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

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.

Doped Zinc Oxide Nanoparticles: Synthesis, Characterization and Potential Use in Nanomedicine

“…A flexible pH sensor based on Al-doped ZnO nanosheets was also obtained. Due to Al doping, the sensitivity of the device was highly improved (50.2 mV/pH) with respect to the pure ZnO nanosheets (34.13 mV/pH) [ 137 ].…”

Metal Hydrogen-Bonded Organic Framework as a pH Sensor for the Detection of Strong Acids

“…As an important indicator of material property, the pH value was widely applied in various fields such as chemical engineering, chemical kinetic mechanism, and chemical industry. − In the past decades, many methods had been studied for pH detection, ranging from low precision to high precision, such as pH meters and acid–base indicators. − The pH meters had been proved to be an effective approach for pH detection because of their convenience, excellent accuracy, and high efficiency. However, its development was limited due to high cost and vulnerability. − As for the acid–base indicator, it was utilized for the detection of pH by changing color in different acidic or alkaline solutions.…”

Electrochemical pH regulation in droplet microfluidics

“…Measurement of pH in microchannels has previously been carried out using fluorimetry, 25,48,49 colorimetry, [50][51][52] and electrochemical methods. 40,[53][54][55] We used ratiometric colorimetry to quantitatively measure microdroplet pH. 52 Ratiometric colorimetry is a robust method for microfluidic pH measurement as it is insensitive to variation in pathlength and dye concentration.…”