Design and fabrication of a rapid conductometric pH sensor based on metal-oxide technology

A micro-fabricated metal-oxide based conductometric pH sensor is designed and fabricated in this manuscript. pH sensors have applications in various areas from farming to food processing, human health monitoring, industrial waste products investigation, etc. Accordingly, there is a relatively high demand for a reliable, rapid and precise pH sensor in the market. Relatively precise pH sensors have been already demonstrated for in-vitro analysis. Nevertheless, design and fabrication of pH sensors for in-vivo applications are still challenging. In this work, a relatively minute pH sensor is designed and fabricated. Thanks to the adopted fabrication method, the small footprint makes it suitable for monitoring of human stomach acid. A mixture of ZnO and SnO2 powders is used as the metal-oxide pH sensitive layer. Impedance spectroscopy is applied to investigate the frequency characteristics of the sensor. The pH sensitive layer behaves like a resistive load in relatively low frequencies and a reactive load in relatively high frequencies, as investigated using Impedance spectrometer. Interdigitated microelectrodes coated with the pH sensitive layer is used to detect the variations of impedance when introduced to a pH sample. The sensor demonstrated a relatively good sensitivity and short response time (less than 0.5 s) for monitoring of pH in the range of 1 to 7.