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.
Continuous monitoring of arterial and tissue Pco2
Catheter-tip sensors used to measure arterial and tissue Pco2 produced a baseline drift less than 2 torr during 1 to 5 h of monitoring. Clot formation during Paco2 monitoring was avoided by continuous infusion of a small amount of heparin solution around the sensor. PaCO2 sometimes fluctuated periodically during spontaneous breathing but not during mechanical ventilation. Subcutaneous tissue PCO2, monitored by placing the sensor under the skin on the chest, showed an almost parallel movement to PaCO2 with a time delay of a few minutes. This PCO2 sensor was durable and accurate for up to 5 h of continuous clinical monitoring.