Analytica Chimica Acta 556 (2006) 164–170 Integration of multiple-ion-sensing on a capillary-assembled microchip Hideaki Hisamoto ∗ , Midori Yasuoka, Shigeru Terabe Graduate School of Material Science, University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako-gun, Hyogo 678-1297 Japan Received 16 March 2005; received in revised form 6 May 2005; accepted 9 May 2005 Available online 9 June 2005 Abstract Multiple-ion-sensing functions are integrated on a capillary-assembled microchip (CAs-CHIP). Since the CAs-CHIPs are fabricated by embedding various chemically functionalized square capillaries onto a lattice PDMS channel plate having same channel dimensions as outer dimensions of square capillaries, integration of parallel multiple-ion-sensing is easily realized. Here, three ion-sensing capillaries are prepared and used for integrating these functions onto a single microchip. Ion-sensing square capillaries (sodium, potassium, calcium) are prepared by attaching ion-selective optode membranes to inner wall of capillaries, and are characterized in terms of response time, response range, and ion selectivity. Finally, fully characterized ion-sensing capillaries are embedded into PDMS channel plate in parallel to fabricate a multiple-ion-sensing chip. The CAs-CHIP-based strategy is promising for integrating multiple chemical sensing functions onto a single microchip. © 2004 Elsevier B.V. All rights reserved. Keywords: Ion-selective optode; Ion sensor; Microchip; Polydimethylsiloxane; Square capillary 1. Introduction During the past decade, the fields of micro total analysis systems (-TAS) have extensively grown [1–4]. Among the -TAS researches, one recent direction is the inte- gration of various chemical or biochemical functions at a defined position in the microchannel. These researches aim at development of highly functionalized microfluidic devices allowing complex chemical operations, which are difficult to carry out by conventional microfluidic devices without any chemical modification of the channel. In order to integrate chemical functions, multiphase flow patterning or photopolymerization are frequently employed as experimental techniques [5–13]. These techniques are very promising for the immobilization of a single chemical function on a ready-made microfluidic device; however, as pointed out elsewhere [14,15], immobilization of several different chemical functions using these techniques requires complicated experimental procedures, i.e., step-by-step ∗ Corresponding author. Tel.: +81 791 58 0171; fax: +81 791 58 0493. E-mail address: hisamoto@sci.u-hyogo.ac.jp (H. Hisamoto). introduction of highly reactive reagent solutions into the whole microchannel, which leads to a detrimental effect on the previously patterned chemical function at the defined channel surface. In general, position-selective surface mod- ification inside the microchannel “after” chip fabrication is encountered by many technical difficulties when different functional molecules are immobilized. Very recently, we developed a new method for fabricating a multi-functional microchip, called “capillary-assembled microchip (CAs-CHIP)” [14,15]. In this case, different kinds of chemically functionalized square capillaries are prepared and cut into required lengths, then embedded into a lattice polydimethylsiloxane (PDMS) microchannel plate having same channel dimensions as the outer dimensions of square capillaries. Thus, current problems associated with the inte- gration of multiple chemical functions on a single microchip can be solved with relative ease. Furthermore, many kinds of surface modification methods for the inner surface of the cap- illary have been well known [16,17]. Therefore, assembling many square capillaries having different chemical functions would allow us fabrication of highly functionalized microflu- idic devices. 0003-2670/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2005.05.028