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.
A fully automated pH measurement system for 96-well microplates using a semiconductor-based pH sensor
Abstract The pH values of solutions have been commonly measured by glass electrodes, devices which respond on a time scale of minutes and require complicated operations such as calibration at every measurement. The development of a fast, automated pH measurement system for analytes in small volumes would be quite useful in many fields. Yet the practical application of such a device has been hampered by the need for rapid measurement and precise calibration. Our group has constructed a fully automated, self-calibrating pH measurement system capable of consecutively measuring 96 samples. The system uses a flow-through-type differential pH sensor probe based on a tiny, quickly responding pH-sensitive field-effect transistor (pH-FET) technology. The system was confirmed to measure the pH values of 26 μl solutions over a 135 s cycle (60 s for wash, 20 s for movement, 3 s for suction, and 52 s for measurement). The measurement error of multiple sample measurements, including measurements of solutions with low buffering capacity, was −0.0116 ± 0.0481 pH (average error ± S.D.). The high accuracy and high reproducibility of the results suggest that this automatic pH measurement system based on pH-FET can be applied for versatile uses.
A Rapid Microfluidic Switching System for Analysis at the Single Cellular Level
Analysis of cellular responses to chemicals at high spatiotemporal resolution is required for precise understanding of intracellular signal transduction. Here, we demonstrated a novel method for applying different solutions to a part of or all of a cell at high spatiotemporal resolution. We fabricated a microfluidic device using polydimethylsiloxane, and the sharp interface between the two solution streams flowing in the channel was used for the application of different solutions. We constructed a computer-controlled system to control the interface movement precisely, rapidly, and reproducibly during positioning, and spatial and temporal resolutions attained were 1.6 ¿m and 189 ms, respectively. We then applied the present system to the analysis of intracellular responses to chemicals. We were able to measure [Ca2+]i increases within 500 ms, when one laminar stream covered a part of the cell. This method can be used as a generic platform to investigate responses against drugs at the single cell level.