A sampling mechanism employing the phase transition of a gel and its application to a micro analysis system imitating a mosquito

Poly(N-isopropylacrylamide) gel swells and shrinks in response to a variation in temperature. This phenomenon was utilized to construct a micro sampling mechanism. A 2 mm x 10 mm x 19 mm gel used in the mechanism changed its volume immediately in response to a step change in temperature and stabilized within I min. Also, the gel could change its volume reproducibly in response to repeated thermal cycles. The sampling mechanism was incorporated in a micro system with a micro glucose sensor based on the detection of hydrogen peroxide. After the gel was shrunk at 40 degreesC making contact with a buffer solution, the inlet of the sampling mechanism was placed in contact with a sample solution at 30 degreesC. It was observed that the sample solution was introduced and moved into the interior of the system following the swelling of the gel. The micro glucose sensor showed a distinct response accompanying a peak with a 90% response time between 2 and 10 s. A linear calibration curve was obtained for glucose concentrations less than 2.5 mM. A microneedle of an inner diameter of 50 mum was connected to the inlet of the flow channel. Sampling and sensing could also be conducted successfully with a 90% response time between 1 and 4 min. The linear range of the calibration curve was expanded to 5 mM by sucking through the microneedle. (C) 2001 Elsevier Science B.V. All rights reserved.