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.