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 for measuring the pH of the human stomach. Thanks to the relatively small footprint, it is possible to insert the sensor into the tip of a nasogastric (NG) tube to be inserted inside the stomach. 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 layer behaves like a resistive load in relatively low frequencies and a capacitive load in relatively high frequencies, as investigated using Impedance spectrometer. Interdigitated microelectrodes coated by the pH sensitive layer is used to detect the variations of impedance when encountered to a pH sample. The sensor represents a relatively good sensitivity and short response time (less than 0.5 s) for monitoring of pH in the range of 1 to 7.