A miniaturized microfluidic pH measurement device using ISFET sensors
We have succeeded in producing a new micro fluidic pH measurement device downsized from our previous model. The new device body has dimensions of ϕ15×5 mm and a channel section measuring 0.75×1.0 mm (width and height). The operability of the sensor probe and high-responsiveness and stability of the electrode are key preconditions to effective pH measurement. Our method combines a micro fluidic device made of polydimethylsiloxane (PDMS) and an ion-sensitive field-effect transistor (ISFET). The ISFET sensor is microscopic in scale and responds quickly to solutions with low buffering capacities. As the sample solution and baseline solution (BLS) flow in the channel of the micro fluidic device, a liquid junction forms between them. The flowing junction improves the stability of the measurement. The present device performed measurements at a rate of 120 sec/sample and consumed samples of 0.3 ml in volume. The measurement error of 9 sample solutions, including 3 diluted solutions with low buffering capacities, was 0.00992 ± 0.179.
Expansion of a linear range of the ion-concentration measurement system using microfluidic device with ISFET sensors
We have previously reported a pH measurement device using a microfluidic technology and ion-sensitive field-effect transistor (ISFET). The device has successfully measured pH values, however the range of linearity was limited within neutral range. In this paper we have evaluated the linearity of the sensor signal with a wide range of pH. The present device obtained high linearity in the range of pH 1-10 with the correlation factor of 0.9985. The averaged measurement error and standard deviation were -0.0083 and 0.0085 pH, respectively.
Application of catheter-tip i.s.f.e.t. for continuousin vivo measurement
A catheter-tip pH sensor was developed for possible clinical and biomedical application, using an ion-sensitive field-effect transistor (i.s.f.e.t.). Its signal drift in buffer solutions during continuous measurement was less than 3 mV in 24 h (equivalent to about 0·05 pH in 24 h). The electric insulation was perfect when soaked in buffer solutions for more than 3 months. A continuousin vivo pH measurement was successfully achieved in nonheparinised arterial blood of a japanese monkey. There was no significant sign of clot formation for 8 hours. It revealed quick responses to respiratory acidosis and alkalosis, and the observed pH values were in accordance with those confirmed by a blood pH analyser. Also, a catheter-tip pCO2 sensor was prepared, using the catheter-tip pH i.s.f.e.t. The response time was 2 min for a 90% change in CO2 tension. The muscle pCO2 monitoring tested with it indicated a similar result to those with medical mass spectrometer.