrode Lab-on-a-chip device Particle manipulation MEMS abstract We have developed an electrorotation (ER) chip that has a sandwich structure in which interdigitated array (IDA) electrodes are arranged face-to-face. These IDA electrodes on the top and bottom of the chip were orthogonally arranged to form over 2000 square regions having rotating electric fields between the IDA electrodes. Since rotating electric fields can be generated by arranging the electrical connections to produce a /2 phase difference between adjacent electrodes, a large number of measurement areas for ER were incorporated within a single ER chip. The ER properties of glass microrods at the individual measurement areas were investigated using this ER chip. The present ER chip was found to be a useful tool for performing high-throughput assays to analyze the dielectric properties of microparticles. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Alternating current (AC) electrokinetic techniques such as elec- trorotation (ER), dielectrophoresis (DEP) and traveling-wave DEP have been utilized for manipulating, separating and analyzing cellular-scale particles [1]. These phenomena, which originate from the interaction of dipoles induced by applying an electric field, cause a variety of motions, including attraction, repulsion and rotation, depending on the nature of the dynamic field. ER is the rotational motion of a polarized particle in a rotating electric field and it is commonly generated by using four sinusoidal electrical sig- nals with a /2 phase difference between adjacent electrodes [2]. Since the particle polarization is frequency dependent, the behavior of a particle varies depending on its dielectric properties [3]. ER is a non-invasive technique for investigating the dielectric properties of particles. Consequently, it is popular in cellular biophysics as it can be used to measure cellular properties such as the conductivity and permittivity of cellular compartments and their surrounding membranes. Several lab-on-a-chip devices have recently been developed for particle manipulation that exploit these electrokinetic tech- niques [4–6]. We have previously fabricated lab-on-a-chip devices for bioparticle manipulation using interdigitated array (IDA) ∗ Corresponding author. Tel.: +81 22 795 7209; fax: +81 22 795 7209. E-mail address: matsue@bioinfo.che.tohoku.ac.jp (T. Matsue). electrodes [7–12]. In the previous study, polystyrene beads or mammalian cells were manipulated by DEP for immunoassays and cell culture chips. In the present study, we develop an ER chip using IDA electrodes. The ER chip consists of three-dimensional IDA elec- trodes that induce rotating electric fields in 2401 regions that have a total area of 1.74 mm 2 . We investigated the performance of the ER chip for rotating microrods trapped in a large number of rotational regions. The present study demonstrates that ER chips can be used to perform high-throughput assays of the dielectric properties of microparticles. 2. Materials and methods 2.1. Fabrication of the ER chip IDA electrodes were fabricated by photolithography and elec- trochemical etching [7]. Briefly, IDA patterns of a positive photoresist (S-1818, Shipley, Marlborough, MA) were fabricated on an indium–tin-oxide (ITO) substrate. The ITO substrate was chemically etched with a HNO 3 /HCl/water solution. The patterned resist was removed with acetone to produce the IDA electrodes. An insulating layer (thickness: 10 m) of a negative photoresist (SU-8 3010, MicroChem Corp., USA) was then prepared on the IDA elec- trodes to insulate the lead wires. The IDA electrodes were observed using a nanosearch microscope (SFT-3500; Shimadzu, Japan). After fabricating the IDA electrodes, a polyester film (thickness: 10 m) as a space was placed on the insulating layer and the two glass 0925-4005/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2010.11.012