Integration of valving and sensing on a capillary-assembled microchip

A simple integration of both flow control valves and a reaction-based sensing function on a single microchip was performed by using capillary-assembled microchip (CAs-CHIP: Hisamoto, H.; Nakashima, Y.; Kitamura, C.; Funano, S.-i.; Yasuoka, M.; Morishima, K.; Kikutani, Y.; Kitamori, T.; Terabe, S. Anal. Chem. 2004, 76, 3222-3228.). In contrast to the previously reported on-chip valving systems, where the simple valving functions were integrated, our system can integrate not only valving function but also many other chemical functions to perform a complex chemical operation on a single microchip. Here, an enzymatic reaction-based readout system is employed as an example. A square capillary immobilizing N-isopropylacrylamide polymer monolith (referred to as "valving capillary") is used as a thermoresponsive "valving part" and the immobilizing enzyme-modified glycidyl methacrylate polymer monolith (referred to as "sensing capillary") is used as a "sensing part" of the CAs-CHIP. These capillaries are embedded into a lattice microchannel network fabricated on poly(dimethylsiloxane), which has the same channel dimensions as the outer dimensions of the square capillaries. After bonding, a small Peltier device (2 mm x 2 mm) for temperature control is placed on the embedded valving capillaries to control fluid flow. Using this for heating or cooling, fast operation times of 1.4 and 3.2 s for opening and closing valves, respectively, are successfully achieved. Finally, two valving capillaries are independently controlled to trap sample solution within a bypass channel, where the enzyme-immobilized capillary is embedded, and then enzymatic reaction-based sensing of chemical species is performed as an example. The fundamental characteristics of the valve-integrated microchip are fully investigated, and an application to the analysis of an enzyme substrate by using two independent valving capillaries and a sensing capillary is demonstrated.