A Microfluidic pH Measurement Device with a Flowing Liquid Junction

Abstract

The pH values of aqueous solutions are conventionally measured with pH-sensitive electrodes such as glass electrodes or ion-sensitive field-effect transistors (ISFETs) used in conjunction with Ag/AgCl reference electrodes and KCl solutions. The speed of pH measurement with these systems can be deficient, however, as the glass electrode responds slowly during measurements of sample solutions with low buffering capacities. Our group has constructed a new pH measurement system using a microfluidic device and ISFET sensors. The device has a channel with two inlets and one outlet, with a junction connected to a Y-shaped channel on the same plane. Two ISFET sensors and an Ag/AgCl pseudo reference electrode are fitted into the channel to construct a differential measurement device. A sample solution and baseline solution supplied into the inlets by gravity-driven pumps form a flowing liquid junction during measurement. The small size and fast response of the ISFET sensors enable measurement of about 2.0 mL of sample solution over a measurement period of 120 s. The 90% response time is within 2 s. The calibrated sensor signal exhibits a wide range (pH 1.68–10.0) of linearity with a correlation factor of 0.9997. The measurement error for all solutions tested, including diluted solutions, was 0.0343 ± 0.0974 pH (average error ± standard deviation (S.D.), n = 42). The new device developed in this research will serve as an innovative technology in the field of potentiometry.

Enhancement in the limit of detection of lab‐on‐chip microfluidic devices using functional nanomaterials

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Recent Progress toward Microfluidic Quality Control Testing of Radiopharmaceuticals

“…pH measurements in the range pH 2 to 10 could be made using only ~0.5 µL sample volume and 200 s duration. Yamada and Suzuki developed a flow-based microfluidic pH measurement system using ion-sensitive field-effect transistor (ISFET) sensors for measurement of the proton concentration ( Figure 2 G) [ 42 ]. Two ISFET sensors and an Ag/AgCl pseudo reference electrode are fitted into a microfluidic Y-junction such that the reference ISFET and reference electrode are always immersed in a stream of baseline solution and the measurement ISFET is immersed in baseline solution or the sample, depending on a switchable flow.…”

“…Modulation of flow rates moves the liquid junction and allows measurement of the sample solution (SS) after an initialization process using a baseline solution (BLS). Adapted from [ 42 ] with permission from MDPI AG.…”