In this study, we deposited zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) on the electroless nickel immersion gold (ENIG) of a flexible printed circuit board (FPCB) as a potentiometric pH sensor. The sensing films of the pH sensor were fabricated by a radio frequency (RF) sputtering system and analyzed by field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). In the pH 2 to 10 buffer solutions, it was observed that the characteristics of the pH sensor through the voltage–time (V-T) measurement system include average sensitivity and linearity, drift effect, and repeatability. According to the experimental results, the pH sensors in this study could exhibit good characteristics.

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This study prepared an enzymatic potentiometric uric acid sensor based on zinc oxide (ZnO) and uricase. Also, we develop a potentiometric differential measurement system. We applied Nafion, APTES, and glutaraldehyde to immobilize the enzyme and increase sensitivity to prevent enzyme leakage. Thus, the uric acid sensor was integrated into FPCB which could provide flexibility to the sensor. In the uric acid concentration range of 2 mg/dL-10 mg/dL, we analyzed the characteristics of sensors with the voltage-time measurement system, measuring the average sensitivity, linearity, response time, limit of detection (LOD), and interference effects. The modification of Nafion and uricase improved the performance of the uric acid sensor.

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