Fast Detection and Flexible Microfluidic pH Sensors Based on Al-Doped ZnO Nanosheets with a Novel Morphology

You-Ting Tsai; Shoou-Jinn Chang; Liang-Wen Ji; Yu-Jen Hsiao; I-Tseng Tang

doi:10.1021/acsomega.9b02778

Fast Detection and Flexible Microfluidic pH Sensors Based on Al-Doped ZnO Nanosheets with a Novel Morphology

ACS Omega. 2019 Nov 15;4(22):19847-19855. doi: 10.1021/acsomega.9b02778. eCollection 2019 Nov 26.

Authors

You-Ting Tsai¹, Shoou-Jinn Chang¹, Liang-Wen Ji², Yu-Jen Hsiao³, I-Tseng Tang⁴

Affiliations

¹ Institute of Microelectronics & Department of Electrical Engineering, Center for Micro/Nano Science and Technology, Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan.
² Institute of Electro-Optical and Materials Science, National Formosa University, Yunlin 632, Taiwan.
³ Department of Mechanical Engineering, Southern Taiwan University of Science and Technology, Tainan 710, Taiwan.
⁴ National University of Tainan, Department of Greenergy, Tainan 700, Taiwan.

Abstract

In this study, a flexible and stable pH sensor based on aluminum-doped zinc oxide nanosheets (Al-doped ZnO NSs) was developed by a low-cost hydrothermal method. The results obtained from this study indicated that Al ions could be doped successfully into the ZnO nanostructure, which could change the morphology and improve the pH-sensing properties. The pH sensitivity of Al-doped ZnO nanosheets reached 50.2 mV/pH with a correlation coefficient of around 0.99468 when compared with that of ZnO film (34.13 mV/pH) and pure ZnO nanowires (45.89 mV/pH). The test range of pH values was widened by Al-doping, and the Al-doped ZnO NS sensor could detect the pH value ranging from 2 to 12. It was observed that in a more acidic environment, especially at pH 2, the sensor, Al-doped ZnO nanosheet, was strongly stable over 12 weeks of testing. It was noted that the response time was utterly fast and the response time of the sensors for each pH standard buffer solutions was around 0.3 s. Thus, the response time and performance were quite stable. The microchannel provided a novel testing method for the pH sensor, where the liquid to be tested was just 5 mL. Hence, it was suggested to be useful for many medical diagnoses and treatments. The benefits of Al-doped ZnO nanosheet pH sensor were high sensitivity, good long-term usage, good flexible property, and requirement of a small amount of test liquid, which could make the sensors viable candidates for practical applications.