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×10 mm×19 mm gel used in the mechanism changed its volume immediately in response to a step change in temperature and stabilized within 1 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°C making contact with a buffer solution, the inlet of the sampling mechanism was placed in contact with a sample solution at 30°C. 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 μm 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.